General Forums => The O' Club => Topic started by: Chalenge on January 30, 2008, 08:43:03 AM
Title: Airplane on a Conveyor Belt...
Post by: Chalenge on January 30, 2008, 08:43:03 AM
On 'Myth Busters' tonight at 9 EST on DSC.
Title: Airplane on a Conveyor Belt...
Post by: WWhiskey on January 30, 2008, 08:47:12 AM
Talked about this last night for a bit, there was some confusion about the factors effecting this and alot of different answers to a very simple question! Ask this of the players in here but make sure you get all the factors into the question.
Title: Airplane on a Conveyor Belt...
Post by: sluggish on January 30, 2008, 09:23:12 AM
NO!! PLEASE!! LOCK IT NOW!!!
Title: Airplane on a Conveyor Belt...
Post by: Chairboy on January 30, 2008, 09:37:11 AM
There are some well intentioned but mistaken folks here who say the plane won't take off. These are the people who, I imagine, concentrate on the GV side of AH. :D
Title: Airplane on a Conveyor Belt...
Post by: Curval on January 30, 2008, 09:40:27 AM
I never did any GV stuff in AH...but it won't take off.
:D
Title: Airplane on a Conveyor Belt...
Post by: WWhiskey on January 30, 2008, 09:58:12 AM
the thing i want to know is how is the plane staying on the conveyer belt . is it tied to an anchorpoint or are the engines running to develop thrust? is the conveyer belt stationary and only the belt moving in the oposite direction of the way the plane is faceing? the way i heard the ? is that the plane,s wheels and the belt are goin in oposite directions at the same speed if this is so then the plane is not moving and will not fly as lift to the wings is needed for that! what is stoping the plane from falling off the belt? it must be anchored as the props turning would create forward thrust not relavent to the test and the plane would move forward off the belt! either way the plane must be anchored to the ground to keep it from moving back or forward while the wheels roll underneath and it wont fly if its tied to the ground!:aok
Title: Airplane on a Conveyor Belt...
Post by: sluggish on January 30, 2008, 10:18:03 AM
For those of you that weren't here the first time, here's your chance to bone up on your "airplane on a conveyor belt" theory...
Title: Airplane on a Conveyor Belt...
Post by: Chairboy on January 30, 2008, 10:39:28 AM
Once again, for Curval and the rest of the folks who don't get it.... planes are not propelled by their wheels. A car driving 30mph on a 30mph conveyor belt would sit motionless.
...but a plane is blowing air with a propeller. Doesn't matter if the wheels are spinning twice as fast, the plane will move.
Some of the people, in their fervid attempts to prove that the treadmill will prevent the plane from moving, will start talking about things like clamps holding the plane in place, and that's where their well intentioned mistake transitions to borderline maliciousness. C'mon.
The plane will take off tonight. If he applies normal takeoff power, it will take off just fine. If he only gooses the throttle enough to keep position on the fast moving canvas, then it won't.... .....but that's not the legend.
So it'll take off.
Title: Airplane on a Conveyor Belt...
Post by: WWhiskey on January 30, 2008, 10:45:59 AM
ok now that i have read the real question if the plane moves forward at 100 knots it will fly and the belt cannot stop it! my theory is that the belt will continue to accelerate and the wheels may explode but the plane will fly if it is still in one peice when it reaches 100 knots
i stand corrected at first the question seemed to be misleading :noid
Title: Airplane on a Conveyor Belt...
Post by: rabbidrabbit on January 30, 2008, 10:50:08 AM
I birthed a monster thread. Yay me!:aok
Title: Airplane on a Conveyor Belt...
Post by: WWhiskey on January 30, 2008, 11:16:44 AM
Quote
Originally posted by sluggish For those of you that weren't here the first time, here's your chance to bone up on your "airplane on a conveyor belt" theory...
a little way down this forum is a link to the real question!
read this more than once and hopefully you will understand the plane does not have to stay stationary and the belt is not compinsating for movement of the plane it is only going 100 knots in the oposite direction hence wheel speed 200 knots! plane speed 100 knots!
Title: Airplane on a Conveyor Belt...
Post by: Curval on January 30, 2008, 11:35:55 AM
Quote
Originally posted by Chairboy So it'll take off.
No it won't.
:)
Title: Airplane on a Conveyor Belt...
Post by: sluggish on January 30, 2008, 11:46:08 AM
If we are able to defy the laws of physics with a conveyor belt that can instantly and infinitely compensate for the thrust of the plane, then we must also throw out any wheel drag or cetrifugal wheel force or wheel bearing limitation physics.
The plane will fly.
Title: Airplane on a Conveyor Belt...
Post by: Chairboy on January 30, 2008, 11:54:49 AM
Quote
Originally posted by Curval No it won't.
:)
I've put together a quick list of excuses you can call on tonight or tomorrow after the episode for why it took off:
"They did it wrong, they-":
1. "Weren't supposed to give it full throttle!" 2. "Should have tied it down to prevent it from moving!" 3. "Didn't make the conveyor belt move infinitely fast!" 4. "Aren't real scientists, they didn't understand the problem!"
Hope one or more of these fit your outrage. :D
If the plane doesn't take off for some reason (like, they tie it down or don't give it the right throttle or something) then I'll be sad, but I'll face my fate here like a man. Can you commit to the same?
Title: Airplane on a Conveyor Belt...
Post by: WWhiskey on January 30, 2008, 11:56:14 AM
The thing is the belt is not supposed to compinsate for the speed of the plane it is only going 100knots and the plane is supposed to add power for 100 knot takeoff hence 200 knot wheel speed! the plane does not have too stay stationary! this is what threw me at first because i thought that the belt was goin to go faster and faster and the plane had to stay in one spot but those are not the peramiters of the question i dont know how too link this thread to the real question or i would then i would break it down for you IT will fly
Title: Airplane on a Conveyor Belt...
Post by: Chairboy on January 30, 2008, 12:05:17 PM
When the plane flies, that crowd will just say it "wasn't set up right" and proceed to re-define the experiment until it gives them the results they've decided on. Not a great scientific method, btw.
Title: Airplane on a Conveyor Belt...
Post by: sluggish on January 30, 2008, 12:06:45 PM
Quote
Originally posted by WWhiskey The thing is the belt is not supposed to compinsate for the speed of the plane it is only going 100knots and the plane is supposed to add power for 100 knot takeoff hence 200 knot wheel speed! the plane does not have too stay stationary! this is what threw me at first because i thought that the belt was goin to go faster and faster and the plane had to stay in one spot but those are not the peramiters of the question i dont know how too link this thread to the real question or i would then i would break it down for you IT will fly
Title: Airplane on a Conveyor Belt...
Post by: Yknurd on January 30, 2008, 12:22:17 PM
A' trollin' we will go, a' trollin' we will go, hi-ho the merry-o, a' trollin' we will go.
Title: Airplane on a Conveyor Belt...
Post by: Curval on January 30, 2008, 12:24:02 PM
It will not take off.
Final answer.
:lol
Title: Airplane on a Conveyor Belt...
Post by: Chairboy on January 30, 2008, 12:30:46 PM
Nobody ever said a final answer needed to be correct. Didn't see you commit to posting after the episode, though, you're not nervous are ya?
Title: Airplane on a Conveyor Belt...
Post by: GtoRA2 on January 30, 2008, 12:46:43 PM
Quote
Originally posted by Curval It will not take off.
Final answer.
:lol
I dont know Curv the previews for the show look like the plane is going to not be tied down in any way, its just going to be on a big tarp that drag behind a truck....
Its going to fly.
Title: Airplane on a Conveyor Belt...
Post by: Chairboy on January 30, 2008, 12:55:03 PM
In which case Curval can simply say "#2" without sounding whiny. Everyone wins!
Title: Airplane on a Conveyor Belt...
Post by: Curval on January 30, 2008, 12:57:29 PM
Whatever...I'm just having fun watching Chairboy get his panties all wadded up.
Sure I'll post after the show whatever way it goes. I failed physics and don't fly planes. Why anyone would take my opinion seriously on this issue is beyond me.
Title: Airplane on a Conveyor Belt...
Post by: FrodeMk3 on January 30, 2008, 01:18:25 PM
For the life of me, I can't believe that this got dredged up again.
Look, if the aircraft has enough air flowing fast enough over it's wings, It will fly.
If it doesn't, it won't.
The brakes' could be set and locked, but if the airplane is propelled forward fast enough for it's wings to generate sufficient lift, the s.o.b. will fly.
The landing gear wheels' could spin at the road speed equivalent of 400 mph on a conveyor belt, but if there's insufficient airflow over the wings' to generate enough lift to lift the weight of the plane, the damn thing will not fly. It's as simple as that.
Title: Airplane on a Conveyor Belt...
Post by: john9001 on January 30, 2008, 01:22:39 PM
how do seaplanes fly, they don't even have wheels. :confused:
Title: Airplane on a Conveyor Belt...
Post by: WWhiskey on January 30, 2008, 02:04:25 PM
i just got thru watching the comercial for tonights mythbusters lol this is goin to be fun any bets?
Title: Airplane on a Conveyor Belt...
Post by: Yknurd on January 30, 2008, 02:04:25 PM
Quote
Originally posted by FrodeMk3 For the life of me, I can't believe that this got dredged up again.
Look, if the aircraft has enough air flowing fast enough over it's wings, It will fly.
If it doesn't, it won't.
The brakes' could be set and locked, but if the airplane is propelled forward fast enough for it's wings to generate sufficient lift, the s.o.b. will fly.
The landing gear wheels' could spin at the road speed equivalent of 400 mph on a conveyor belt, but if there's insufficient airflow over the wings' to generate enough lift to lift the weight of the plane, the damn thing will not fly. It's as simple as that.
lol. I don't think you really understand, do you?
Title: Airplane on a Conveyor Belt...
Post by: Coshy on January 30, 2008, 03:19:24 PM
If a helicopter were on a treadmill that moved just as fast as the helicopters wheels moved, would it be able to take off?
:noid :noid
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on January 30, 2008, 03:25:53 PM
The plane will take off, piece-of-cake. The treadmill could go 800 mph and the plane would still take off. One thing that they will never be able to prove in RL, however, is the similar question where the treadmill must match the planes wheel speed. That’s a surprisingly different question, with a surprisingly different answer.
Title: Airplane on a Conveyor Belt...
Post by: TracerX on January 30, 2008, 04:11:34 PM
I think the question has been sufficiently answered. The thrust of the propeller and the speed of the wheels operate completely independently of each other. The attempts of the conveyor belt to keep the plane from moving are futile. In fact, the plane will have the same takeoff roll that it normally has with very little effect from the increased speed the wheels see from the movements of the conveyor belt. The more interesting question is how fast will the wheels be spinning when it takes off at (lets set a standard) 100 mph.
I suppose that it depends on the operating limitations of the conveyor belt. But assuming that there are no limits, the speed would be infinitely large since as soon as the plane moves forward one mph, the conveyor belt will enter a never ending acceleration loop as there is nothing it can do to recover the movement of the airplane, thus eventually accelerating to infinity (assuming it could accelerate that fast).
Title: Airplane on a Conveyor Belt...
Post by: Shuffler on January 30, 2008, 04:26:00 PM
The plane will fly.....
The belt can do 500 mph the wheels will freewheel, the prop will still pull it forward to rotation.
Drag at some point will affect the speed but the prop pulls the plane through the air regardless of ground speed hence IAS, TAS.
Title: Airplane on a Conveyor Belt...
Post by: Furious on January 30, 2008, 04:42:58 PM
For Funked:
bearing friction.
Title: Airplane on a Conveyor Belt...
Post by: hitech on January 30, 2008, 05:07:45 PM
No thanks, trying to answerer a problem that is not clearly defined is futile.
Assume wheel speed = the speed of the out side of the wheel.
First the wheel and the conveyor only can be traveling the same speed when the plane is not moving. If the plane is moving then the wheel is always moving faster then the conveyor. So the question does not make any since from the definition of match speed.
Assume wheel speed = the speed at which the axle would move across the ground.
Then for the plane to not move the conveyor must be always at 0 speed. Again the problem does not make since.
So the question does not make any since from the definition of match speed.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on January 30, 2008, 05:14:45 PM
Quote
Originally posted by TracerX I suppose that it depends on the operating limitations of the conveyor belt. But assuming that there are no limits, the speed would be infinitely large since as soon as the plane moves forward one mph, the conveyor belt will enter a never ending acceleration loop as there is nothing it can do to recover the movement of the airplane, thus eventually accelerating to infinity (assuming it could accelerate that fast).
OK then, answer this:
Here’s a story that simplifies the problem: (Note that the term wheels in this story refers to wheels and tires)
Identical triplets Al, Bob and Chuck buy three identical bush planes. Since they live in Alaska, all three brothers buy and install large balloon “tundra tires” and wheels. The wheels, planes and brothers are identical. All three planes will take off from a normal runway in exactly 100 feet and at exactly 50 mph. The brothers fly their planes to an air show in Wisconsin. At the air show Bob finds and buys a set of fantastic wheels. These wheels are exactly like the wheels he has on his plane in every way except they have half the mass. Their mass is distributed in the same proportion as the wheels that he plans on replacing. Al thinks Bob is silly and is content with his old wheels. Bob thinks that Al will eventually want a set, so he buys a second set to give to Al on their birthday.
Bob finds a buyer for his old heavy wheels and installs a set of his new lightweight ones. He loads the second set into his plane so that it is balanced just as it was before. Bob’s plane now weighs exactly the same as Al’s and Chuck’s, but its wheels have half the mass.
Meanwhile, Chuck runs into a magician who sells him a set of magic wheels. These wheels are exactly like the wheels he has on his plane in every way except they have no mass. Chuck installs his magic wheels. He loads his old set into his plane so that it is balanced just as it was before. Chuck’s plane now weighs exactly the same as Al’s and Bob’s, but its wheels have no mass.
When the brothers leave the air show they request a formation take off. They line up wing tip to wing tip and apply power at exactly the same time. All three planes weigh exactly the same and must hit 50 mph to lift off. When Chuck’s plane lifts off his wheels stop spinning instantly since they have no mass. Since they have no mass, they also have no rotational inertia. When Al’s plane lifts off his heavy wheels are spinning at 50 mph and have considerable rotational inertia. When Bob’s plane lifts off his half-weight wheels are spinning at 50 mph and have exactly half the rotational inertia as Al’s wheels.
Where did the rotational inertia and energy in Bob’s and Al’s wheels come from? How did the rotational inertia and energy now stored in Bob’s and Al’s wheels affect the take off distance of their planes? We know that Al’s plane will still take off in exactly 100 feet; where will Bob’s and Chuck’s planes take off?
Title: Airplane on a Conveyor Belt...
Post by: john9001 on January 30, 2008, 05:18:38 PM
Chuck has a float plane and takes off from the lake.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on January 30, 2008, 06:20:39 PM
Quote
Originally posted by Chairboy There are some well intentioned but mistaken folks here who say the plane won't take off. These are the people who, I imagine, concentrate on the GV side of AH. :D
I don't think anyone here believes the plane won't take off under the conditions in this TV show.
There are some here who fail to understand that the question can be interpreted two ways. One allows the plane to take off, the other does not. They are reproducing the method which will allow the plane to take off.
Ooops, didn't read Curval's proclamation. Okay, one person then.
Title: Airplane on a Conveyor Belt...
Post by: john9001 on January 30, 2008, 07:55:36 PM
it doesnt matter which way the belt runs, it will have no effect on the plane.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on January 30, 2008, 08:07:50 PM
Quote
Originally posted by john9001 it doesnt matter which way the belt runs, it will have no effect on the plane.
Be careful, and answer this:
Here’s a story that simplifies the problem: (Note that the term wheels in this story refers to wheels and tires)
Identical triplets Al, Bob and Chuck buy three identical bush planes. Since they live in Alaska, all three brothers buy and install large balloon “tundra tires” and wheels. The wheels, planes and brothers are identical. All three planes will take off from a normal runway in exactly 100 feet and at exactly 50 mph. The brothers fly their planes to an air show in Wisconsin. At the air show Bob finds and buys a set of fantastic wheels. These wheels are exactly like the wheels he has on his plane in every way except they have half the mass. Their mass is distributed in the same proportion as the wheels that he plans on replacing. Al thinks Bob is silly and is content with his old wheels. Bob thinks that Al will eventually want a set, so he buys a second set to give to Al on their birthday.
Bob finds a buyer for his old heavy wheels and installs a set of his new lightweight ones. He loads the second set into his plane so that it is balanced just as it was before. Bob’s plane now weighs exactly the same as Al’s and Chuck’s, but its wheels have half the mass.
Meanwhile, Chuck runs into a magician who sells him a set of magic wheels. These wheels are exactly like the wheels he has on his plane in every way except they have no mass. Chuck installs his magic wheels. He loads his old set into his plane so that it is balanced just as it was before. Chuck’s plane now weighs exactly the same as Al’s and Bob’s, but its wheels have no mass.
When the brothers leave the air show they request a formation take off. They line up wing tip to wing tip and apply power at exactly the same time. All three planes weigh exactly the same and must hit 50 mph to lift off. When Chuck’s plane lifts off his wheels stop spinning instantly since they have no mass. Since they have no mass, they also have no rotational inertia. When Al’s plane lifts off his heavy wheels are spinning at 50 mph and have considerable rotational inertia. When Bob’s plane lifts off his half-weight wheels are spinning at 50 mph and have exactly half the rotational inertia as Al’s wheels.
Where did the rotational inertia and energy in Bob’s and Al’s wheels come from? How did the rotational inertia and energy now stored in Bob’s and Al’s wheels affect the take off distance of their planes? We know that Al’s plane will still take off in exactly 100 feet; where will Bob’s and Chuck’s planes take off?
Title: Airplane on a Conveyor Belt...
Post by: MiloMorai on January 30, 2008, 08:13:27 PM
Title: Airplane on a Conveyor Belt...
Post by: C(Sea)Bass on January 30, 2008, 08:46:02 PM
Quote
Originally posted by eskimo2 We know that Al’s plane will still take off in exactly 100 feet; where will Bob’s and Chuck’s planes take off?
The runway?
Title: Airplane on a Conveyor Belt...
Post by: Arlo on January 30, 2008, 08:57:48 PM
Dunno if anyone else mentioned this basic element of aerodynamics:
Airfoils create lift via airflow across them .... root to tip creating the most lift.
:D
Title: Airplane on a Conveyor Belt...
Post by: Treize69 on January 30, 2008, 08:59:38 PM
You can pull the "ground" 100 mph faster backwards than the plane goes forward, the planes engines don't turn the wheels, they pull through the air.
I am totally confused as to why they think this won't work. This is the dumbest myth I've ever seen them try.
Title: Airplane on a Conveyor Belt...
Post by: Chairboy on January 30, 2008, 09:01:48 PM
It's a perfect myth because of all the folks like Curval citing "common sense" explanations for why it won't fly.
Title: Airplane on a Conveyor Belt...
Post by: WWhiskey on January 30, 2008, 09:03:58 PM
show is over, planes all flew, even the pilot didnt think it would work! well there you go! :rofl :rofl :rofl :rofl
Title: Airplane on a Conveyor Belt...
Post by: Treize69 on January 30, 2008, 09:05:23 PM
Hey, what a surprise, the plane took off just fine. Waste of an episode.
(and yes, I am watching on a delay)
Title: Airplane on a Conveyor Belt...
Post by: WWhiskey on January 30, 2008, 09:06:28 PM
oops sorry!!! nice avatar tho!
Title: Airplane on a Conveyor Belt...
Post by: Holden McGroin on January 30, 2008, 09:07:36 PM
Quote
Originally posted by eskimo2
When the brothers leave the air show they request a formation take off. They line up wing tip to wing tip and apply power at exactly the same time. All three planes weigh exactly the same and must hit 50 mph to lift off. When Chuck’s plane lifts off his wheels stop spinning instantly since they have no mass. Since they have no mass, they also have no rotational inertia.
Why would they stop spinning? Zero rotational inertia at zero RPM would be equal to zero rotational inertia at 1000 RPM.
That being said, airplanes fly due to airspeed, not groundspeed.
Title: Airplane on a Conveyor Belt...
Post by: Donzo on January 30, 2008, 09:08:22 PM
Plane + steel cable hooked to a winch.
Plane sits on conveyor belt.
Conveyor belt moving in opposite direction while winch pulls the plane the forward will not prevent the plane from moving forward.
This is exactly what the engine(s) of the plane will do...move the plane forward no matter what the ground underneath is doing.
Title: Airplane on a Conveyor Belt...
Post by: Treize69 on January 30, 2008, 09:12:27 PM
As long as the ground isn't moving faster than the wheels can rotate safely, you could have the belt moving 200mph for a plane with an extremely low takeoff speed (like a real ultralight, not the one they used) and it'll still take off.
This is one of those things thats so redicuoulsy obvious that the people who get it have no clue why those who don't can't, and the ones who think it won't work will never understand why they are wrong. Either you get it or you don't.
Title: Airplane on a Conveyor Belt...
Post by: Chairboy on January 30, 2008, 09:15:04 PM
Nothing from Curval yet...
Title: Airplane on a Conveyor Belt...
Post by: Holden McGroin on January 30, 2008, 09:21:26 PM
Convair tested this 50 years ago...(http://www.nationalmuseum.af.mil/shared/media/photodb/web/061128-F-1234S-034.jpg)
Title: Airplane on a Conveyor Belt...
Post by: Treize69 on January 30, 2008, 09:24:10 PM
Title: Airplane on a Conveyor Belt...
Post by: Yknurd on January 30, 2008, 10:28:16 PM
Quote
Originally posted by Holden McGroin Why would they stop spinning? Zero rotational inertia at zero RPM would be equal to zero rotational inertia at 1000 RPM.
That being said, airplanes fly due to airspeed, not groundspeed.
So you are saying that airplanes could life off the ground if a strong enough wind blew?!?
Why, simply amazing!!!111
Wait, even if the plane was on a tread mill?
Astonishing, it is!!!111
Title: Airplane on a Conveyor Belt...
Post by: FBBone on January 30, 2008, 10:30:45 PM
Quote
Originally posted by Yknurd So you are saying that airplanes could life off the ground if a strong enough wind blew?!?
Why, simply amazing!!!111
Ever heard of a kite?:rolleyes:
Title: Airplane on a Conveyor Belt...
Post by: Russian on January 31, 2008, 12:01:01 AM
So they took off.....not surprising.
Title: Airplane on a Conveyor Belt...
Post by: Chairboy on January 31, 2008, 12:20:12 AM
Well, evidence (and by that I mean some posts here) suggests that there are some folks here that'll be pretty surprised.
Still no Curval...
Title: Airplane on a Conveyor Belt...
Post by: Holden McGroin on January 31, 2008, 12:21:17 AM
Curval's trying to jump off his treadmill: No luck so far.
Title: Airplane on a Conveyor Belt...
Post by: Arlo on January 31, 2008, 12:49:04 AM
Quote
Originally posted by Chairboy Well, evidence (and by that I mean some posts here) suggests that there are some folks here that'll be pretty surprised.
Still no Curval...
I'm not surprised but thrust versus drag seems just as important in formula as lift according to basic aerodynamics. I'd hate to see them try it with an ultralight .... for the pilot's sake. :D ;)
Title: Airplane on a Conveyor Belt...
Post by: Yknurd on January 31, 2008, 06:08:01 AM
Quote
Originally posted by FBBone Ever heard of a kite?:rolleyes:
You are quite the literary Illuminati aren't you?
Title: Airplane on a Conveyor Belt...
Post by: C(Sea)Bass on January 31, 2008, 06:39:41 AM
Quote
Originally posted by FBBone Ever heard of a kite?
A who?
Title: Airplane on a Conveyor Belt...
Post by: Curval on January 31, 2008, 07:45:13 AM
I cared so much about this issue...that I actually forgot to watch it.
It took off.
Congrats...you are teh winnnar.
Funny, I've now become the poster child for the "it won't take off" side of this argument and yet as I have previously stated I failed physics and don't fly planes (except as a passenger). I posted here just to bunch up people's panties.
I hope this major intardnet victory makes you feel really great about yourselves.
:rofl
Title: Airplane on a Conveyor Belt...
Post by: AKIron on January 31, 2008, 11:10:17 AM
Here's a better one. Who's faster, Superman or The Flash?
Title: Airplane on a Conveyor Belt...
Post by: Maverick on January 31, 2008, 11:51:02 AM
Curv,
Don't feel bad, the pilot that Mythbusters hired to do the stunt also figured the plane would "sit there like a brick" and not fly. Both the small scale and full scale results were the same, myth soundly busted.
Title: Airplane on a Conveyor Belt...
Post by: Chalenge on January 31, 2008, 12:59:46 PM
Whoever posted this problem to the MB group must have missed a few of the criteria I remember reading. Not that it would make any difference but I was disappointed to see the runway moving at takeoff speed only. I wanted to see smoking bearings and ludicrous speed! :D
Title: Airplane on a Conveyor Belt...
Post by: Treize69 on January 31, 2008, 01:01:41 PM
Quote
Originally posted by Chalenge ...smoking bearings and ludicrous speed! :D
Title: Airplane on a Conveyor Belt...
Post by: MajIssue on January 31, 2008, 02:53:24 PM
Quote
Originally posted by Chairboy I've put together a quick list of excuses you can call on tonight or tomorrow after the episode for why it took off:
"They did it wrong, they-":
1. "Weren't supposed to give it full throttle!" 2. "Should have tied it down to prevent it from moving!" 3. "Didn't make the conveyor belt move infinitely fast!" 4. "Aren't real scientists, they didn't understand the problem!"
Hope one or more of these fit your outrage. :D
If the plane doesn't take off for some reason (like, they tie it down or don't give it the right throttle or something) then I'll be sad, but I'll face my fate here like a man. Can you commit to the same?
I saw it last night and it was TOTAL BUNK. The Piper Cub they used was moving FORWARD. It was NOT stationary. The Mythbusters got it totally WRONG!! Anybody with any knowledge of how an airplane flies was throwing things at the television when they saw this episode.
FACT: An aircraft w/ zero Indicacated Air Speed will NOT fly.
Mythbusters: BUSTED for bad science
Title: Airplane on a Conveyor Belt...
Post by: Treize69 on January 31, 2008, 03:02:15 PM
{{Sung to the famouS "da da da daaaaaa" from Beethovens 5th}}
NOBODY CARES.... NOBODY CAAAARES.......
Title: Airplane on a Conveyor Belt...
Post by: AKIron on January 31, 2008, 03:04:53 PM
I didn't watch it. I'm curious though, did the plane take off before it reached the end of the "belt".
Title: Airplane on a Conveyor Belt...
Post by: Treize69 on January 31, 2008, 03:06:18 PM
IT TOOK OFF IN EXACTLY THE SAME DISTANCE IT DID WITHOUT THE BELT.
EDIT- Whoops, caps.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on January 31, 2008, 03:08:38 PM
Quote
Originally posted by Treize69 IT TOOK OFF IN EXACTLY THE SAME DISTANCE IT DID WITHOUT THE BELT.
EDIT- Whoops, caps.
I bet that's not true but it wasn't what I was asking.
It is highly unlikely a plane will ever take off in "exactly" the same distance twice in it's life. ;)
Title: Airplane on a Conveyor Belt...
Post by: Donzo on January 31, 2008, 03:12:12 PM
Quote
Originally posted by MajIssue I saw it last night and it was TOTAL BUNK. The Piper Cub they used was moving FORWARD. It was NOT stationary. The Mythbusters got it totally WRONG!! Anybody with any knowledge of how an airplane flies was throwing things at the television when they saw this episode.
FACT: An aircraft w/ zero Indicacated Air Speed will NOT fly.
Mythbusters: BUSTED for bad science
First of all, it was not a Piper Cub.
Secondly, the whole point was the the aircraft WOULD move forward, regardless of what the ground underneath it was doing.
Title: Airplane on a Conveyor Belt...
Post by: Treize69 on January 31, 2008, 03:12:32 PM
I know what you're asking, and the belt had no effect at all. Just like it didn't with the R/C plane, and just like anyone with brain in their heads would know it wouldn't.
God, can't we let this pointless argument die??? Its a stupid idea, it was a waste of an episode, and its a rediculous thing to keep going over ad nauseum. Either you get it or you don't, and it absolutely rediculous how many people do not, and will not, EVER understand it.
The ignorance and stubbornness of people never ceases to disturb me.
Title: Airplane on a Conveyor Belt...
Post by: Russian on January 31, 2008, 03:15:38 PM
http://uk.youtube.com/watch?v=IbRcg3ji_Pc
here's video in question .....
Title: Airplane on a Conveyor Belt...
Post by: AKIron on January 31, 2008, 03:16:05 PM
Quote
Originally posted by Treize69 I know what you're asking, and the belt had no effect at all. Just like it didn't with the R/C plane, and just like anyone with brain in their heads would know it wouldn't.
God, can't we let this pointless argument die??? Its a stupid idea, it was a waste of an episode, and its a rediculous thing to keep going over ad nauseum. Either you get it or you don't, and it absolutely rediculous how many people do not, and will not, EVER understand it.
The ignorance and stubbornness of people never ceases to disturb me.
I didn't ask if the belt had an effect. I never doubted the plane would take off. The "belt" had a limited length. I am simply curious if the plane took off before they ran out of belt. Dosen't sound like a hard question for someone who watched it. Did you watch it?
Title: Airplane on a Conveyor Belt...
Post by: Treize69 on January 31, 2008, 03:17:28 PM
Yes, and I've now said THREE times that it got off well before the end.
I am typing in English right? I get distracted sometimes.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on January 31, 2008, 03:17:42 PM
Quote
Originally posted by Russian http://uk.youtube.com/watch?v=IbRcg3ji_Pc
here's video in question .....
Thanks.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on January 31, 2008, 03:18:24 PM
Quote
Originally posted by Treize69 Yes, and I've now said THREE times that it got off well before the end.
I am typing in English right? I get distracted sometimes.
Sheesh, talk about stubborness.
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on January 31, 2008, 03:33:51 PM
Quote
Originally posted by Curval
"I posted here just to bunch up people's panties."
I hope this major intardnet victory makes you feel really great about yourselves.
You took a position in an arguement, you had no convictions on, just to rile people?
Get a life.
Title: Airplane on a Conveyor Belt...
Post by: Curval on January 31, 2008, 03:39:08 PM
Quote
Originally posted by VERTEX
Quote
Originally posted by Curval
"I posted here just to bunch up people's panties."
I hope this major intardnet victory makes you feel really great about yourselves.
You took a position in an arguement, you had no convictions on, just to rile people?
Get a life. [/B]
LOL
If you look and see how many posts I have you would have already figured out I don't have much of a life.
Freaking newb.
:lol
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on January 31, 2008, 03:54:28 PM
So now we resort to name calling.
I just don't understand taking a particular side of a discussion just to annoy.
Title: Airplane on a Conveyor Belt...
Post by: WilldCrd on January 31, 2008, 03:58:07 PM
Quote
Originally posted by VERTEX So now we resort to name calling.
I just don't understand taking a particular side of a discussion just to annoy.
You must be new around these parts. We do this JUST to argue at times. Sometimes its more serious, usually some take the opposite side just to be part of the argument. Its a continuous dynamic kinda thing. After you have been here awhile you may understand.
p.s. ya "might" wanna go out and buy a flame retardant suit first :D
Title: Airplane on a Conveyor Belt...
Post by: Curval on January 31, 2008, 04:00:26 PM
Quote
Originally posted by WilldCrd You must be new around these parts. We do this JUST to argue at times. Sometimes its more serious, usually some take the opposite side just to be part of the argument. Its a continuous dynamic kinda thing. After you have been here awhile you may understand.
p.s. ya "might" wanna go out and buy a flame retardant suit first :D
What he said.
After telling me to "Get a life" you claim that I am name calling?
Good for you...you are starting to *get it*.
:aok :rofl
Title: Airplane on a Conveyor Belt...
Post by: Yknurd on January 31, 2008, 04:06:07 PM
The real funny thing is that this "argument" serves no purpose.
Pixels in virtual world = victory?
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on January 31, 2008, 04:06:18 PM
In that case;
Any experiments shown to date, which demonstrate the ability of an airplane to take off normally while on a conveyor traveling in the opposite direction are clearly conspiracies of the worst kind meant to deliberately deceive an otherwise well informed public.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on January 31, 2008, 04:10:42 PM
Quote
Originally posted by Treize69 I know what you're asking, and the belt had no effect at all. Just like it didn't with the R/C plane, and just like anyone with brain in their heads would know it wouldn't.
God, can't we let this pointless argument die??? Its a stupid idea, it was a waste of an episode, and its a rediculous thing to keep going over ad nauseum. Either you get it or you don't, and it absolutely rediculous how many people do not, and will not, EVER understand it.
The ignorance and stubbornness of people never ceases to disturb me.
Quote
Originally posted by Treize69 ...and the belt had no effect at all.
So many folks insist that they are so smart; yet not one of them can answer or even comprehend the very question that will force them to view the problem in a new light:
Here’s a story that simplifies the problem: (Note that the term wheels in this story refers to wheels and tires)
Identical triplets Al, Bob and Chuck buy three identical bush planes. Since they live in Alaska, all three brothers buy and install large balloon “tundra tires” and wheels. The wheels, planes and brothers are identical. All three planes will take off from a normal runway in exactly 100 feet and at exactly 50 mph. The brothers fly their planes to an air show in Wisconsin. At the air show Bob finds and buys a set of fantastic wheels. These wheels are exactly like the wheels he has on his plane in every way except they have half the mass. Their mass is distributed in the same proportion as the wheels that he plans on replacing. Al thinks Bob is silly and is content with his old wheels. Bob thinks that Al will eventually want a set, so he buys a second set to give to Al on their birthday.
