Mythbusters to take on "the plane and the treadmill" conundrum?

[felony27]

Originally posted by: Amused

Originally posted by: felony27
okay i dont understand what the hell is going on and i read this thread...

airplanes NEED air going over the wings to fly. if that need is fulfilled than the plane cannot and will not take off. no matter how much those huge engines thrust the plane forward it its force will just be matched by the treadmill but in the opposite direction. the myth states the treadmill matches. meaning engines thrust to 50 mph treadmill go in opposite direction 50 mph engines thrust to 50,000mph treadmill go in opposite direction 50,000mph. the total NET speed will always be 0mph. now with calm wind and 0mph how is a 164,800lb (empty weight) plane suppose to get airborn. the wheels can spin at a speed of infinity only to be matched by treadmill...stop focusing on friction, wheels, axels, rc planes, all that bs...no AIR over the WINGS no LIFT.
air over wings=lift...theres no other way to get lift on an airplane.

and like i said the myth state the treadmill will always match the speed of the airplane...meaning u can slam on the brakes or put the thrust to 100% or whatever u want to do but the treadmill will alwasy match the speed of the plane.

so lets look at these formulas. if any of these are wrong please correct me.

air over wings=lift
no air over wings=no lift

please prove me wrong.

Very easily. The treadmill is irrelevant to the airspeed of the plane because the plane moves itself by pushing air behind it, NOT by force through the wheels.

You are applying the drive train of a car to this problem. How fast the ground is moving is completely irrelevant to the airspeed of the plane (given the UNPOWERED wheels can withstand the extra speed). If it were, a plane would gain speed on a regular runway, take off, lose thrust and be forced to land again.

The wheels ONLY exist to reduce friction. They do not drive the plane... so how fast the ground is moving is, again, totally irrelevant. This is why planes on skids, pontoons and skis can take off.

wow ur a genius...that is the exact point im trying to make buddy. wheels have absolutely nothing to do with anything...no matter the speed of the wheels no air can ever go over the wings due to the fact the plane is stationary

 

[ElFenix]

Originally posted by: sao123

Originally posted by: ElFenix
the whole thing depends on how much force the treadmill can put through the wheels.
if you've got 10,000 lbs of thrust from the turbines, you're going to need 10,000 pounds of force coming through the wheels to keep the plane from moving.

free spinning wheels will allow on a transfer of force up to a maximum of the friction generated between the wheels, the lubricant, and the center axle. Which in this case is not significant.

which is why this whole problem is stupid. for the plane to take off, the wheels are going to be spinning much faster than the conveyor belt. but the question has assumed that the wheels and conveyor belt are spinning at exactly the same rate. no normal wheel will do that. the only way it'd happen is if there is lots of friction in the wheel. so the problem has already assumed that the necessary friction is there. so the plane won't take off, but only because the problem is stupid and has nothing to do with reality.

 

[Thraxen]

Originally posted by: ElFenix
which is why this whole problem is stupid. for the plane to take off, the wheels are going to be spinning much faster than the conveyor belt. but the question has assumed that the wheels and conveyor belt are spinning at exactly the same rate. no normal wheel will do that. the only way it'd happen is if there is lots of friction in the wheel. so the problem has already assumed that the necessary friction is there. so the plane won't take off, but only because the problem is stupid and has nothing to do with reality.

I've always assumed that the belt was moving to oppose the forward motion of the plane, not the speed of the wheels. So if the plane is moving forward at 10 MPH then the belt would be moving in the opposite direction at 10 MPH.

