Aces High Bulletin Board
General Forums => The O' Club => Topic started by: Chairboy on December 20, 2007, 05:27:18 PM
-
On the AOPA forums, the airplane vs. treadmill debate has flared anew. Mythbusters _is_ doing an episode where they'll test this, I've seen a teaser video. A canvas tarp a few hundred feet long will be rolled out on the runway and be towed by a truck at 40-50mph while the plane throttles up. Obviously, the treadmill is a red herring and has no real bearing on whether the plane takes off, but it's disheartening to see so many folks over there who are pilots getting this one wrong.
Unless... are there people here who think the plane on a treadmill won't take off? That'd be fun.
-
For any AOPA'ers, here's the most recent thread:
http://forums.aopa.org/showthread.php?t=37492
-
Originally posted by Chairboy
On the AOPA forums, the airplane vs. treadmill debate has flared anew. Mythbusters _is_ doing an episode where they'll test this, I've seen a teaser video. A canvas tarp a few hundred feet long will be rolled out on the runway and be towed by a truck at 40-50mph while the plane throttles up. Obviously, the treadmill is a red herring and has no real bearing on whether the plane takes off, but it's disheartening to see so many folks over there who are pilots getting this one wrong.
Unless... are there people here who think the plane on a treadmill won't take off? That'd be fun.
Depends on how fast the treadmill will go of course. We've been there and done that more than a few times.
Reread, of course under the conditions given the plane will takeoff easily, but not before hitting the end of the tarp I bet.
-
It... really doesn't matter how fast the treadmill goes. The friction of the bearings in the wheels is insignificant compared to the thrust of the propeller.
-
Like I said in the other thread, give the treadmill unlimited speed and strength and the wheels and bearing unlimited strength and the treadmill will keep the plane in place. It will have nothing to do with bearing friction and everything to do with loading kinetic rotational energy into the wheels at a rate equal to the thrust output of the motor.
Mythbusters will prove that a plane can take off if the treadmill matches the plane’s speed.
A treadmill that matches the plane’s wheel’s speed, however, would be impossible to build or test because it would need to achieve speeds beyond what could be built by man.
-
Originally posted by Chairboy
It... really doesn't matter how fast the treadmill goes. The friction of the bearings in the wheels is insignificant compared to the thrust of the propeller.
Easy enough for you to test since you have your own plane. Next time you prepare to take just hold your brakes as hard as you can and see if you can take off with those tires not rolling but skidding down the runway.
-
Why in the world would you think that the bearing friction of having wheels free spin twice as fast would be as much as applying full brakes?
-
AkIron, hope this helps ya visualize the physics, I may be using unclear language:
http://www.straightdope.com/columns/060203.html
and then the following when you're ready to leap up from your chair in fury:
http://www.straightdope.com/columns/060303.html
-
Originally posted by Chairboy
Why in the world would you think that the bearing friction of having wheels free spin twice as fast would be as much as applying full brakes?
Phrased that way of course they would not. The debate long ago though led to the question as to what the belt was actually matching in speed. As the question was then phrased and possibly on the board you are now visiting it meant that the belt would spin ever faster attempting to match the speed of wheel. So long as the plane was moving even slightly forward the belt would have to accelerate to infinite speed which would of course freeze the wheel bearings long before a black hole would be created.
-
Originally posted by AKIron
Easy enough for you to test since you have your own plane. Next time you prepare to take just hold your brakes as hard as you can and see if you can take off with those tires not rolling but skidding down the runway.
the runway is covered with ice.
-
Originally posted by john9001
the runway is covered with ice.
I play the global warming card and melt your puny runway ice.
-
I don't get it. lift is achieved by air flow over the wings.......the wheels have nothing to do with it
-
Originally posted by Gunslinger
I don't get it. lift is achieved by air flow over the wings.......the wheels have nothing to do with it
Bingo.
-
Originally posted by Chairboy
Bingo.
so what's the big deal again?
-
There's two ways to interpret the wheel/belt thing.
1. Does the surface of the belt match the airspeed of the plane but in the opposite direction
or
2. Does the belt surface match the speed of the surface of the spinning tire but in the opposite direction
If #1, the plane takes off easily. If #2, and the belt isn't constrained by realistic mechanical properties but the tires are then the tire will quickly blow due to speed of the belt.
-
Originally posted by Gunslinger
so what's the big deal again?
Ask the folks who think a plane won't take off from a treadmill because of some sort of magical super gravity effect made by the mere presence of the moving surface. :D
-
Originally posted by AKIron
There's two ways to interpret the wheel/belt thing.