Bob finds a buyer for his old heavy wheels and installs a set of his new lightweight ones. He loads the second set into his plane so that it is balanced just as it was before. Bob’s plane now weighs exactly the same as Al’s and Chuck’s, but its wheels have half the mass.
Meanwhile, Chuck runs into a magician who sells him a set of magic wheels. These wheels are exactly like the wheels he has on his plane in every way except they have no mass. Chuck installs his magic wheels. He loads his old set into his plane so that it is balanced just as it was before. Chuck’s plane now weighs exactly the same as Al’s and Bob’s, but its wheels have no mass.
When the brothers leave the air show they request a formation take off. They line up wing tip to wing tip and apply power at exactly the same time. All three planes weigh exactly the same and must hit 50 mph to lift off. When Chuck’s plane lifts off his wheels stop spinning instantly since they have no mass. Since they have no mass, they also have no rotational inertia. When Al’s plane lifts off his heavy wheels are spinning at 50 mph and have considerable rotational inertia. When Bob’s plane lifts off his half-weight wheels are spinning at 50 mph and have exactly half the rotational inertia as Al’s wheels.
Where did the rotational inertia and energy in Bob’s and Al’s wheels come from? How did the rotational inertia and energy now stored in Bob’s and Al’s wheels affect the take off distance of their planes? We know that Al’s plane will still take off in exactly 100 feet; where will Bob’s and Chuck’s planes take off?
Title: Airplane on a Conveyor Belt...
Post by: Curval on January 31, 2008, 04:10:46 PM
Quote
Originally posted by VERTEX In that case;
Any experiments shown to date, which demonstrate the ability of an airplane to take off normally while on a conveyor traveling in the opposite direction are clearly conspiracies of the worst kind meant to deliberately deceive an otherwise well informed public.
They are indeed. Well said.
I suspect this guy is going to fit right in.:aok
Title: Airplane on a Conveyor Belt...
Post by: rabbidrabbit on January 31, 2008, 04:33:28 PM
Quote
Originally posted by eskimo2 So many folks insist that they are so smart; yet not one of them can answer or even comprehend the very question that will force them to view the problem in a new light:
Here’s a story that simplifies the problem: (Note that the term wheels in this story refers to wheels and tires)
Identical triplets Al, Bob and Chuck buy three identical bush planes. Since they live in Alaska, all three brothers buy and install large balloon “tundra tires” and wheels. The wheels, planes and brothers are identical. All three planes will take off from a normal runway in exactly 100 feet and at exactly 50 mph. The brothers fly their planes to an air show in Wisconsin. At the air show Bob finds and buys a set of fantastic wheels. These wheels are exactly like the wheels he has on his plane in every way except they have half the mass. Their mass is distributed in the same proportion as the wheels that he plans on replacing. Al thinks Bob is silly and is content with his old wheels. Bob thinks that Al will eventually want a set, so he buys a second set to give to Al on their birthday.
Bob finds a buyer for his old heavy wheels and installs a set of his new lightweight ones. He loads the second set into his plane so that it is balanced just as it was before. Bob’s plane now weighs exactly the same as Al’s and Chuck’s, but its wheels have half the mass.
Meanwhile, Chuck runs into a magician who sells him a set of magic wheels. These wheels are exactly like the wheels he has on his plane in every way except they have no mass. Chuck installs his magic wheels. He loads his old set into his plane so that it is balanced just as it was before. Chuck’s plane now weighs exactly the same as Al’s and Bob’s, but its wheels have no mass.
When the brothers leave the air show they request a formation take off. They line up wing tip to wing tip and apply power at exactly the same time. All three planes weigh exactly the same and must hit 50 mph to lift off. When Chuck’s plane lifts off his wheels stop spinning instantly since they have no mass. Since they have no mass, they also have no rotational inertia. When Al’s plane lifts off his heavy wheels are spinning at 50 mph and have considerable rotational inertia. When Bob’s plane lifts off his half-weight wheels are spinning at 50 mph and have exactly half the rotational inertia as Al’s wheels.
Where did the rotational inertia and energy in Bob’s and Al’s wheels come from? How did the rotational inertia and energy now stored in Bob’s and Al’s wheels affect the take off distance of their planes? We know that Al’s plane will still take off in exactly 100 feet; where will Bob’s and Chuck’s planes take off?
In this case we don't know the mass of the original wheels so a calculation is impossible. However, a relationship can.
The rotational force needed for Bob and Al's wheels are taken as an initial and inertial resistance force that detracts from thrust.
From that we assume they will take less than 100 ft to take off with Bob being 100-x and Al being 100-2x less. X being the force imparted on Bob's wheels to rotate them up to 50mph.
Title: Airplane on a Conveyor Belt...
Post by: john9001 on January 31, 2008, 04:46:05 PM
eskimo2, i think you are putting too much emphasis on the amount of energy required to spin a wheel, but to answer your question, bob's plane will take off in 99 feet and 11 inches and chucks plane will take off in 99 feet and 10.5 inches.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on January 31, 2008, 04:47:27 PM
Quote
Originally posted by rabbidrabbit In this case we don't know the mass of the original wheels so a calculation is impossible. However, a relationship can.
The rotational force needed for Bob and Al's wheels are taken as an initial and inertial resistance force that detracts from thrust.
From that we assume they will take less than 100 ft to take off with Bob being 100-x and Al being 100-2x less. X being the force imparted on Bob's wheels to rotate them up to 50mph.
Bravo!
Now, are you ever going to explain where you got the version of the original AH BBS thread from? Where did “the conveyor exactly matches the plane’s wheel’s speed” twist come from?
Title: Airplane on a Conveyor Belt...
Post by: rabbidrabbit on January 31, 2008, 04:52:53 PM
Me.
I'm just that fricken evil.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on January 31, 2008, 04:55:09 PM
Quote
Originally posted by john9001 eskimo2, i think you are putting too much emphasis on the amount of energy required to spin a wheel, but to answer your question, bob's plane will take off in 99 feet and 11 inches and chucks plane will take off in 99 feet and 10.5 inches.
As it applies to the question where the conveyor exactly matches the plane’s speed; the difference is so slight that it wouldn’t hardly matter. The plane will take off almost exactly within the same distance.
The original AH BBS thread question said: “the conveyor exactly matches the plane’s wheel’s speed”. This changes everything. In this instance, the conveyor must assume an accelerate rate that loads as much rotational energy into the ever increasing wheel speed to match the thrust of the engine/prop.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on January 31, 2008, 04:56:42 PM
Quote
Originally posted by rabbidrabbit Me.
I'm just that fricken evil.
OMG! Did you make the change with the twist to the solution in mind? Or was it accidental?
Title: Airplane on a Conveyor Belt...
Post by: BlkKnit on January 31, 2008, 05:10:55 PM
Quote
the conveyor exactly matches the plane’s wheel’s speed”. This changes everything. In this instance, the conveyor must assume an accelerate rate that loads as much rotational energy into the ever increasing wheel speed to match the thrust of the engine/prop.
This is not possible. The wheels only rotate upon movement of the aircraft. If the aircraft can move, it can develop lift. If the belt matches the speed of the wheels EXACTLY then the wheels can never spin to start with because the aircraft has not moved.
Hey! this is fun?:huh
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on January 31, 2008, 05:42:51 PM
Quote
Originally posted by eskimo2 How did the rotational inertia and energy now stored in Bob’s and Al’s wheels affect the take off distance of their planes? We know that Al’s plane will still take off in exactly 100 feet; where will Bob’s and Chuck’s planes take off?
Please, tell the answers and explain in such manner, that dumb people like me, will understand. Pretty please....
Title: Airplane on a Conveyor Belt...
Post by: AKIron on January 31, 2008, 05:46:19 PM
Quote
Originally posted by BlkKnit This is not possible. The wheels only rotate upon movement of the aircraft. If the aircraft can move, it can develop lift. If the belt matches the speed of the wheels EXACTLY then the wheels can never spin to start with because the aircraft has not moved.
Hey! this is fun?:huh
I think it is assumed that the belt must only try to match the wheels speed and be successful to within say a few nanometers per second. For the umpteenth time (not directed at anyone in particular), which speed? The forward speed of the wheel as measured at the center point of the axle or the speed of the wheel as measured at the surface of the tire? These two will yield dramatically different results.
Title: Airplane on a Conveyor Belt...
Post by: Yknurd on January 31, 2008, 05:58:38 PM
My brain hurts.
Title: Airplane on a Conveyor Belt...
Post by: BlkKnit on January 31, 2008, 06:00:24 PM
Just my opinion here, but it seems that many of the "restrictions" placed on this myth (yes, myth) are physically impossible.
Belt matches plane speed, then so what, wheels turn twice as fast and the plane takes off.
Belt matching wheel speed (outside of the tire circumference) is impossible. Something will be different (unless there is no movement at all). The only thing that will make the tire spin (and thus the belt) is if the plane is moving.
IF there is just a plane, sitting on a free wheeling conveyor belt with no outside forces applied to the belt or the tires, the tires will not necessarily turn at all! However, the plane will still take off because the belt will move WITH the aircraft.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on January 31, 2008, 06:15:56 PM
Quote
Originally posted by 2bighorn Please, tell the answers and explain in such manner, that dumb people like me, will understand. Pretty please....
Chuck’s wheels have no mass, and no rotational energy. Bob’s wheels have half the mass of Al’s wheels. Therefore, at 50 mph Chuck’s wheels are storing 0 energy, Bob’s wheels are storing ½ X energy and Al’s wheels are storing X energy. Chuck’s plane must take off first, then Bob’s, then Al’s. It doesn’t matter if Chuck’s plane takes off 4 feet before Al’s or 4 mm; the concept shows that getting the wheels up to speed consumes energy. A conveyor belt of unlimited speed and power can constantly load enough energy into the wheels to counter-act the plane’s thrust.
Note: this ONLY applies to the question where “the conveyor exactly matches the plane’s wheel’s speed”.
Also note: After the plane runs out of gas, the energy stored in the wheels would be equal to the energy consumed by the full tank of gas (minus the inefficiency of the engine and prop, etc.).
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on January 31, 2008, 06:23:52 PM
Quote
Originally posted by BlkKnit Just my opinion here, but it seems that many of the "restrictions" placed on this myth (yes, myth) are physically impossible.
Belt matches plane speed, then so what, wheels turn twice as fast and the plane takes off.
Belt matching wheel speed (outside of the tire circumference) is impossible. Something will be different (unless there is no movement at all). The only thing that will make the tire spin (and thus the belt) is if the plane is moving.
IF there is just a plane, sitting on a free wheeling conveyor belt with no outside forces applied to the belt or the tires, the tires will not necessarily turn at all! However, the plane will still take off because the belt will move WITH the aircraft.
Imagine that “exactly matches” really means that YOU have a big acceleration control dial for the conveyor and your job is to keep it in place. The plane fires up and begins to inch forward; you see this and crank the acceleration dial. You go too far, however, so the plane drifts back behind its starting point. Seeing this you back off on the acceleration dial and adjust it to keep the plane pretty much where it started.
Look at the concept; don’t get caught up in the semantics of the word “exactly”.
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on January 31, 2008, 06:47:38 PM
Quote
Originally posted by eskimo2 Chuck�s wheels have no mass, and no rotational energy. Bob�s wheels have half the mass of Al�s wheels. Therefore, at 50 mph Chuck�s wheels are storing 0 energy, Bob�s wheels are storing � X energy and Al�s wheels are storing X energy. Chuck�s plane must take off first, then Bob�s, then Al�s. It doesn�t matter if Chuck�s plane takes off 4 feet before Al�s or 4 mm; the concept shows that getting the wheels up to speed consumes energy. A conveyor belt of unlimited speed and power can constantly load enough energy into the wheels to counter-act the plane�s thrust.
No offence, you just say it happens and I'd like to know how and why.
What I'd like to see is the clear answer on your very specific question: How did the rotational inertia and energy now stored in Bob�s and Al�s wheels affect the take off distance of their planes?
Quote
Originally posted by eskimo2 Note: this ONLY applies to the question where the conveyor exactly matches the plane's wheels speed.
There is no conveyor in your identical triplets story. Got to read it again. Maybe I've missed something.
Quote
Originally posted by eskimo2 Also note: After the plane runs out of gas, the energy stored in the wheels would be equal to the energy consumed by the full tank of gas (minus the inefficiency of the engine and prop, etc.).
Interesting, very very interesting. I must admit I didn't know that.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on January 31, 2008, 06:52:37 PM
Quote
Originally posted by 2bighorn No offence, you just say it happens and I'd like to know how and why.
What I'd like to see is the clear answer on your very specific question: How did the rotational inertia and energy now stored in Bob�s and Al�s wheels affect the take off distance of their planes?
There is no conveyor in your identical triplets story. Got to read it again. Maybe I've missed something.
Interesting, very very interesting. I must admit I didn't know that.
uh oh, here comes the belt sander ;)
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on January 31, 2008, 06:57:42 PM
Quote
Originally posted by 2bighorn
There is no conveyor in your identical triplets story. Got to read it again. Maybe I've missed something.
The conveyor belt is the confusing part. This question allows the reader to understand the principle of rotational acceleration consuming power without the conveyor. Understand this, and you should then be able to transfer the concept to the conveyor question.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on January 31, 2008, 07:01:46 PM
Quote
Originally posted by AKIron uh oh, here comes the belt sander ;)
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on January 31, 2008, 07:05:52 PM
Quote
Originally posted by eskimo2 The conveyor belt is the confusing part.
Indeed, even after third reading, I still don't see conveyor in that story
Quote
Originally posted by eskimo2 This question allows the reader to understand the principle of rotational acceleration consuming power without the conveyor.
The principle which you resist to explain.
Quote
Originally posted by eskimo2 Understand this, and you should then be able to transfer the concept to the conveyor question.
I'd really like to, but I need your help, and the best way to help me, would be to answer your own question: How did the rotational inertia and energy now stored in Bob's and Al's wheels affect the take off distance of their planes? Since you understand the principle (and you're a teacher), it should be easy to explain (I'd really like to know).
Title: Airplane on a Conveyor Belt...
Post by: AKIron on January 31, 2008, 07:12:39 PM
Quote
Originally posted by 2bighorn Indeed, even after third reading, I still don't see conveyor in that story
The principle which you resist to explain.
I'd really like to, but I need your help, and the best way to help me, would be to answer your own question: How did the rotational inertia and energy now stored in Bob's and Al's wheels affect the take off distance of their planes? Since you understand the principle (and you're a teacher), it should be easy to explain (I'd really like to know).
Energy transferred to the wheels is energy not used to move the plane forward.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on January 31, 2008, 07:20:55 PM
I explained it here:
Chuck’s wheels have no mass, and no rotational energy. Bob’s wheels have half the mass of Al’s wheels. Therefore, at 50 mph Chuck’s wheels are storing 0 energy, Bob’s wheels are storing ½ X energy and Al’s wheels are storing X energy. Chuck’s plane must take off first, then Bob’s, then Al’s. It doesn’t matter if Chuck’s plane takes off 4 feet before Al’s or 4 mm; the concept shows that getting the wheels up to speed consumes energy. A conveyor belt of unlimited speed and power can constantly load enough energy into the wheels to counter-act the plane’s thrust.
A wheel that has a mass of X and has an outside speed of 50 mph will have twice the rotational energy of a wheel that has a mass of 1/2 X and has an outside speed of 50 mph. The one with no mass, has no energy.
Does that make sense?
Title: Airplane on a Conveyor Belt...
Post by: BlkKnit on January 31, 2008, 09:03:53 PM
Quote
Originally posted by eskimo2 Imagine that “exactly matches” really means that YOU have a big acceleration control dial for the conveyor and your job is to keep it in place. The plane fires up and begins to inch forward; you see this and crank the acceleration dial. You go too far, however, so the plane drifts back behind its starting point. Seeing this you back off on the acceleration dial and adjust it to keep the plane pretty much where it started.
Look at the concept; don’t get caught up in the semantics of the word “exactly”.
I still dont see it. Matching the tires rotational speed in this way causes the tires to spin. Thats creating a false result using outside influence. There is no way the belt affects anything without those outside influences.
I think this myth has degenerated to this level and probably was not the original question. It must have started as a simple trick question of logic.
But, of course, if you can keep the aircraft stationary you can keep it from lifting. I just think my understanding of the question may be incorrect and if so, then the question is incorrect. It must be, I cant be wrong! :D
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on January 31, 2008, 09:16:39 PM
Quote
Originally posted by AKIron Energy transferred to the wheels is energy not used to move the plane forward.
That is true.
But in his story (apart from the wheels), all planes are identical. The difference in wheel mass is compensated with airframe ballast.
So, size, rolling friction, drag, and total weight is the same, therefore thrust needed (Force) to move the plane would be the same. (at least according to the Newton).
It does not matter if mass of some parts vary slightly (ie wheels). The total inertial mass to be accounted remains equal among all three systems (planes), so does sum of all forces.
That said, take off distance would still vary for about 0.08%, not due to Eskimo's theory, but because the plane with lightest wheel would have the heaviest frame and therefore exercise slightly larger force on the wheel bearings hence bearing friction would increased slightly...
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on January 31, 2008, 09:23:35 PM
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on January 31, 2008, 09:42:15 PM
Quote
Originally posted by eskimo2 2bighorn, Watch the AVI's:
Film 1: Find two more wheels of equal size but different weight, compensate that with different strength of attachment (dont know if it's spring or rubber) for each wheel and repeat.
Film 2: Attach objects of different mass to each of your rotating body, so that all three groups have the same mass and repeat the experiment.
That's what you did with your planes, you compensated difference in wheel mass with ballast mass.
If total mass does not change, nor forces applied, the distance of movement should neither.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on January 31, 2008, 09:44:24 PM
Assume 2bighorn that each of eskimo's planes must reach exactly the same airspeed to lift off. To make things simple, since I don't recall if eskimo specified, also assume that each of the 3 wheel sets all have the same diameter.
Since they are all spinning at the same rate on each plane for a given speed the wheels with more mass will have more energy. That energy didn't mystically appear, it was created by the plane's engine. Let's also assume that each of the three planes were running at full power and they were all three putting out the same amount of power. All other things being equal, the plane(s) that put the least amount of it's energy into the wheels will accelerate and takeoff faster.
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on January 31, 2008, 11:55:15 PM
Quote
Originally posted by AKIron Since they are all spinning at the same rate on each plane for a given speed the wheels with more mass will have more energy. That energy didn't mystically appear, it was created by the plane's engine. Let's also assume that each of the three planes were running at full power and they were all three putting out the same amount of power. All other things being equal, the plane(s) that put the least amount of it's energy into the wheels will accelerate and takeoff faster.
Yes, but he specified all planes have same weight. Therefore the energy you save with lighter wheels goes into moving heavier frame. Heavy airframe + light wheels = light airframe + heavy wheels Same mass, same force needed...
Title: Airplane on a Conveyor Belt...
Post by: SD67 on February 01, 2008, 03:30:12 AM
I remember reading an piece about this on AVweb by the CEO of the Cockpit. Funny guy, always a good read. http://www.avweb.com/news/pilotlounge/191034-1.html
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 07:45:38 AM
Quote
Originally posted by 2bighorn Yes, but he specified all planes have same weight. Therefore the energy you save with lighter wheels goes into moving heavier frame. Heavy airframe + light wheels = light airframe + heavy wheels Same mass, same force needed...
Okay but think about this. Assume the tire riding in the back seat has the same mass as the tire rolling under the plane. Which has more energy at takeoff? They are both moving forward with the same amount of energy relative to the fixed starting point but the one rolling has more energy because it is both moving forward and spinning. That energy could have been used to accelerate the plane but wasn't.
Title: Airplane on a Conveyor Belt...
Post by: Yknurd on February 01, 2008, 08:05:55 AM
The fat pilot who just ate the bean burrito at Taco Bell has the most kinetic energy in the plane.
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 01, 2008, 08:14:51 AM
it takes very little energy to spin a wheel, and that energy is coming from the belt, not the planes thrust.
the belt is spinning the wheel. all the energy put into the wheel has come from the belt.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 08:21:55 AM
Quote
Originally posted by john9001 it takes very little energy to spin a wheel, and that energy is coming from the belt, not the planes thrust.
the belt is spinning the wheel. all the energy put into the wheel has come from the belt.
It takes energy from the plane's engine to keep the wheel from rolling backwards with the belt. Amounts are relative to the speed of the belt. With a belt moving at only 100mph that amount of energy is insignificant relative to what's used to get the plane off the ground.
Accelerate that belt to say 10,000 mph and the plane's engine will be transferring a lot more of it's power to keep that wheel from rolling backwards with the belt. It may not have enough left to move the plane forward.
Title: Airplane on a Conveyor Belt...
Post by: Chairboy on February 01, 2008, 08:44:53 AM
That's just about entirely inaccurate.
Frictional force between two surfaces is u*N (coefficient of rolling friction * Normal Force). The treadmill applies EXACTLY the same force of friction, without regard to whether it's moving at zero, 100, 1,000, or 50,000 mph.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 08:47:58 AM
Quote
Originally posted by Chairboy That's just about entirely inaccurate.
Frictional force between two surfaces is u*N (coefficient of rolling friction * Normal Force). The treadmill applies EXACTLY the same force of friction, without regard to whether it's moving at zero, 100, 1,000, or 50,000 mph.
That's not entirely accurate. The coefficient of friction will most certainly change as the tire heats up due to increasing speed.
But I wasn't including friction as a factor (though of course it is).
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 08:58:28 AM
There are a lot variables in these scenarios and several scenarios have been supposed to illustrate the forces involved. It's easy to mix these up which is probably why this discussion/argument has been so long lived.
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 01, 2008, 09:03:25 AM
Quote
Originally posted by AKIron It takes energy from the plane's engine to keep the wheel from rolling backwards with the belt.
the tire can not roll backwards because the belt can only match the wheel speed, and where does the energy from the belt go?
the energy required to spin the wheels is greatly over estimated.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 09:05:36 AM
It occurred to me that you are probably thinking of a fixed speed belt rather than an accelerating belt Chairboy. Which will apply more force to the wheel (which must be countered by the plane's engine), a belt that accelerates from 0-100 mph in 1 minute or a belt that accelerates from 0-10,000 mph in 1 minute?
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 09:08:33 AM
Quote
Originally posted by john9001 the tire can not roll backwards because the belt can only match the wheel speed, and where does the energy from the belt go?
the energy required to spin the wheels is greatly over estimated.
Before we go there we have to establish which speed the belt must match. Are we talking about the belt matching the wheels axis (and therefore the plane's speed relative to a tree sitting next to the belt) or the surface of the tire?
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 09:13:39 AM
Once we agree on the what speed the belt must match we must then agree on how quick the belt is allowed to respond to changes in the wheel and how fast the belt is allowed to go.
Title: Airplane on a Conveyor Belt...
Post by: Chairboy on February 01, 2008, 09:15:49 AM
Quote
Originally posted by AKIron It occurred to me that you are probably thinking of a fixed speed belt rather than an accelerating belt Chairboy. Which will apply more force to the wheel (which must be countered by the plane's engine), a belt that accelerates from 0-100 mph in 1 minute or a belt that accelerates from 0-10,000 mph in 1 minute?
Akiron, why are you changing the problem? Now you're talking about something called 'force to the wheel' as if it means anything to this conversation. Have you moved on from the treadmill 'problem' to something else?
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 09:18:00 AM
Quote
Originally posted by Chairboy Akiron, why are you changing the problem? Now you're talking about something called 'force to the wheel' as if it means anything to this conversation.
Force to the wheel is relevant and is the focus of Eskimo's question about Bob, Al, and whatever his name is.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 09:22:17 AM
More importantly though Chairboy, you just demonstrated the nature of the problem, that being that we don't all agree on what the problem actually is. For that matter, I think many of us don't even understand or agree that we don't agree on what the problem is. Kinda like RL.
Title: Airplane on a Conveyor Belt...
Post by: Yknurd on February 01, 2008, 09:25:34 AM
I think we can safely make the following assumptions:
AKIron will unconditionally continue to think that Chairboy is wrong.
Chairboy will unconditionally continue to think that AKIron is wrong.
A lot of homosexual sexual tension has been building.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 09:40:19 AM
I'm thinking that plane would roll a lot better with Yknurd under the wheels. :p
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 09:45:50 AM
Eskimo made some excellent videos to illustrate the forces involved. His story about Bill, Ted, and Alice also illustrates the problem well though it may be a tad hard to follow. As has been repeated here ad nauseam, there are basically two scenarios. The first was just demonstrated on the who cares channel. The second is much more interesting as there are a lot of variables. It is this second to which all my replies address.
Title: Airplane on a Conveyor Belt...
Post by: sluggish on February 01, 2008, 09:47:43 AM
Quote
Originally posted by eskimo2 As it applies to the question where the conveyor exactly matches the plane’s speed; the difference is so slight that it wouldn’t hardly matter. The plane will take off almost exactly within the same distance.
The original AH BBS thread question said: “the conveyor exactly matches the plane’s wheel’s speed”. This changes everything. In this instance, the conveyor must assume an accelerate rate that loads as much rotational energy into the ever increasing wheel speed to match the thrust of the engine/prop.
Your theory relies on unfairly applying the laws of physics to the wheel while totally disregarding them for the belt. If the belt can defy the laws of physics and instantly ramp up to infinitey, those same non-laws must also apply to the wheels.
The plane flies.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 09:48:53 AM
Quote
Originally posted by sluggish Your theory relies on unfairly applying the laws of physics to the wheel while totally disregarding them for the belt. If the belt can defy the laws of physics and instantly ramp up to infinitey, those same non-laws must also apply to the wheels.
The plane flies.
Uh, if that belt can ramp up to infinity that plane most definitely won't be flying, at least in this universe.
Seriously though Sluggish, set some parameters for the belt. The math can be done to determine if the plane can fly.
Title: Airplane on a Conveyor Belt...
Post by: Yknurd on February 01, 2008, 09:50:46 AM
Quote
Originally posted by AKIron I'm thinking that plane would roll a lot better with Yknurd under the wheels. :p
LOL
Title: Airplane on a Conveyor Belt...
Post by: sluggish on February 01, 2008, 10:05:33 AM
Quote
Originally posted by AKIron Uh, if that belt can ramp up to infinity that plane most definitely won't be flying, at least in this universe.
Seriously though Sluggish, set some parameters for the belt. The math can be done to determine if the plane can fly.
Why do I have to set parameters for the belt? In order for the belt to instanly compensate for the movement of the wheel, there can be no parameters. In order for this to be fair, the wheel must also follow the same non-parameters.
the plane flies.
Title: Airplane on a Conveyor Belt...
Post by: Chairboy on February 01, 2008, 10:09:00 AM
Sluggish, the problem here, it seems, is that some folks (unsatisfied perhaps with the result) are now trying to re-define the problem until they find a way that makes it not fly. Constantly repasting the 'tundra tires' puzzle is one method, another has to do with creating mathematical abstractions that attempt to violate the laws of physics by "just going faster" and pretty soon, people are throwing around concepts like 'infinite speed'.
Science is a harsh mistress. u*N is the law of the land, and no amount of mental bananay is going to get this girl pregnant.
Title: Airplane on a Conveyor Belt...
Post by: Fishu on February 01, 2008, 10:21:26 AM
To keep the plane from moving there would have to be an opposing force to the thrust, which would be headwind. However that wouldn't stop it from moving in vertical axis, but the effect would then be the same as with car on a conveyor belt - it wouldn't move forward.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 10:21:52 AM
The problem here Sluggish is that since the problem was ill defined, it can be resolved in many ways with different outcomes. Some of us, perhaps foolishly, enjoy exploring the possibilities.
Title: Airplane on a Conveyor Belt...
Post by: WWhiskey on February 01, 2008, 10:30:59 AM
Quote
Originally posted by Fishu To keep the plane from moving there would have to be an opposing force to the thrust, which would be headwind. However that wouldn't stop it from moving in vertical axis, but the effect would then be the same as with car on a conveyor belt - it wouldn't move forward.
headwind? think that will cause lift, then flight,hence movement in the vertical= flying!!!
Title: Airplane on a Conveyor Belt...
Post by: sluggish on February 01, 2008, 10:34:29 AM
If we have a "magic" conveyor belt that can instanly and infinately compensate and react to the movement of a "normal" wheel that must remain within the parameters of mass and enertia, the wheel masses acceleration enertia will prevent the plane from moving.
the plane doesn't fly.
Title: Airplane on a Conveyor Belt...
Post by: BlkKnit on February 01, 2008, 10:41:49 AM
I still say that this is impossible. The tires do not turn unless the plane moves, but the belt will counteract the tire rotation, in which case, the aircraft does not move.
I understand the argument of:
Quote
Originally posted by eskimo2 Imagine that “exactly matches” really means that YOU have a big acceleration control dial for the conveyor and your job is to keep it in place. The plane fires up and begins to inch forward; you see this and crank the acceleration dial. You go too far, however, so the plane drifts back behind its starting point. Seeing this you back off on the acceleration dial and adjust it to keep the plane pretty much where it started.
Look at the concept; don’t get caught up in the semantics of the word “exactly”.
But very soon after tire rotational speed is established, it is only maintained by forces from the belt, NOT by forces from the aircraft. This skews the results. I do realize that there are forces from the aircraft involved, but those same forces would move the aircraft, only spinning the tires as a result of the movement. If the aircraft does not move the tires do not spin unless there is an outside force applied to the belt (which is a given as stated in earlier arguments). Thats what I want to see: Make the belt match the tires rotation. Is it mathematically possible? I'm no math guru, but I am pretty sure that you can prove anything mathematically if you go about it right.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 11:02:28 AM
Quote
Originally posted by sluggish If we have a "magic" conveyor belt that can instanly and infinately compensate and react to the movement of a "normal" wheel that must remain within the parameters of mass and enertia, the wheel masses acceleration enertia will prevent the plane from moving.
the plane doesn't fly.
Don't blame those of us that say in scenario #2 the plane may not fly for a magic conveyor belt. We did not establish the criteria. The problem as interpreted one way requires a "magic" conveyor belt. I'm simply assuming that the poser of the problem intended this.
In reality, something far less than infinite speed would be required to keep the plane stationary for several minutes or hours at full power.
Title: Airplane on a Conveyor Belt...
Post by: Chairboy on February 01, 2008, 11:10:31 AM
This is kinda embarrassing to watch. Since you're fixating on wheels, consider for a moment the vectors involved. Bottom of the wheel goes one way, top goes the other. They cancel each other out, there is _no effect_ on the plane.
And since the friction coefficient remains the same at any speed, the end result is that the plane takes off.
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on February 01, 2008, 11:25:55 AM
Quote
Originally posted by AKIron Okay but think about this. Assume the tire riding in the back seat has the same mass as the tire rolling under the plane. Which has more energy at takeoff? They are both moving forward with the same amount of energy relative to the fixed starting point but the one rolling has more energy because it is both moving forward and spinning. That energy could have been used to accelerate the plane but wasn't.
OK, the only thing I wanted to know is why Eskimo thinks planes wouldn't have same take off distance, and I wanted to see what kind of logic he applied.
Obviously, we live in the same universe, unless by some internet magic, I actually communicate with the parallel universe Eskimo, the same laws of physics apply.
And whilst we mention laws and physics, I'll remind you and Eskimo about one of the most important, most basic and most known law applicable in this story.
The second law of motion. F=ma
Until the time you guys actually apply that, there's no point going any further.
Title: Airplane on a Conveyor Belt...
Post by: sluggish on February 01, 2008, 11:45:52 AM
Eskimo’s wheel story is very relevant. Inertia = an object at rest stays at rest, an object in motion stays in motion. The energy required to make a still object move is directly proportional to the amount it moves.
Rotational inertia. The amount of time a planes wheels remain spinning after take-of is directly proportional to the energy used to get them spinning. Said energy is subtracted from the energy used to move the plane forward.
If enough continuous (acceleration) rotational inertia is applied to the wheels of the plane, (enough so that the total power of the thrust is consumed) the plane will not move forward.
The plane doesn't fly.
This is all based on the theory of a "magic" conveyor belt which doesn't have to follow the same rules as the wheel. If the wheel lives in the same fairy tale land as the belt, and is not bound by the rules of physics, there will be no rotational inertia.
The plane flies.
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 01, 2008, 12:00:03 PM
Quote
Originally posted by sluggish Rotational inertia. The amount of time a planes wheels remain spinning after take-of is directly proportional to the energy used to get them spinning. Said energy is subtracted from the energy used to move the plane forward.
the energy to spin the wheels comes from the belt, not the planes thrust.
according to the "it won't fly" people it would be impossible to drive a car because all the power from the engine would be used up putting "Rotational inertia" into the cars wheels.
Title: Airplane on a Conveyor Belt...