 

[Amused]

Originally posted by: felony27

Originally posted by: Amused

Originally posted by: felony27
okay i dont understand what the hell is going on and i read this thread...

airplanes NEED air going over the wings to fly. if that need is fulfilled than the plane cannot and will not take off. no matter how much those huge engines thrust the plane forward it its force will just be matched by the treadmill but in the opposite direction. the myth states the treadmill matches. meaning engines thrust to 50 mph treadmill go in opposite direction 50 mph engines thrust to 50,000mph treadmill go in opposite direction 50,000mph. the total NET speed will always be 0mph. now with calm wind and 0mph how is a 164,800lb (empty weight) plane suppose to get airborn. the wheels can spin at a speed of infinity only to be matched by treadmill...stop focusing on friction, wheels, axels, rc planes, all that bs...no AIR over the WINGS no LIFT.
air over wings=lift...theres no other way to get lift on an airplane.

and like i said the myth state the treadmill will always match the speed of the airplane...meaning u can slam on the brakes or put the thrust to 100% or whatever u want to do but the treadmill will alwasy match the speed of the plane.

so lets look at these formulas. if any of these are wrong please correct me.

air over wings=lift
no air over wings=no lift

please prove me wrong.

Very easily. The treadmill is irrelevant to the airspeed of the plane because the plane moves itself by pushing air behind it, NOT by force through the wheels.

You are applying the drive train of a car to this problem. How fast the ground is moving is completely irrelevant to the airspeed of the plane (given the UNPOWERED wheels can withstand the extra speed). If it were, a plane would gain speed on a regular runway, take off, lose thrust and be forced to land again.

The wheels ONLY exist to reduce friction. They do not drive the plane... so how fast the ground is moving is, again, totally irrelevant. This is why planes on skids, pontoons and skis can take off.

wow ur a genius...that is the exact point im trying to make buddy. wheels have absolutely nothing to do with anything...no matter the speed of the wheels no air can ever go over the wings due to the fact the plane is stationary

The engines on a plane thrust it through the AIR. The plane WILL gain speed relative to the AIR. Thus it will obtain the necessary lift to take off. The ground speed is TOTALLY IRRELEVANT.

The plane is NOT stationary. NO where in this problem is the plane EVER assumed to be stationary. Only that the threadmill speed is adjusted to match the forward speed of the plane. The ONLY time the plane would be stationary is when its engines are idling.

 

[ElFenix]

Originally posted by: Thraxen

Originally posted by: ElFenix
which is why this whole problem is stupid. for the plane to take off, the wheels are going to be spinning much faster than the conveyor belt. but the question has assumed that the wheels and conveyor belt are spinning at exactly the same rate. no normal wheel will do that. the only way it'd happen is if there is lots of friction in the wheel. so the problem has already assumed that the necessary friction is there. so the plane won't take off, but only because the problem is stupid and has nothing to do with reality.

I've always assumed that the belt was moving to oppose the forward motion of the plane, not the speed of the wheels. So if the plane is moving forward at 10 MPH then the belt would be moving in the opposite direction at 10 MPH.

if that were happening then the wheels would be spinning at 20 and the plane would continue to accelerate and take off.

the way i read it, though, the wheels are going at the treadmill speed.

 

[sao123]

Originally posted by: ElFenix

Originally posted by: sao123

Originally posted by: ElFenix
the whole thing depends on how much force the treadmill can put through the wheels.
if you've got 10,000 lbs of thrust from the turbines, you're going to need 10,000 pounds of force coming through the wheels to keep the plane from moving.

free spinning wheels will allow on a transfer of force up to a maximum of the friction generated between the wheels, the lubricant, and the center axle. Which in this case is not significant.

which is why this whole problem is stupid. for the plane to take off, the wheels are going to be spinning much faster than the conveyor belt. but the question has assumed that the wheels and conveyor belt are spinning at exactly the same rate. no normal wheel will do that. the only way it'd happen is if there is lots of friction in the wheel. so the problem has already assumed that the necessary friction is there. so the plane won't take off, but only because the problem is stupid and has nothing to do with reality.

The question makes no such assumption. read my post at 1/18 1:23pm... One of the original authors of the question even explicitly states that the question does not make that assumption.

 

[Amused]

Originally posted by: Thraxen

Originally posted by: ElFenix
which is why this whole problem is stupid. for the plane to take off, the wheels are going to be spinning much faster than the conveyor belt. but the question has assumed that the wheels and conveyor belt are spinning at exactly the same rate. no normal wheel will do that. the only way it'd happen is if there is lots of friction in the wheel. so the problem has already assumed that the necessary friction is there. so the plane won't take off, but only because the problem is stupid and has nothing to do with reality.

