Author Topic: plane on a conveyor belt? (Read 25265 times)

eskimo2 · « **Reply #615 on:** January 31, 2007, 04:48:35 PM »

Many people are looking at wheel bearing friction and rolling/tread friction as the only forces that can possibly act on the wheel of a plane. It takes energy to accelerate a rotating objects RPM. If a wheel’s RPM is accelerated by a treadmill, it will gain RPM AND the entire wheel will want to move in the direction of the treadmill. My movies show and prove this:

Here is a glimpse into how a treadmill pushes a wheel back as it accelerates. Note the set-up:

The fire extinguisher is an anchor (overkill, I know) for the rubber band that is tied to a wire that is looped through the axel of the wheel. To keep everything aligned, the wire goes through tubes that are taped to the green stool.

The wheel is resting on the belt sander. When the sander is turned on, the sander and the wheel gain RPM for less than ½ a second. During this time, the wheel shoots to the right, stretching the rubber band. When the sander and wheel stop accelerating and the RPM become constant, the wheel is no longer gaining significant energy from the belt and the rubber band pulls the wheel back to the left where it spins merrily in a steady state of energy.

The acceleration of the wheel stretched the rubber band in the direction of the treadmill (belt sander). This is an example of how a treadmill of unlimited speed could load energy into a wheel of unlimited strength (and through a perfect bearing) through rotational acceleration. Since the force is only applied to the bottom of the wheel where it contacts the treadmill, it is not balanced. A vector of the force is applied to the axel in the same direction of the belt. Note that it will not prevent the plane from moving if it only accelerates for ½ a second. The acceleration (increase in RPM) must be constant, and must be massive.

I hooked a crappy variable speed Dremel motor control to the sander. I sort of got the 2 speed effect. Both movies are available in AVI and QuickTime. The QuickTime ones are in the original Nikon format and are a bit sharper and are easier to move frame by frame.

Watch the movie and imagine things on a much greater scale.

1/250th exposure wheel on sander:
http://hallbuzz.com/movies/wheel_on_sander_250th.AVI
http://hallbuzz.com/movies/wheel_on_sander_250th.MOV

1/250th exposure 2-speed wheel on sander:
http://hallbuzz.com/movies/wheel_on_sander_2_speed.AVI
http://hallbuzz.com/movies/wheel_on_sander_2_speed.MOV

Better movies:

Here is a paper treadmill; the source off acceleration is a falling shoe tied to the paper. On the paper treadmill are a mouse ball, a copper pipe with a rubber band glued around it for traction, and an acrylic ball that may have skid/slip some.

Picture of the set up:

AVI:
http://hallbuzz.com/movies/paper_treadmill.AVI

QuickTime
http://hallbuzz.com/movies/paper_treadmill.MOV

WhiteHawk · « **Reply #616 on:** January 31, 2007, 04:57:25 PM »

Quote

Originally posted by Holden McGroin
the question is flawed as posted....

Ponder this: If there is no forward speed, there is no need for the conveyor to move. 0 = 0

Now the plane begins to creep forward, but it does not because the conveyor pulls it back. But that means it hasn't moved, so 0 = 0 and therefore the conveyor is not moving.

What causes a plane to move forward? Thrust that is independant of the wheels, air cushion, skiis, or whatever else it has to keep the paint from being scratched on the tarmac. Thrust is independant of the landing gear.

Net thrust causes acceleration, regardless of whatever rotational acceleration does to the wheel.....

End this thread now!

Thank you! I say we take a vote.

WhiteHawk · « **Reply #617 on:** January 31, 2007, 04:59:16 PM »

Quote

Originally posted by nexus69
My Question is. Where is the plane going?

The plane or the wheel?

eskimo2 · « **Reply #618 on:** January 31, 2007, 05:04:23 PM »

So far everyone who has dismissed the idea that a rapidly accelerating treadmill can keep a plane at full power from moving has not been able to answer the questions at the end of this story. If you don’t believe or understand what Hitech and I have been trying to say, please read on.

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 the second 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?

WhiteHawk · « **Reply #619 on:** January 31, 2007, 05:09:03 PM »

Quote

Originally posted by WhiteHawk
So there is really not enough information to answer this question. We need a drag variable for the wheels or if the wheels are sufficient, the plane will take off. .

Me first reply to this thread. I consider myself to be in the correct crowd. Someboyd come up with another one. Im on fire:t

lukster · « **Reply #620 on:** January 31, 2007, 05:30:27 PM »

Quote

Originally posted by 2bighorn
I was thinking that same is valid for conveyor bearings

Before that happens, conveyor breaks into pieces

and you'd be fixing the damn conveyor, if I remember right, many posts ago....