Post by: WWhiskey on February 01, 2008, 12:21:12 PM
magic belts exist in what world? might be the same one where magic wheels exist,and it doesnt matter! if you want to test a relavent question you must use real objects not mythical devices! there are no belts that will run at unlimited speed, they to will fail, just like the wheels of the plane if you turn them to fast, tires explode,drive boxes in belts fail, the belt itself will separate at some point! if you go too this magical world where belts have unlimited speed then the plane must also have wheels that can go at unlimited speed as well! its not fair too say the belt is indestructible but not the plane's wheels.
the plane will fly as long as you dont destroy it trying to run the speed of the belt to an equal amount of the wheel speed of the plane! just try landing at over 200mph in AH and what happens? you die! if you run the landing gear up to a speed like that it will fail then the plane crashes into the belt and you die!
to have an expirement like this you must have control factors. the relavant factor in this test is that the belt is going an equal amount of speed to the takeoff speed of the plane, to find this speed you must takeoff in the plane without the belt and find out how fast that speed is, that speed is the speed of the belt no more no less!
Title: Airplane on a Conveyor Belt...
Post by: sluggish on February 01, 2008, 12:38:21 PM
Think of that big wheel on The Price is Right. It takes quite a bit of force to get that thing moving. Once it’s moving it spins freely, but that’s not what we’re concerned with. We’re talking about rotational acceleration. Now imagine the wheel instead of being mounted in a fixed position, mounted on the end of a pendulum. Now spin the wheel, but instead of pushing down on the wheel to turn it, push it along the arc of the pendulum. What happens? The wheel begins to turn but is also pushed along the arc of the pendulum. The amount of the spin (speed and time) is directly proportionate to the amount of thrust (your push) that was used to overcome the rotational resistance (inertia) of the wheel and not used to propel the wheel forward (hence wasted). Looking at it from this point, if enough rotational inertia (the conveyor belt going faster and faster, continuously exerting more and more rotational resistance) is exerted, all of the planes thrust will be used just to overcome it and the plane will not fly. This theory requires a super god-like conveyor belt which completely ignores the very rules it is using to keep the plane in place, but under these circumstances the plane will not fly. However, if the plane’s wheels have zero mass (thereby bringing the wheels into the same la-la land as the conveyor belt), and therefore zero rotational resistance (inertia), the plane will fly.
As far as automobiles go, rotational inertia is very important. Lighter flywheels, drive shafts and wheels are all used to make engines rev faster (as in getting from one rpm to another more quickly) and to make cars accelerate faster.
Another example of rotational inertia is a car engines torque. Back in the old days when you put a car in neutral and revved the engine up it would rock from side to side. Today when you do that the car rocks back and forth (most front-wheel-drive cars have the engine in sideways…). This is a direct result of the engine reacting to the rotational inertia of the crank shaft and the fly wheel and is also an example of energy loss due to the nasty laws of physics.
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 01, 2008, 12:38:55 PM
The only way the wheel starts moving is through the forward movement of the plane. The wheel rotates/increases because the forward speed of the plane is increasing. The wheel speed is in reaction to the plane's speed.
The plane will take off.
What some are confusing (IMHO) is if the speed of the plane was the result of the wheels being powered (like in a car). The car (or any vehicle relying on it's movement from its wheels) will remain stationary in this conveyor bely sample.
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on February 01, 2008, 12:52:22 PM
Quote
Originally posted by sluggish Looking at it from this point, if enough rotational inertia (the conveyor belt going faster and faster, continuously exerting more and more rotational resistance) is exerted, all of the planes thrust will be used just to overcome it and the plane will not fly.
Do you understand that conveyor is rotating the wheel in the same direction plane would do on the normal runway? By what logic thrust has to overcome that angular momentum?
Normal runway: Planes thrust alone has to overcome wheels inertia
Plane on the conveyor: Plane gets little helper (conveyor)
Title: Airplane on a Conveyor Belt...
Post by: trax1 on February 01, 2008, 12:59:05 PM
Put a plane on ski's it will still take off, the wheels moving have nothing to do with a plane taking off.
Title: Airplane on a Conveyor Belt...
Post by: sluggish on February 01, 2008, 01:01:04 PM
Quote
Originally posted by 2bighorn Do you understand that conveyor is rotating the wheel in the same direction plane would do on the normal runway? By what logic thrust has to overcome that angular momentum?
Normal runway: Planes thrust alone has to overcome wheels inertia
Plane on the conveyor: Plane gets little helper (conveyor)
Nope. In my little world the conveyor is moving in the oposite direction of the plane to try to stop it. If the belt is running the same direction as the plane in order to stop the wheels, then of course the plane would take off. Anyone who doesn't believe the plane would take off under those circumstances is daft.
I'm going to go back and reread the thread. You should do the same...
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on February 01, 2008, 01:09:24 PM
Quote
Originally posted by sluggish Nope. In my little world the conveyor is moving in the oposite direction of the plane to try to stop it.
Now rotate your 'little world' conveyor 180 degrees so it's on top of the wheel. It will rotate wheel in same direction it did before, yet the conveyor belt goes in the opposite direction.
Title: Airplane on a Conveyor Belt...
Post by: Donzo on February 01, 2008, 01:21:52 PM
Quote
Originally posted by 2bighorn Now rotate your 'little world' conveyor 180 degrees so it's on top of the wheel. It will rotate wheel in same direction it did before, yet the conveyor belt goes in the opposite direction.
What are you talking about? Who said anything about the conveyor being on TOP of the wheel?
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on February 01, 2008, 01:39:20 PM
Quote
Originally posted by Donzo What are you talking about? Who said anything about the conveyor being on TOP of the wheel?
It doesn't matter where conveyor is. What matter is direction of wheel rotation and if conveyor is actually opposing force or not.
Some claim because conveyor's belt is running in the opposite direction of the plane, it exercises the opposing force, yet when you rotate that same conveyor to the top, nothing really changes, except the belt touching the wheel is now running in direction of plane movement.
By their logic (or how they place force vectors), bottom, belt would be opposing force and when on top it would be contributing force.
All what this thread proves is, that similarly to religion, you cannot convince believers, just thinkers...
Title: Airplane on a Conveyor Belt...
Post by: Yknurd on February 01, 2008, 01:39:36 PM
I would think drag from the plane trying to move through wind would be greater than anything induced from wheel rotation or friction.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 01:54:00 PM
Quote
Originally posted by 2bighorn OK, the only thing I wanted to know is why Eskimo thinks planes wouldn't have same take off distance, and I wanted to see what kind of logic he applied.
Obviously, we live in the same universe, unless by some internet magic, I actually communicate with the parallel universe Eskimo, the same laws of physics apply.
And whilst we mention laws and physics, I'll remind you and Eskimo about one of the most important, most basic and most known law applicable in this story.
The second law of motion. F=ma
Until the time you guys actually apply that, there's no point going any further.
Eskimo can certainly explain why probably better then me but I have some time to kill. A plane that accelerates down that runway more slowly will use up more of the runway to reach takeoff speed.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 02:00:50 PM
There are a lot of forces involved here.
Here's the simplest way I can explain that given a powerful enough conveyor belt, a normal cessna 172 will not take off.
1. Conveyor belt sits ready for the slightest motion of the plane 2. Full takeoff power applied by the pilot 3. Plane moves forward. 4. Belt counters the speed of the spinning tire. 5. So long as the plane continues to accelerate forward the wheel is increasing it's rate of spin 6. The belt, sensing this, increases it's opposite spin 7. The belt, being enormously powerful, has accelerated to over 10,000 mph in a few seconds 8. The planes tires, wheels, bearings, etc... were not designed to endure these speeds and fail 9. The plane comes to a grinding halt on blown tires and bearings on fire
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on February 01, 2008, 02:08:09 PM
Quote
Originally posted by AKIron Eskimo can certainly explain why probably better then me but I have some time to kill. A plane that accelerates down that runway more slowly will use up more of the runway to reach takeoff speed.
OK, let's see how that would work and if acceleration rate differs among those three planes.
Back to second law of motion: "The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma" (in it's simplest form).
F is actually net sum of all the forces, that is thrust minus drag, minus friction, etc, and we determined that is the same for all three planes, since they are identical in shape and build, according to Eskimo.
mass sum is also identical for all three, the wheel and ballast weight differ though. Lets say, it's 3000lbs total for each
Lets say all three are propelled by electro motor with battery so our mass does not become variable (due to fuel burn), so we can keep formula simple.
Does the acceleration differs? a = F/m
Since F (net sum of all forces) and m (total mass) are the same for all three planes, so must be acceleration.
If acceleration is the same and they all take off at 50mph, then the length of take off run is the same as well.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 02:10:36 PM
Maybe this will help 2bighorn. Assume that all three planes have an airconditioner but only one has it turned on. Will it use more of the runway than the others? same principle here.
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on February 01, 2008, 02:25:52 PM
Quote
Originally posted by AKIron same principle here.
Yes and no. In Eskimo's story all of the thrust is used (for all three planes) to propel aircraft.
In your example, part of the thrust (energy) is converted to do something completely unrelated and we get differential of usable thrust among planes.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 02:30:14 PM
Quote
Originally posted by 2bighorn Yes and no. In Eskimo's story all of the thrust is used (for all three planes) to propel aircraft.
In your example, part of the thrust (energy) is converted to do something completely unrelated and we get differential of usable thrust among planes.
No, all of thrust is not being used to propel the planes. Some of it is being used to spin those more massive tires. Same as spinning that pump in an A/C.
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on February 01, 2008, 02:36:58 PM
Quote
Originally posted by AKIron No, all of thrust is not being used to propel the planes. Some of it is being used to spin those more massive tires. Same as spinning that pump in an A/C.
For Christ sake, read it again and pay attention to wheel weight. I did not invent the story. Eskimo is responsible for all the parameters, he defined them. He couldn't give satisfactory answer on his own question.
Whenever you guys get the answer, you redefine the question. Suddenly we got air conditioners, what's next? Ann Coulter in the trunk?
Quote
Originally posted by 2bighorn OK, let's see how that would work and if acceleration rate differs among those three planes.
Back to second law of motion: "The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma" (in it's simplest form).
F is actually net sum of all the forces, that is thrust minus drag, minus friction, etc, and we determined that is the same for all three planes, since they are identical in shape and build, according to Eskimo.
mass sum is also identical for all three, the wheel and ballast weight differ though. Lets say, it's 3000lbs total for each
Lets say all three are propelled by electro motor with battery so our mass does not become variable (due to fuel burn), so we can keep formula simple.
Does the acceleration differs? a = F/m
Since F (net sum of all forces) and m (total mass) are the same for all three planes, so must be acceleration.
If acceleration is the same and they all take off at 50mph, then the length of take off run is the same as well.
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 01, 2008, 02:46:18 PM
Quote
Originally posted by AKIron 8. The planes tires, wheels, bearings, etc... were not designed to endure these speeds and fail 9. The plane comes to a grinding halt on blown tires and bearings on fire
sorry, but my plane doesn't have wheels, it has the same rollers and bearings as the belt, and they are capable of infinite speeds.:lol
Title: Airplane on a Conveyor Belt...
Post by: Chairboy on February 01, 2008, 02:49:12 PM
God forbid someone brings a skiplane to this airport.
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on February 01, 2008, 02:51:10 PM
Quote
Originally posted by Chairboy God forbid someone brings a skiplane to this airport.
:aok
Title: Airplane on a Conveyor Belt...
Post by: sluggish on February 01, 2008, 02:52:26 PM
I haven't redefined anything. I'm sticking to my story. You claim that resistance to rotational inertia doesn't exist, that the belt is moving the same direction as the plane (and that it doesn't make any difference which way the belt is moving...)
I'm starting to think that you are intentionally being silly for your own amusement.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 02:55:06 PM
Quote
Originally posted by 2bighorn For Christ sake, read it again and pay attention to wheel weight. I did not invent the story. Eskimo is responsible for all the parameters, he defined them. He couldn't give satisfactory answer on his own question.
Whenever you guys get the answer, you redefine the question. Suddenly we got air conditioners, what's next? Ann Coulter in the trunk?
Only trying to help you understand the forces involved. Wheels spinning under the plane have more energy than wheels in the back seat. Same as the A/C pump under the cowling. All have the same mass but the pump spinning stole more of that engine power, same as did those more massive spinning wheels.
Not just at you 2bighorn but I try to avoid ridiculing others when there's a possbility I don't understand something. Less foot in the mouth when the light comes on. Just saying. :)
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 01, 2008, 02:57:39 PM
Quote
Originally posted by sluggish I haven't redefined anything. I'm sticking to my story. You claim that resistance to rotational inertia doesn't exist, that the belt is moving the same direction as the plane (and that it doesn't make any difference which way the belt is moving...)
I'm starting to think that you are intentionally being silly for your own amusement.
this whole argument is hypothetical and silly.
and the plane will fly, and if you turn the whole thing upside down the plane will fall off the belt no matter how fast the belt runs.
why don't we discuss something important like how many angels can sit on the head of a pin?
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 03:05:00 PM
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Originally posted by john9001 sorry, but my plane doesn't have wheels, it has the same rollers and bearings as the belt, and they are capable of infinite speeds.:lol
The wheels have only to accelerate their rate of spin fast enough to acquire enough energy to match the plane's power output. May not be an impossible task to create this situation.
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on February 01, 2008, 03:20:19 PM
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Originally posted by AKIron Only trying to help you understand the forces involved.
So, you claim that Eskimo is right and there will be difference in take off run due to different wheel mass (which you compensated for with the ballast, btw) and that applying the law of physics is not enough?
You are trying to help me understand, yet you can't write down simple formula, which will disapprove second law of motion which I used to disapprove Eskimo's claim?
Anyways, I'm thankful you're trying to educate me, but please, try it the way I CAN understand why physic's laws do not apply in this particular case.
Title: Airplane on a Conveyor Belt...
Post by: hitech on February 01, 2008, 03:30:22 PM
Chairboy: The one I calculated last year.
(http://www.hitechcreations.com/hitech/rveq.jpg)
Did some simple estimations of my RV on the conveyor.
Some how I knew I was going to have to do a drawing.
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 01, 2008, 03:31:42 PM
it is the energy from the belt that is spinning the wheels , not the thrust from the plane.
wheels are designed to roll, that is their job, all the wheels do is keep the fuselage from dragging on the ground.
the belt can not stop the plane, all the belt can do is spin the wheels.
Title: Airplane on a Conveyor Belt...
Post by: hitech on February 01, 2008, 03:41:28 PM
john9001: with out an axle, and a force on that axle. A wheel does not roll on a conveyor. That force is from the engine.
Unless of course the conveyor is accelerating , them there also a force from the mass of the wheel being accelerated that will start the wheel rotating but it will also be moving in the direction of the conveyor.
HiTech
Title: Airplane on a Conveyor Belt...
Post by: sluggish on February 01, 2008, 03:43:39 PM
So what does all that mean HiTech? Does the dam thing fly or not??
My theory is that with enough constant exceleration moment of inertia will over come the thrust of the plane and t5he plane won't fly. Unless the wheels have zero mass in which case moment of inertia doesn't exist and the plane will fly.
Title: Airplane on a Conveyor Belt...
Post by: balance1 on February 01, 2008, 03:51:48 PM
oh god......we've even got the big man in on this one, this cant be good
Title: Airplane on a Conveyor Belt...
Post by: hitech on February 01, 2008, 04:02:45 PM
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Originally posted by sluggish So what does all that mean HiTech? Does the dam thing fly or not??
My theory is that with enough constant exceleration moment of inertia will over come the thrust of the plane and t5he plane won't fly. Unless the wheels have zero mass in which case moment of inertia doesn't exist and the plane will fly.
Sluggish: If you continually accelerate the conveyor at 910 Feet per second per second. Then the plane will not move.
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on February 01, 2008, 04:03:09 PM
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Originally posted by hitech Unless of course the conveyor is accelerating , them there also a force from the mass of the wheel being accelerated that will start the wheel rotating but it will also be moving in the direction of the conveyor.
...If you continually accelerate the conveyor at 910 Feet per second per second. Then the plane will not move.
We stopped short in last thread because we couldn't agree on which direction the wheel/belt friction torque should point after we moved it tangentially to the pivot point of the opposing vector, and for how much we have to adjust the magnitude of radial component of torque's pseudo vector, although we came pretty close.
Title: Airplane on a Conveyor Belt...
Post by: sluggish on February 01, 2008, 04:17:33 PM
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Originally posted by hitech Sluggish: If you continually accelerate the conveyor at 910 Feet per second per second. Then the plane will not move.
Thank you sir. I consider this case closed.
I WIN!!
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 01, 2008, 04:26:40 PM
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Originally posted by hitech Sluggish: If you continually accelerate the conveyor at 910 Feet per second per second. Then the plane will not move.
the tire will spin, the plane will move.
Title: Airplane on a Conveyor Belt...
Post by: Chairboy on February 01, 2008, 04:32:38 PM
The problem w/ the 910^2 answer is that it implicitly seems to assume that the power is being transferred through the tires. The diagram doesn't explain how this overcomes the u*N friction co-efficient math that shows the bearing friction as linear and constant. A wheel spinning at 5 rpm induces as much bearing drag (the relevant figure here) as one at 100rpm.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 01, 2008, 04:33:25 PM
OK, I'm back.
Argue all you want. These AVI's show the force we are talking about in RL action:
Note that the sander accelerates for only an instant. When it gets up to speed after that split second the lateral force on the wheel becomes nil and the wheel drifts back.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 01, 2008, 04:35:51 PM
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Originally posted by Chairboy The problem w/ the 910^2 answer is that it implicitly seems to assume that the power is being transferred through the tires. The diagram doesn't explain how this overcomes the u*N friction co-efficient math that shows the bearing friction as linear and constant. A wheel spinning at 5 rpm induces as much bearing drag (the relevant figure here) as one at 100rpm.
Bearing friction is not the force we are talking about.
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on February 01, 2008, 04:37:01 PM
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Originally posted by sluggish I WIN!!
No you don't.
All Hitech calculated is, how much conveyor has to accelerate in order to create wheel/belt friction torque to match the plane thrust.
How much of that torque is transfered through bearings to the airframe is another story...
Title: Airplane on a Conveyor Belt...
Post by: Chairboy on February 01, 2008, 04:38:27 PM
That's the only way the treadmill can impart backwards force on an airplane. The rest is rotational energy with zero impact on the actual acceleration of the aircraft. Sure, the bottom of the wheel is pushed back, but then the top goes the other way, and back and forth.
If rotational force could be converted to a 'push' the way y'all keep assuming, then the Dean Drive would have revolutionized everything from flying cars to spaceships.
It just doesn't work that way.
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on February 01, 2008, 04:42:16 PM
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Originally posted by eskimo2 Bearing friction is not the force we are talking about.
Yes we are, since bearings are the force transfer bridge.
If you have a car and put in bearings instead of gears, it'll take helluva time before you start moving, no mother how big your engine is.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 01, 2008, 04:44:20 PM
Chairboy,
Think about what happens when you land you plane. Even if you grease it in there’s a chirp when the wheels touch and a lateral “bump”. Some of your forward speed gets scrubbed off in an instant to get those non spinning wheels up to speed in an instant. It’s only slight if the plane’s tires/wheel are small and light. If you’ve ever landed in a bush plane with big tundra tires you’d note that the force is pretty significant. Now imagine that the “instant” becomes a constant. At the end of say, ¼ second the wheels go from stopped to 50 mph, at ½ sec = 100 mph, 1 second 200 mph, 10 seconds 2,000 mph… We are talking about a real force here.
Title: Airplane on a Conveyor Belt...
Post by: sluggish on February 01, 2008, 04:44:39 PM
Wow. I give up. HiTech agrees with us, Eskimo films elaborate videos that prove it, we give you mind-numbingly simplistic explanations and yet you refuse to see...
there is no hope for mankind.
Title: Airplane on a Conveyor Belt...
Post by: hitech on February 01, 2008, 04:47:15 PM
Chairboy: I am not speaking of friction of the bearing. I agree with you that bearing friction is a constant. Think of the force needed to simply accelerate the spin of the wheel.
If there was not a force of the prop I assume you do not the the wheel would stay at one point in space but would start rolling and move backwards like it does in the sample on the Belt sander?
Chairboy: It does work as I described. If you look at some of the basic physics I posted in the old thread, I did scans of how to do this analysis as my proof.
Chairboy. Spin a wheel on a axle that you are holding in your hands. Drop the spinning wheel on the ground, does it roll forward?
If you believe it moves forward, then think of the entire process in reverse. That is where the translation force comes from.
HiTech
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 01, 2008, 04:48:14 PM
Why does the wheel move back as it starts to spin?
Why are the balls pulled off the table? They should just stay in one place and spin as long as the paper is accelerating under them, from how you describe things. Be sure to watch in slo-mo.
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on February 01, 2008, 05:15:34 PM
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Originally posted by hitech If there was not a force of the prop I assume you do not the the wheel would stay at one point in space but would start rolling and move backwards like it does in the sample on the Belt sander?
Only until initial inertia is overcome. And that's only wheels. You'd have to account for the plane's inertia as well. If you include thrust, and you'd still want to keep it back you'd have to accelerate at such rate you'd need quite a traction between belt and tire. Pretty soon we'd approach insane numbers close to infinity and we know what happens then.
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 01, 2008, 05:33:51 PM
Interesting...
From what I understand of the question is that magical the conveyor belt matches the speed of the wheel.
What forces the plane's wheel to rotate in the first place?
The forward movement of the plane.
The conveyor belt has to react to the wheel's speed, not the other way around.
The only way the wheel's speed changes is through the forward motion of the plane.
Plane takes off.
Just a hunch.
... or put wheels made of glass and the plane will just slide forward and take off :)
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 01, 2008, 05:41:20 PM
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Originally posted by 2bighorn Only until initial inertia is overcome. And that's only wheels. You'd have to account for the plane's inertia as well. If you include thrust, and you'd still want to keep it back you'd have to accelerate at such rate you'd need quite a traction between belt and tire. Pretty soon we'd approach insane numbers close to infinity and we know what happens then.
2bighorn,
That “initial inertia” that you are talking about is acceleration. It’s important to understand the difference between acceleration and speed. Acceleration is a force that is constantly applied; such as speed increasing regularly.
“And that's only wheels.” Yes it’s only the wheels because it makes it easier to see the force. Suppose the plane were to weigh 1,000 times the weight of the wheel; just increase the acceleration rate by 1,000 fold and you have the same result as the wheel alone at 1X acceleration.
Believe it or not, the traction requirements for this scenario are no greater than the traction needed to hold a plane on a tarmac with its engines on full power and it brakes on full – locked.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 01, 2008, 05:44:30 PM
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Originally posted by SaburoS Interesting...
From what I understand of the question is that magical the conveyor belt matches the speed of the wheel.
What forces the plane's wheel to rotate in the first place?
The forward movement of the plane.
The conveyor belt has to react to the wheel's speed, not the other way around.
The only way the wheel's speed changes is through the forward motion of the plane.
Plane takes off.
Just a hunch.
... or put wheels made of glass and the plane will just slide forward and take off :)
Imagine that “exactly matches” really means that YOU have a big acceleration control dial for the conveyor and your job is to keep it in place. The plane fires up and begins to inch forward; you see this and crank the acceleration dial. (Or are you going to say, "I give up" the instant you see the plane budge?) You go too far, however, so the plane drifts back behind its starting point. Seeing this you back off on the acceleration dial and adjust it to keep the plane pretty much where it started.
Look at the concept; don’t get caught up in the semantics of the word “exactly”.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 01, 2008, 05:49:01 PM
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Originally posted by sluggish Thank you sir. I consider this case closed.
I WIN!!
Sluggish,
I hate to break it to you, but you already knew that you knew the answer, as did many others here. The point/challenge of a BBS argument like this is to explain your point so that others can see/get it. You’re failing until they get it bro!
Title: Airplane on a Conveyor Belt...
Post by: vorticon on February 01, 2008, 05:52:32 PM
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Originally posted by eskimo2 Sluggish,
I hate to break it to you, but you already knew that you knew the answer, as did many others here. The point/challenge of a BBS argument like this is to explain your point so that others can see/get it. You’re failing until they get it bro!
or just repeat yourself until they grow weary and leave, which is more common.
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on February 01, 2008, 05:54:26 PM
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Originally posted by eskimo2 Believe it or not, the traction requirements for this scenario are no greater than the traction needed to hold a plane on a tarmac with its engines on full power and it brakes on full – locked.
Is that why ball in second film doesn't stick to your belt (paper, fabric or whatever it is)?
Why don't you calculate real world example, a small plane like Cessna 172?
Here, some data to start with: # Length: 27 ft 2 in (8.28 m) # Wingspan: 36 ft 1 in (11.0 m) # Height: 8 ft 11 in (2.72 m) # Wing area: 174 ft² (16.2 m²) # Airfoil: NACA 2412 (modified) # Empty weight: 1,620 lb (736 kg) # Useful load: 830 lb (376 kg) # Max takeoff weight: 2,450 lb (1,113 kg) # Powerplant: 1× Lycoming IO-360-L2A flat-4 engine, 160 hp (120 kW) at 2,400 rpm # * Zero-lift drag coefficient: 0.0319 # Drag area: 5.58 ft² (0.52 m²) # Aspect ratio: 7.32 # Lift-to-drag ratio: 11.6 # Wing loading: 14.1 lb/ft² (68.8 kg/m²) # Power/mass: 15.3 lb/hp (9.25 kg/kW)
Of course, you can chose other type, maybe jet, so you'll know amount of thrust for certain.
Let us know when you have results, I'll be happy to check them out and admit defeat if it turns out that way.
Heck I'll even say you were right about your triplets.
Until then I'm out of this thread. :aok
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 01, 2008, 06:11:53 PM
#1 Hitech already did the math for a real plane. How many do you want?
#2 If you don’t get the concept from these simpler concepts, you will certainly get lost in the more complicated math behind a RL problem.
#3 The paper treadmill accelerates at a bit under 1G. You’re looking at a rubber-coated mouse ball, a copper tube with rubber bands around it for traction, and a clear acrylic sphere. Clearly the clear acrylic sphere skids; it has very little traction/coefficient of friction. If the plane had acrylic tires and the treadmill was paper, I’d bet the wheels would slip and the plane would take off. So what?
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 01, 2008, 06:17:34 PM
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Originally posted by eskimo2 #1 Hitech already did the math for a real plane. How many do you want?
whats a real plane doing on a make believe conveyor belt?
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 01, 2008, 06:23:10 PM
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Originally posted by vorticon or just repeat yourself until they grow weary and leave, which is more common.
That’s their choice. A lot of folks will never get this concept, I know that. Many folks will never really try because they assume they already know the answer.
I’d like to point out that in the original AH BBS thread, I was the first to explain the rotational inertia/plane won’t fly answer. Hitech was the only person who got it on the first reading. Many others have gotten it through a variety of examples and explanations. I repeat myself because so many people make the wrong assumptions and can’t answer the very questions that will force them to understand the concept if they just make an effort.
AKIron, Hitech & sluggish have also given excellent explanations and examples.
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on February 01, 2008, 06:31:16 PM
Uhh, this is getting personal :D (ok, I lied, I have to reply this one)
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Originally posted by eskimo2 #1 Hitech already did the math for a real plane. How many do you want?
Umm no, he didn't.
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Originally posted by eskimo2 #2 If you don’t get the concept from these simpler concepts, you will certainly get lost in the more complicated math behind a RL problem.
LOL, kinda like your triplets story? No worries, my math will always (at least) match yours.
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Originally posted by eskimo2 So what?
When it comes to physics, you don't say "So, what", you got to prove it, and there are few ways to do it, either to calculate, do practical experiment or both.
As far as practical experiment goes, that thing on TV beats hell outta your sander. Plane took off.
For all other (hypotetical) scenarios, which includes super conveyor, you'll have to do something more than post your films and triplets story at every possible opportunity.
Have a good one :aok
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 01, 2008, 06:34:58 PM
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Originally posted by eskimo2 Imagine that “exactly matches” really means that YOU have a big acceleration control dial for the conveyor and your job is to keep it in place. The plane fires up and begins to inch forward; you see this and crank the acceleration dial. (Or are you going to say, "I give up" the instant you see the plane budge?) You go too far, however, so the plane drifts back behind its starting point. Seeing this you back off on the acceleration dial and adjust it to keep the plane pretty much where it started.
Look at the concept; don’t get caught up in the semantics of the word “exactly”.
But at no point is the concept to keep the plane's airspeed at zero. The job of the conveyor belt is to match wheel speed, not counter the plane's forward movement. That is your mistake (If I read your post(s) correctly). If the job was to keep the plane in one place, then you'd be right. The moment you try to make the plane go back to its starting point, you are exceeding the wheel's speed.
The plane's wheel isn't doing a thing until the plane starts rolling forward. At each point of adjustment, the conveyor belt is reacting to match the wheel's speed.
The wheels turn because of the plane's forward movement, not the other way around. The plane has to move forward to get the wheels to rotate. The conveyor won't do a thing until it senses wheel rotation. The wheel won't start rotating until the plane moves forward.
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 01, 2008, 06:43:12 PM
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Originally posted by eskimo2 That’s their choice. A lot of folks will never get this concept, I know that. Many folks will never really try because they assume they already know the answer.
I’d like to point out that in the original AH BBS thread, I was the first to explain the rotational inertia/plane won’t fly answer. Hitech was the only person who got it on the first reading. Many others have gotten it through a variety of examples and explanations. I repeat myself because so many people make the wrong assumptions and can’t answer the very questions that will force them to understand the concept if they just make an effort.
AKIron, Hitech & sluggish have also given excellent explanations and examples.
Actually I do hope you continue with the subject as I'm no expert. I know we all are thinking within our own box and I know I'm doing the same. I enjoy discovering new things outside of 'my box' as that never hurts. Right now I am not seeing the same as you.
Title: Airplane on a Conveyor Belt...
Post by: Donzo on February 01, 2008, 06:49:04 PM
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Originally posted by SaburoS But at no point is the concept to keep the plane's airspeed at zero. The job of the conveyor belt is to match wheel speed, not counter the plane's forward movement. That is your mistake (If I read your post(s) correctly). If the job was to keep the plane in one place, then you'd be right. The moment you try to make the plane go back to its starting point, you are exceeding the wheel's speed.
The plane's wheel isn't doing a thing until the plane starts rolling forward. At each point of adjustment, the conveyor belt is reacting to match the wheel's speed.
The wheels turn because of the plane's forward movement, not the other way around. The plane has to move forward to get the wheels to rotate. The conveyor won't do a thing until it senses wheel rotation. The wheel won't start rotating until the plane moves forward.
Good points...this makes sense to me.
I'd like to know what would happen if we pulled the plane forward with a cable attached to a winch. With all this talk of rotational inertia, what would happen? Would the cable simply snap or the winch motor burn out trying to pull the plane that's being held back by the conveyor?
Title: Airplane on a Conveyor Belt...
Post by: sluggish on February 01, 2008, 06:56:57 PM
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Originally posted by Donzo Good points...this makes sense to me.
I'd like to know what would happen if we pulled the plane forward with a cable attached to a winch. With all this talk of rotational inertia, what would happen? Would the cable simply snap or the winch motor burn out trying to pull the plane that's being held back by the conveyor?
Theoretically yes if we are using an infinately powerful conveyor belt. We are attempting to use constant acceleration to create enough rotational inertia to prevent the plane from moving forward. Even a winch would be unable to move the plane unless it was powerful enough to drag the plane even with it's wheels locked.
edit-even
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 01, 2008, 07:06:19 PM
why would the wheels be locked?
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 01, 2008, 07:09:31 PM
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Originally posted by SaburoS But at no point is the concept to keep the plane's airspeed at zero. The job of the conveyor belt is to match wheel speed, not counter the plane's forward movement. That is your mistake (If I read your post(s) correctly). If the job was to keep the plane in one place, then you'd be right. The moment you try to make the plane go back to its starting point, you are exceeding the wheel's speed.
The plane's wheel isn't doing a thing until the plane starts rolling forward. At each point of adjustment, the conveyor belt is reacting to match the wheel's speed.
The wheels turn because of the plane's forward movement, not the other way around. The plane has to move forward to get the wheels to rotate. The conveyor won't do a thing until it senses wheel rotation. The wheel won't start rotating until the plane moves forward.
The conveyor’s job is to match the wheel’s speed. If the plane to moves forward, the wheel must be moving faster than the treadmill. The treadmill’s job is to match the speed of the wheel; if it start’s “losing ground” the only thing that it can do is speed up. (It certainly wouldn’t just give up.) But how much? To the speed of the plane? No, it’s supposed to match the wheel speed. So it speeds up to whatever speed/acceleration-rate it takes to keep the plane in place. When the plane is in place the conveyor is doing its job! Be it taxi power or full throttle.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 01, 2008, 07:20:09 PM
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Originally posted by john9001 why would the wheels be locked?
Only to illustrate that most planes’ tires have enough traction to hold the plane still at full power. A plane with enough power to skid on full locked brakes and take off on a normal runway would also have enough power to skid its wheels on the wheel-speed treadmill as well. I don’t think normal planes can do that however.
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 01, 2008, 07:21:35 PM
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Originally posted by eskimo2 Snip~ So it speeds up to whatever speed/acceleration-rate it takes to keep the plane in place. When the plane is in place the conveyor is doing its job! Be it taxi power or full throttle.
Sorry but its job is not to keep the plane in place but to match the wheel speed. Therein lies the difference in our school's of thought. If its job was to keep the plane in one place then I'd say you'd be right as it could exceed the wheel's speed to bring the plane back to its starting point. The losing battle of our conveyor belt is that it has to forever react to the wheel speed which is the result of the plane moving forward. The moment you stop the plane's forward acceleration/movement, you are now exceeding the wheel's speed forcing the plane to react accordingly.