I've always assumed that the belt was moving to oppose the forward motion of the plane, not the speed of the wheels. So if the plane is moving forward at 10 MPH then the belt would be moving in the opposite direction at 10 MPH.

Which means the plane would be moving forward at 10 MPH relative to the air, but the wheels would be moving at 20 MPH realtive to the treadmill surface.

 

[spidey07]

exdeath, good analogy - but you broke the problem by the skateboard moving forward.

Answer me this - if the circumference of the wheel is 10 meters and rotates once in one second, no acceleration. And if the treadmill surface moves 10 meters once per second has the plane advanced?

Disregard any other forces at this point. Just making the scenario obvious. If you can understand this then you understand why the plane cannot take off. In order for the plane to take off the treadmill must not have done what is described in the problem - ie, you left the bounds of the problem and are now talking about something different.

 

[MercenaryForHire]

Originally posted by: Amused

Originally posted by: felony27

Originally posted by: Amused

Originally posted by: felony27
okay i dont understand what the hell is going on and i read this thread...

airplanes NEED air going over the wings to fly. if that need is fulfilled than the plane cannot and will not take off. no matter how much those huge engines thrust the plane forward it its force will just be matched by the treadmill but in the opposite direction. the myth states the treadmill matches. meaning engines thrust to 50 mph treadmill go in opposite direction 50 mph engines thrust to 50,000mph treadmill go in opposite direction 50,000mph. the total NET speed will always be 0mph. now with calm wind and 0mph how is a 164,800lb (empty weight) plane suppose to get airborn. the wheels can spin at a speed of infinity only to be matched by treadmill...stop focusing on friction, wheels, axels, rc planes, all that bs...no AIR over the WINGS no LIFT.
air over wings=lift...theres no other way to get lift on an airplane.

and like i said the myth state the treadmill will always match the speed of the airplane...meaning u can slam on the brakes or put the thrust to 100% or whatever u want to do but the treadmill will alwasy match the speed of the plane.

so lets look at these formulas. if any of these are wrong please correct me.

air over wings=lift
no air over wings=no lift

please prove me wrong.

Very easily. The treadmill is irrelevant to the airspeed of the plane because the plane moves itself by pushing air behind it, NOT by force through the wheels.

You are applying the drive train of a car to this problem. How fast the ground is moving is completely irrelevant to the airspeed of the plane (given the UNPOWERED wheels can withstand the extra speed). If it were, a plane would gain speed on a regular runway, take off, lose thrust and be forced to land again.

The wheels ONLY exist to reduce friction. They do not drive the plane... so how fast the ground is moving is, again, totally irrelevant. This is why planes on skids, pontoons and skis can take off.

wow ur a genius...that is the exact point im trying to make buddy. wheels have absolutely nothing to do with anything...no matter the speed of the wheels no air can ever go over the wings due to the fact the plane is stationary

The engines on a plane thrust it through the AIR. The plane WILL gain speed relative to the AIR. Thus it will obtain the necessary lift to take off. The ground speed is TOTALLY IRRELEVANT.

The plane is NOT stationary. NO where in this problem is the plane EVER assumed to be stationary. Only that the threadmill speed is adjusted to match the forward speed of the plane. The ONLY time the plane would be stationary is when its engines are idling.

Everyone seems to think that the plane is on a very, very small treadmill and that it will somehow obtain the necessary 280mph airspeed without moving from it. At which point it will magically attain flight, break the neck of every passenger on board, and then release the muthaf*ckin' snakes.