1. Does the surface of the belt match the airspeed of the plane but in the opposite direction
or
2. Does the belt surface match the speed of the surface of the spinning tire but in the opposite direction
If #1, the plane takes off easily. If #2, and the belt isn't constrained by realistic mechanical properties but the tires are then the tire will quickly blow due to speed of the belt.
There's no air flow over the wings though......no air flow = no lift.
A treadmill is a usually a stationary object......thus no flowing of air.
EDIT:
OK I'll concede that if you put a powerfull enough engine on a dump truck you can get it off the ground from a treadmill.....thus an airplane can take off from a treadmill.
HOWEVER, the treadmill is irrellevent, STOL planes can take off from the ground reguardless of the how fast the surface underneith them move. With that said it kinda negates the whole discussion.
-
I withdraw my bingo, you appear to be caught in the same illogic loop.
The plane isn't propelled by the wheels, it's pushed forward by the prop.
-
Chairboy;
Read and answer:
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?
-
Originally posted by Gunslinger
There's no air flow over the wings though......no air flow = no lift.
A treadmill is a usually a stationary object......thus no flowing of air.
The plane must move forward through the air to generate lift on the wings. If the wheels are spinning a million miles an hour as the belt attempts to counter the speed of the spinning wheels there will be a lot of friction effectively applying the brakes. As Eskimo mentioned, there are other forces in effect besides friction too.
-
Originally posted by eskimo2
Chairboy;
Read and answer:
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?
at 100ft. The air flow over the wings makes the plane take off, not the wheels. From a physics stand point (IM un eduacted HO) the only difference might be some type of gyroscopic effect produced by the spinning wheels. I don't know what effect this has in flight.
With a powerfull enough engine anything can get off the ground with or without wings.
-
wait wait, my airplane has a 50 mph head wind.
-
Originally posted by AKIron
The plane must move forward through the air to generate lift on the wings. If the wheels are spinning a million miles an hour as the belt attempts to counter the speed of the spinning wheels there will be a lot of friction effectively applying the brakes. As Eskimo mentioned, there are other forces in effect besides friction too.
If I run on a treadmill I sweat more.......because there isn't any airflow on my body. Again no air flow no lift.
as long as the prop is clear of the ground you might even be able to get off on the belly. Wheels and friction are irrelevent to lift.
-
Originally posted by john9001
wait wait, my airplane has a 50 mph head wind.
But you forgot to remove your control lock.
-
Originally posted by Gunslinger
If I run on a treadmill I sweat more.......because there isn't any airflow on my body. Again no air flow no lift.
as long as the prop is clear of the ground you might even be able to get off on the belly. Wheels and friction are irrelevent to lift.
Try to generate enough lift to take off with flat tires or the brakes fully applied.
-
Originally posted by AKIron
Try to generate enough lift to take off with flat tires or the brakes fully applied.
You could put the brakes on full and chain the thing to the ground and you'll get the same effect of magical frictionless tires on a treadmill
-
Originally posted by Gunslinger
so what's the big deal again?
That's the first thing I thought..."ya need air flow for lift..." :rolleyes:
-
And we're off!
The last thread on the subject when 27 pages and 673 posts.
What do you say O'Club? Can we overcome frictions, angular momentums, illegal immigration, and global warming to pass the 673 posts mark with this thread?
The long holiday weekend is near so I think there will be a lot of people with a lot of time on their hands.
I predict we make it to the 850 posts range.
-
Originally posted by Donzo
And we're off!
The last thread on the subject when 27 pages and 673 posts.
What do you say O'Club? Can we overcome frictions, angular momentums, illegal immigration, and global warming to pass the 673 posts mark with this thread?
The long holiday weekend is near so I think there will be a lot of people with a lot of time on their hands.
I predict we make it to the 1100 posts range.
BUT THERE'S NO AIR FLOW OVER THE WINGS!!!!!!!
:furious
-
Lift? Where we're going we don't need lift.
(http://www.aviapedia.com/files/fighters/F-35/F-35_4.jpg)
-
Originally posted by Gunslinger
BUT THERE'S NO AIR FLOW OVER THE WINGS!!!!!!!
:furious
Why not?
-
http://www.youtube.com/watch?v=OWDEYpqS0yw&feature=related
runway, we don need no steenkn runway.
-
Originally posted by AKIron
Lift? Where we're going we don't need lift.
(http://www.aviapedia.com/files/fighters/F-35/F-35_4.jpg)
nore treadmills....hell no wheels either!
Just thought of this.
It's the same concept of tail wind on take off. Increased tail wind on take off reduces lift and requires more speed to counter effect it.