We're not talking an immediate wheel speed of 200knts but a gradual increase from zero. The conveyor has to react to a plane that is in motion for that is the only way the wheels start rotating.
Try your sander experiment but starting at a crawl and moving it faster slowly. What happens to the wheel then? Keep in mind that is without additional thrust acting on the wheel's forward movement.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 01, 2008, 07:36:14 PM
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Originally posted by SaburoS Sorry but its job is not to keep the plane in place but to match the wheel speed. Therein lies the difference in our school's of thought. If its job was to keep the plane in one place then I'd say you'd be right as it could exceed the wheel's speed to bring the plane back to its starting point. The losing battle of our conveyor belt is that it has to forever react to the wheel speed which is the result of the plane moving forward. The moment you stop the plane's forward acceleration/movement, you are now exceeding the wheel's speed forcing the plane to react accordingly.
We're not talking an immediate wheel speed of 200knts but a gradual increase from zero. The conveyor has to react to a plane that is in motion for that is the only way the wheels start rotating.
Try your sander experiment but starting at a crawl and moving it faster slowly. What happens to the wheel then? Keep in mind that is without additional thrust acting on the wheel's forward movement.
Suppose the wheel is only rolling 2 mph on the treadmill, but its center/axle is not moving down the runway. The treadmill also must be going 2 mph… In this case the treadmill is matching the wheel’s speed.
Now imagine the wheel is only rolling 2 mph on the treadmill, and its center/axle is moving down the runway at 1 mph. The treadmill must be going only 1 mph… In this case the treadmill is not matching the wheel’s speed.
Now imagine the wheel is rolling 1,002 mph on the treadmill, and its center/axle is moving down the runway at 1 mph. The treadmill must be going only 1,001 mph… In this case also, the treadmill is not matching the wheel’s speed.
When the treadmill is matching the wheel’s speed, the plane is stationary.
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 01, 2008, 07:48:48 PM
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Originally posted by eskimo2 Only to illustrate that most planes’ tires have enough traction to hold the plane still at full power. A plane with enough power to skid on full locked brakes and take off on a normal runway would also have enough power to skid its wheels on the wheel-speed treadmill as well. I don’t think normal planes can do that however.
that does not answer the question, why do you want the wheels locked when a wench cable is attached to the plane?
lets try this, put a sail plane on the belt and the tow plane off the belt, when the tow plane takes off will the sailplane take off or will the belt hold both planes at 0 mph ground speed.
Title: Airplane on a Conveyor Belt...
Post by: sluggish on February 01, 2008, 08:01:15 PM
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Originally posted by john9001 that does not answer the question, why do you want the wheels locked when a wench cable is attached to the plane?
lets try this, put a sail plane on the belt and the tow plane off the belt, when the tow plane takes off will the sailplane take off or will the belt hold both planes at 0 mph ground speed.
If you'll look you'll see I went back and edited the post to make it more easily understood. The planes wheels aren't locked. The winch will be able to pull the plane forward if it were powerful enough to drag the plane when it's wheels are locked.
If the tow plane has enough thrust to drag the sail plane with it's wheel locked then it will move. If not, it won't move.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 01, 2008, 08:04:46 PM
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Originally posted by john9001 that does not answer the question, why do you want the wheels locked when a wench cable is attached to the plane?
lets try this, put a sail plane on the belt and the tow plane off the belt, when the tow plane takes off will the sailplane take off or will the belt hold both planes at 0 mph ground speed.
I’m sorry. I think we are talking about two different things. My wheels locked example was addressing whether there would be sufficient traction for the treadmill to keep the plane in place through loading rotational inertia into the wheels. Your talking about the cable illustration.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 09:14:07 PM
Here's an argument to say the guys that did this on TV did it wrong. Obviously they ran the belt at the same speed but opposite direction of the plane. If the original poser of the question intended for the belt to match the speed of the plane then why were "wheels" specifically mentioned instead of just saying the belt must match the speed of the plane?
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 01, 2008, 10:13:57 PM
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Originally posted by AKIron Here's an argument to say the guys that did this on TV did it wrong. Obviously they ran the belt at the same speed but opposite direction of the plane. If the original poser of the question intended for the belt to match the speed of the plane then why were "wheels" specifically mentioned instead of just saying the belt must match the speed of the plane?
The original AH BBS question last year by rabbidrabbit specified wheel speed. We found out in that thread that this question has been around the Internet, but specified the treadmill matches the plane’s speed.
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 01, 2008, 10:13:59 PM
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Originally posted by eskimo2 Suppose the wheel is only rolling 2 mph on the treadmill, but its center/axle is not moving down the runway. The treadmill also must be going 2 mph… In this case the treadmill is matching the wheel’s speed.
Now imagine the wheel is only rolling 2 mph on the treadmill, and its center/axle is moving down the runway at 1 mph. The treadmill must be going only 1 mph… In this case the treadmill is not matching the wheel’s speed.
Now imagine the wheel is rolling 1,002 mph on the treadmill, and its center/axle is moving down the runway at 1 mph. The treadmill must be going only 1,001 mph… In this case also, the treadmill is not matching the wheel’s speed.
When the treadmill is matching the wheel’s speed, the plane is stationary.
Hmmm. I think the question has to do with the wheel's rotational speed, not the ground speed of the plane. If the wheels were powered by the vehicle then one can say that wheel speed and ground speed are the same (provided traction isn't lost).
In this case the wheel speed is independent of the ground speed. The conveyor must react and try to match the wheel's rotational speed, not have the conveyor set up the speed(s) to which the wheel has to match.
As it stands in real life, the runway and the wheel speed is the same as it is the plane that is moving forward and taking off.
Now think of this sample:
The magic conveyor has little to no rotational inertia (very little mass) so it takes practically no force to get it to accelerate. Now we line up our Cesna but it has very poor bearings in its wheels (the wheels are hard to turn). Pilot guns the throttle on the Cesna on this conveyor. The plane goes down the runway and takes off with zero wheel speed (remember that the conveyor has to match the wheel speed in our example) at 100knts ground speed.
In my sample (extreme, I know) the conveyor fulfills the matching wheel speed as it has to react to the wheel speed. In your extreme example, the conveyor is setting and controlling the wheel speed, not the plane.
Therefore it does not meet the criteria (as I've interpreted the question).
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 01, 2008, 10:19:38 PM
Quote
Originally posted by eskimo2 The original AH BBS question last year by rabbidrabbit specified wheel speed. We found out in that thread that this question has been around the Internet, but specified the treadmill matches the plane’s speed.
If that's the case then the plane that takes off at 100knts then the conveyor matches that speed in the other direction. The conveyor doesn't add additional speed to other than to match.
Now if the question was that 'is it possible to have a magic conveyor runway go so fast as to keep the plane from taking off', then yes, you would be right. But that's not the puzzle/question. Plane still takes off.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 01, 2008, 10:49:13 PM
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Originally posted by eskimo2 The original AH BBS question last year by rabbidrabbit specified wheel speed. We found out in that thread that this question has been around the Internet, but specified the treadmill matches the plane’s speed.
Ah, well, there ya have it.
It should be fairly obvious to all that matching the plane's speed will have little effect on the outcome. Matching the spinning wheel speed is a much more interesting question.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 12:31:41 AM
Some may wonder how many angels can dance on the head of a pin but I'm sure you're wondering how many:
Title: Aircraft on a conveyor
Post by: VERTEX on February 02, 2008, 03:01:19 AM
This issue has become unnecessarily confused and complex.
The conveyor can do three things. 1) Rotate in the same direction the aircraft moves, which if the speed matches the forward speed of the aircraft the wheels rotation will be zero rpm. 2) Rotate on the opposite direction the aircraft moves, which will impart an rpm higher than normal to the wheels. 3) Rotate in the direction the aircraft moves but at a greater rate, which will cause the wheels to rotate backwards.
In all cases the aircraft will take off as normal because the direction and speed of rotation of the wheels has nothing to do with the forward motion of the aircraft. The propeller, spun by the engine pulls the aircraft forward as the propeller, "screws" itself through the air. The aircraft will fly at the point the wings generate enough lift as the aircraft travels forward trough the air which surrounds it. The wheels could be accelerating in a backwards rpm direction and the aircraft would still fly.
Granted, the takeoff roll would be slightly greater but it would be a small difference.
Note, I have assumed the conveyor has its own power source to drive the belt.
It really is this simple.
Thanks for reading
Vertex.
Title: Airplane on a Conveyor Belt...
Post by: SD67 on February 02, 2008, 05:00:17 AM
This is getting out of hand. An aircrafts' engine moves air, period. This air generates thrust and it is the thrust that moves the aircraft forward. If the belt is started only once the aircraft starts to move, the aircraft will continue to move forward regardless whether the belt is going faster or slower, speeding up or slowing down. The airflow will build until sufficient lift is generated and the aircraft will fly. The only thing that will be affected is the relative rolling resistance due to the speed of the belt. Only if the belt is started before the aircraft starts to move, the aircraft will move backwards initially until the level of thrust reaches a level sufficient to overcome the backwards motion of the belt. In this case if the speed of the belt is increased (exponentially?) to prevent parity will the aircraft fail to build sufficient airflow to generate lift.
Title: Airplane on a Conveyor Belt...
Post by: WWhiskey on February 02, 2008, 06:53:21 AM
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Originally posted by AKIron Here's an argument to say the guys that did this on TV did it wrong. Obviously they ran the belt at the same speed but opposite direction of the plane. If the original poser of the question intended for the belt to match the speed of the plane then why were "wheels" specifically mentioned instead of just saying the belt must match the speed of the plane?
the original question did state that the speed of the belt would be equal to the take off speed of the plane I.E. 100 knots! the belt would be moving in the opposite direction of the plane! most planes differ in takeoff speed so whatever plane you use, if its take off speed is 50 or 60 or 75 then that is the speed of the belt! no more no less!
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 07:22:57 AM
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Originally posted by SaburoS Hmmm. I think the question has to do with the wheel's rotational speed, not the ground speed of the plane. If the wheels were powered by the vehicle then one can say that wheel speed and ground speed are the same (provided traction isn't lost).
In this case the wheel speed is independent of the ground speed. The conveyor must react and try to match the wheel's rotational speed, not have the conveyor set up the speed(s) to which the wheel has to match.
As it stands in real life, the runway and the wheel speed is the same as it is the plane that is moving forward and taking off.
Now think of this sample:
The magic conveyor has little to no rotational inertia (very little mass) so it takes practically no force to get it to accelerate. Now we line up our Cesna but it has very poor bearings in its wheels (the wheels are hard to turn). Pilot guns the throttle on the Cesna on this conveyor. The plane goes down the runway and takes off with zero wheel speed (remember that the conveyor has to match the wheel speed in our example) at 100knts ground speed.
In my sample (extreme, I know) the conveyor fulfills the matching wheel speed as it has to react to the wheel speed. In your extreme example, the conveyor is setting and controlling the wheel speed, not the plane.
Therefore it does not meet the criteria (as I've interpreted the question).
SaburoS,
Think about this: imagine the wheel is only rolling 2 mph on the treadmill, and its center/axle is moving down the runway at 1 mph. The treadmill must be going only 1 mph… In this case the treadmill is not matching the wheel’s speed.
Do you see this?
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 07:29:44 AM
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Originally posted by SaburoS If that's the case then the plane that takes off at 100knts then the conveyor matches that speed in the other direction. The conveyor doesn't add additional speed to other than to match.
Now if the question was that 'is it possible to have a magic conveyor runway go so fast as to keep the plane from taking off', then yes, you would be right. But that's not the puzzle/question. Plane still takes off.
Why would the conveyor be satisfied with 100knts? Why choose to have the conveyor fail at that particular speed?
If you were asked to match the speed a hare and a turtle also happened to be running along as well, would you just all of a sudden decide to match the turtle's speed as soon as the hare got a tad ahead of you? No, you would do you best to keep up with the hare.
Title: Re: Aircraft on a conveyor
Post by: eskimo2 on February 02, 2008, 08:23:09 AM
Quote
Originally posted by VERTEX
Granted, the takeoff roll would be slightly greater but it would be a small difference.
Vertex.
So, you do recognize that there would be a difference... Now imagine that the acceleration rate of the conveyor is doubled. That “slightly greater takeoff roll” would now be “slightly greater” times 2… Right? Now imagine that the acceleration rate of the conveyor is 10,000 times what you were initially imagining… It is a very big force now.
Imagine a question that asks, “Could a team of mice be as strong as a team of men?” If you assume that there are the same number of mice as men, then clearly the answer is no, the men are stronger. But “team” is not defined. “Team” for men could be two, and “Team” for mice could be 200,000.
In the question where the conveyor must match the plane’s speed, an analogy could be: pitting men against the same number of mice. In the question where the conveyor must match the plane’s wheel speed, however, an analogy could be: pitting men against a much larger number of mice. Don’t assume that they have to be the same number!
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 08:27:10 AM
Argue all you want; here is proof that the force exists. [/B][/QUOTE] At this point eskimo, you're just preaching to the choir. I went back and read the original thread last night and it was neat to see the light bulb go on in the heads of the few people that eventually got it (yourself included). At this point the idea of converting any more people is futile. Those that refuse to see have decided that the problem is so ridiculously simple that any further thought on the subject would be a waste of time.
I wonder how many epiphanies we miss each day because the solution is so close and easy to see that we look right past it...
I do hereby concede to ignorance.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 09:49:05 AM
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Originally posted by sluggish At this point the idea of converting any more people is futile.
Hope springs eternal, as does this subject.
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 10:44:05 AM
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Originally posted by SD67 This is getting out of hand. An aircrafts' engine moves air, period. This air generates thrust and it is the thrust that moves the aircraft forward. If the belt is started only once the aircraft starts to move, the aircraft will continue to move forward regardless whether the belt is going faster or slower, speeding up or slowing down. The airflow will build until sufficient lift is generated and the aircraft will fly. The only thing that will be affected is the relative rolling resistance due to the speed of the belt. Only if the belt is started before the aircraft starts to move, the aircraft will move backwards initially until the level of thrust reaches a level sufficient to overcome the backwards motion of the belt. In this case if the speed of the belt is increased (exponentially?) to prevent parity will the aircraft fail to build sufficient airflow to generate lift.
Bingo. But the 'aircraft will not take off' crowd just won't see that.
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 10:47:49 AM
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Originally posted by eskimo2 SaburoS,
Think about this: imagine the wheel is only rolling 2 mph on the treadmill, and its center/axle is moving down the runway at 1 mph. The treadmill must be going only 1 mph… In this case the treadmill is not matching the wheel’s speed.
Do you see this?
Of course I see what you're saying and your line of thinking. However, it is flawed.
I've already stated the reason(s) previously.
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 10:54:37 AM
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Originally posted by eskimo2 Why would the conveyor be satisfied with 100knts? Why choose to have the conveyor fail at that particular speed?
If you were asked to match the speed a hare and a turtle also happened to be running along as well, would you just all of a sudden decide to match the turtle's speed as soon as the hare got a tad ahead of you? No, you would do you best to keep up with the hare.
Where in this question does it mention ground speed? Notice that you used the term "fail" of the conveyor. That illustrates your line of thought here. You feel the plane will not take off so you will keep it from taking off by creating a situation that ensures it. Anything outside that box of reasoning you won't consider.
Read on as I'll post a response to the appropriate post of yours.
Title: Airplane on a Conveyor Belt...
Post by: WWhiskey on February 02, 2008, 10:55:30 AM
really wont take off you think? ok give the paramiters of the plane! ill do it for you, fixed wing, propeller drivin, must have wheels,------------ i bet it will fly no matter what you do or what the belt does. come to amaillo texas and ill show just bring lots of money they dont fly those v-22's for nothing! o and bring your belt, just make sure its big enough to go under the plane.(ever heard of vertical take off) foul you say! you bring in a magical belt with infinite speed that does not exist, i bring you a plane that does exist right now today that will fly with zero wheel speed or zero ground speed. now who wins?:aok you try to tie the airplane to 20th century tech. but use future or non existince tech. for your belt. not fair, the plane was never even described in the original question only that the belt was going to be traveling 100knots!
Title: Airplane on a Conveyor Belt...
Post by: sluggish on February 02, 2008, 11:06:56 AM
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Originally posted by SaburoS Where in this question does it mention ground speed? Notice that you used the term "fail" of the conveyor. That illustrates your line of thought here. You feel the plane will not take off so you will keep it from taking off by creating a situation that ensures it. Anything outside that box of reasoning you won't consider.
Read on as I'll post a response to the appropriate post of yours.
Last post.
Google a few things-
moment of inertia rotational inertia
learn the difference between speed and acceleration
Also understand that the force is being applied at the edge of the wheel by the belt therefore creating directional force unlike if the force were applied at the hub Therefore creating rotational force effectively cancelling itself out (like chairboy thinks).
Your basic arguement SaburoS is that we don't understand the question. We all agree that in it's simplest form (where the the belt goes the same speed as the plane but in the opposite direction), that the plane will fly. We are discussing whether or not the plane will fly if the belt matches the WHEEL's speed. In this instance the plane, due to the forces of rotational inertia, WILL NOT FLY.
outy
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 11:21:06 AM
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Originally posted by eskimo2 To see this force watch these AVI's:
Argue all you want; here is proof that the force exists. [/B][/QUOTE]
Okay here we go:
Example #1.
Here you have a belt sander starting off at full speed almost instantaneously.
a) Why is the belt sander dictating the wheel speed? b) Isn't it supposed to react to the wheel and not the other way around? c) The conveyor belt in this example is the sole source of power here. d) Remember the conveyor's belt speed is to match the wheel's speed, not the other way around. e) Now try your experiment in a real world fashion in that the wheel is being pushed forward at a realistic acceleration rate (starts off at zero and gradually increases in speed from there (to match the wheel's speed). f) Then try this one. Pull the wheel back against the spring tension. Bring the sander to full speed and let the wheel and belt match their respective speeds. Let go of the wheel. What happens? g) The moment you allow the conveyor to dictate the wheel rpm speed, you go outside of the intention of the original question. h) Remember that unless the aircraft actually starts rolling forward, the wheel speed is zero, hence the conveyor's speed is zero. The conveyor is always going to have to react to match, not create a greater force to bring the plane back to its starting position. It's a losing battle for the conveyor as the wheel speed is going to increase by virtue of the plane's ground speed increasing. Remember that the wheels are powered by the forward movement of the aircraft, not by engine torque.
Example #2
Again you load up the test to prove a point that will not be valid for the question. The glass ball, tube with rubber bands, and the rubber ball(?) is starting at rest. The paper starts out at full force. Notice that non of the objects have an external force acting on them to accelerate? You are confusing the question of 'matching the wheel's speed' to that of 'neutralizing the forward movement of the plane.'
Again, in the original question the aircraft's forward movement dictates wheel speed which will then dictate conveyor runway speed, not the other way around.
Go you get this principal?
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 11:23:24 AM
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Originally posted by SaburoS Where in this question does it mention ground speed? Notice that you used the term "fail" of the conveyor. That illustrates your line of thought here. You feel the plane will not take off so you will keep it from taking off by creating a situation that ensures it. Anything outside that box of reasoning you won't consider.
Read on as I'll post a response to the appropriate post of yours.
Here is the original question from the original thread:
Quote
Originally posted by rabbidrabbit A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's wheel speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill.
The question is:
Will the plane take off or not?
Pay attention to the sentence: "This conveyor has a control system that tracks the plane's wheel speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill."
If it is supposed to “track and tune the plane's wheel speed to the speed of the conveyor”, why would it do anything else? Why would it try to match the plane’s speed? That’s not what it is supposed to do…
If you are at a light in a hot rod, and there is lesser hot rod to your right and he wants to race, and there also is a moped to your left, and your buddy tells you that he’ll give you $1,000 if you can tie the other hot rod, why in the world would you try to tie the moped?
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 02, 2008, 11:34:04 AM
but the hot rod will not move, when the driver starts to go the rotational inertia of the drive wheels will use up all the engine power and the hot rod will not move. :rolleyes:
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 11:35:22 AM
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Originally posted by sluggish Argue all you want; here is proof that the force exists.
At this point eskimo, you're just preaching to the choir. I went back and read the original thread last night and it was neat to see the light bulb go on in the heads of the few people that eventually got it (yourself included). At this point the idea of converting any more people is futile. Those that refuse to see have decided that the problem is so ridiculously simple that any further thought on the subject would be a waste of time.
I wonder how many epiphanies we miss each day because the solution is so close and easy to see that we look right past it...
I do hereby concede to ignorance. [/B][/QUOTE]
My it's so nice of you to grace us with your superior intellect. I'm glad you're not charging a monthly fee for this enlightenment.
Quote
Originally posted by sluggish Last post.
Google a few things-
moment of inertia rotational inertia
learn the difference between speed and acceleration
Also understand that the force is being applied at the edge of the wheel by the belt therefore creating directional force unlike if the force were applied at the hub Therefore creating rotational force effectively cancelling itself out (like chairboy thinks).
Your basic arguement SaburoS is that we don't understand the question. We all agree that in it's simplest form (where the the belt goes the same speed as the plane but in the opposite direction), that the plane will fly. We are discussing whether or not the plane will fly if the belt matches the WHEEL's speed. In this instance the plane, due to the forces of rotational inertia, WILL NOT FLY.
I know very well the difference between acceleration and speed. Inertia? Acceleration? Action/reaction? Yup, those too. Rotational acceleration and rotational inertia? Yup. Friction? Yup.
You are confusing wheel speed (RPM) and ground speed.
You care to show the question because I'm not even sure at this point that we're answering the same question?
Answer this. From where and how does the wheel get its rpm speed from the aircraft?
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 11:39:00 AM
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Originally posted by eskimo2 Here is the original question from the original thread:
Pay attention to the sentence: "This conveyor has a control system that tracks the plane's wheel speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill."
If it is supposed to “track and tune the plane's wheel speed to the speed of the conveyor”, why would it do anything else? Why would it try to match the plane’s speed? That’s not what it is supposed to do…
If you are at a light in a hot rod, and there is lesser hot rod to your right and he wants to race, and there also is a moped to your left, and your buddy tells you that he’ll give you $1,000 if you can tie the other hot rod, why in the world would you try to tie the moped?
What gets the aircraft's wheel going to even start the wheel rpm? The forward movement of the aircraft or the conveyor belt?
You're stuck on the conveyor belt's powering the wheel speed and ignoring the aircraft's forward movement dictating the wheel speed.
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 11:40:04 AM
Plane flies.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 11:42:01 AM
There are several aspects to this question. Sometimes it's difficult to understand exactly where the disagreement lies. Breaking down a problem oftens helps to solve it. From my perspective there are two fundamental questions:
1. Does the belt match the plane or wheel speed? 2. If the latter, will the belt cause the wheel to spin increasingly faster at a rate limited only by the mechanical ability of the belt? and the power of the plane
I don't think there's any point arguing until both of these questions are answered and agreed upon.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 11:45:43 AM
Quote
Originally posted by SaburoS Argue all you want; here is proof that the force exists.
Okay here we go:
Example #1.
Here you have a belt sander starting off at full speed almost instantaneously.
a) Why is the belt sander dictating the wheel speed? b) Isn't it supposed to react to the wheel and not the other way around? c) The conveyor belt in this example is the sole source of power here. d) Remember the conveyor's belt speed is to match the wheel's speed, not the other way around. e) Now try your experiment in a real world fashion in that the wheel is being pushed forward at a realistic acceleration rate (starts off at zero and gradually increases in speed from there (to match the wheel's speed). f) Then try this one. Pull the wheel back against the spring tension. Bring the sander to full speed and let the wheel and belt match their respective speeds. Let go of the wheel. What happens? g) The moment you allow the conveyor to dictate the wheel rpm speed, you go outside of the intention of the original question. h) Remember that unless the aircraft actually starts rolling forward, the wheel speed is zero, hence the conveyor's speed is zero. The conveyor is always going to have to react to match, not create a greater force to bring the plane back to its starting position. It's a losing battle for the conveyor as the wheel speed is going to increase by virtue of the plane's ground speed increasing. Remember that the wheels are powered by the forward movement of the aircraft, not by engine torque.
Example #2
Again you load up the test to prove a point that will not be valid for the question. The glass ball, tube with rubber bands, and the rubber ball(?) is starting at rest. The paper starts out at full force. Notice that non of the objects have an external force acting on them to accelerate? You are confusing the question of 'matching the wheel's speed' to that of 'neutralizing the forward movement of the plane.'
Again, in the original question the aircraft's forward movement dictates wheel speed which will then dictate conveyor runway speed, not the other way around.
Go you get this principal? [/B][/QUOTE]
I used the sander and paper treadmill because they were easy to build with household items and they illustrate the forces involved that most people could not see. The sander must start at rest, because the only time the force described can be shown is while it accelerates; a constant speed does not show the effect. Looking at the clip frame by frame shows that the acceleration phase may be about ½ a second (around 15 frames out of 30 fps). Also note that the wheel is being pulled to the left by a rubber band that is stretched during acceleration. The rubber bands represent the force of the plane’s motor. Of course all forces are greatly skewed, but that doesn’t matter. The force exists and can be increased in acceleration rate and duration.
If the original question had a twist that stated that the conveyor had a governor that limited its speed to max-out at 100,000 mph, the system would hold the plane in place until the conveyor reached 100,000 mph, at that point it would hold steady at 100,000 mph and the plane would then take off normally!
Title: Airplane on a Conveyor Belt...
Post by: Regulator on February 02, 2008, 11:46:34 AM
I baffles me that anyone would even stop to wonder if a conveyor belt would have any effect on the force of a propeller against the relative wind being able to move an aircraft. Of course the plane would take off. The only effect on the aircraft would be wheel rotational speed. Fast enough conveyor you might burn out the wheel bearings, or if enough wheel speed were attained, you might cause tire cord seperation and failure, but the fuselage will still be pulled forward.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 11:48:47 AM
Quote
Originally posted by eskimo2 If the original question had a twist that stated that the conveyor had a governor that limited its speed to max-out at 100,000 mph, the system would hold the plane in place until the conveyor reached 100,000 mph, at that point it would hold steady at 100,000 mph and the plane would then take off normally!
Sure, but could it turn with wheels spinning at 100,000 mph? :D
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 11:49:31 AM
Quote
Originally posted by Regulator I baffles me that anyone would even stop to wonder if a conveyor belt would have any effect on the force of a propeller against the relative wind being able to move an aircraft. Of course the plane would take off. The only effect on the aircraft would be wheel rotational speed. Fast enough conveyor you might burn out the wheel bearings, or if enough wheel speed were attained, you might cause tire cord seperation and failure, but the fuselage will still be pulled forward.
I smell a troll.
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 02, 2008, 11:51:18 AM
Come on you guys, picture it in your mind, the conveyor cannot counteract the forward motion of the aircraft, it can only make the wheels spin faster.
The wheels free wheel on an axle independantly of the force of the propeller pulling the aircraft through the air.
Case closed.
Heres another scenario, have the aircraft held stationary by a wire attached begind. Spin up the conveyor to some rpm causing the wheels to spin backwards. Apply power to the engine while simultaneously releasing the cable, the aircraft propeller will pull the aircraft forward through the air and the aircraft will fly when take off airspeed is reached.
Done.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 11:53:40 AM
Quote
Originally posted by VERTEX Come on you guys, picture it in your mind, the conveyor cannot counteract the forward motion of the aircraft, it can only make the wheels spin faster.
The wheels free wheel on an axle independantly of the force of the propeller pulling the aircraft through the air.
Case closed.
Heres another scenario, have the aircraft held stationary by a wire attached begind. Spin up the conveyor to some rpm causing the wheels to spin backwards. Apply power to the engine while simultaneously releasing the cable, the aircraft propeller will pull the aircraft forward through the air and the aircraft will fly when take off airspeed is reached.
Done.
No need to picture it in your mind. Just watch Eskimo's belt sander video.
Of course he could be executing a little sleight of hand there. I'm pretty sure he didn't really try to launch his daughter into orbit in another of his famous videos. ;)
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 11:57:45 AM
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Originally posted by SaburoS What gets the aircraft's wheel going to even start the wheel rpm? The forward movement of the aircraft or the conveyor belt?
You're stuck on the conveyor belt's powering the wheel speed and ignoring the aircraft's forward movement dictating the wheel speed.
Imagine this; You and I are each holding an end of a trough with a ball bearing in the middle. Your job is to keep the bearing “exactly” in the center. I lower my end one inch and the ball starts to roll toward me. When you see this, are you going to immediately give up and allow the bearing to roll all the way to my end? Or, are you going to lower your end to get the bearing back to the center?
Title: Airplane on a Conveyor Belt...
Post by: Brownshirt on February 02, 2008, 12:00:42 PM
Imagine a Piper Cub taking off from a speeding carrier, starting its take-off run from the ship's bow and running to stern.
Do you really think it won't be able to take off ?
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 12:01:38 PM
Quote
Originally posted by VERTEX Come on you guys, picture it in your mind, the conveyor cannot counteract the forward motion of the aircraft, it can only make the wheels spin faster.
The wheels free wheel on an axle independantly of the force of the propeller pulling the aircraft through the air.
Case closed.
Heres another scenario, have the aircraft held stationary by a wire attached begind. Spin up the conveyor to some rpm causing the wheels to spin backwards. Apply power to the engine while simultaneously releasing the cable, the aircraft propeller will pull the aircraft forward through the air and the aircraft will fly when take off airspeed is reached.
Done.
It sounds like you are so sure of yourself that you never bothered to watch these AVI's:
You certainly have not bothered to explain what is going on in them.
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 12:01:49 PM
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Originally posted by eskimo2 I used the sander and paper treadmill because they were easy to build with household items and they illustrate the forces involved that most people could not see. The sander must start at rest, because the only time the force described can be shown is while it accelerates; a constant speed does not show the effect. Looking at the clip frame by frame shows that the acceleration phase may be about ½ a second (around 15 frames out of 30 fps). Also note that the wheel is being pulled to the left by a rubber band that is stretched during acceleration. The rubber bands represent the force of the plane’s motor. Of course all forces are greatly skewed, but that doesn’t matter. The force exists and can be increased in acceleration rate and duration.
If the original question had a twist that stated that the conveyor had a governor that limited its speed to max-out at 100,000 mph, the system would hold the plane in place until the conveyor reached 100,000 mph, at that point it would hold steady at 100,000 mph and the plane would then take off normally!
But you are still ignoring this:
The aircraft wheels rpm is controlled only by the forward movement of the aircraft. Without that forward movement the wheel does nothing. Hence the conveyor does nothing for it has nothing to track and match. The wheel is freewheeling in that it has no independent power source providing torque to the wheel. The conveyor can only match the speed of the wheel which is dictated only by the forward movement of the aircraft. If the aircraft does not move, the wheels don't move.
Plane flies.
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 12:04:13 PM
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Originally posted by eskimo2 Imagine this; You and I are each holding an end of a trough with a ball bearing in the middle. Your job is to keep the bearing “exactly” in the center. I lower my end one inch and the ball starts to roll toward me. When you see this, are you going to immediately give up and allow the bearing to roll all the way to my end? Or, are you going to lower your end to get the bearing back to the center?
To stop that forward momentum, you have to apply a greater than matching force.
Plane flies.
Title: Re: Re: Aircraft on a conveyor
Post by: VERTEX on February 02, 2008, 12:04:14 PM
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Originally posted by eskimo2 So, you do recognize that there would be a difference... Now imagine that the acceleration rate of the conveyor is doubled. That “slightly greater takeoff roll” would now be “slightly greater” times 2… Right? Now imagine that the acceleration rate of the conveyor is 10,000 times what you were initially imagining… It is a very big force now.
Imagine a question that asks, “Could a team of mice be as strong as a team of men?” If you assume that there are the same number of mice as men, then clearly the answer is no, the men are stronger. But “team” is not defined. “Team” for men could be two, and “Team” for mice could be 200,000.
In the question where the conveyor must match the plane’s speed, an analogy could be: pitting men against the same number of mice. In the question where the conveyor must match the plane’s wheel speed, however, an analogy could be: pitting men against a much larger number of mice. Don’t assume that they have to be the same number!
Actually upon thinking about it I take that back, I doubt the take off roll would change.
I think the added rolling resistance from the wheels extra rpm imparted by the conveyor would be negligable.
Just to clear up your belt sander test results, the reason the wheel is pulled back by the sander belt when its turned on is due to the inertia of the wheel at rest. The rest inertia must be overcome while the wheel spins up to belt sander speed.
At real life scales this wheel inertia would have a minimal effect on the take off roll distance of the aircraft.
But you are right, there is an effect. But not a large enough effect to counteract the final result that the airplane would fly.
Eskimo, do you agree the airplane will fly?
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 12:04:59 PM
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Originally posted by Brownshirt Imagine a Piper Cub taking off from a speeding carrier, starting its take-off run from the ship's bow and running to stern.
Do you really think it won't be able to take off ?
Please go back and read AKIron’s, eskimo2’s, Hitech’s and sluggish’s posts. We are so beyond that level of explanation.
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 12:05:22 PM
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Originally posted by eskimo2 It sounds like you are so sure of yourself that you never bothered to watch these AVI's:
You certainly have not bothered to explain what is going on in them.