- M4H

 

[exdeath]

Originally posted by: ElFenix

Originally posted by: sao123

Originally posted by: ElFenix
the whole thing depends on how much force the treadmill can put through the wheels.
if you've got 10,000 lbs of thrust from the turbines, you're going to need 10,000 pounds of force coming through the wheels to keep the plane from moving.

free spinning wheels will allow on a transfer of force up to a maximum of the friction generated between the wheels, the lubricant, and the center axle. Which in this case is not significant.

which is why this whole problem is stupid. for the plane to take off, the wheels are going to be spinning much faster than the conveyor belt. but the question has assumed that the wheels and conveyor belt are spinning at exactly the same rate. no normal wheel will do that. the only way it'd happen is if there is lots of friction in the wheel. so the problem has already assumed that the necessary friction is there. so the plane won't take off, but only because the problem is stupid and has nothing to do with reality.

The wheel speed will match the belt speed only if the belt is the only force acting on the wheels and the plane remains stationary by providing the minimal force neccessary to counter the friction of rolling.

This is like standing on a skateboard on a treadmill and holding yourself in place with the rail. It would take very little effort to hold yourself still. The wheels would be moving the same speed as the treadmill. With a little more effort in pulling yourself, you can move forward, and the wheels will start moving faster than the treadmill. The difference in wheel speed and treadmill speed is caused by a net movement of the skateboard relative to a fixed object (ie: the railing on the side of the treadmill).

 

[ElFenix]

Originally posted by: sao123


The question makes no such assumption. read my post at 1/18 1:23pm... One of the original authors of the question even explicitly states that the question does not make that assumption.

going by what is stated there, it should be perfectly obvious that the plane takes off with the wheels spinning 2x what they normally would. that's the first time i've seen it formulated that way.

then again, i haven't read much of this thread and almost none of the first 4 or 5 threads.

 

[smack Down]

Originally posted by: ElFenix

Originally posted by: sao123

Originally posted by: ElFenix
the whole thing depends on how much force the treadmill can put through the wheels.
if you've got 10,000 lbs of thrust from the turbines, you're going to need 10,000 pounds of force coming through the wheels to keep the plane from moving.

free spinning wheels will allow on a transfer of force up to a maximum of the friction generated between the wheels, the lubricant, and the center axle. Which in this case is not significant.

which is why this whole problem is stupid. for the plane to take off, the wheels are going to be spinning much faster than the conveyor belt. but the question has assumed that the wheels and conveyor belt are spinning at exactly the same rate. no normal wheel will do that. the only way it'd happen is if there is lots of friction in the wheel. so the problem has already assumed that the necessary friction is there. so the plane won't take off, but only because the problem is stupid and has nothing to do with reality.

The wheel doesn't need friction.

If the wheel was on the treadmill with out the plane it would not spin. Nothing is connected to the axle so not torque is applied.

The wheels on the plane spin so a force must be applied to the torque must be applied to the wheels otherwise they would not spin. Friction itself can not make the wheels spin. The kinetic energy of the spinning wheel increased the kinetic energy of the plane must decrease.

 

[chrisms]

My cat's breath smells like cat food.

 

[CityShrimp]

I don't see why this would be confusing.
Plane is stationary = no lift, so won't fly
Plane is moving = lift, so will fly

So assuming, the treadmill can go infinite speed and match however fast the plane's thrust pushes air, and the plane doesn't move an inch from it's current location, it won't fly.
But if the treadmill cannot match the speed, and the wheels start spinning faster than the treadmill, then it'll move and fly.

What's the debate here again?

 

[ElFenix]

Originally posted by: exdeath

The wheel speed will match the belt speed only if the belt is the only force acting on the wheels and the plane remains stationary by providing the minimal force neccessary to counter the friction of rolling.

This is like standing on a skateboard on a treadmill and holding yourself in place with the rail. It would take very little effort to hold yourself still. The wheels would be moving the same speed as the treadmill. With a little more effort in pulling yourself, you can move forward, and the wheels will start moving faster than the treadmill. The difference in wheel speed and treadmill speed is caused by a net movement of the skateboard relative to a fixed object (ie: the railing on the side of the treadmill).

i believe i said exactly that with the first post about 10,000 lbs of thrust. the only way the plane doesn't move is if there is 10,000 lbs of force coming through the wheels in the opposite direction.