I didn't pose the initial question. However, using real existing materials and real existing planes I think we could build a belt more than capable of destroying the tires and/or wheel bearings before some planes could take off. The coefficient of friction we will use for the belt will be equal to a concrete runway.

2bighorn · « **Reply #621 on:** January 31, 2007, 05:31:19 PM »

Quote

Originally posted by hitech
Just had a thought, can you draw a diagram of how bearing friction turns into drag?

Not sure if you mean the same, but formula bellow should work since both are expressed in unit of force

Friction = ((plane mass + wheel mass) * gravitational acceleration) * bearing rolling friction coefficient) divided with number of bearings (one per wheel)

rolling friction coefficient is about 0.025 for very low quality radial friction only bearings (creates most of the friction)

eskimo2 · « **Reply #622 on:** January 31, 2007, 06:11:47 PM »

For those who did not watch the movie, here is the spoiler:

Please explain how the balls and hollow cylinder moved to the left when a paper treadmill moved to the left at an acceleration rate of a little under 9.8 meters per second per second if a force other than pure rotation did not act upon them? Rotation is not the only resultant of rotational acceleration when a force is applied to only one place.

2bighorn · « **Reply #623 on:** January 31, 2007, 06:41:09 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?

all planes take off at the same distance at the same speed.

Quote

thrust has to overcome total inertia that is wheel inertia + plane inertia. Since both are depended on mass, if you just move the mass around from plane to the wheel or from wheel to the plane and the total sum doesn't change then necessary force to get plane in motion doesn't change either.

This is not my theory, this is according to conservation law.

If you disagree I'd like to see some physical definitions which would support your claim.

2bighorn · « **Reply #624 on:** January 31, 2007, 06:56:40 PM »

Quote

Originally posted by eskimo2
Please explain how the balls and hollow cylinder moved to the left when a paper treadmill moved to the left at an acceleration rate of a little under 9.8 meters per second per second if a force other than pure rotation did not act upon them? Rotation is not the only resultant of rotational acceleration when a force is applied to only one place.

You applied external torque to your objects. What's so magical about?

eskimo2 · « **Reply #625 on:** January 31, 2007, 07:01:20 PM »

Quote

Originally posted by 2bighorn
all planes take off at the same distance at the same speed.

This is not my theory, this is according to conservation law.

If you disagree I'd like to see some physical definitions which would support your claim.

If they take off at the same time and distance, how in the world could Al’s plane’s wheels have a rotational energy state of 2X, Bob’s plane’s wheels have a rotational energy state of 1X and Chucks plane’s wheels have an energy state of 0? What happened to conservation of energy?

Al’s plane must have traded some forward acceleration/power of his entire plane for the 2X rotational energy now stored in his wheels. Bob’s plane also must have traded some forward acceleration/power of his entire plane for the 1X rotational energy now stored in his wheels, and he took off before and in less distance than Al. Chuck’s plane lost nothing to rotational inertia and took off first and in the least distance.

Golfer · « **Reply #626 on:** January 31, 2007, 07:06:37 PM »

Eskimo I have to admit I've found it funny you keep saying "looooook at my movies" when they're not describing at all the question.

If I pull a table cloth out from under a place setting...I'm gonna break dishes.

What you're doing is having the conveyor apply force to the objects on it. Of course they're going to move with it a little bit...we've got gravity!

The basic problem is that your paper treadmill does not react to the movement of the balls...instead it acts upon them. If the treadmill only matches the speed of the wheels...its never going to work.

I do understand that the treamill will continue to accelerate as the questions described ultimately going faster than we'd ever hope to see. Assuming that the bearings and wheels won't break under any circumstances...and the conveyor too is indestrucible to any forces that it can apply the airplane is still going to fly.

If you sat an airplane without its engine on just on top of a treadmill and went right to a sprint...it'd get thrown off too. That's not what we or the question asks, however. You've offered a solution to a problem you've created.

lukster · « **Reply #627 on:** January 31, 2007, 07:18:25 PM »

Golfer what happens to a wheel when it is spinning at a certain rate on a treadmill that then matches that rate?

eskimo2 · « **Reply #628 on:** January 31, 2007, 07:25:45 PM »

Quote

Originally posted by Golfer
If the treadmill only matches the speed of the wheels...its never going to work.

Why?

eskimo2 · « **Reply #629 on:** January 31, 2007, 07:30:02 PM »

Quote

Originally posted by 2bighorn
You applied external torque to your objects. What's so magical about?

Well if you still think that a plane taking off on an opposing direction treadmill will have an easier time than it will on a regular runway, this should seem like magic.