I have and you have yet to address each comment that I attached.
Plane flies.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 12:05:30 PM
Just a little tangent to give us a break from this heated battle.
You're standing in boxcar that is sitting on a rail that is virtually frictionless. You're standing at one end of the boxcar and you throw a baseball at the far wall. What is the net result of this action?
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 02, 2008, 12:08:38 PM
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Originally posted by AKIron Just a little tangent to give us a break from this heated battle.
You're standing in boxcar that is sitting on a rail that is virtually frictionless. You're standing at one end of the boxcar and you throw a baseball at the far wall. What is the net result of this action?
The boxcar would move in the direction you are not facing, when the ball hits the far wall of the boxcar the boxcar would stop.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 12:09:25 PM
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Originally posted by SaburoS To stop that forward momentum, you have to apply a greater than matching force.
Plane flies.
So you'd give up?
I think most folks would lower their end an inch and a quarter, ease the ball back to the center and level out the trough.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 12:11:15 PM
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Originally posted by AKIron Just a little tangent to give us a break from this heated battle.
You're standing in boxcar that is sitting on a rail that is virtually frictionless. You're standing at one end of the boxcar and you throw a baseball at the far wall. What is the net result of this action?
Ball flies and the boxcar rolls ever so slowing in the opposite direction.
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 02, 2008, 12:12:36 PM
Let me correct myself, when the ball is thrown the boxcar would move in the direction you are not facing, when the ball re-bounds off the far wall the boxcar would move in the direction you are facing, if you catch the ball on its return the boxcar would come to rest again. This assumes no air friction to slow the ball, and the ball has no energy losses on the rebound.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 12:13:21 PM
What happens when the ball hits the wall? The car stop? What if you walk over pick up the ball, walk back and throw it again? Could you move the car to California (assuming the tracks were inclined to go that way and you are a hippy)?
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 02, 2008, 12:16:15 PM
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Originally posted by AKIron What happens when the ball hits the wall? The car stop? What if you walk over pick up the ball, walk back and throw it again? Could you move the car to California (assuming the tracks were inclined to go that way and you are a hippy)?
When you try to walk the boxcar moves under you in the opposite direction. You stay motionless with respect to the tracks.
Title: Re: Re: Re: Aircraft on a conveyor
Post by: eskimo2 on February 02, 2008, 12:16:32 PM
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Originally posted by VERTEX
Just to clear up your belt sander test results, the reason the wheel is pulled back by the sander belt when its turned on is due to the inertia of the wheel at rest. The rest inertia must be overcome while the wheel spins up to belt sander speed.
Been there, done that, watch this: http://hallbuzz.com/movies/wheel_on_sander_2_speed.AVI
Note the second pulse as the sander accelerates from a constant speed to a faster one.
Title: Re: Re: Re: Re: Aircraft on a conveyor
Post by: VERTEX on February 02, 2008, 12:17:35 PM
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Originally posted by eskimo2 Been there, done that, watch this: http://hallbuzz.com/movies/wheel_on_sander_2_speed.AVI
Note the second pulse as the sander accelerates from a constant speed to a faster one.
Fine, do you agree the plane flies?
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 12:19:34 PM
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Originally posted by eskimo2 So you'd give up?
I think most folks would lower their end an inch and a quarter, ease the ball back to the center and level out the trough.
No. This isn't about giving up.
At no point does the question allow a greater force to be used. It is to match the wheel's speed. Unless the aircraft moves forward the wheel's speed is zero and the conveyor's counter speed is zero. Unless the aircraft is accelerating the conveyor won't accelerate. Once you grasp that, you'll see where I'm coming from and why I see your reasoning as flawed. We're not talking about a car that gets its forward movement from its wheels.
The plane flies. The conveyor fights the losing battle for it has to react to the plane's forward movement for its speed. No forward movement/acceleration, no conveyor speed.
You just haven't grasped the fact of all the forces involved. You keep confusing ground speed to wheel rpm speed.
Plane flies.
Title: Re: Re: Re: Aircraft on a conveyor
Post by: eskimo2 on February 02, 2008, 12:20:37 PM
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Originally posted by VERTEX Actually upon thinking about it I take that back, I doubt the take off roll would change.
...
At real life scales this wheel inertia would have a minimal effect on the take off roll distance of the aircraft.
But you are right, there is an effect. But not a large enough effect to counteract the final result that the airplane would fly.
So which is it?
Why must the force remain small?
Imagine a question that asks, “Could a team of mice be as strong as a team of men?” If you assume that there are the same number of mice as men, then clearly the answer is no, the men are stronger. But “team” is not defined. “Team” for men could be two, and “Team” for mice could be 200,000.
Title: Re: Re: Re: Re: Re: Aircraft on a conveyor
Post by: eskimo2 on February 02, 2008, 12:22:44 PM
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Originally posted by VERTEX Fine, do you agree the plane flies?
If the conveyor matches the plane’s speed; it flies no problem. If the conveyor matches the plane’s wheel speed; it will not fly.
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 02, 2008, 12:23:37 PM
Eskimo, first I need to know if you agree the airplane will fly, and if you agree with my 3 possible conveyor belt options, then I will get into the nitty gritty, with respect to the extraneous forces involved.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 12:24:14 PM
The virtually frictionless part is kind of a rub.
You might liken this scenario to standing on a skateboard. You can shift your weight causing the skateboard to move. By slowly regaining your original position you prepare yourself to do it again without moving the skateboard in the opposite direction. You can do this because friction is working with you in this.
In a closed system without friction (yes, even without that caused by internal air I neglected to account for) I think it would go more like this:
1. You throw the ball, the car moves +1. 2. Ball hits wall, the car stops. 3. Walk over to pick up the ball, the car moves another +1. 4. Walk back with ball, the car moves -2 (more mass moving back)
Title: Re: Re: Re: Re: Re: Re: Aircraft on a conveyor
Post by: VERTEX on February 02, 2008, 12:25:32 PM
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Originally posted by eskimo2 If the conveyor matches the plane’s speed; it flies no problem. If the conveyor matches the plane’s wheel speed; it will not fly.
What can I say, the wheels rpm is indepandant from the aircrafts forward motion, the wheels free wheel on an axle, if you cant get that part its no use continuing.
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 02, 2008, 12:27:56 PM
The conveyor cannot match the planes speed, the free wheeling nature of the wheels prevents this, the conveyor can only act on the wheels.
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 02, 2008, 12:30:04 PM
The plane on a conveyor is a trick question in the first place, its like asking if a an electric train was moving forward at 50 mph and the wind was blowing in the direction the train was moving which way would the smoke move?
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 12:31:55 PM
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Originally posted by AKIron Just a little tangent to give us a break from this heated battle.
You're standing in boxcar that is sitting on a rail that is virtually frictionless. You're standing at one end of the boxcar and you throw a baseball at the far wall. What is the net result of this action?
Well if the boxcar is sitting on an electromagnetic zero friction cushion, the boxcar moves ever so slightly in the opposite direction. The ball then transfers the force on the opposite wall and reverses the progress (canceling it out). The boxcar then returns to its original position. This is of course if no energy is lost from the transfer points (kinetic-heat).
Kind of like trying to use a boat mounted fan to power the sails. The boat stays.
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 02, 2008, 12:36:37 PM
Heres one for you to ponder.
An airplane sits on a runway, with a huge fan behind it. As the airplane engine is sped up the fan blows air towards the airplane. The fan matches the velocity and volume of air moving over the wings exactly.
What happens to the airplane as the engine is revved up?
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 12:37:43 PM
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Originally posted by SaburoS Well if the boxcar is sitting on an electromagnetic zero friction cushion, the boxcar moves ever so slightly in the opposite direction. The ball then transfers the force on the opposite wall and reverses the progress (canceling it out). The boxcar then returns to its original position. This is of course if no energy is lost from the transfer points (kinetic-heat).
Kind of like trying to use a boat mounted fan to power the sails. The boat stays.
The ball only stops the boxcar when it hit's the far wall. If it moved it back in the opposite direction why would it stop in the original place with no friction?
Assume that my statement about the car moving, stopping, and then moving back with the walking is correct. Is work being done? Not the sort that your boss would be happy with but the sort defined in a physics 101 book.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 12:40:15 PM
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Originally posted by SaburoS No. This isn't about giving up.
At no point does the question allow a greater force to be used. It is to match the wheel's speed. Unless the aircraft moves forward the wheel's speed is zero and the conveyor's counter speed is zero. Unless the aircraft is accelerating the conveyor won't accelerate. Once you grasp that, you'll see where I'm coming from and why I see your reasoning as flawed. We're not talking about a car that gets its forward movement from its wheels.
The plane flies. The conveyor fights the losing battle for it has to react to the plane's forward movement for its speed. No forward movement/acceleration, no conveyor speed.
You just haven't grasped the fact of all the forces involved. You keep confusing ground speed to wheel rpm speed.
Plane flies.
You are getting hung up on the semantics and precision of the word exactly and how the control mechanism could work. Maybe by exactly it anticipates the power output of the engine/prop and responds at the same instant. Maybe it has a tolerance of one mm.
The point is that the conveyor could push the plane back, even if the plane is at full power. The point is that the question forces a solution that is counter intuitive and hard to imagine, even by very bright people.
In the version of the question where the conveyor matches the plane’s speed, I think most children would have trouble understanding why the plane would fly. It’s still a good question though. This question appears to put a twist on that one; it appears to be geared to be understood by some adults. It really is a higher level question. Rabbidrabbit indicated that he intentionally put the twist on it. If he did so with an understanding of this solution; I’d say it was a moment of brilliance.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 12:43:45 PM
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Originally posted by VERTEX The conveyor cannot match the planes speed, the free wheeling nature of the wheels prevents this, the conveyor can only act on the wheels.
In the version of the question where the conveyor matches the plane’s speed, the plane takes off at 50 mph, its wheels are spinning at 100 mph and the conveyor is moving at 50 mph in the opposite direction.
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 12:45:26 PM
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Originally posted by AKIron The ball only stops the boxcar when it hit's the far wall. If it moved it back in the opposite direction why would it stop in the original place with no friction?
Assume that my statement about the car moving, stopping, and then moving back with the walking is correct. Is work being done? Not the sort that your boss would be happy with but the sort defined in a physics 101 book.
Bounce collision? I was taking into account that there would be zero energy lost in this magic example.
Conservation of energy?
Title: Re: Re: Re: Re: Re: Re: Re: Aircraft on a conveyor
Post by: eskimo2 on February 02, 2008, 12:46:30 PM
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Originally posted by VERTEX What can I say, the wheels rpm is indepandant from the aircrafts forward motion, the wheels free wheel on an axle, if you cant get that part its no use continuing.
Imagine the wheel is only rolling 2 mph on the treadmill, and its center/axle is moving down the runway at 1 mph. The treadmill must be going only 1 mph… In this case the treadmill is not matching the wheel’s speed.
Do you agree?
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 12:48:55 PM
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Originally posted by SaburoS Bounce collision? I was taking into account that there would be zero energy lost in this magic example.
Conservation of energy?
It's not really a magic situation. I could move the car far out into space where the universe's gravitational effect is balanced or negligible.
To avoid a hijack I'll just answer. Yes, even though there is no net progress in a specific direction when a cycle was completed, there was work performed since mass was moved over time.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 12:49:45 PM
SaburoS, Back to the beginning, suppose we take the wheel out of the question:
A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill.
What happens?
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 12:58:33 PM
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Originally posted by AKIron The ball only stops the boxcar when it hit's the far wall. If it moved it back in the opposite direction why would it stop in the original place with no friction?
Assume that my statement about the car moving, stopping, and then moving back with the walking is correct. Is work being done? Not the sort that your boss would be happy with but the sort defined in a physics 101 book.
I maybe wrong since it's been some (cough) decades(cough) since I've opened a physics book.
I throw the ball to the far wall. The boxcar moves in the opposite direction. The ball impacts the far wall (bounce collision) and double the force is transferred and forces the car to not only stop but to go in the opposite direction. When I catch the ball, the boxcar stops.
Purely a guess and provided this is with zero energy lost at each impact/transfer point. In a vacuum too so none lost to drag.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 01:00:11 PM
Here's another way to look at it.
A plane is sitting on a conveyor belt without it's engine running. The belt starts to move and the plane moves with it. The faster the belt moves the faster the plane goes. By definition, the faster the plane goes the more energy it has. This energy came from the belt. Suppose that the belt is accelerating fast enough so that the plane can't keep up and the wheels start spinning. Does that mean there is energy being lost or is it being transferrred to the rolling wheels?
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 01:08:11 PM
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Originally posted by eskimo2 SaburoS, Back to the beginning, suppose we take the wheel out of the question:
A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill.
What happens?
Eskimo,
Example one: A plane is on the runway that has a conveyor system that is designed to counter the forward movement of the plane using greater force as necessary where the conveyor controls the speed where it can maintain an acceleration so great that the plane's wheel's rotational inertia overcomes the thrust of the plane's engines to keep it at zero ground speed. Is this likely?
Yes. I've understood this from the beginning.
Notice that the conveyor is dictating the force here.
I just don't see this coming from the original question.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 01:10:00 PM
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Originally posted by SaburoS Eskimo,
Example one: A plane is on the runway that has a conveyor system that is designed to counter the forward movement of the plane using greater force as necessary where the conveyor controls the speed where it can maintain an acceleration so great that the plane's wheel's rotational inertia overcomes the thrust of the plane's engines to keep it at zero ground speed. Is this likely?
Yes. I've understood this from the beginning.
Notice that the conveyor is dictating the force here.
I just don't see this coming from the original question.
Are you not seeing the energy being transferred by an accelerating belt or are you not seeing the reason why the belt would accelerate?
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 01:12:07 PM
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Originally posted by AKIron Here's another way to look at it.
A plane is sitting on a conveyor belt without it's engine running. The belt starts to move and the plane moves with it. The faster the belt moves the faster the plane goes. By definition, the faster the plane goes the more energy it has. This energy came from the belt. Suppose that the belt is accelerating fast enough so that the plane can't keep up and the wheels start spinning. Does that mean there is energy being lost or is it being transferrred to the rolling wheels?
No energy is lost. But that's not the question. Kind of like saying you are in a small dingy and you blow on the sail. Do you move forward based on that action alone?
What dictates wheel speed in our original question? The plane's forward movement or the conveyor belt?
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 01:16:04 PM
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Originally posted by AKIron Are you not seeing the energy being transferred by an accelerating belt or are you not seeing the reason why the belt would accelerate?
Why does the belt accelerate? What is it monitoring? Based on the original question, the belt is to match the wheels speed, not impart more force to increase the wheel speed. It is no longer matching wheel speed but increasing it.
Do you see that?
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 01:17:02 PM
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Originally posted by eskimo2 SaburoS, Back to the beginning, suppose we take the wheel out of the question:
A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill.
What happens?
Please answer the question; does the plane take off or not?
I need to know if you understand this version of the question.
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 01:19:23 PM
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Originally posted by eskimo2 Please answer the question; does the plane take off or not?
I need to know if you understand this version of the question.
(Sigh!) Reposting this:
Eskimo,
Example one: A plane is on the runway that has a conveyor system that is designed to counter the forward movement of the plane using greater force as necessary where the conveyor controls the speed where it can maintain an acceleration so great that the plane's wheel's rotational inertia overcomes the thrust of the plane's engines to keep it at zero ground speed. Is this likely?
Yes. I've understood this from the beginning.
Notice that the conveyor is dictating the force here.
I just don't see this coming from the original question.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 01:25:48 PM
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Originally posted by SaburoS No energy is lost. But that's not the question. Kind of like saying you are in a small dingy and you blow on the sail. Do you move forward based on that action alone?
What dictates wheel speed in our original question? The plane's forward movement or the conveyor belt?
1. The plane moves forward an inch at a speed of 1 mph. 2. The belt "sees" this and moves backward at 1 mph. 3. Because the plane was moving at 1 mph and the belt is moving in the opposite direct at 1 mph the wheel is now spinning at 2mph 4. The belt sees that and increases it's speed to 2 mph 5. The plane is still moving forward at 1 mph but the wheels are now spinning at 3mph 6. The belt sees this and increases it's speed to 3mph 7. The plane is still moving at 1mph but the wheels are now spinning at 4mph
I think you can see where this is going.
This all happens very fast, limited only by the belt's ability to accelerate.
The belt only slows when the plane cannot overcome the energy being imparted to the wheels and slows. As the belt slows the plane inches forward repeating steps 1 through maximum power of the plane
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 01:32:29 PM
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Originally posted by SaburoS (Sigh!) Reposting this:
Eskimo,
Example one: A plane is on the runway that has a conveyor system that is designed to counter the forward movement of the plane using greater force as necessary where the conveyor controls the speed where it can maintain an acceleration so great that the plane's wheel's rotational inertia overcomes the thrust of the plane's engines to keep it at zero ground speed. Is this likely?
Yes. I've understood this from the beginning.
Notice that the conveyor is dictating the force here.
I just don't see this coming from the original question.
I’m not asking you to comment at all on the wheel speed question. Please forget about it for one post and answer this plane-speed question only:
A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill.
If you are really tired of it, just say, “It flies”. Or “It does not fly”.
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 01:39:21 PM
Quote
Originally posted by AKIron 1. The plane moves forward an inch at a speed of 1 mph. 2. The belt "sees" this and moves backward at 1 mph. 3. Because the plane was moving at 1 mph and the belt is moving in the opposite direct at 1 mph the wheel is now spinning at 2mph 4. The belt sees that and increases it's speed to 2 mph 5. The plane is still moving forward at 1 mph but the wheels are now spinning at 3mph 6. The belt sees this and increases it's speed to 3mph 7. The plane is still moving at 1mph but the wheels are now spinning at 4mph
I think you can see where this is going.
This all happens very fast, limited only by the belt's ability to accelerate.
The belt only slows when the plane cannot overcome the energy being imparted to the wheels and slows. As the belt slows the plane inches forward repeating steps 1 through maximum power of the plane
The plane is still accelerating but you fail to factor that in your equation above. The wheels are free wheeling, not powered.
Plane takes off.
Title: Airplane on a Conveyor Belt...
Post by: WWhiskey on February 02, 2008, 01:40:48 PM
the original question from the Neal Boortz show that started this whole thing
" If an airplane is on a large conveyor belt and is trying to take off by exerting the thrust needed to move forward at 100knots, and the conveyor belt starts moving backwards at 100 knots, will the plane be able to take off, or will it just sit stationary relative to the ground, with the backwards speed of the conveyor belt counteracting the forward thrust of the plane?"
that is all it asks, nothing more, nothing less. the plane will fly! where everyone got the rest of the problems for this riddle is from other peoples answers and solutions to a problem that did not exist in the original question!
http://txfx.net/2005/12/08/airplane-on-a-conveyor-belt/ this shows the original question from december of 2005
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 01:41:58 PM
Quote
Originally posted by eskimo2 I’m not asking you to comment at all on the wheel speed question. Please forget about it for one post and answer this plane-speed question only:
A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill.
If you are really tired of it, just say, “It flies”. Or “It does not fly”.
Your question is vague. I answered that if the ground speed is zero then, no, the plane will not fly. No one disputes that.
edit: Eskimo, my response did mention ground speed, not wheel speed.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 01:45:47 PM
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Originally posted by SaburoS The plane is still accelerating but you fail to factor that in your equation above. The wheels are free wheeling, not powered.
Plane takes off.
I kept it simple. An accelerating plane will only cause the belt to accelerate faster.
Watch Eskimo's belt sander video and tell me why the wheel moves in the direction of the belt if it is "free wheeling". It requires a force to keep it from rolling off the sander. In his case it is a spring. In the case of the plane it is the engine.
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 01:48:21 PM
Quote
Originally posted by AKIron I kept it simple. An accelerating plane will only cause the belt to accelerate faster.
Watch Eskimo's belt sander video and tell me why the wheel moves in the direction of the belt if it is "free wheeling". It requires a force to keep it from rolling off the sander. In his case it is a spring. In the case of the plane it is the engine.
Sorry but in this case, the belt controlled the speed. It didn't match wheel speed but dictated it. Apples and oranges.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 01:50:43 PM
Quote
Originally posted by SaburoS Your question is vague. I answered that if the ground speed is zero then, no, the plane will not fly. No one disputes that.
edit: Eskimo, my response did mention ground speed, not wheel speed.
So you think in this question, the plane won't fly? What keeps it from flying?
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 01:55:42 PM
Quote
Originally posted by SaburoS Sorry but in this case, the belt controlled the speed. It didn't match wheel speed but dictated it. Apples and oranges.
The belt does cause the speed of the wheel to increase by matching it. However, it is the plane that dictates this. The belt only responds to the planes movement.
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 02:05:30 PM
Quote
Originally posted by eskimo2 So you think in this question, the plane won't fly? What keeps it from flying?
From my example where the conveyor can use a force that keeps the plane at zero airspeed then it will not fly. I'm saying that allowing a greater force to bring the plane back to zero ground speed is not matching anything but exceeding it. If we allow the conveyor belt to do this then it has the force/energy necessary to keep the plane back. In this case though it is not matching.
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 02:09:06 PM
Quote
Originally posted by AKIron The belt does cause the speed of the wheel to increase by matching it. However, it is the plane that dictates this. The belt only responds to the planes movement.
I was talking about the sanding belt in Eskimo's video.
Title: Airplane on a Conveyor Belt...
Post by: Brownshirt on February 02, 2008, 02:09:46 PM
Quote
Originally posted by eskimo2
A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill.
What happens? [/B]
Plane takes off without any problems. Next question.
Aircaft really doesn't care if the runway is moving or not; that can be seen pretty well in carrier take-offs and landings.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 02:14:36 PM
Quote
Originally posted by SaburoS From my example where the conveyor can use a force that keeps the plane at zero airspeed then it will not fly. I'm saying that allowing a greater force to bring the plane back to zero ground speed is not matching anything but exceeding it. If we allow the conveyor belt to do this then it has the force/energy necessary to keep the plane back. In this case though it is not matching.
I don't think you've read the question carefully. Please do not skim it. This is not your example and it is not the question where the conveyor matches the wheel speed. Please read carefully and try to understand what THIS question is asking:
"A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill."
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 02:17:52 PM
Eskimo and AKIron,
You have a super high powered jet plane with super low mass indestructible wheels and zero friction electromagnetic bearings. You also have the super conveyor of your dreams.
The wheels truly freewheel here with no energy loss.
Does the plane take off?
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 02, 2008, 02:20:46 PM
Quote
Originally posted by eskimo2 I don't think you've read the question carefully. Please do not skim it. This is not your example and it is not the question where the conveyor matches the wheel speed. Please read carefully and try to understand what THIS question is asking:
"A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill."
I tell you what, I'll need a break and revisit this further. I need to get some work done!!! My answering at this time will not yield any new results.
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 02, 2008, 02:36:45 PM
the belt has no effect on the speed of the plane, as someone said the wheels freewheel, thats their job, and don't even get into melting bearings and exploding tires. The original question did not ask if the plane would fly before bill's tundra tires exploded.
the belt cannot push on the plane, it can only spin the tires. Thrust moves the plane.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 02:38:29 PM
Any plane that has enough power to take off on a normal runway with its wheels locked, also could take off on the super-conveyor. In both cases the tires would be skidding/slipping though. F-15 perhaps?
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 02:39:23 PM
Quote
Originally posted by john9001 the belt has no effect on the speed of the plane, as someone said the wheels freewheel, thats their job, and don't even get into melting bearings and exploding tires. The original question did not ask if the plane would fly before bill's tundra tires exploded.
the belt cannot push on the plane, it can only spin the tires. Thrust moves the plane.
Have you watched eskimo's sander video? Seeing is believing in this case. the belt can and does apply force to the wheels. Only massless wheels would be "free wheeling".
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 02:40:38 PM
Quote
Originally posted by SaburoS I tell you what, I'll need a break and revisit this further. I need to get some work done!!! My answering at this time will not yield any new results.
Awe, come on. Just answer the one question with the wheel-speed-match removed from the problem. It really is a much simpler question. Even I concede that it will take off.
Title: Airplane on a Conveyor Belt...
Post by: SFRT - Frenchy on February 02, 2008, 02:45:50 PM
I'm sure it was pointed out already, but how some of you keep persisting on debating that with as much common sense as an Hillari/Obama suckfest is beyond my little brain.
lift force = ¨1/2 p "True airspeed"2 x coefficient of lift x wing area
wing area, angle of attack, relative speed of the air to my aircraft.
That's it, doesn't say about the frecking color of my underwares and what I had yesterday for lunch.
I tell you what, screew this ingeneer mumbojambo : Lift my plane in the air via a crane 50ft above the ground, spin my wheels at mach3, release the line, and I'll pancake myself straight down.
Any of you wanabee geniuses, is more than welcome to stand right below the plane to let you prouve your point to Darwin. :rolleyes:
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 02, 2008, 02:58:23 PM
what do belt sanders have to do with magical conveyor belts?
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 02:58:55 PM
Quote
Originally posted by john9001 what do belt sanders have to do with magical conveyor belts?
they work exactly the same way
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 03:06:00 PM
Quote
Originally posted by SFRT - Frenchy I'm sure it was pointed out already, but how some of you keep persisting on debating that with as much common sense as an Hillari/Obama suckfest is beyond my little brain.
lift force = ¨1/2 p "True airspeed"2 x coefficient of lift x wing area
wing area, angle of attack, relative speed of the air to my aircraft.
That's it, doesn't say about the frecking color of my underwares and what I had yesterday for lunch.
I tell you what, screew this ingeneer mumbojambo : Lift my plane in the air via a crane 50ft above the ground, spin my wheels at mach3, release the line, and I'll pancake myself straight down.
Any of you wanabee geniuses, is more than welcome to stand right below the plane to let you prouve your point to Darwin. :rolleyes:
What in the world are you talking about? I don’t see how your example relates to anything any of us are saying.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 03:07:11 PM
Ya know I never asked but is this whole thing in a vacuum? 'Cause if it is that plane definitely ain't flyin'.
Title: Airplane on a Conveyor Belt...
Post by: SFRT - Frenchy on February 02, 2008, 03:10:26 PM
I'm answering to the title of the thread :lol
How fast my wheels spin don't matter of me getting airborne.
Heck I can even get airborne with my wheels not spining at all, has been dome before on a Metroliner, killed everyone due to brake fire.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 03:25:10 PM
Quote
Originally posted by SFRT - Frenchy I'm answering to the title of the thread :lol
How fast my wheels spin don't matter of me getting airborne.
Heck I can even get airborne with my wheels not spining at all, has been dome before on a Metroliner, killed everyone due to brake fire.
If the wheels weren't spinning how did the brakes get hot?
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 02, 2008, 03:27:38 PM
the tire caught fire and set the brake fluid on fire.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 03:28:55 PM
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Originally posted by john9001 the tire caught fire and set the brake fluid on fire.
;)
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 03:35:07 PM
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Originally posted by SFRT - Frenchy I'm answering to the title of the thread :lol
How fast my wheels spin don't matter of me getting airborne.
Heck I can even get airborne with my wheels not spining at all, has been dome before on a Metroliner, killed everyone due to brake fire.
I just noticed your belts are moving in opposite direction between the two videos. Maybe that's confusing some. ;)
Anyhow, fixed
http://www.sidesconsulting.com/misc/fixed.wmv
Title: Airplane on a Conveyor Belt...
Post by: SFRT - Frenchy on February 02, 2008, 03:45:15 PM
Wow ... those videos were amazing! I do have no clue of what you guys are talking about:confused:
... I just hope it's not about "would my 16,000lbs Metroliner get airborne if the wheels are spining at 115 knots, but my relative wind and Ground Speed are 0".
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 03:47:33 PM
Just stay away from conveyor belts Frenchy and you'll be ok. :D
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 03:49:17 PM
Quote
Originally posted by AKIron I just noticed your belts are moving in opposite direction between the two videos. Maybe that's confusing some. ;)
Anyhow, fixed
http://www.sidesconsulting.com/misc/fixed.wmv
Good point! It's hard to pinpoint exactly what is confusing each person.
The only thing that’s for sure: Everyone KNOWS they are right. I think many people are just not willing to look/think past the obvious.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 03:52:42 PM
Quote
Originally posted by SFRT - Frenchy Wow ... those videos were amazing! I do have no clue of what you guys are talking about:confused:
... I just hope it's not about "would my 16,000lbs Metroliner get airborne if the wheels are spining at 115 knots, but my relative wind and Ground Speed are 0".
Here’s the original AH BBS question:
Quote
Originally posted by rabbidrabbit A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's wheel speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill.
The question is:
Will the plane take off or not?
Read and answer this to see a force you have not considered:
Here’s a story that simplifies the problem: (Note that the term wheels in this story refers to wheels and tires)
Identical triplets Al, Bob and Chuck buy three identical bush planes. Since they live in Alaska, all three brothers buy and install large balloon “tundra tires” and wheels. The wheels, planes and brothers are identical. All three planes will take off from a normal runway in exactly 100 feet and at exactly 50 mph. The brothers fly their planes to an air show in Wisconsin. At the air show Bob finds and buys a set of fantastic wheels. These wheels are exactly like the wheels he has on his plane in every way except they have half the mass. Their mass is distributed in the same proportion as the wheels that he plans on replacing. Al thinks Bob is silly and is content with his old wheels. Bob thinks that Al will eventually want a set, so he buys a second set to give to Al on their birthday.
Bob finds a buyer for his old heavy wheels and installs a set of his new lightweight ones. He loads the second set into his plane so that it is balanced just as it was before. Bob’s plane now weighs exactly the same as Al’s and Chuck’s, but its wheels have half the mass.
Meanwhile, Chuck runs into a magician who sells him a set of magic wheels. These wheels are exactly like the wheels he has on his plane in every way except they have no mass. Chuck installs his magic wheels. He loads his old set into his plane so that it is balanced just as it was before. Chuck’s plane now weighs exactly the same as Al’s and Bob’s, but its wheels have no mass.
When the brothers leave the air show they request a formation take off. They line up wing tip to wing tip and apply power at exactly the same time. All three planes weigh exactly the same and must hit 50 mph to lift off. When Chuck’s plane lifts off his wheels stop spinning instantly since they have no mass. Since they have no mass, they also have no rotational inertia. When Al’s plane lifts off his heavy wheels are spinning at 50 mph and have considerable rotational inertia. When Bob’s plane lifts off his half-weight wheels are spinning at 50 mph and have exactly half the rotational inertia as Al’s wheels.
Where did the rotational inertia and energy in Bob’s and Al’s wheels come from? How did the rotational inertia and energy now stored in Bob’s and Al’s wheels affect the take off distance of their planes? We know that Al’s plane will still take off in exactly 100 feet; where will Bob’s and Chuck’s planes take off?
Title: Airplane on a Conveyor Belt...
Post by: Chairboy on February 02, 2008, 03:59:24 PM
Do you get a commission every time you repaste that?
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 04:00:05 PM
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 04:06:45 PM
Quote
Originally posted by Chairboy Do you get a commission every time you repaste that?
You still don't get it, do you?
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 04:17:14 PM
I don't know about eskimo but I expect extra virgins for bringing the light of understanding to the darkness of conveyor belt land.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 04:25:56 PM
Chairboy,
I repost it because it forces you to see a point that you are ignoring. You have yet to answer which plane takes off first. I can only conclude that you are not bright enough to comprehend the question, or too arrogant to even consider carefully reading it. Hitech gets it. Hitech said that it was a good analogy. Many bright people have been converted to “the plane won’t fly” side of the wheel speed question based on the explanations presented.
I was on the plane will fly side as well. I also thought “the plane won’t fly” answer was silly until this concept presented itself.
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 02, 2008, 04:26:16 PM
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Originally posted by AKIron Here, this should make it plain for everyone:
the rotational energy of the wheels in this case does not come from the planes thrust, it comes from the belt, so there no loss of thrust. The belt is moving and putting the rotational energy into the wheel. The thrust is moving the plane forward.
a small amount of rotational energy goes into the wheels from the forward movement of the plane itself, but it very small and not enough to keep the plane from taking off as on a normal runway.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 04:34:35 PM
Quote
Originally posted by john9001 the rotational energy of the wheels in this case does not come from the planes thrust, it comes from the belt, so there no loss of thrust. The belt is moving and putting the rotational energy into the wheel. The thrust is moving the plane forward.
a small amount of rotational energy goes into the wheels from the forward movement of the plane itself, but it very small and not enough to keep the plane from taking off as on a normal runway.
It is small. Especially if the treadmill is only accelerating at the same rate as the plane. Now imagine that the acceleration rate is 10,000 times greater… Small X 10,000 = Big.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 04:34:46 PM
Quote
Originally posted by john9001 the rotational energy of the wheels in this case does not come from the planes thrust, it comes from the belt, so there no loss of thrust. The belt is moving and putting the rotational energy into the wheel. The thrust is moving the plane forward.
a small amount of rotational energy goes into the wheels from the forward movement of the plane itself, but it very small and not enough to keep the plane from taking off as on a normal runway.
Not so fast. As you have suggested in your "free wheeling" comment, the wheel has no ability to produce it's own energy. If it were gaining all of it's energy from the belt it would be moving in the direction the belt is moving. It takes energy from the plane to keep it moving in the opposite direction or even stationary. How much of the plane's energy it takes is dependent on how fast the belt is accelerating, not moving but accelerating.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 04:57:09 PM
Nothing new in this thread so far so I may as well make another previously made point. A very powerful belt could accelerate faster than a wheel with a loaded plane sitting on top of it can keep up. The wheel would begin "skidding". That is the point at which the belt can no longer increase the amount of energy stored in the wheel. The plane could roll forward if it can drag the skidding wheels. This is little different than a plane trying to take off with full brakes applied. Some planes may be able to do it. Most can't.