Originally posted by: smack Down

The wheel doesn't need friction.

If the wheel was on the treadmill with out the plane it would not spin. Nothing is connected to the axle so not torque is applied.

The wheels on the plane spin so a force must be applied to the torque must be applied to the wheels otherwise they would not spin. Friction itself can not make the wheels spin. The kinetic energy of the spinning wheel increased the kinetic energy of the plane must decrease.

no, the friction doesn't cause the wheel to spin. i never said that. the friction allows force to be transferred from the conveyor belt to the plane. without that, the plane takes off normally, except for the wheels spinning extra fast.

 

[Amused]

Originally posted by: CityShrimp
I don't see why this would be confusing.
Plane is stationary = no lift, so won't fly
Plane is moving = lift, so will fly

So assuming, the treadmill can go infinite speed and match however fast the plane's thrust pushes air, and the plane doesn't move an inch from it's current location, it won't fly.
But if the treadmill cannot match the speed, and the wheels start spinning faster than the treadmill, then it'll move and fly.

What's the debate here again?

:::sigh:::

A plane pushes itself through the air by its engines, not it's wheels.

The plane will move forward relative to both the treadmill AND the air. The wheels merely have to spin at twice their normal takeoff speed (plane moving forard at 140 + treadmill moving back at 140 = 280 MPH to the wheels) to allow the plane to achive lift and take off.

Stand on a treadmill on rollarskates, and strap rocket to your butt. Now, do you think you'll be pushed forward relative to the air? Or do you think the treadmill will counteract the rocket?

 

[Number1]

Check out the Safeway thread: http://forums.anandtech.com/messageview...atid=38&threadid=1992917&enterthread=y

Funny big time...

 

[ElFenix]

Originally posted by: CityShrimp
I don't see why this would be confusing.
Plane is stationary = no lift, so won't fly
Plane is moving = lift, so will fly

So assuming, the treadmill can go infinite speed and match however fast the plane's thrust pushes air, and the plane doesn't move an inch from it's current location, it won't fly.
But if the treadmill cannot match the speed, and the wheels start spinning faster than the treadmill, then it'll move and fly.

What's the debate here again?

it has nothing to do with speed. it has everything to do with force. it doesn't matter how fast the conveyor belt goes if there is no way to transmit the force to the plane.

 

[MercenaryForHire]

Originally posted by: Amused
The plane will move forward relative to both the treadmill AND the air. The wheels merely have to spin at twice their normal takeoff speed (plane moving forard at 140 + treadmill moving back at 140 = 280 MPH to the wheels) to allow the plane to achive lift and take off.

Disclaimer - I never read the original question

Doesn't it state that the treadmill will always move as fast as the wheels? Therefore, at 140mph, the wheels and treadmill both move at 140mph. If the throttle on the plane gets increased in order to overcome that and get some horizontal velocity, and starts going 150mph, the treadmill goes 150mph in the opposite direction. Repeat until explosion?

- M4H

 

[exdeath]

Originally posted by: spidey07
exdeath, good analogy - but you broke the problem by the skateboard moving forward.

Answer me this - if the circumference of the wheel is 10 meters and rotates once in one second, no acceleration. And if the treadmill surface moves 10 meters once per second has the plane advanced?

Disregard any other forces at this point. Just making the scenario obvious. If you can understand this then you understand why the plane cannot take off. In order for the plane to take off the treadmill must not have done what is described in the problem - ie, you left the bounds of the problem and are now talking about something different.

So ignore the engines, then of course the plane can't move.

First things first, if the wheel spins at the same rate as the treadmill at 10 m/s, there has to be some other force holding the plane in place, and that force is equal to the total friction in the landing gears, otherwise the plane would just sit there and start moving backwards at 10 m/s without the wheels moving at all. There has to be some counter force to get the wheels to start rolling and hold the plane in place relative to a fixed point outside the treadmill surface. This force is a very small fraction of the engine power (see my skateboard/treadmill/pulley experiment I posted).