Thus if you had an infinate amount of space to take off with and a tail wind that constantly matched the speed of the air craft it would never take off. It would continue to accelorate until the mechanical limitations of the AC are exceeded.
DONZO,
A treadmill that matched the speed of the wheels would not allow a plane to accelorate reletive to the position of the earth......thus no air flow over the wings The wheels could be spinning at 300mph but the airplane is going 0.
It's like having a bike or a car on a dyno. The aerodynamics of a car have no play in vehicle on a dyno because there is no air flow over it.
a y
-
Originally posted by Gunslinger
DONZO,
A treadmill that matched the speed of the wheels would not allow a plane to accelorate reletive to the position of the earth......thus no air flow over the wings The wheels could be spinning at 300mph but the airplane is going 0.
It's like having a bike or a car on a dyno. The aerodynamics of a car have no play in vehicle on a dyno because there is no air flow over it.
a y
Try this:
With everything as already stated....hook a super strong steel cable to the nose of the plane. Attach the other end to a powerful winch. Now, will the winch pull the plane forward?
-
Originally posted by Donzo
Try this:
With everything as already stated....hook a super strong steel cable to the nose of the plane. Attach the other end to a powerful winch. Now, will the winch pull the plane forward?
as the question is stated.....no
the pull of the wench would only be counteracted by the treadmill as it matches the speed of the wheel.
-
I'm wondering if many civilizations haven't at some point puzzled over this scenario building both frictionless wheels and lightspeed treadmills to put the question to rest. It could explain the black holes that dot our universe?
-
Originally posted by AKIron
I'm wondering if many civilizations haven't at some point puzzled over this scenario building both frictionless wheels and lightspeed treadmills to put the question to rest. It could explain the black holes that dot our universe?
get rid of gravity all together and lift becomes irrelevent!;)
-
Originally posted by Gunslinger
as the question is stated.....no
the pull of the wench would only be counteracted by the treadmill as it matches the speed of the wheel.
This is from the link Chairboy posted (http://www.straightdope.com/columns/060203.html):
As you point out, one problem here is the wording of the question. Your version straightforwardly states that the conveyor moves backward at the same rate that the plane moves forward. If the plane's forward speed is 100 miles per hour, the conveyor rolls 100 MPH backward, and the wheels rotate at 200 MPH. Assuming you've got Indy-car-quality tires and wheel bearings, no problem. However, some versions put matters this way: "The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation." This language leads to a paradox: If the plane moves forward at 5 MPH, then its wheels will do likewise, and the treadmill will go 5 MPH backward. But if the treadmill is going 5 MPH backward, then the wheels are really turning 10 MPH forward. But if the wheels are going 10 MPH forward . . . Soon the foolish have persuaded themselves that the treadmill must operate at infinite speed. Nonsense. The question thus stated asks the impossible -- simply put, that A = A + 5 -- and so cannot be framed in this way. Everything clear now? Maybe not. But believe this: The plane takes off.
-
Soon the foolish have persuaded themselves that the treadmill must operate at infinite speed. Nonsense. The question thus stated asks the impossible -- simply put, that A = A + 5 -- and so cannot be framed in this way. Everything clear now? Maybe not. But believe this: The plane takes off.
There is a fallacy herein. For the belt to match exactly the speed of the spinning wheel requires that the plane be stationary. If the plane is stationary there is no airlfow over the wings. The plane must move forward relative to the wind to takeoff. As the plane accelerates so does the wheel and therefore the belt.
-
Originally posted by Donzo
This is from the link Chairboy posted (http://www.straightdope.com/columns/060203.html):
but the plane would never move forward reletive to the earth.
-
Why the heck wouldn't it move? You may be assuming that the wheels are motorized, but it's the prop that pulls it through the air.
-
Having reread your excerpt Donzo I realized I misunderstood the point of that poster. Apparently they are saying that since it is impossible for a belt to keep up in the alternate understanding of the scenario it is therefore an incorrect interpretation of the problem given. If I'm reading that right then I say bullocks. Two interpretations lead to two different results. Because only one is practical does not negate the other or make the intrepreter responsible for a poorly defined problem.
-
meh, i can push my brother forward off his bike rollers. those also do what the treadmill does in this question.
-
Originally posted by vorticon
meh, i can push my brother forward off his bike rollers. those also do what the treadmill does in this question.
Can your brother fly? I didn't think so. :p
-
If I run on a treadmill I sweat more.......because there isn't any airflow on my body. Again no air flow no lift.
To simulate a prop plane, mount a winch on the wall in front of the treadmill, engage it when you are at full speed. Or to simulate a jet, get yourself one of those James Bond '60s jet packs and aim the thrust straight back. No matter how fast that belts moving, you ain't staying stationary. :t
meh, i can push my brother forward off his bike rollers. those also do what the treadmill does in this question.