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 02, 2008, 05:02:07 PM
originial question.
"A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill."
<<<>>>>
it says the planes speed, if this plane can rotate and fly at 50 mph then the belt will being moving 50mph in the opposite direction. I doubt the wheels will be turning at 100,000 rpm at that speed.
If the plane holds it's speed at 50mph there will be no more acceleration from the belt, then the plane lifts off.
a note here, it does not mean the plans speed over the belt, it means the planes ground speed.
Title: Airplane on a Conveyor Belt...
Post by: Donzo on February 02, 2008, 05:11:03 PM
So......
If we used this magical conveyor runway when landing a plane, would the plane come to a dead stop immediately after touching down?
Title: Airplane on a Conveyor Belt...
Post by: WWhiskey on February 02, 2008, 05:16:53 PM
v-22 still takes off!
Title: Airplane on a Conveyor Belt...
Post by: SD67 on February 02, 2008, 06:10:09 PM
Quote
Originally posted by Donzo So......
If we used this magical conveyor runway when landing a plane, would the plane come to a dead stop immediately after touching down?
Actually this is pretty close to being true. On landing the aircraft is usually generating very little thrust, most are on what is termed a "glide approach". In this case, landing on a conveyor style runway will actually shorten the apparent landing distance significantly. The actual rolling distance will be similar, but that is absorbed by the belt. It is only when the equation of positive thrust comes into it that the conveyor ceases to be effective in arresting the aircrafts' forward motion.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 07:21:14 PM
Quote
Originally posted by john9001 originial question.
"A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill."
That's an alternate question that has been simplified.
Here’s the original AH BBS question from last year:
Quote
Originally posted by rabbidrabbit A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's wheel speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill.
The question is:
Will the plane take off or not?
Title: Airplane on a Conveyor Belt...
Post by: Chairboy on February 02, 2008, 08:24:00 PM
Quote
Originally posted by eskimo2 I can only conclude that you are not bright enough to comprehend the question, or too arrogant to even consider carefully reading it.
Yep, that must be it.
Title: Airplane on a Conveyor Belt...
Post by: WWhiskey on February 02, 2008, 08:43:08 PM
Quote
Originally posted by WWhiskey the original question from the Neal Boortz show that started this whole thing
" If an airplane is on a large conveyor belt and is trying to take off by exerting the thrust needed to move forward at 100knots, and the conveyor belt starts moving backwards at 100 knots, will the plane be able to take off, or will it just sit stationary relative to the ground, with the backwards speed of the conveyor belt counteracting the forward thrust of the plane?"
that is all it asks, nothing more, nothing less. the plane will fly! where everyone got the rest of the problems for this riddle is from other peoples answers and solutions to a problem that did not exist in the original question!
http://txfx.net/2005/12/08/airplane-on-a-conveyor-belt/ this shows the original question from december of 2005
Eskimo2, this is the original question from 2005, not the one by John9001 some of us are woking on the real question that was answered on Mythbusters not the changed version that came out later, but the V-22 still flies in either question!
Title: Re: Re: Re: Re: Re: Re: Re: Re: Aircraft on a conveyor
Post by: VERTEX on February 02, 2008, 09:08:53 PM
Quote
Originally posted by eskimo2 Imagine the wheel is only rolling 2 mph on the treadmill, and its center/axle is moving down the runway at 1 mph. The treadmill must be going only 1 mph… In this case the treadmill is not matching the wheel’s speed.
Do you agree?
Speed is a measure of distance traveled in a certain period of time. The wheel will have a speed as it is carried forward along with the axle that is the same as the airplane as a whole.
The rotation of the wheel about the axle, and the rotation of the conveyor belt are separate from the forward speed of the airplane. The wheel and conveyor can rotate in any direction, forwards or backwards and the plane will fly since the free wheeling nature of the wheel isolates the airplane from any influence the conveyor might have.
I am repeating myself here, why cant you get this.
Title: Airplane on a Conveyor Belt...
Post by: SFRT - Frenchy on February 02, 2008, 09:43:44 PM
Eskimo, not sure of what you want me to answer here ...
Al's plane will take off in 100ft, Bob's in less than AL's, and Chuck in less than Bob's. No rotational inertia will not mean that Chuck's plane will take off in 0ft.
The rotational inertia will just make it harder to spin the wheels, which will translate to the plane as drag. If you remove the rotational inertia of the wheels, you remove the drag induced by the wheel mass on the wheel axle.
You still have the aerodynamic drag of the wheel, plus the wheel drag induced by the contact of the tire to the ground plus all the gazzilions drag forces that apply to the plane.
So back to the "original question"
" If an airplane is on a large conveyor belt and is trying to take off by exerting the thrust needed to move forward at 100knots, and the conveyor belt starts moving backwards at 100 knots, will the plane be able to take off, or will it just sit stationary relative to the ground, with the backwards speed of the conveyor belt counteracting the forward thrust of the plane?"
Since you guys masturbate your brain with the conveyor, just remove the sucker. All the conveyor does is spin my wheels at 100knots. So suspend my plane in the air with a crane. Get an electric engine that spins my wheels at 100 knots, release me and watch me pancake myself.
Or the question is actually, I'm acceleration to 100kt and at 100kt the wheels spin backward ... will I take off?
Or the question is actually, I'm acceleration to 100kt and at 100kt I lock the wheels ... will I take off?
What needs 13 pages of debating?:confused:
Title: Airplane on a Conveyor Belt...
Post by: Golfer on February 02, 2008, 10:07:47 PM
What if the plane is trying to take off on a belt sander?
What if we vary the grit od the sandpaper?
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 10:38:04 PM
Quote
Originally posted by SFRT - Frenchy
All the conveyor does is spin my wheels at 100knots.
Why 100 knots? Why did you choose that speed?
Title: Re: Re: Re: Re: Re: Re: Re: Re: Re: Aircraft on a conveyor
Post by: eskimo2 on February 02, 2008, 10:41:48 PM
Quote
Originally posted by VERTEX Speed is a measure of distance traveled in a certain period of time. The wheel will have a speed as it is carried forward along with the axle that is the same as the airplane as a whole.
The rotation of the wheel about the axle, and the rotation of the conveyor belt are separate from the forward speed of the airplane. The wheel and conveyor can rotate in any direction, forwards or backwards and the plane will fly since the free wheeling nature of the wheel isolates the airplane from any influence the conveyor might have.
I am repeating myself here, why cant you get this.
Suppose the wheel is only rolling 2 mph on the treadmill, but its center/axle is not moving down the runway. The treadmill also must be going 2 mph… In this case the treadmill is matching the wheel’s speed.
Now imagine the wheel is only rolling 2 mph on the treadmill, and its center/axle is moving down the runway at 1 mph. The treadmill must be going only 1 mph… In this case the treadmill is not matching the wheel’s speed.
Now imagine the wheel is rolling 1,002 mph on the treadmill, and its center/axle is moving down the runway at 1 mph. The treadmill must be going 1,001 mph… In this case also, the treadmill is not matching the wheel’s speed.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 02, 2008, 10:45:08 PM
Quote
Originally posted by WWhiskey Eskimo2, this is the original question from 2005, not the one by John9001 some of us are woking on the real question that was answered on Mythbusters not the changed version that came out later, but the V-22 still flies in either question!
Here is the original AH BBS question from last year:
Quote
Originally posted by rabbidrabbit A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's wheel speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill.
The question is:
Will the plane take off or not?
I have no problem with the plane taking off if the conveyor matches the plane’s speed. This question is different; the wheel speed factor changes everything!
Title: Airplane on a Conveyor Belt...
Post by: SD67 on February 02, 2008, 10:51:21 PM
Some of the reasoning I see in this thread reminds me of the old question about the race between Achilles and a tortoise. Aristotle reasoned that If the tortoise had a head start Achilles could never defeat him in a race because by the time Achilles reached the point where the tortoise was, the tortoise would have move on, and so on and so forth. This is much the same sort of reasoning I see happening here. The bottom line is, deductive reasoning has no place in the world of physics. Physics dictates that as long as the aircraft develops sufficient thrust to overcome the initial backwards force of the conveyor it WILL fly.
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 02, 2008, 11:45:17 PM
i saw a belt sander fly, someone plugged it in when the switch was on , it flew but not very far, i think the rotational energy overcame it's thrust and made it crash.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 11:45:40 PM
Quote
Originally posted by SD67 The bottom line is, deductive reasoning has no place in the world of physics. Physics dictates that as long as the aircraft develops sufficient thrust to overcome the initial backwards force of the conveyor it WILL fly.
Assuming by "initial" you actually mean acceleration, of course it will fly. No one is arguing it won't. What is being said by some of us is that the belt may be capable of sustaining an acceleration and force transfer to the wheels equal to the thrust of the plane which keeps the plane from accelerating. At less than takeoff speed and without acceleration the plane won't fly.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 02, 2008, 11:51:53 PM
Quote
Originally posted by Chairboy Yep, that must be it.
Come on Chairboy, admit there's a force you don't or didn't see here. I won't take it as an admission there might be a God. ;)
Title: Airplane on a Conveyor Belt...
Post by: SD67 on February 02, 2008, 11:57:20 PM
Ahhh so you're theorising upon the existence of some super conveyor. Even so for such a super conveyor to be effective it will still need to be started even a fraction of a second before the aircraft moves. Once the aircraft gains forward momentum the conveyor cannot stop it from flying since the wheels are not the force driving it.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 03, 2008, 12:00:30 AM
Quote
Originally posted by SD67 Ahhh so you're theorising upon the existence of some super conveyor. Even so for such a super conveyor to be effective it will still need to be started even a fraction of a second before the aircraft moves. Once the aircraft gains forward momentum the conveyor cannot stop it from flying since the wheels are not the force driving it.
You're burdening me with this "super conveyor" like others have made the mistake of doing. I didn't create the scenario. I'm simply saying that under conditions given the plane won't take off if the belt can perform as the scenario dictates.
Title: Airplane on a Conveyor Belt...
Post by: SD67 on February 03, 2008, 12:09:59 AM
:lol Sorry Iron, I didn't mean You're in the subjective sense. I can see where the theory comes from, but in order for it to hold true the belt will still have to get the head start otherwise it will be fighting a losing battle. If the belt starts at the moment the aircraft generates forward momentum it cannot prevent the aircraft from flying. The only way the belt can prevent the aircraft from flying is if it gets the upper hand by starting first and forcing the aircraft to catch up.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 03, 2008, 12:13:45 AM
No offense taken SD67, I was not irritated, just making a point.
It's true that the belt lags the plane since it is afterall only responding. I think you're assuming that the belt's max power is limited to that of the plane. That was not a specified parameter. For the belt to keep the plane from accelerating it must have much more power available to it than does the plane.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 03, 2008, 12:22:18 AM
Understanding all aspects of this question as presented by rabbidrabbit reminds me of a riddle. To understand the solution to this riddle you have to look at it a particular way. Here's the riddle.
3 men in jail, one is blind, the other two can see
Warden has five hats, 3 are white, 2 are red
Warden tells men in jail to close their eyes and picks at random from the 5 hats and places one on each of the men's heads
Warden puts the remaining 2 hats out of sight
Warden tells men to open their eyes. Each can see the otehr's hat but cannot see their own. Of course the blind man sees nothing
Warden tells the men whoever knows what color hat is on their own head goes free
The men look at each other and think this over
Finally, 1st man says I don't know
2nd man heard the first man and also says, I don't know
3rd man who is blind, says I know
How did he know?
Title: Airplane on a Conveyor Belt...
Post by: SaburoS on February 03, 2008, 01:16:45 AM
Quote
Originally posted by AKIron Understanding all aspects of this question as presented by rabbidrabbit reminds me of a riddle. To understand the solution to this riddle you have to look at it a particular way. Here's the riddle.
3 men in jail, one is blind, the other two can see
Warden has five hats, 3 are white, 2 are red
Warden tells men in jail to close their eyes and picks at random from the 5 hats and places one on each of the men's heads
Warden puts the remaining 2 hats out of sight
Warden tells men to open their eyes. Each can see the otehr's hat but cannot see their own. Of course the blind man sees nothing
Warden tells the men whoever knows what color hat is on their own head goes free
The men look at each other and think this over
Finally, 1st man says I don't know
2nd man heard the first man and also says, I don't know
3rd man who is blind, says I know
How did he know?
Hmmm good one. The blind man is wearing a white hat. If the blind man were wearing one of the two red ones, then one of the men with sight would know by virtue of what the other man with sight saw. The moment any of the men with sight saw two red hats then by default he would be wearing the white one. The blind man is getting the feedback from two of the men, but the men with sight are only getting one feedback as the blind man can't see the other two. I think that's the answer. I'm tired.
Title: Airplane on a Conveyor Belt...
Post by: Kermit de frog on February 03, 2008, 02:25:26 AM
Blind guy wears a white hat.
edit: Explanation:
If anyone sees 2 Red hats, you'd know you were the one with the White hat. If you saw 2 White hats or 1 white and 1 Red, then you could be wearing either a Red or White hat yourself and you would not know which one you were wearing.
The first guy doesn't know, because he doesn't see 2 red hats.
2nd guy now knows both him and the 3rd guy are wearing white hats or 1 of each color, but not both wearing Red. If the 2nd guy sees a Red hat on the 3rd guy, the 2nd guy would then know he was wearing White. If the 2nd guy sees White on the 3rd guy, the 2nd guy could be wearing Red or White, therefore not knowing the answer.
3rd guy knows the 2nd guy must have seen him wearing a White hat, otherwise the 2nd guy would have known his (2nd guy) own color.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 03, 2008, 07:36:08 AM
Quote
Originally posted by SD67 :lol Sorry Iron, I didn't mean You're in the subjective sense. I can see where the theory comes from, but in order for it to hold true the belt will still have to get the head start otherwise it will be fighting a losing battle. If the belt starts at the moment the aircraft generates forward momentum it cannot prevent the aircraft from flying. The only way the belt can prevent the aircraft from flying is if it gets the upper hand by starting first and forcing the aircraft to catch up.
SD67,
Please answer this question (note that "wheel" has been removed).
A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill.
What happens?
Title: Airplane on a Conveyor Belt...
Post by: stephen on February 03, 2008, 07:43:45 AM
tires have nothing to do with the thrust devloped by the engine, the plane will move normaly across the face of the earth, and will lift off when the reletav air speed of the plane's wings reach take off speed as in a normal takeoff.
Look at it this way if you have to, the tires are rotating but no matter how fast they go, that has nothing to do with the reletave speed of the airplane across the face of the earth,...only the speed at which they turn...of ourse they might be doing one hell of a click by the time the plane reaches take off speed, but the plane will take off none the less.
If as in a car, the plane was drivin by its wheels it wouldnt move, but since airplanes arent given thrust by thier tires, the answer should be inssanly obviouse.:aok
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 03, 2008, 08:06:39 AM
Quote
Originally posted by stephen tires have nothing to do with the thrust devloped by the engine, the plane will move normaly across the face of the earth, and will lift off when the reletav air speed of the plane's wings reach take off speed as in a normal takeoff.
Look at it this way if you have to, the tires are rotating but no matter how fast they go, that has nothing to do with the reletave speed of the airplane across the face of the earth,...only the speed at which they turn...of ourse they might be doing one hell of a click by the time the plane reaches take off speed, but the plane will take off none the less.
If as in a car, the plane was drivin by its wheels it wouldnt move, but since airplanes arent given thrust by thier tires, the answer should be inssanly obviouse.:aok
From what you are saying, the wheel should remain stationary as the sander accelerates. At a constant speed, the speed of the wheels does not consume/absorb energy. Acceleration is a different matter.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 03, 2008, 08:39:01 AM
BTW, here is the original AH BBS thread (http://forums.hitechcreations.com/forums/showthread.php?s=&threadid=197189&perpage=50&highlight=conveyor%20belt&pagenumber=1).
Title: Airplane on a Conveyor Belt...
Post by: WWhiskey on February 03, 2008, 09:10:02 AM
yea and that question was flawed! just a little ways down the page you find the link to the real question from dec 2005! the person that started that thread did not state the question correctly, hence the correction! if anyone would have paid attention then we might not be having all this fun now!! never the less V-22 osprey still flies on either test!:aok im still waiting for you to tell me it wont and why tho
Title: Airplane on a Conveyor Belt...
Post by: moot on February 03, 2008, 09:45:53 AM
How do a few landing gear wheels generate enough drag to stop a few jet engines from accelerating a plane to minimum takeoff speed?
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 03, 2008, 10:21:35 AM
Both of you who responded got the hat riddle right.
That riddle and plane puzzle are similar in that with the hats you take into consideration what the two seeing guys saw and the fact that they couldn't solve the problem. Not so intuitive. With the plane/belt problem you must see that while the plane's powerplant applies thrust to the plane through it's engine mounts the belt is capable of applying an equal force in the opposite direction through the plane's wheels. Again, not easy to intuit.
Title: Airplane on a Conveyor Belt...
Post by: SlapShot on February 03, 2008, 10:25:37 AM
Quote
Originally posted by AKIron Here's an argument to say the guys that did this on TV did it wrong. Obviously they ran the belt at the same speed but opposite direction of the plane. If the original poser of the question intended for the belt to match the speed of the plane then why were "wheels" specifically mentioned instead of just saying the belt must match the speed of the plane?
I can't believe you guys are still debating this even after the "Mythbusters" busted it.
One thing you must have missed Iron ... Jamie said that as soon as the plane rolled ... HE GUNNED IT !!! ... meaning he went above the 25mph speed of the "tarp/conveyor" trying to make more of an effect ... and it had none ... the plane still took off.
The wheels are "freewheeling" and that is the key, and what everyone seems to ignore. Jamie could have had that tarp going 100mph (4 x the takeoff speed) and the plane would have rotated just the same.
The video of the belt sander with the wheel on it does show some force imparted on the wheels ... what lacks in the video is an "opposite" force ... such as an airplane engine ... so in essence ... that video really means nothing as far as this puzzle is concerned.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 03, 2008, 10:35:06 AM
Mythbuster's did not test the scenario we are debating here Slapshot. Read some of the hundreds of posts made in the various threads on this subject and that should become clear to you.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 03, 2008, 01:31:07 PM
The plane-speed question is a very good one. Why is it good? Because it fools so many people. Last year I initially read the wheel-speed question in the same way as the plane-speed question. I was surprised that it was even a question, that anyone wouldn’t intuitively get it the instant they read it. Honestly, I thought rabbidrabbit was either joking or completely clueless. As people chimed in, however, I realized that it really does fool many people. I even asked some bright people in RL, most of them were fooled and thought the plane wouldn’t fly. It is a good question because it separates people with different levels of understanding: those who DON’T get it even after reading thorough explanations, those who DO get it after reading thorough explanations and those who get it intuitively on their own.
The wheel-speed question is an even better one. Why is it better? Because it fools nearly everyone; the answer does not jump right out at you. Even after reading thorough explanations, very few people are capable of understanding the answer. It really does add a whole new tier of physics comprehension into the mix. No one intuitively saw the answer in the first reading. It took thorough discussions of the two paradoxes presented by this question for the answer to evolve. Most people do not understand the difference between the rotational energy absorption answer and the most basic level of misunderstanding where there’s a misunderstanding that the propeller turns the wheels.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 03, 2008, 01:57:00 PM
btw, I posted in that original thread as lukster.
Title: Airplane on a Conveyor Belt...
Post by: Chairboy on February 03, 2008, 02:10:00 PM
(http://hallert.net/images/helionturntable.jpg) Just for you, lukster.
Title: Airplane on a Conveyor Belt...
Post by: Donzo on February 03, 2008, 02:11:05 PM
Quote
Originally posted by Chairboy (http://hallert.net/images/helionturntable.jpg) Just for you, lukster.
LMAO :rofl
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 03, 2008, 02:12:06 PM
:rofl
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 03, 2008, 02:14:22 PM
That's great Chairboy!
Title: Airplane on a Conveyor Belt...
Post by: clerick on February 04, 2008, 01:53:41 AM
Quote
Originally posted by hitech I agree with you that bearing friction is a constant.
Only in a non-lubricated bearing. If there is any kind of liquid lubrication (grease, oil et.c.) the drag induced by the fluid will induce a force opposite the direction of rotation that increases as an inverse square to velocity. Granted that isn't true "friction" but it will act in the same direction.
Title: Airplane on a Conveyor Belt...
Post by: Overlag on February 04, 2008, 06:12:32 AM
if the conveyor belt is stopping the plane move forward then surely there is no airspeed? (apart from the area near the prop)
Title: Airplane on a Conveyor Belt...
Post by: hitech on February 04, 2008, 09:56:27 AM
clerick: Agreed, also with a rubber tire at higher speeds it becomes a none constant also.
But for general analysis , first pass it is generally treated as a constant.
HiTech
Title: Airplane on a Conveyor Belt...
Post by: clerick on February 04, 2008, 10:38:26 AM
I hate when rubber isn't a constant. First she wants them, then not, then does....
:noid
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 05, 2008, 01:13:44 PM
Quote
Originally posted by eskimo2 That's an alternate question that has been simplified.
Here’s the original AH BBS question from last year:
Ok eskimo, but then;
By "wheel speed" do they mean the rpm of the wheel about the axle or wheel velocity? And if it is wheel velocity is it with respect to the conveyor, the ground, or the air.
Bear in mind that the rotation of the wheel does not give it "speed".
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 05, 2008, 03:36:47 PM
Quote
Originally posted by VERTEX Ok eskimo, but then;
By "wheel speed" do they mean the rpm of the wheel about the axle or wheel velocity? And if it is wheel velocity is it with respect to the conveyor, the ground, or the air.
Bear in mind that the rotation of the wheel does not give it "speed".
If someone said that he did a front wheels-brakes locked burnout and his rear tires were going 60 mph, pretty much anyone would assume that he meant the car was still, but where the rubber that meets the road part of the tire was spinning at 60 mph. Certainly you could argue that the wheels really weren’t moving though.
If someone said that an airport baggage pick-up conveyor travels at 5 mph, pretty much anyone would assume that top surface, where the bags ride, moves along at 5 mph. Certainly you could argue that the conveyor really isn’t moving at all because the lower layer of the conveyor travels at 5 mph in the opposite direction which cancels it all out.
Now in the plane-conveyor wheel-speed question, you could figure that the wheels are really moving at the same speed as the wing, rudder or flap indicator light. I think that it’s pretty reasonable to assume, however, that the term “…plane’s wheel speed” was specifically used to indicate where the rubber meets the conveyor.
I suppose that you could add a twist to any speed problem by including the Earth’s rotational speed, or the Earth’s orbiting speed around the sun, or the solar system’s speed in relation to the center of the Universe (big-bang).
Not that’s its wrong to think outside of the box and consider all possibilities; I’d considered this as well. But since the language of the question appears to be short and sweet instead of ultra detailed and specific and the question ends with the phrase, “similar to a treadmill”, I think it clear that we are talking about where the rubber meets the conveyor. Otherwise it would have been more succinct to just state that the control system that tracks the plane’s speed.
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 05, 2008, 06:08:45 PM
eskimo.
Ok, so the conveyors job is to cancell out the wheels speed, and by this we mean the rotation of the tire?
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 05, 2008, 06:22:37 PM
Quote
Originally posted by VERTEX eskimo.
Ok, so the conveyors job is to cancell out the wheels speed, and by this we mean the rotation of the tire?
Straight acceleration requires energy. Rotational acceleration also requires energy. If not for an axle, a rotationally accelerating wheel on a conveyor belt also accelerates linearly down the belt. This force applied to an axle is transferred to the plane. If the rotational acceleration were enough, a full throttle plane could be held in place, or even pushed back.
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 05, 2008, 06:24:11 PM
you have not answered my question.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 05, 2008, 06:31:31 PM
No.
It is supposed to match the wheel’s speed. It just so happens that when it does this it cancels out the planes speed/acceleration
Title: Airplane on a Conveyor Belt...
Post by: Holden McGroin on February 05, 2008, 06:41:54 PM
Quote
Originally posted by eskimo2 Straight acceleration requires energy. Rotational acceleration also requires energy. If not for an axle, a rotationally accelerating wheel on a conveyor belt also accelerates linearly down the belt. This force applied to an axle is transferred to the plane. If the rotational acceleration were enough, a full throttle plane could be held in place, or even pushed back.
a 747 airliner, weighs around 400,000 pounds at landing lands at about 130 mph
When touching down, the mains spin up to 130 mph tangential speed within a fraction of a second.
During the chirp of the tires spinning up, the momentum of the aircraft is changed almost imperceptivity. Wheel brakes and thrust reversers are employed to slow the aircraft, which under only air and wheel drag would probably roll for several miles before coming to rest.
This ridiculous problem only makes sense if you suspend disbelief in a conveyor capable of ridiculous speeds. Speed of the conveyor would have to be hypersonic before wheel drag could overcome engine thrust.
Hypersonic speed would destroy not only the gear but the conveyor itself.
Hence under any real world conditions, this problem is stupid.
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 05, 2008, 06:48:45 PM
Quote
Originally posted by eskimo2 No.
It is supposed to match the wheel’s speed. It just so happens that when it does this it cancels out the planes speed/acceleration
This is where you are fundamentally wrong, the conveyor is incapable of doing what you claim, it can only act on the wheels, the airplanes forward motion is independant because the wheels are free wheeling and the forward motion of the airplane is caused by thrust.
As a side note, I noticed in the other airplane on conveyor thread you answered correctly that the airplane would fly, so what the heck is up here?
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 05, 2008, 06:51:19 PM
Quote
Originally posted by Holden McGroin a 747 airliner, weighs around 400,000 pounds at landing lands at about 130 mph
When touching down, the mains spin up to 130 mph tangential speed within a fraction of a second.
During the chirp of the tires spinning up, the momentum of the aircraft is changed almost imperceptivity. Wheel brakes and thrust reversers are employed to slow the aircraft, which under only air and wheel drag would probably roll for several miles before coming to rest.
This ridiculous problem only makes sense if you suspend disbelief in a conveyor capable of ridiculous speeds. Speed of the conveyor would have to be hypersonic before wheel drag could overcome engine thrust.
Hypersonic speed would destroy not only the gear but the conveyor itself.
Hence under any real world conditions, this problem is stupid.
You are right, the question is worded to confuse people, to make them think the wheels spin rate is important. Or that some how the travel of the conveyor belt affects the airplanes thrust. It has worked on some.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 05, 2008, 07:02:16 PM
Quote
Originally posted by Holden McGroin a 747 airliner, weighs around 400,000 pounds at landing lands at about 130 mph
When touching down, the mains spin up to 130 mph tangential speed within a fraction of a second.
During the chirp of the tires spinning up, the momentum of the aircraft is changed almost imperceptivity. Wheel brakes and thrust reversers are employed to slow the aircraft, which under only air and wheel drag would probably roll for several miles before coming to rest.
This ridiculous problem only makes sense if you suspend disbelief in a conveyor capable of ridiculous speeds. Speed of the conveyor would have to be hypersonic before wheel drag could overcome engine thrust.
Hypersonic speed would destroy not only the gear but the conveyor itself.
Hence under any real world conditions, this problem is stupid.
I agree that it would be impossible to build, or if it were built as best we could it would probably explode after a second or two.
I have landed in light bush planes with big tires, however, the force is more than perceptible.
The point of this question isn’t to debate how such a conveyor could be built, what materials the belt could be made of, how wide or long it must be, what the power source might be. It also does not matter how the conveyor matches the plan’s speed “exactly”.
In the plane speed question, the one where the conveyor only has to match the speed of the plane, the one where the plane takes off, we naturally accept that the conveyor somehow works: power, size, controls and all. It doesn’t matter how impractical it would be to build such a contraption, or that it would be nearly impossible to make one that could handle a 747. It doesn’t matter that some aircraft might experience tire failure when the effective wheel speed is doubled.
The point is that the question brings to light how many people misunderstand the forces at work; that the thrust of the prop is counteracted by the acceleration rate of the plane diminishing into the air drag on the wings and airframe. The extra energy loaded into the wheels at these speed is negligible, not even worth mentioning in this question, the plane takes off. For many people, studying this question opens up a new level of understanding not-so-obvious forces.
In the wheel speed question, if you also just accept that the conveyor exists as described, it opens up a new level of understanding not-so-obvious forces.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 05, 2008, 07:03:52 PM
Quote
Originally posted by VERTEX This is where you are fundamentally wrong, the conveyor is incapable of doing what you claim, it can only act on the wheels, the airplanes forward motion is independant because the wheels are free wheeling and the forward motion of the airplane is caused by thrust.
As a side note, I noticed in the other airplane on conveyor thread you answered correctly that the airplane would fly, so what the heck is up here?
I'm talking about the original AH BBS question from last year:
Quote
Originally posted by rabbidrabbit A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's wheel speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill.
The question is:
Will the plane take off or not?
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 05, 2008, 07:05:52 PM
Quote
Originally posted by VERTEX This is where you are fundamentally wrong, the conveyor is incapable of doing what you claim, it can only act on the wheels, the airplanes forward motion is independant because the wheels are free wheeling and the forward motion of the airplane is caused by thrust.
From what you are saying, the wheel should remain stationary as the sander accelerates. At a constant speed, the speed of the wheels does not consume/absorb energy. Acceleration is a different matter.
Title: Airplane on a Conveyor Belt...
Post by: Holden McGroin on February 05, 2008, 07:15:09 PM
Quote
Originally posted by eskimo2 I agree that it would be impossible to build, or if it were built as best we could it would probably explode after a second or two.
I have landed in light bush planes with big tires, however, the force is more than perceptible.
More than perceptable? Can you have that?
Quote
Originally posted by eskimo2 The point of this question isn’t to debate how such a conveyor could be built, what materials the belt could be made of, how wide or long it must be, what the power source might be. It also does not matter how the conveyor matches the plan’s speed “exactly”.
So... ignoring that this is an impossible situation, we discuss that it takes energy to spin up a wheel.
All you need is a gyroscope or a spinning top or a flywheel and you can show that in a much simpler situation.
Title: Airplane on a Conveyor Belt...
Post by: AKIron on February 05, 2008, 09:10:56 PM
Bowing out of this one until next year or so.
Title: Airplane on a Conveyor Belt...
Post by: WWhiskey on February 05, 2008, 11:32:06 PM
Quote
Originally posted by eskimo2 I'm talking about the original AH BBS question from last year:
Again you are working on a false premiss!(spell check)
In order to have a test you must first find a base in reality, the second question does not have a basis in reality therefore cannot be tested! the 2nd question was not posed by an expert in the feild but was an adaptation of the original! he has not come back in this thread and said otherwise that i have seen! if he does then i will stand corrected. theory can be debated all day long but the facts can only be found in reality!
The v-22 will fly in either test, it exists in this world but your magic belt does not! i would like to see your explanation if you think it wont!
Title: Airplane on a Conveyor Belt...
Post by: jigsaw on February 06, 2008, 02:01:25 AM
Here's a different way to look at it....
You're putting along in your shiny spamcan at an airspeed of 100kts*. Flying into a direct headwind of 100kts. Your groundspeed is 0. Why don't you fall out of the sky?
*for conversation sake TAS/IAS are the same and just listed as knots.
Title: Airplane on a Conveyor Belt...
Post by: SD67 on February 06, 2008, 03:21:27 AM
The Force? :lol
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 06, 2008, 05:43:53 AM
Quote
Originally posted by WWhiskey Again you are working on a false premiss!(spell check)
In order to have a test you must first find a base in reality, the second question does not have a basis in reality therefore cannot be tested! the 2nd question was not posed by an expert in the feild but was an adaptation of the original! he has not come back in this thread and said otherwise that i have seen! if he does then i will stand corrected. theory can be debated all day long but the facts can only be found in reality!
The v-22 will fly in either test, it exists in this world but your magic belt does not! i would like to see your explanation if you think it wont!
It is found in reality. Did you watch the movie? How do you explain what happened in the movie?
Like I said, both questions are theoretical, but can be proven on a smaller scale.
Look at the simpler version of the question:
“A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill.
The question is:
Will the plane take off or not?”
What’s the answer to this one (wheel removed)?
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 06, 2008, 10:34:57 AM
Quote
Originally posted by eskimo2 Please explain this then:
From what you are saying, the wheel should remain stationary as the sander accelerates. At a constant speed, the speed of the wheels does not consume/absorb energy. Acceleration is a different matter.
I'm not sure what you think those vids prove, or how they relate to the airplane on conveyor question.
ask me a question and I will try to answer it.
Title: Airplane on a Conveyor Belt...
Post by: hitech on February 06, 2008, 01:28:17 PM
Vertex: The video shows how acceleration of the belt and hence acceleration of the rotating wheel, generates a force on the plane. The belt sander shows a plane setup with the prop being replaced by a spring.
In the 3 different piece film shows how a larger moment generates a larger force.
So the basic question is , do you agree that a constant acceleration of the belt can generate a force holding an airplane back.
If you do not agree, then please explain why the wheel moves when the sander is being accelerated, and then the wheel moves back when at a steady state speed.
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 06, 2008, 02:05:23 PM
Two factors make the wheel move back as the sander belt accelerates.
1 - friction between the axle and wheel
2 - inertia of the wheel
It takes more energy to overcome friction when an object is at rest than when it is in motion
the mass of the wheel resists acceleration as it spins up.
Once the rest friction is overcome, and the wheel has spun up to match the sander, the distance the wheel has been defected returns to zero.
The amount of wheel deflection that occurs can be reduced by,
1 - placing a large mass on the axle
2 - reducing the friction between the axle and the wheel,
3 - reducing the mass of the wheel
4 - reducing the rate of acceleration of the conveyor/belt sander
an airplane is a large mass, relative to its wheels airplane wheels have pretty good bearings. the airplane accelerates slowly as compared to the belt sander.
The airplane flies.
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 06, 2008, 02:06:33 PM
Quote
Originally posted by hitech Vertex: The video shows how acceleration of the belt and hence acceleration of the rotating wheel, generates a force on the plane. The belt sander shows a plane setup with the prop being replaced by a spring.
the plane needs a stronger spring, more thrust.
to replace the prop with a spring you cannot start with the spring in a de-tensioned state, to simulate the thrust you need to stretch the spring out to max and then turn on the belt and let the plane go.
the belt cannot move until the plane moves. And the belt will not equal the pull of the spring.
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 06, 2008, 02:09:40 PM
To specifically answer your question, a constant acceleration will not hold the airplane back because the forces acting on deflecting the wheel are smaller during a constant acceleration, than during the initial acceleration from rest.
In practice, the force the conveyor belt would impart by constantly accelerating to match the planes forward motion would be too small to be a factor large enough to keep the plane grounded.
Unless the airplane had really crappy bearings, or hugely massive wheels, both of which would keep the plane grounded without a conveyor.
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 06, 2008, 02:11:21 PM
john is on the right track.
He points out some non parallels between the sander experiment and the airplane on the conveyor experiment.
Title: Airplane on a Conveyor Belt...
Post by: hitech on February 06, 2008, 02:26:11 PM
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Originally posted by VERTEX To specifically answer your question, a constant acceleration will not hold the airplane back because the forces acting on deflecting the wheel are smaller during a constant acceleration, than during the initial acceleration from rest.
Vertex: We can choose the Acceleration. The force will vary linearly with the Acceleration. So if we double the Acceleration we double the force.
Hence with enough acceleration we equal the force of the Propeller.
I did real calculations on My RV8. My plane would require a belt acceleration of 910 Feet per sec per sec to hold the plane.
HiTech
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 06, 2008, 02:30:38 PM
you realize thats 620 mph right.
(910 x 60 x 60) / 5280
Any way, do you disagree with anything i said?
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on February 06, 2008, 02:33:13 PM
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Originally posted by hitech So the basic question is , do you agree that a constant acceleration of the belt can generate a force holding an airplane back.
Your usable acceleration rate, or better said torque exercised on the wheel by belt, can be no greater than traction (friction) allows it, otherwise slippage occurs. By your own calculation you got the rate of about 910 ft per s^ which is equivalent of 0.17 mps^ or after only one second of acceleration, you hit velocity of 620 mph. (you'd reach speed of light in just over 1,081,639 seconds) No aircraft tire in this world has that amount of traction.
Without doing any calculation I'd say tires could hold up to no more than 100 fps^ of constant acceleration before considerable slippage occurs, hence most of your torque would go into the air (heat).
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 06, 2008, 02:36:09 PM
In order to hold you plane back the belt would have to accelerate at 620mph/sec/sec
That means 620 mph in the first second, 1240 in the second second, 1860mph in the 3rd second, 2480mph in the 4th second etc etc.
One must conclude that a high rate of acceleration is required to hold back your airplane.
Have you worked out what the actual speed of the conveyor would be for your airplane at take off airspeed?
I'll bet the conveyor does impart a force to increase the take off roll of you airplane but it would be small to insignificant.
Title: Airplane on a Conveyor Belt...
Post by: hitech on February 06, 2008, 02:37:14 PM
Yes Vertex it is 610 MPHPS, but it does not change the fact that with that acceleration the plane stands still.
And yes I disagree with your statement about the plane takes off, the question is generic , we can set our numbers as we wish.
Your # items I agree with.
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 06, 2008, 02:37:28 PM
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Originally posted by hitech I did real calculations on My RV8. My plane would require a belt acceleration of 910 Feet per sec per sec to hold the plane.
HiTech
910 ft /sec is about 680 mph, i wonder what the boundary layer air flow over the belt ( and wing) would be?
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 06, 2008, 02:47:05 PM
1 - If we put your airplane with you in it on the conveyor as specified in the original question will you be able to get to rotation speed and fly away?
2 - You are correct in theory that a conveyor could be set up to accelerate at a rate that would prevent take off, but you could not overcome the practical engineering challenges to make it real.
3 - When I say the plane flies I am referring to the original question.
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 06, 2008, 02:48:52 PM
Let me ask another question, what do you think would happen if the bearings were frictionless, and the wheels had zero mass?
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 06, 2008, 02:52:45 PM
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Originally posted by VERTEX Let me ask another question, what do you think would happen if the bearings were frictionless, and the wheels had zero mass?
The conveyor would jump to light speed/infinity instantly and the plane would take off almost normally. (not counting for the conveyor expanding/exploding due to hitting light speed, etc... It would have to be massless too.)
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 06, 2008, 02:53:18 PM
you mean like chuck's airplane?
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 06, 2008, 03:04:24 PM
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Originally posted by john9001 you mean like chuck's airplane?
Yes
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 06, 2008, 03:09:42 PM
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Originally posted by VERTEX 1 - If we put your airplane with you in it on the conveyor as specified in the original question will you be able to get to rotation speed and fly away?
2 - You are correct in theory that a conveyor could be set up to accelerate at a rate that would prevent take off, but you could not overcome the practical engineering challenges to make it real.
3 - When I say the plane flies I am referring to the original question.
This is the original AH BBS question from last year:
Quote
Originally posted by rabbidrabbit A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's wheel speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill.
The question is:
Will the plane take off or not?
However, we found out that a simpler version of the question had been around the net since about 2005. This one had the conveyor matching the plane's speed. This is much like the one that Mythbusters tested, I believe.
So, by original, which are you referring too?
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 06, 2008, 03:25:20 PM
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Originally posted by eskimo2 The conveyor would jump to light speed/infinity instantly and the plane would take off almost normally. (not counting for the conveyor expanding/exploding due to hitting light speed, etc... It would have to be massless too.)
Thats just silly.
What would really happen is there would be a zero backward motion imparted to the airplane because friction and inertia would be eliminated.
Title: Airplane on a Conveyor Belt...
Post by: hitech on February 06, 2008, 03:26:11 PM
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Originally posted by VERTEX 1 - If we put your airplane with you in it on the conveyor as specified in the original question will you be able to get to rotation speed and fly away?
2 - You are correct in theory that a conveyor could be set up to accelerate at a rate that would prevent take off, but you could not overcome the practical engineering challenges to make it real.
3 - When I say the plane flies I am referring to the original question.
1. If you are speaking of the wheel speed version, I submit that there is not a control system that can be conceived to do what it ask. Assuming wheel speed is the speed of the tread the only time the speed of the belt can match the speed of the wheel is when the plane is not moving. When the plane is not moving the belt speed will always match the plane speed. Any other time (assuming the wheel does not slip on the belt) the speeds can not match.
So in the end I say the question is not valid and hence has no answer.
You would have to state the question in terms of force not speeds.
If you are referring to the Myth buster question of belt speed = plane take off speed. Then of course it will take off.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 06, 2008, 03:27:35 PM
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Originally posted by VERTEX Thats just silly.
What would really happen is there would be a zero backward motion imparted to the airplane because friction and inertia would be eliminated.
I said "the plane would take off almost normally."
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 06, 2008, 03:32:32 PM
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Originally posted by hitech 1. If you are speaking of the wheel speed version, I submit that there is not a control system that can be conceived to do what it ask. Assuming wheel speed is the speed of the tread the only time the speed of the belt can match the speed of the wheel is when the plane is not moving. When the plane is not moving the belt speed will always match the plane speed. Any other time (assuming the wheel does not slip on the belt) the speeds can not match.
So in the end I say the question is not valid and hence has no answer.
You would have to state the question in terms of force not speeds.
If you are referring to the Myth buster question of belt speed = plane take off speed. Then of course it will take off.
How about like this:
A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's wheel speed and (with a short reaction time) tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill.
The question is:
Will the plane take off or not?
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 06, 2008, 03:39:36 PM
A better question eskimo is what do YOU think?
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 06, 2008, 03:40:40 PM
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Originally posted by eskimo2 I said "the plane would take off almost normally."
The conveyor light speed thing is silly.
Title: Airplane on a Conveyor Belt...
Post by: Holden McGroin on February 06, 2008, 03:43:24 PM
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Originally posted by eskimo2 How about like this:
A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's wheel speed and (with a short reaction time) tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill.
The question is:
Will the plane take off or not?
Why don't we have a more generalized question like:
Can we make an impossible situation possible... and then is it still an impossible situation, or is the premise itself an unsolvable paradox?
Title: Airplane on a Conveyor Belt...
Post by: hitech on February 06, 2008, 03:50:07 PM
Eskimo: It still does not make any sense. When the conveyor speeds up the wheel speeds up, hence once the plane starts to move a system can never do what is stated to make the speeds exactly match. By definition the wheel speed = Plane speed + Conveyor speed. So Conveyor speed only = P + C when P = 0.
It has nothing to do with a delay, every thing to do with definition.
Also how you state the original question of plane speed also does not make any sense if the belt was to ever hold the plane, because it would mean the belt had to not move for the plane to not move. Once again a bad question with out an answerer.
Notice how the Myth Buster avoided this problem by stating conveyor at Take off speed.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 06, 2008, 03:50:32 PM
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Originally posted by VERTEX The conveyor light speed thing is silly.
Why?
When the plane rolls forward, the conveyor can only speed up in attempt to match the wheels speed. It never will since the wheel has no mass. How long it takes to reach light speed or infinity would be derived by how quick its reaction time is. Since it is designed to match the plane’s wheel speed exactly, it must have a perfect, or instant reaction time. This would drive it to light speed or infinity instantly.
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 06, 2008, 04:03:47 PM
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Originally posted by eskimo2 Why?
When the plane rolls forward, the conveyor can only speed up in attempt to match the wheels speed. It never will since the wheel has no mass. How long it takes to reach light speed or infinity would be derived by how quick its reaction time is. Since it is designed to match the plane’s wheel speed exactly, it must have a perfect, or instant reaction time. This would drive it to light speed or infinity instantly.
Read Hitech's post.
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 06, 2008, 04:07:12 PM
Time for a new question:
Lets say eskimo can run 10 times faster than a turtle, and he gives the turtle a 100m head start.
At the start of the race eskimo makes up the 100m but the turtle runs another 10m, eskimo runs the 10m but the turtle runs another 1m, eskimo runs the 1m but the turtle runs 1/10m, etc etc, ad infinitum.
Conclusion: Eskimo will never catch the turtle.
If this is wrong, state why.
Good luck
Title: Airplane on a Conveyor Belt...
Post by: hitech on February 06, 2008, 04:07:51 PM
Also on a trivia note, what did HiTech do for 10 years before writing flight sims?
Title: Airplane on a Conveyor Belt...
Post by: 2bighorn on February 06, 2008, 04:09:50 PM
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Originally posted by hitech Also on a trivia note, what did HiTech do for 10 years before writing flight sims?
IIRC, you were designing conveyors or something like that, no?
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 06, 2008, 04:11:10 PM
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Originally posted by hitech Eskimo: It still does not make any sense. When the conveyor speeds up the wheel speeds up, hence once the plane starts to move a system can never do what is stated to make the speeds exactly match. By definition the wheel speed = Plane speed + Conveyor speed. So Conveyor speed only = P + C when P = 0.
It has nothing to do with a delay, every thing to do with definition.
Also how you state the original question of plane speed also does not make any sense if the belt was to ever hold the plane, because it would mean the belt had to not move for the plane to not move. Once again a bad question with out an answerer.
Notice how the Myth Buster avoided this problem by stating conveyor at Take off speed.
Imagine it works like an automobile’s cruise control as a car changes from level ground to an uphill.
In a car, when the speed drops a bit, the cruise control “steps” on the gas, it keeps pressing harder until the car stops decelerating and starts accelerating. As the speed nears the set speed, the cruise control backs off and tries to ease it into the set speed. If the car goes faster than the set speed as it crests the hill, the cruise control backs off on the gas.
The conveyor control could work the same way; the plane moves forward so the control speeds up the conveyor to “catch up” with the wheel. When the conveyor acceleration rate passes 910 ft per second per second, the RV-4 starts backing up. The conveyor control eases back to an acceleration rate of 910 ft per second per second. When the pilot give up and chops the throttle, the acceleration rate also drops.
When the pilot kills the engine the acceleration rate drops to 0. The belt, however, is still moving at a zillion mph. The pilot does not notice this and steps out onto the moving belt and is instantly turned into a long smear!
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 06, 2008, 04:13:30 PM
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Originally posted by hitech Also on a trivia note, what did HiTech do for 10 years before writing flight sims?
Hmm let me see,
He studied physics at the undergraduate level as a minor while working on a computer science degree???
Title: Airplane on a Conveyor Belt...
Post by: hitech on February 06, 2008, 04:17:26 PM
Eskimo: But what you imagine is not what the problem states. It states "Exactly matches wheel speed"
Your version states Accelerates constantly until the desired speed is obtained.
2 very very different requirements.
HiTech
Title: Airplane on a Conveyor Belt...
Post by: john9001 on February 06, 2008, 04:20:23 PM
what means "wheel speed"?
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 06, 2008, 04:21:08 PM
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Originally posted by hitech Eskimo: But what you imagine is not what the problem states. It states "Exactly matches wheel speed"
Your version states Accelerates constantly until the desired speed is obtained.
2 very very different requirements.
HiTech
How would you answer this version:
A plane is standing on a runway that can move like a giant conveyor belt. The plane applies full forward power and attempts to take off. This conveyor has a control system that tracks the plane's speed and tunes the speed of the conveyor to be exactly the same but in the opposite direction, similar to a treadmill.
The question is:
Will the plane take off or not?
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 06, 2008, 04:26:19 PM
Ya it still takes off.
Title: Airplane on a Conveyor Belt...
Post by: hitech on February 06, 2008, 04:28:53 PM
By definition of the question it will take off.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 06, 2008, 04:46:24 PM
I agree…
But wait a minute, the question is bogus because the conveyor could never match the plane’s speed “exactly”… Right?
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 06, 2008, 04:53:41 PM
Note that the point of this question isn’t to debate how such a conveyor could be built, what materials the belt could be made of, how wide or long it must be, what the power source might be. It also does not matter HOW the conveyor matches the plan’s speed “exactly”.
We naturally accept that the conveyor somehow works: power, size, controls and all.
The point is that the question brings to light how many people misunderstand the forces at work; that the thrust of the prop is counteracted by the acceleration rate of the plane diminishing into the air drag on the wings and airframe. The extra energy loaded into the wheels at these speed is negligible, not even worth mentioning in this question, the plane takes off. For many people, studying this question opens up a new level of understanding not-so-obvious forces.
In the wheel speed question, if we also just accept that the conveyor exists as described, it opens up a new level of understanding not-so-obvious forces. It’s a great question because it fools so many people and has such a counter-intuitive solution/answer that most people cannot even comprehend.
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 06, 2008, 04:57:07 PM
Often when engaging in thought experiments like these, one must first separate the relevant from the non relevant, and concentrate on the spirit of the question rather than get bogged down with small details.
Anyway, its been fun.
Hitech, are you going to tell us what you did for 10 years before writing sim games?
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 06, 2008, 04:58:44 PM
P.S. Be sure to note that the paradox of the conveyor matching the plane’s speed is the same paradox as matching the wheel’s speed. The conveyor must react to the plane in the plane-speed question; it will constantly adjusting to the increasing speed and decreasing acceleration rate of the plane.
Title: Airplane on a Conveyor Belt...
Post by: eskimo2 on February 06, 2008, 05:01:06 PM
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Originally posted by VERTEX Often when engaging in thought experiments like these, one must first separate the relevant from the non relevant, and concentrate on the spirit of the question rather than get bogged down with small details.
Anyway, its been fun.
Hitech, are you going to tell us what you did for 10 years before writing sim games?
I'll second both of these statements and the question!
Title: Airplane on a Conveyor Belt...
Post by: hitech on February 06, 2008, 05:05:24 PM
Vertex: I developed and designed electrical control systems for conveyors.
Eskimo: Different then the wheel speed question, the change of speed of the conveyor will effect the acceleration of the plane, but not change its current speed. You could even integrate the acceleration back in to the controller to remove all conveyor delay.
Hence the theoretical system is valid.
HiTech
Title: Airplane on a Conveyor Belt...
Post by: USRanger on February 06, 2008, 05:08:57 PM
That was not HiTech. Look at that grammar!
:D
Title: Airplane on a Conveyor Belt...
Post by: VERTEX on February 06, 2008, 05:31:27 PM
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Originally posted by hitech Vertex: I developed and designed electrical control systems for conveyors.
Eskimo: Different then the wheel speed question, the change of speed of the conveyor will effect the acceleration of the plane, but not change its current speed. You could even integrate the acceleration back in to the controller to remove all conveyor delay.
Hence the theoretical system is valid.
HiTech
Thats rich, lmao.
Its been fun debating with you
Title: Airplane on a Conveyor Belt...
Post by: WWhiskey on February 06, 2008, 08:07:05 PM
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Originally posted by john9001 what means "wheel speed"?
I was going to ask that question at one point as well, but got sidetracked on something else, is wheel speed the forward motion of the wheel or the rpm of the wheel itself? If the belt could move at the same speed of the wheel it would have zero speed .if the rpm's are the question? well i give up
and V-22 still flies
Title: Airplane on a Conveyor Belt...
Post by: WWhiskey on February 06, 2008, 08:07:06 PM
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Originally posted by john9001 what means "wheel speed"?
I was going to ask that question at one point as well, but got sidetracked on something else, is wheel speed the forward motion of the wheel or the rpm of the wheel itself? If the belt could move at the same speed of the wheel it would have zero speed .if the rpm's are the question well i give up
and V-22 still flies
Title: Re: Airplane on a Conveyor Belt...
Post by: quig on November 08, 2016, 07:54:57 AM
So... I'm still wondering....
Do the stupid plane take off or not???
Title: Re: Airplane on a Conveyor Belt...
Post by: Bizman on November 08, 2016, 09:53:00 AM
You've been wondering for eight years? See for yourself:
Title: Re: Airplane on a Conveyor Belt...
Post by: Zimme83 on November 08, 2016, 10:12:43 AM
I would say that whats happen is that the belt causes the planes wheels to spin faster but the plane itself is still moving forward as normal. It would have been different with something like a seaplane on a river, taking off up streams increases the take off distance.
Title: Re: Airplane on a Conveyor Belt...
Post by: quig on November 15, 2016, 08:35:49 PM
Actually, if the conveyor matched the wheel speed exactly but in the opposite direction, the plane would never leave the ground without the conveyor itself moving. It would sit still and make a lot of noise, but it would never take off.
The video above does not emulate a conveyor moving in the opposite direction while exactly matching the WHEEL SPEED.
It's would be physically impossible for the plane to take off if the struts of the plane never move, thus no air being generate for the wings.
Title: Re: Airplane on a Conveyor Belt...
Post by: GScholz on November 15, 2016, 09:22:54 PM
Nah... As soon as the wheels start rotating the conveyor belt will start accelerating the wheels and generate a feedback that will cause uncontrolled acceleration of the whole system. The conveyor belt will break from overspend long before the wheels thus freeing the wheels to do their thing. Plane takes off. ;)
But seriously, that's just an inaccurate description of the situation, and pedantics arguing over semantics. The way most people think the problem is meant to read is that the conveyor belt match the planes speed in the opposite direction. If so then if the take-off speed in 100 mph, the convenor belt is moving 100 mph in the opposite direction at take-off. So the wheels must rotate at 200 mph at take-off speed. Sure there will be some added friction, but not enough to prevent the plane from reaching 100 mph.
Title: Re: Airplane on a Conveyor Belt...
Post by: Spitter on November 15, 2016, 10:20:32 PM
Actually, if the conveyor matched the wheel speed exactly but in the opposite direction, the plane would never leave the ground without the conveyor itself moving. It would sit still and make a lot of noise, but it would never take off.
The video above does not emulate a conveyor moving in the opposite direction while exactly matching the WHEEL SPEED.
It's would be physically impossible for the plane to take off if the struts of the plane never move, thus no air being generate for the wings.
You couldn't be more wrong. Assuming perfect control of the conveyor, with no lag, the only affect would be that wheels (which have no affect whatsoever on the plane's ability to take off) would be rotating at twice the speed they would without the conveyor.
Mythbusters showed this with a scale model, and then again with a full sized aircraft. If you continue to disagree, take it up with reality.
Disclaimer: I am an actual aerospace engineer. :grin:
Title: Re: Airplane on a Conveyor Belt...
Post by: SFRT - Frenchy on November 16, 2016, 12:13:46 AM
Remind me to never fly something you built :rofl
Title: Re: Airplane on a Conveyor Belt...
Post by: NatCigg on November 16, 2016, 04:30:41 AM
The plane is only attached to the conveyor by the negligible force of gravity and the friction force related to the wheel bearing and tire grip. when the attachment force is overcome by thrust, any increase in attachment brought forth by the speed of the conveyor increasing, up to infinite speed, could easily be overcome by jet engine thrust, and maybe a properly leveraged 200 lb man. any additional thrust from the engine would move the object forward. :devil
lets try it!
no i did not watch the video. :D
Title: Re: Airplane on a Conveyor Belt...
Post by: Chalenge on November 16, 2016, 01:29:46 PM
The way the airplane operates with respect to air doesn't change at all, so the plane will still accelerate and function as usual. I think Myth Busters messed up when they did not create a conveyor belt that accelerates at an ever increasing speed. After all, the original condition was that sensors detect motion and accelerate the belt to match aircraft speed. It doesn't matter in the end, just the same, because there really isn't anything that will stop the plane from flying.
Title: Re: Airplane on a Conveyor Belt...
Post by: quig on November 23, 2016, 07:31:28 PM
The spirit of the original question centered on the wheels and conveyor moving at the same speed in opposite directions.
If you chock the wheels of an airplane with wheel chocks, will the plane move if it cannot roll the wheels over the chocks? No.
If the conveyor is spinning at exactly the wheel speed for any given RPM, the situation will become the same as if the plane had the wheels chocked. The conveyor spinning in the opposite direction will create a force that will nullify the plane's forward movement.
The plane doesn't need the wheels to fly, no. But it does need them to move along the ground while taking off. If they don't move, for whatever reason, then the plane doesn't fly.
Title: Re: Airplane on a Conveyor Belt...
Post by: EskimoJoe on November 23, 2016, 07:46:03 PM
This argument is mind boggling and technically I think both sides are right in some way.
The aircraft needs air over the wings in order to takeoff, yes.
But in order for the air to move over the wings, the aircraft needs to generate forward movement (rolling forward on wheels).
I imagine if the engine and prop was dragging the plane along by the wheels, and a conveyor belt was preventing forward motion of those wheels, it would then not generate enough airflow over the wings to achieve flight.
I wonder what the Wright Brothers would say.
Title: Re: Airplane on a Conveyor Belt...
Post by: 100Coogn on November 23, 2016, 08:55:00 PM
This argument is mind boggling and technically I think both sides are right in some way.
The aircraft needs air over the wings in order to takeoff, yes.
But in order for the air to move over the wings, the aircraft needs to generate forward movement (rolling forward on wheels).
I imagine if the engine and prop was dragging the plane along by the wheels, and a conveyor belt was preventing forward motion of those wheels, it would then not generate enough airflow over the wings to achieve flight.
I wonder what the Wright Brothers would say.
They would 'probably say 'don't be a handsomehunk people. The wings need to move through the air for lift. And I would agree. Look closely at the Myth Busters test. They were not pulling that belt fast enough to equate the planes torque. The plane still had positve force. Therefore I call bubkiss on the whole experiment..
Coogan
Title: Re: Airplane on a Conveyor Belt...
Post by: Karnak on November 23, 2016, 11:56:12 PM
They would 'probably say 'don't be a handsomehunk people. The wings need to move through the air for lift. And I would agree. Look closely at the Myth Busters test. They were not pulling that belt fast enough to equate the planes torque. The plane still had positve force. Therefore I call bubkiss on the whole experiment..
Coogan
It isn't possible for the belt to move fast enough.
Title: Re: Airplane on a Conveyor Belt...
Post by: 100Coogn on November 24, 2016, 12:04:21 AM
It isn't possible for the belt to move fast enough.
Maybe not that thing they made. I'm pretty sure someone could build something that could go around a couple of gears and drums with a belt, you know, like a real conveyor belt, that could match take-off speed. I have no idea with that plane what the take-off speed is. To me that was a cheesy experiment.
Coogan
Title: Re: Airplane on a Conveyor Belt...
Post by: Karnak on November 24, 2016, 12:15:34 AM
Maybe not that thing they made. I'm pretty sure someone could build something that could go around a couple of gears and drums with a belt, you know, like a real conveyor belt, that could match take-off speed. I have no idea with that plane what the take-off speed is. To me that was a cheesy experiment.
Coogan
The conveyor belt would need to move fast enough to cause the bearings in the airplane's wheels to fail and seize. Merely moving at the airplane's takeoff speed would simply result in the wheels rolling at twice the takeoff speed when the plane took off.
Remember, the wheels are not moving the plane. The wheels are simply along for the ride as the plane moves itself through the air. Because it is the plane moving itself through the air it doesn't matter what the ground is doing, at least along the direction the airplane is traveling through the air. Airspeed is what matters for takeoff and flight, not ground speed.
Title: Re: Airplane on a Conveyor Belt...
Post by: 100Coogn on November 24, 2016, 12:31:02 AM
The conveyor belt would need to move fast enough to cause the bearings in the airplane's wheels to fail and seize. Merely moving at the airplane's takeoff speed would simply result in the wheels rolling at twice the takeoff speed when the plane took off.
Remember, the wheels are not moving the plane. The wheels are simply along for the ride as the plane moves itself through the air. Because it is the plane moving itself through the air it doesn't matter what the ground is doing, at least along the direction the airplane is traveling through the air. Airspeed is what matters for takeoff and flight, not ground speed.
I agree. Airspeed is what matters. So if setting stationary on a conveyor belt=no air speed, so no take-off. (I'm intrigued by this stuff, whether it works or not. :) )
Coogan
Title: Re: Airplane on a Conveyor Belt...
Post by: NatCigg on November 24, 2016, 07:59:08 AM
The fact the belt did not rip shows how little force is put to the conveyor from the plane. Not to mention the airspeed gained would create lift.
Title: Re: Airplane on a Conveyor Belt...
Post by: quig on November 24, 2016, 08:43:21 AM
The conveyor belt would need to move fast enough to cause the bearings in the airplane's wheels to fail and seize. Merely moving at the airplane's takeoff speed would simply result in the wheels rolling at twice the takeoff speed when the plane took off.
It wouldn't have to go so fast that the wheel bearing seized. There is a point where the propeller is not going to spin any faster at max RMPs. At that point things level out. The conveyor only needs to spin fast enough to hit this point and then the plane will just sit there and make a lot of noise.
Title: Re: Airplane on a Conveyor Belt...
Post by: Mar on November 24, 2016, 02:48:26 PM
It wouldn't have to go so fast that the wheel bearing seized. There is a point where the propeller is not going to spin any faster at max RMPs. At that point things level out. The conveyor only needs to spin fast enough to hit this point and then the plane will just sit there and make a lot of noise.
What?
Title: Re: Airplane on a Conveyor Belt...
Post by: GScholz on November 24, 2016, 04:02:12 PM
This is a great question to spread around the internet to profile people for the great culling.
Title: Re: Airplane on a Conveyor Belt...
Post by: 100Coogn on November 24, 2016, 09:28:37 PM
I'm 'Murican, so I'm going to say MPH.
Say the plane needs 85PMH to take off. The belt is moving at that same speed. Plane no move. The plane can not take off.
Coogan
Title: Re: Airplane on a Conveyor Belt...
Post by: Mar on November 24, 2016, 09:36:50 PM
This is a great question to spread around the internet to profile people for the great culling.
Well before you kill me at least tell me if the damned plane will take off!!!
Title: Re: Airplane on a Conveyor Belt...
Post by: NatCigg on November 25, 2016, 06:20:35 AM
It really depends on the speedometer is used. If it is the manual type then the conveyor could give the plane a false takeoff clearance resulting in a premature takeoff. when the plane got off the conveyor and the speedometer slowed below takeoff speed the plane would descend. It is kinda funny if you think about it, the plane would takeoff and land repeatedly, like a bunny rabbit, as it moves along the conveyor.
Title: Re: Airplane on a Conveyor Belt...
Post by: Zimme83 on November 25, 2016, 08:17:35 AM
Aircrafts gets their speed from the pitot tube, it only measure Air speed so a conveyor belt can never give a false reading.
But if you block the pitot tube with some tape then the plane cannot reach take off speed and will be stuck on the ground..
Title: Re: Airplane on a Conveyor Belt...
Post by: GScholz on November 25, 2016, 09:41:37 AM
It really depends on the speedometer is used. If it is the manual type then the conveyor could give the plane a false takeoff clearance resulting in a premature takeoff. when the plane got off the conveyor and the speedometer slowed below takeoff speed the plane would descend. It is kinda funny if you think about it, the plane would takeoff and land repeatedly, like a bunny rabbit, as it moves along the conveyor.
Well before you kill me at least tell me if the damned plane will take off!!!
The plane will take off. The guys who think otherwise are too locked into automobile thinking.
There is no way the conveyor belt can spin fast enough to cause the bearings in the wheels to provide enough resistance to overcome the thrust generated by the propeller or jet engine of the aircraft. The bearings or tires on the wheels will fail before they provide enough resistance to stop the plane from taking off, and then the question changes.
Title: Re: Airplane on a Conveyor Belt...
Post by: Zimme83 on November 27, 2016, 05:30:30 AM
The plane will take off. The guys who think otherwise are too locked into automobile thinking.
There is no way the conveyor belt can spin fast enough to cause the bearings in the wheels to provide enough resistance to overcome the thrust generated by the propeller or jet engine of the aircraft. The bearings or tires on the wheels will fail before they provide enough resistance to stop the plane from taking off, and then the question changes.
Yes. Jokes aside: The wheels will spin faster but the plane will fly with ease. Its the speed relative to the air that matters.
Title: Re: Airplane on a Conveyor Belt...
Post by: DREDIOCK on November 29, 2016, 09:59:55 PM
LMAO
Funny. I actually remember reading this thread when it first started
8 years ago
Title: Re: Airplane on a Conveyor Belt...
Post by: earl1937 on December 05, 2016, 07:44:24 AM
Where is the air flow coming from. A small plane like that, maybe the prop? Is that enough for take-off though? :headscratch:
Coogan
:airplane: This a/c could stay on the belt till hell freezes over and it isn't going to fly! The only thing that will make it fly is air flow over the wings and with it standing still, no way that is going to happened!
Title: Re: Airplane on a Conveyor Belt...
Post by: Golfer on December 05, 2016, 08:04:26 AM
What if it's on the step, though?
Title: Re: Airplane on a Conveyor Belt...
Post by: Vraciu on December 05, 2016, 10:12:48 AM
The plane will fly. The amount of resistance generated by the wheels is so small that only God could hope to move a conveyor belt fast enough to neutralize the propulsive force of an airplane--any airplane.
The wheels will be spinning like mad but they won't impart enough resistance to stop the thing from moving forward.
Title: Re: Airplane on a Conveyor Belt...
Post by: 100Coogn on December 05, 2016, 10:21:26 AM
:airplane: This a/c could stay on the belt till hell freezes over and it isn't going to fly! The only thing that will make it fly is air flow over the wings and with it standing still, no way that is going to happened!
That's kinda' what I'm thinking too. :cheers:
Coogan
Title: Re: Airplane on a Conveyor Belt...
Post by: Vraciu on December 05, 2016, 10:23:28 AM
:airplane: This a/c could stay on the belt till hell freezes over and it isn't going to fly! The only thing that will make it fly is air flow over the wings and with it standing still, no way that is going to happened!
It's not standing still. The conveyor just spins the wheels, it doesn't hold the aircraft in place.
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 06, 2016, 08:32:18 PM
This was a fun thread and old like me. Myth Busters didn't do the premise justice though. Obvious to all, a plane must get enough air flowing over the wings to generate lift to "take off". If a conveyor belt could hold a plane stationary relative to the wind how would the wing generate lift?
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 06, 2016, 08:41:39 PM
A conveyor belt that moves fast enough will apply enough force to a plane through its wheels to hold it stationary relative to the wind. Eskimo demonstrated that effect with his belt sander. The argument is how to interpret how fast the conveyor belt should move.
Title: Re: Airplane on a Conveyor Belt...
Post by: deSelys on December 07, 2016, 03:18:39 AM
In the real world, the plane will take off, the propeller acts on the air and the resistance of the wheels spinning freely on the conveyor belt is insignificant.