All it takes is just one devious mother ****er to outthink the hive mind of humanity. :aok :t
-
Chairboy;
Read and answer:
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?
-
So we put a hang glider into the loop with Vorticons brother riding a bike on a set of rollers.
When Vorticon pushes his brother off the rollers, will he be able to fly?
a. if he has enough airspeed he can.
Does it matter if he was riding the rollers fast or slowly?
a. nope
-
PS,
Watch my video:
http://hallbuzz.com/movies/paper_treadmill.AVI
(1MB AVI)
Or this one:
http://hallbuzz.com/movies/wheel_on_sander_250th.AVI
-
Originally posted by Chairboy
Mythbusters _is_ doing an episode where they'll test this, I've seen a teaser video.
That episode will be airing on Wednesday: Plane on a conveyer belt (http://www.tv.com/mythbusters/airplane-on-conveyor-belt!/episode/1163441/preshow.html) :)
edit: better link (http://dsc.discovery.com/tv-schedules/series.html?paid=1.13056.24704.3913.x&start=10)
-
Originally posted by Octavius
That episode will be airing on Wednesday: Plane on a conveyer belt (http://www.tv.com/mythbusters/airplane-on-conveyor-belt!/episode/1163441/preshow.html) :)
edit: better link (http://dsc.discovery.com/tv-schedules/series.html?paid=1.13056.24704.3913.x&start=10)
O'Rly??
(http://i195.photobucket.com/albums/z125/JB73Mustaine/orly.jpg)
-
You really took the time to screen capture, edit, resize, and host just to tell me that?
-
Originally posted by Octavius
You really took the time to screen capture, edit, resize, and host just to tell me that?
yup :D
I am bored in a hotel in Grand Rapids, MI...
what else can I do? :lol :cry
-
Here ya go, for those unable to navigate the treacherous waters of discovery.com:
(http://hallert.net/images/mbusters.JPG)
It was so tempting to open tabs called 'TrannyCentral' or something for someone to 'discover', but I didn't have the heart. Too easy.
-
I think this thread may end up killing the server.. :noid
And, I have an idea. If the treadmill is allowed to keep the speed of the airplane, but not react simultaneously, couldn't you take a 747, apply reverse thrusters to get the plane attempting to go backwards. Then if you can manage this without blowing up the engines! Throw them into full throttle forward, so the plane launches forward. Leaving the treadmill trying to react. :confused:
-
Of course it will take off... in the same amount of runway it normally takes to get air over the wings. The conveyor has absolutely no effect on the takeoff though.... it's just increasing wheelspin.
-
I can't believe, with as many of you that play AH, that don't know the basic's of flight. Not all, many stated the correct answer that lift is generated by airflow over the wings' and control surfaces.
The stupid treadmill thing only makes the wheels spin faster than normal.
Airplanes such as WWII carrier aircraft that launched from carriers' not equipped with a catapult, usually had their CV steaming into the wind at full or flank speed, helping to give an extra 30+ knots' of airflow over the wings' by the time they reached the forward edge of the deck. If the aircraft could reach 60+ knots on the deck on their own, the combined total of 60+(Plane) and 30+(Ship into the wind) would give 90+. Usually enough to rotate off, with the use of flaps.
That was the first thing I thought of, when I saw this.
-
Originally posted by Gunslinger
nore treadmills....hell no wheels either!
Just thought of this.
It's the same concept of tail wind on take off. Increased tail wind on take off reduces lift and requires more speed to counter effect it.
Thus if you had an infinate amount of space to take off with and a tail wind that constantly matched the speed of the air craft it would never take off. It would continue to accelorate until the mechanical limitations of the AC are exceeded.
DONZO,
A treadmill that matched the speed of the wheels would not allow a plane to accelorate reletive to the position of the earth......thus no air flow over the wings The wheels could be spinning at 300mph but the airplane is going 0.
It's like having a bike or a car on a dyno. The aerodynamics of a car have no play in vehicle on a dyno because there is no air flow over it.
a y
I believe, gunslinger, that the Propellor or Jet thrust, depending on what you're using, would push against that tailwind, accelerating the A/C even faster than what wind there was, Thus getting airflow in the right direction over the wings (But you might have a higher ground takeoff speed as a result.) I believe that the A/C would still fly...
-
Eskimo, I raise your inertia-less and infinite speed conveyor belt with an infinite air grip propeller and the plane will be airborne. I win!
This problem is infinitely stupid and useless IMO.