If the conveyor belt has the theoretical ability to move so (insanely) fast that the resistance of the spinning wheels is high enough to prevent the plane from moving, the belt will also act on the air and generate such a headwind that the plane should be able to take off with ground speed = 0, so the question is moot :P
Title: Re: Airplane on a Conveyor Belt...
Post by: NatCigg on December 07, 2016, 04:29:01 AM
:rofl yes yes, the drag on the air surrounding the belt would cause the air to move with the conveyor belt, and against the planes forward direction. while there is not much wing over the conveyor the increased air flow would be present (nevermind the prop stream :old:). Unfortunately, since air movement decreases as distance from the energy source increases, the faster air flow under the wing versus the more distant top part of the wing, will actually cause DOWNFORCE! further increasing the weight of the plane and therefore stationary force on the conveyor. :old:
Title: Re: Airplane on a Conveyor Belt...
Post by: Vraciu on December 07, 2016, 09:07:45 AM
A conveyor belt that moves fast enough will apply enough force to a plane through its wheels to hold it stationary relative to the wind. Eskimo demonstrated that effect with his belt sander. The argument is how to interpret how fast the conveyor belt should move.
It would have to be a conveyor belt capable of light speed (or at least Warp One).
The airplane's wing cares about air.
Title: Re: Airplane on a Conveyor Belt...
Post by: Kuhn on December 07, 2016, 09:52:11 AM
then the gear rip off :D
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 07, 2016, 06:32:18 PM
One debate we had, maybe in the other thread, was whether the belt was required to match the rotational speed of the spinning wheels or the fuselage. If the latter then the planes takes off easily. If the former then the belt will rapidly accelerate as the wheels attempt to roll. This applies force to plane as Eskimo demonstrated and is quite capable of holding the plane in place given the belt is capable of unlimited acceleration and speed.
Title: Re: Airplane on a Conveyor Belt...
Post by: 100Coogn on December 07, 2016, 06:56:42 PM
If the planes take-off speed is 100 mph and the belt is moving at 100 mph opposite direction, the plane should not get airborne. :airplane:
Coogan
Title: Re: Airplane on a Conveyor Belt...
Post by: Vraciu on December 07, 2016, 07:56:07 PM
One debate we had, maybe in the other thread, was whether the belt was required to match the rotational speed of the spinning wheels or the fuselage. If the latter then the planes takes off easily. If the former then the belt will rapidly accelerate as the wheels attempt to roll. This applies force to plane as Eskimo demonstrated and is quite capable of holding the plane in place given the belt is capable of unlimited acceleration and speed.
How was this "demonstrated"?
Title: Re: Airplane on a Conveyor Belt...
Post by: FLOOB on December 07, 2016, 08:51:39 PM
Not even the same thing as a self-propelled vehicle that doesn't generate forward motion through its wheels.
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 07, 2016, 09:30:24 PM
His video shows that there is force applied to the wheel by the accelerating belt. The greater the acceleration, the greater the force that the engine of the plane will have to overcome to move the plane forward. I don't want to rehash this beat to death many years old argument but it was fun dropping by. :D
Title: Re: Airplane on a Conveyor Belt...
Post by: Vraciu on December 07, 2016, 09:35:11 PM
His video shows that there is force applied to the wheel by the accelerating belt. The greater the acceleration, the greater the force that the engine of the plane will have to overcome to move the plane forward. I don't want to rehash this beat to death many years old argument but it was fun dropping by. :D
As I said, you would need a belt traveling the speed of light if true. The force required to stop a jet at takeoff thrust? Now figure how fast that treadmill would need to go.
Perhaps in absolute terms you are right.
Title: Re: Airplane on a Conveyor Belt...
Post by: NatCigg on December 08, 2016, 12:00:54 AM
If the planes take-off speed is 100 mph and the belt is moving at 100 mph opposite direction, the plane should not get airborne. :airplane:
Coogan
this would only be true if the wheels were linked to the vehicle. If the planes brakes are not applied, then think of the vehicle as being in neutral. no matter how much the road moves nothing is transferred to the vehicle, the wheels just spin. (https://media1.giphy.com/media/ZG26wemO3Qh7W/200.gif#54)
Now if a plane applied full brakes, on a 100 mph conveyor it would look something like this.
One debate we had, maybe in the other thread, was whether the belt was required to match the rotational speed of the spinning wheels or the fuselage. If the latter then the planes takes off easily. If the former then the belt will rapidly accelerate as the wheels attempt to roll. This applies force to plane as Eskimo demonstrated and is quite capable of holding the plane in place given the belt is capable of unlimited acceleration and speed.
According to HiTech's calculations it would require a ludicrous 910 meters per second per second of acceleration on the belt in order to stop his plane from taking off. While that is possible with the magical, infinite speed and acceleration belt, it is not feasible in reality.
The original idea posited a belt that matched the speed of the airplane, in other words the fuselage.
Title: Re: Airplane on a Conveyor Belt...
Post by: Shuffler on December 08, 2016, 09:24:41 AM
According to HiTech's calculations it would require a ludicrous 910 meters per second per second of acceleration on the belt in order to stop his plane from taking off. While that is possible with the magical, infinite speed and acceleration belt, it is not feasible in reality.
The original idea posited a belt that matched the speed of the airplane, in other words the fuselage.
If the belt spins at the speed the plane body is moving then the wheels will be going twice the speed they normally would. Barring bearing failure, the plane would still be moving forward at speed and lift off.
Title: Re: Airplane on a Conveyor Belt...
Post by: 100Coogn on December 08, 2016, 09:25:23 AM
The wheels roll freely and do not drive the plane. The prop will pull the aircraft through the air. The ground does not matter.
Thanks Shuffler.
Yeah, I read this article Airplane On A Conveyor Belt] (http://c-aviation.net/plane-conveyor-belt-explained-debunked/). It pretty much says the same thing. So now I am of the opinion that it will take off.
Coogan
Title: Re: Airplane on a Conveyor Belt...
Post by: earl1937 on December 08, 2016, 01:25:21 PM
It's not standing still. The conveyor just spins the wheels, it doesn't hold the aircraft in place.
:airplane: You mean to tell me that since the aircraft can't move, even though the wheels are spinning because of the conveyor belt moving, there by turning the wheels, would you please explain to us where the air flow over the wings are coming from? No matter your thoughts on this thread, it is not going to fly until air flows over the wings, generating lift, which is what makes the aircraft fly to begin with!
Title: Re: Airplane on a Conveyor Belt...
Post by: Golfer on December 08, 2016, 01:48:24 PM
Earl man...
It ain't a car where the wheels drive the vehicle along the road and any movement is predicated on transmitting that energy via the wheels.
It's an airplane where the propeller pulls it thru the air and the wheels are just along for the ride.
She'll fly. The wheels don't mean squat. It's why I can fly a Cub with skis on it in the winter. Or floats in summer.
One could use skis in the summer too but it'd take a whole lot of lube.
Title: Re: Airplane on a Conveyor Belt...
Post by: Zimme83 on December 08, 2016, 03:03:35 PM
For a longer explanation: http://www.animations.physics.unsw.edu.au/jw/plane-conveyor.htm
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 09, 2016, 02:42:37 PM
This is not the original thread here for this. In the original, the question was phrased ambiguously and addressed accordingly. Both conditions were discussed/argued with every permutation possible confused and misconstrued. It was a fun time.
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 09, 2016, 02:48:48 PM
Assuming a belt capable of infinite and instant acceleration the wheels would never move. If the belt were capable of infinite acceleration but not instantaneously then the plane would move a bit and stop. Move a bit and stop. Eventually, it would come to the end of the belt and then roll on the ground for takeoff. That is one aspect not addressed previously I believe. So, we would have to define the length of the belt also.
Title: Re: Airplane on a Conveyor Belt...
Post by: Shuffler on December 09, 2016, 03:22:46 PM
Assuming a belt capable of infinite and instant acceleration the wheels would never move. If the belt were capable of infinite acceleration but not instantaneously then the plane would move a bit and stop. Move a bit and stop. Eventually, it would come to the end of the belt and then roll on the ground for takeoff. That is one aspect not addressed previously I believe. So, we would have to define the length of the belt also.
The only way the plane will stop is if you hit the brakes. Otherwise the plane will be pulled through the air by the prop. The wheels will free roll and the belt will not affect the acceleration of the aircraft other than nominal friction of the wheel bearings.
Title: Re: Airplane on a Conveyor Belt...
Post by: Wiley on December 09, 2016, 03:35:19 PM
The only way the plane will stop is if you hit the brakes. Otherwise the plane will be pulled through the air by the prop. The wheels will free roll and the belt will not affect the acceleration of the aircraft other than nominal friction of the wheel bearings.
I am guessing that given the instant and infinite acceleration mentioned above the idea is that it would be going so fast that the nominal friction of the wheel bearings would overcome the engine's ability to pull it through the air.
More or less pointless argument at that stage.
It frankly shocks me that real life pilots would think that it wouldn't take off if the conveyer was moving at takeoff speed though.
I distinctly remember the Mythbusters episode and the test pilot claiming he was surprised it took off. All I could think was I would never fly with a guy who had that poor a grasp on how the vehicle worked.
Wiley.
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 09, 2016, 03:41:39 PM
If you want to deal with the practical instead of theoretical then let's create a scenario that is possible. A Cessna 172 sitting on a conveyor belt that can very quickly spin up to 2,000 miles per hour. What would happen to that Cessna at full power sitting on a conveyor spinning at 2,000 mph?
I think the tires would disintegrate, the gear collapse, and unless you have an ejection seat you would be toast.
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 09, 2016, 03:47:09 PM
The point of Eskimo's belt sander video was to show there is inertia involved. Friction is of course necessary but not the force being demonstrated. When the belt accelerates there is a force applied to the wheels that is in opposition to the thrust. It is not insignificant.
Title: Re: Airplane on a Conveyor Belt...
Post by: Shuffler on December 09, 2016, 03:47:47 PM
If you want to deal with the practical instead of theoretical then let's create a scenario that is possible. A Cessna 172 sitting on a conveyor belt that can very quickly spin up to 2,000 miles per hour. What would happen to that Cessna at full power sitting on a conveyor spinning at 2,000 mph?
I think the tires would disintegrate, the gear collapse, and unless you have an ejection seat you would be toast.
You can always shoot the plane with a bazooka and see if that helps it fly.
Barring some kind of damage to the aircraft, the plane will fly.
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 09, 2016, 04:11:26 PM
You can always shoot the plane with a bazooka and see if that helps it fly.
Barring some kind of damage to the aircraft, the plane will fly.
Barring some kind of damage? A Cessna with indestructible wheels? Are you reverting to the theoretical then? In that case give me my infinite acceleration conveyor belt.
There are some pretty fast real world conveyor belts btw: http://www.sacramentorubberproducts.com/story-time-interesting-facts-about-conveyor-belts/
I have doubts about the 900 miles a minute speed though.
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 09, 2016, 04:21:47 PM
I think whoever wrote that article on the fastest conveyor belt got meters mixed up with miles.
Title: Re: Airplane on a Conveyor Belt...
Post by: Wiley on December 09, 2016, 04:33:45 PM
If you want to deal with the practical instead of theoretical then let's create a scenario that is possible. A Cessna 172 sitting on a conveyor belt that can very quickly spin up to 2,000 miles per hour. What would happen to that Cessna at full power sitting on a conveyor spinning at 2,000 mph?
I think the tires would disintegrate, the gear collapse, and unless you have an ejection seat you would be toast.
At that point, about all you're really discussing is how fast can the landing gear wheels spin before failure.
Wiley.
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 09, 2016, 04:42:28 PM
Yes, that is the practical aspect of it.
In theory, so long as my belt can continue to accelerate it can exactly counter the thrust of the engine holding the plane stationary relative to the wind. There is an upper limit to this even theoretically and that is the speed of light. Of course when you get close to that limit strange things happen with mass and energy so all bets are off at that point.
Title: Re: Airplane on a Conveyor Belt...
Post by: FLOOB on December 11, 2016, 01:12:40 AM
Except that the belt does not counter the thrust of the propeller even a little bit and would not hold a plane stationary ever.
Title: Re: Airplane on a Conveyor Belt...
Post by: FLOOB on December 11, 2016, 01:23:52 AM
It frankly shocks me that real life pilots would think that it wouldn't take off if the conveyer was moving at takeoff speed though
I know right. I remember somebody on this forum asked how a wing creates lift and someone told him that a wing creates lift because it has an upward angle the air pushes up on the underside of the wing like the bow of a boat. I was surprised that any adult, let alone one who played this game for years, still did not understand how an airfoil works.
Title: Re: Airplane on a Conveyor Belt...
Post by: Vraciu on December 11, 2016, 10:34:41 AM
I know right. I remember somebody on this forum asked how a wing creates lift and someone told him that a wing creates lift because it has an uhpward angle the air pushes up on the underside of the wing like the bow of a boat. I was surprised that any adult, let alone one who played this game for years, still did not understand how an airfoil works.
Actually there is Newtonian action on the underside of a wing (depending on AOA). Anyone who doubts this should stick a board out the window of a moving car.
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 11, 2016, 10:56:31 AM
You need to watch the belt sander video Eskimo made many years ago if you don't believe an accelerating belt will apply force to a wheel sitting on it. That force is applied to the plane through the axle and landing gear and is in opposition to the thrust produced by the plane's engine and prop.
Title: Re: Airplane on a Conveyor Belt...
Post by: Reaper90 on December 11, 2016, 11:52:52 AM
This thread is a hilarious (and somewhat frightening/depressing) example of people who don't seem to have a firm grasp on why and how aircraft are able to attain flight.
The aircraft could care less about the ground speed of its wheels across a surface, only the airflow over the wings, which is a product of thrust created by the prop/turbine etc. The only way the speed of the "conveyor belt" would matter is if the aircraft's engine were powering its wheels to move it forward, then the surface speed of the conveyor would matter relative to the aircraft's speed forward. But, in our case, with the exception of a minimal amount of rotational resistance from the tires and parasitic drag caused by the bearings in the wheel hubs..... whether the tires are turning at 25 rpm or 2500rpm matters not (unless one of them blows from the excessive heat, but let's assume a perfect world and tires made of indestructanium). The method of propulsion is acting on the air around the aircraft, not on the ground, to propel the aircraft forward. Airspeed creates lift, not groundspeed. The only way this extra drag from the tires and bearings keeps the plane from becoming airborne is if the craft is so woefully underpowered that is can't overcome this extra drag... and I would say such an aircraft would already be utterly lacking in airworthiness, and a deathtrap. Look at the massively greater resistance that a seaplane contends with, trying to gather speed through and over water. Exponentially greater resistance than an asphalt runway.... yet the seaplane's thrust is more than enough to overcome the resistance.
The only other way a silly conveyor belt causes an aircraft not to be able to gather the speed required to rotate and become airborne is if the increased speeds experienced by the landing gear couple with excessive yaw from engine torque (why you have to apply opposite rudder to counteract torque during takeoff) to exert such side loads to the undercarriage that the aircraft ground loops or becomes unsteerable. Otherwise........ it flies.
This is a silly argument that even a basic understanding of "how do airplanes fly" should settle.
Title: Re: Airplane on a Conveyor Belt...
Post by: Vraciu on December 11, 2016, 11:56:18 AM
You need to watch the belt sander video Eskimo made many years ago if you don't believe an accelerating belt will apply force to a wheel sitting on it. That force is applied to the plane through the axle and landing gear and is in opposition to the thrust produced by the plane's engine and prop.
It's a fraction of the force needed to stop the plane. The belt would need to travel at the speed of light.
Title: Re: Airplane on a Conveyor Belt...
Post by: FLOOB on December 11, 2016, 12:02:33 PM
You need to watch the belt sander video Eskimo made many years ago if you don't believe an accelerating belt will apply force to a wheel sitting on it. That force is applied to the plane through the axle and landing gear and is in opposition to the thrust produced by the plane's engine and prop.
I did bruh, the other day. Prolly even watched it when eskimo posted it the first time.
Title: Re: Airplane on a Conveyor Belt...
Post by: Reaper90 on December 11, 2016, 12:10:05 PM
You need to watch the belt sander video Eskimo made many years ago if you don't believe an accelerating belt will apply force to a wheel sitting on it. That force is applied to the plane through the axle and landing gear and is in opposition to the thrust produced by the plane's engine and prop.
The belt sander is applying its thrust to the conveyor, by way of its belt which is representative of the aircraft's tire, in order to move forward. On a conveyor belt or otherwise, I have never seen a belt sander attain powered flight. Not even when thrown in anger.
The aircraft is applying its thrust by interacting with the air to create forward motion, what the ground is doing below the tires is irrelevant. The aircraft, it's prop, and the wing only care about the air. No conveyor belt exists that can produce a high enough ground speed to impart parasitic drag on the tires of the aircraft sufficient to counteract the thrust created by even a low-powered aircraft.
This is an exercise in silliness.
Title: Re: Airplane on a Conveyor Belt...
Post by: Bizman on December 11, 2016, 01:02:09 PM
Now if free rolling wheels with bearings would prevent an aircraft from taking off, planes on skis or floaters shouldn't be able to fly at all because of friction.
Title: Re: Airplane on a Conveyor Belt...
Post by: Reaper90 on December 11, 2016, 01:40:13 PM
Now if free rolling wheels with bearings would prevent an aircraft from taking off, planes on skis or floaters shouldn't be able to fly at all because of friction.
EXACTLY.
Title: Re: Airplane on a Conveyor Belt...
Post by: Vraciu on December 11, 2016, 02:02:05 PM
Now if free rolling wheels with bearings would prevent an aircraft from taking off, planes on skis or floaters shouldn't be able to fly at all because of friction.
TECHNICALLY, snow and water (short of rapids) don't actively impart rearward force like a conveyer belt would.
But the amount of speed a conveyer belt would need to even appreciably slow a plane is beyond anything I can imagine.
Title: Re: Airplane on a Conveyor Belt...
Post by: Shuffler on December 11, 2016, 02:09:58 PM
You need to watch the belt sander video Eskimo made many years ago if you don't believe an accelerating belt will apply force to a wheel sitting on it. That force is applied to the plane through the axle and landing gear and is in opposition to the thrust produced by the plane's engine and prop.
I guess some have never landed a plane. The ground is moving at the same speed as the plane. The wheels touch down and the plane continues forward. You can rev up and the plane will take off. Even if the ground were moving twice the speed, the plane will do very closely to the same.
Title: Re: Airplane on a Conveyor Belt...
Post by: Mar on December 11, 2016, 02:16:32 PM
One of you geniuses claiming it can't take off need to try landing a plane with no wheel brakes on a moving conveyor belt with a brick wall at the end. It should slow down and stop way before reaching the wall right? I'll bring the popcorn.
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 11, 2016, 02:56:22 PM
I guess some have never landed a plane. The ground is moving at the same speed as the plane. The wheels touch down and the plane continues forward. You can rev up and the plane will take off. Even if the ground were moving twice the speed, the plane will do very closely to the same.
Ever notice what happens to airplane tires when a jet touches down? Ever seen all the skid marks at the end of the runway? Have you ever been pushed forward in your seat when those wheels touched down? Those wheels that are not spinning (or at least not very fast) have a rotational inertia state. To spin them up to ground speed takes force. There are many variables in this debate which is one of the reasons it was fun. Without clearly defined conditions though there will never be full agreement. Probably not even when the conditions are set in cement. Kinda like the probability question also.
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 11, 2016, 03:01:52 PM
Think of it like this. A jetliner about to touch down is like a throttled down plane sitting on a conveyor belt. The belt has yet to spin. As soon as the tires touch down it's like the belt just spun up to 130mph. The wheels/tires have an inertia that resists being spun up. While they are skidding force is definitely being applied in the direction opposite that of thrust. The amount of force is relative to the acceleration of belt of the speed of the plane when it touches down. Imagine that force if the plane touched down at 500mph?
Remember, no brakes applied, why do the tires skid?
Title: Re: Airplane on a Conveyor Belt...
Post by: Mar on December 11, 2016, 04:12:32 PM
It's gonna take a long time to clean the mess off of that wall...
Title: Re: Airplane on a Conveyor Belt...
Post by: morfiend on December 11, 2016, 05:35:46 PM
I prefer belt sander racing to this nonsense!
60 grit belt on a souped up portercable 4x21,it real fun till the extension cord gets pulled out..... :x
:salute
Title: Re: Airplane on a Conveyor Belt...
Post by: 100Coogn on December 11, 2016, 05:53:44 PM
Coogan
Title: Re: Airplane on a Conveyor Belt...
Post by: Vraciu on December 11, 2016, 06:09:07 PM
Direct link those who can't see the video box on your device (like me).
https://www.youtube.com/watch?v=4owlyCOzDiE
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 11, 2016, 06:14:21 PM
You guys do realize there is a difference between matching the speed of the fuselage of the plane and matching the speed of the spinning wheels right. If you don't get that difference then you are missing half of the argument.
(if only one person can be enlightened) :D
Title: Re: Airplane on a Conveyor Belt...
Post by: FLOOB on December 11, 2016, 06:24:55 PM
Iron let me ask you this, if the takeoff speed of the aircraft is 100mph, and the conveyor belt is moving 120mph, will the plane takeoff?
Title: Re: Airplane on a Conveyor Belt...
Post by: NatCigg on December 11, 2016, 06:26:33 PM
Think of the pulling the table cloth trick. Here's a test will a plane on a conveyor move at all? :angel: you know, if a plane does not have the thrust to overcome being at rest it is not going to take off on a conveyor :old:
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 11, 2016, 06:29:45 PM
The original question (not as posted here) was probably intended as a more simple debate aimed at those who can't distinguish between plane and car wheels. Obviously a conveyor belt that spins only to a hundred miles an hour isn't going to prevent most planes from taking off. The debate became more about physics and inertia when the question of what speed is being matched was raised. Newton's first law comes into play then. A wheel not spinning tends to stay not spinning. Of course you can counter any thrust of the engine if you are allowed to apply any belt acceleration in opposition to the wheels. If you don't get this then you don't understand the forces involved.
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 11, 2016, 06:30:18 PM
Think of it like this. A jetliner about to touch down is like a throttled down plane sitting on a conveyor belt. The belt has yet to spin. As soon as the tires touch down it's like the belt just spun up to 130mph. The wheels/tires have an inertia that resists being spun up. While they are skidding force is definitely being applied in the direction opposite that of thrust. The amount of force is relative to the acceleration of belt of the speed of the plane when it touches down. Imagine that force if the plane touched down at 500mph?
Remember, no brakes applied, why do the tires skid?
That is because it is instantaneous. It does not stop the plane and the plane cane take right off.
A conveyor belt is not going to spin up near that fast. Also understand that any loads that cause destruction of the belt as well as the tires. And both the plane and the belt have bearing.
Title: Re: Airplane on a Conveyor Belt...
Post by: FLOOB on December 11, 2016, 06:33:15 PM
Think of the pulling the table cloth trick. Here's a test will a plane on a conveyor move at all? :angel: you know, if a plane does not have the thrust to overcome being at rest it is not going to take off on a conveyor :old:
You just said that if a plane isn't able to move then it's not going to be able to move..
Here's your sign.
Maybe it's not what you meant to say, but it's what you said.
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 11, 2016, 06:37:33 PM
That may be the question as you understand it but it was not the question as it was originally asked here.
Will a plane take off if the belt is spinning at 10,000 miles per hour?
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 11, 2016, 06:42:54 PM
The original question, if I recall correctly, was if the belt matched the speed of the wheels. I couldn't find the original thread so not sure on that. The question then became what does that mean, the wheels? Are we talking the theoretical center of the axle which would then be the same as the fuselage or are we talking the rotational velocity of the wheels? The asker then stated he intentional left that ambiguous to spur debate, if I recall correctly.
Title: Re: Airplane on a Conveyor Belt...
Post by: FLOOB on December 11, 2016, 06:50:38 PM
a little way down this forum is a link to the real question!
read this more than once and hopefully you will understand the plane does not have to stay stationary and the belt is not compinsating for movement of the plane it is only going 100 knots in the oposite direction hence wheel speed 200 knots! plane speed 100 knots!
Title: Re: Airplane on a Conveyor Belt...
Post by: NatCigg on December 11, 2016, 07:08:20 PM
You just said that if a plane isn't able to move then it's not going to be able to move..
Here's your sign.
Maybe it's not what you meant to say, but it's what you said.
right, if a plane cant move then it cant take off on a conveyor. I also implied that it is very plausible that a plane on a conveyor could sit in one spot despite being on a moving conveyor. :lol
Title: Re: Airplane on a Conveyor Belt...
Post by: Reaper90 on December 12, 2016, 11:15:00 AM
right, if a plane cant move then it cant take off on a conveyor. I also implied that it is very plausible that a plane on a conveyor could sit in one spot despite being on a moving conveyor. :lol
Why wouldn't the plane move? If I put a freewheeling plane on a belt sander and pull a string attached to the nose, the plane would move. Propellers or jet engines equal the string, they have nothing to do with the ground below. If they had, no plane could ever fly.
Title: Re: Airplane on a Conveyor Belt...
Post by: Shuffler on December 12, 2016, 03:58:52 PM
Why wouldn't the plane move? If I put a freewheeling plane on a belt sander and pull a string attached to the nose, the plane would move. Propellers or jet engines equal the string, they have nothing to do with the ground below. If they had, no plane could ever fly.
For such a simple thing folks who are generally intelligent just lose it. LOL
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 12, 2016, 04:52:02 PM
For those who see no counter force to thrust being applied by the belt answer whether the speed of the belt makes any difference?
Title: Re: Airplane on a Conveyor Belt...
Post by: Shuffler on December 12, 2016, 04:57:18 PM
For those who see no counter force to thrust being applied by the belt answer whether the speed of the belt makes any difference?
They original post says the belt is traveling the opposite direction at the same speed as the plane.
For those that dream about a conveyor belt moving instantly, you can also dream about tires that will not shred just as the belt does not shred.
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 12, 2016, 05:05:17 PM
Pretty sure the original post in the original thread said the wheels. This thread is referencing the other thread which I could not find. It has been a loooong time ago.
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 12, 2016, 05:18:04 PM
Just to be clear. A plane can take off on any conveyor belt that is moving only as fast as the fuselage of the plane with respect to the ground or wind. No problem. Anyone who thought it wouldn't was confusing the thrust of the prop with the wheels that drive a car. That is settled.
Now for a question that could have been inferred from the original.
Can a plane on a conveyor belt take off if the belt can instantly match the rotational speed of the wheels, without limit?
Title: Re: Airplane on a Conveyor Belt...
Post by: NatCigg on December 12, 2016, 05:34:47 PM
since any good airplane would apply a very large amount of thrust, independent of the conveyor, that will move the plane forward almost as if it was on solid ground. because of the planes acceleration in space, the wheels will always be moving faster than the conveyor, causing the conveyor to speed up, depending on the conveyors ability to accelerate and the tire and bearing assemblies ability to handle the speed, a theoretical infinite speed would be obtained until the plane reached takeoff airspeed and the tires leave the conveyor. :D
Title: Re: Airplane on a Conveyor Belt...
Post by: Vraciu on December 12, 2016, 05:42:14 PM
For those who see no counter force to thrust being applied by the belt answer whether the speed of the belt makes any difference?
Negligible.
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 12, 2016, 11:02:25 PM
Given indestructible wheels and an infinite speed belt there is still inertia and force to be considered. An infinite speed belt can easily counter the force of a non-infinite thrust power plant in a plane thus holding it in place.
Given an infinitely powerful engine which will win? The immovable object or the irresistible force? One will be proved false. Both cannot exist relative to the other.
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 12, 2016, 11:16:19 PM
Even if the wheels were theoretically frictionless they still have mass and thus inertia. An accelerating belt can apply force to those wheels opposite the direction of the plane's thrust. How much force just depends on how fast the belt accelerates. The plane's thrust is not infinite but unless you apply a limit, the belt's acceleration and thus "drag" is infinite.
Find the original thread and see how the question can be interpreted two ways. No one who understands the inertia question believes the plane won't take off with a belt moving a mere 200mph.
Title: Re: Airplane on a Conveyor Belt...
Post by: Zimme83 on December 13, 2016, 01:14:56 AM
The original question was if the plane could take off from a conveyor belt that matched the speed of the plane but in the opposite direction. But of course you can get any result you want by creating a theoretical setup were the belt can move at infinite speed etc..
The plane will take off - if the wheels can take the load of spinning twice as fast. The belt cannot hold the plane down but it can destroy the wheels. For a General Aviation aircraft it should be no problem since they get airborne at 60 or so knot so twice that is 120 knot, which is not extremely fast. For a jet liner however, with a rotation speed of let say 160-170 knots it would probably be some issues. 320+ knots on the wheels would almost certainly shred them apart.
But still: Its crucial to understand that a plane is not like a car in this case, a car need to use engine power to match the speed of the belt and will quickly run out of power, a plane don't need to do it since it moves by moving air and the belt only affect the free spinning wheels.
So there you have it - again.....
Title: Re: Airplane on a Conveyor Belt...
Post by: Bizman on December 13, 2016, 02:27:39 AM
Let's turn the question around: What would happen if an aeroplane landed on a conveyor belt moving in the opposite direction matching the speed of the plane? Would that make the plane land on a spot? And if so, why hasn't this been applied to carriers?
Title: Re: Airplane on a Conveyor Belt...
Post by: FLOOB on December 13, 2016, 02:37:07 AM
Let's turn the question around: What would happen if an aeroplane landed on a conveyor belt moving in the opposite direction matching the speed of the plane? Would that make the plane land on a spot? And if so, why hasn't this been applied to carriers?
Obama?
Title: Re: Airplane on a Conveyor Belt...
Post by: Zimme83 on December 13, 2016, 04:14:07 AM
Let's turn the question around: What would happen if an aeroplane landed on a conveyor belt moving in the opposite direction matching the speed of the plane? Would that make the plane land on a spot? And if so, why hasn't this been applied to carriers?
It hasn't been applied to carriers because it doesn't work and would be very expensive to do. And even if it did work it would be a bad idea since thanks to the acceleration. Land a plane flying at 130-140 knots on the spot will inevitable rip the plane apart and most likely kill the pilot.
In reality it would be like a normal landing, except that the wheels are accelerated to twice their normal speed. A much better idea would be to build a huge fan to blow the air over the ship/runway at a speed that matched the speed of the plane.
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 13, 2016, 08:22:34 AM
The original question was if the plane could take off from a conveyor belt that matched the speed of the plane but in the opposite direction. But of course you can get any result you want by creating a theoretical setup were the belt can move at infinite speed etc..
The plane will take off - if the wheels can take the load of spinning twice as fast. The belt cannot hold the plane down but it can destroy the wheels. For a General Aviation aircraft it should be no problem since they get airborne at 60 or so knot so twice that is 120 knot, which is not extremely fast. For a jet liner however, with a rotation speed of let say 160-170 knots it would probably be some issues. 320+ knots on the wheels would almost certainly shred them apart.
But still: Its crucial to understand that a plane is not like a car in this case, a car need to use engine power to match the speed of the belt and will quickly run out of power, a plane don't need to do it since it moves by moving air and the belt only affect the free spinning wheels.
So there you have it - again.....
Maybe that was the original question posted to Mythbusters but it was not the original question posted here. That was well before this particular thread was started in 2008.
Title: Re: Airplane on a Conveyor Belt...
Post by: Bizman on December 13, 2016, 10:54:05 AM
Have I already made it clear that I believe in takeoff unless the landing gear fall apart on the conveyor belt?
Title: Re: Airplane on a Conveyor Belt...
Post by: Vraciu on December 13, 2016, 04:51:52 PM
The original question was if the plane could take off from a conveyor belt that matched the speed of the plane but in the opposite direction. But of course you can get any result you want by creating a theoretical setup were the belt can move at infinite speed etc..
The plane will take off - if the wheels can take the load of spinning twice as fast. The belt cannot hold the plane down but it can destroy the wheels. For a General Aviation aircraft it should be no problem since they get airborne at 60 or so knot so twice that is 120 knot, which is not extremely fast. For a jet liner however, with a rotation speed of let say 160-170 knots it would probably be some issues. 320+ knots on the wheels would almost certainly shred them apart.
But still: Its crucial to understand that a plane is not like a car in this case, a car need to use engine power to match the speed of the belt and will quickly run out of power, a plane don't need to do it since it moves by moving air and the belt only affect the free spinning wheels.
So there you have it - again.....
160-170 is F-105 territory not an airliner.
Title: Re: Airplane on a Conveyor Belt...
Post by: morfiend on December 13, 2016, 06:40:22 PM
Go offline enable storch on the CV and set wind at 10 mph south,now set course due north for CV and take off in storch!
If you film and run the film backwards it will look like a landing! The storch will takeoff as the CV motors away infront of you!
:salute
Title: Re: Airplane on a Conveyor Belt...
Post by: AKIron on December 13, 2016, 08:53:00 PM
I've never flown a Piper Cub but my Dad said he landed one almost at a stop once. You could even land one going backward but it would be trickier than it sounds. For that would require a significant headwind and those little planes are like leafs in the wind. You don't usually get wind that strong without gusts or gusting side components.
Title: Re: Airplane on a Conveyor Belt...
Post by: Vraciu on December 13, 2016, 11:46:25 PM
I have landed a 152 going backwards.
Title: Re: Airplane on a Conveyor Belt...
Post by: -gg- on July 12, 2022, 09:18:16 PM