Ie: if a 1000 lb loaded tool box on wheels was on a level treadmill moving with the treadmill (the wheels are stopped), you could hold out a single hand and hold all 1000 lbs in place and cause the wheels to start spinning to match the treadmill speed.

So first, your requirement of disregarding all other forces is invalid even to simply hold the object in place. There is a normal force exerted on the axles, bearings, wheels, treadmill surface, etc, that will keep the object stationary with respect to the treadmill despite being on wheels. A small amount of constant force is neccessary to break the static friction between the body and rotating parts order to hold it in place as you described.

Second, think about the tool box example. Here you are with a 1000 lb tool box coming at you on a treadmill, and you can simply hold out one hand to hold it in place as the treadmill is brought to speed.

Since it takes little effort to hold it in place, you have more power available that you could actually push the tool box against the treadmill.

The amount of power a planes engines have over the friction in its landing gears is far greater than your ability to overpower the crappy wheels on a tool box.

 

[randay]

Originally posted by: MercenaryForHire

Originally posted by: Amused
The plane will move forward relative to both the treadmill AND the air. The wheels merely have to spin at twice their normal takeoff speed (plane moving forard at 140 + treadmill moving back at 140 = 280 MPH to the wheels) to allow the plane to achive lift and take off.

Disclaimer - I never read the original question

Doesn't it state that the treadmill will always move as fast as the wheels? Therefore, at 140mph, the wheels and treadmill both move at 140mph. If the throttle on the plane gets increased in order to overcome that and get some horizontal velocity, and starts going 150mph, the treadmill goes 150mph in the opposite direction. Repeat until explosion?

- M4H

wow.

 

[SSSnail]

Plane's thrust = Force.
Tread mill's speed = Opposite and equal force
Lift = 0

I just solved the freaking problem. Actually, I haven't seen the original problem, so if someone can be so kind and send me a link to the original problem, I'll take a look at it and will determine the absolutes. Once that is figured out, it's a matter of simple physics to see if the plane would indeed fly, or not. If we are bound by a certain constraints, then those would have to be taken into consideration for the calculation.

I've read arguments from both sides, and frankly, everyone want to be right and smart by breaking all sort boundaries to support their arguments with contradicting properties (zero frictions to the wheel... hahaha, on what freaking planet?), or my favorite, wheels that are capable of free rolling 280 mph unpowered (from how many vertical miles free fall?).

Anyways, send me the link to the original problem, and from that context, I'll tell you if it'll fly or not.

 

[MercenaryForHire]

Originally posted by: randay

Originally posted by: MercenaryForHire

Originally posted by: Amused
The plane will move forward relative to both the treadmill AND the air. The wheels merely have to spin at twice their normal takeoff speed (plane moving forard at 140 + treadmill moving back at 140 = 280 MPH to the wheels) to allow the plane to achive lift and take off.

Disclaimer - I never read the original question

Doesn't it state that the treadmill will always move as fast as the wheels? Therefore, at 140mph, the wheels and treadmill both move at 140mph. If the throttle on the plane gets increased in order to overcome that and get some horizontal velocity, and starts going 150mph, the treadmill goes 150mph in the opposite direction. Repeat until explosion?

- M4H

wow.

Please see bolded, italicized, and highlighted line above.

- M4H

 

[Tommouse]

I haven't read the whole thread, so forgive me, but its a bit big now and I have things to do

My understanding is that the treadmill matches the speed of the thrust of the plane, resulting in it being stationary, relative to the floor(not treadmill) or air. This would mean it's airspeed is 0, and with no airspeed there is no lift and no flight. For example think about a plane that is stationary and with a huge fan in front of it. It would eventually take off as there is enough airspeed but no actual speed, it all comes down to airspeed.

 

[randay]

Originally posted by: MercenaryForHire

Originally posted by: randay

Originally posted by: MercenaryForHire

Originally posted by: Amused
The plane will move forward relative to both the treadmill AND the air. The wheels merely have to spin at twice their normal takeoff speed (plane moving forard at 140 + treadmill moving back at 140 = 280 MPH to the wheels) to allow the plane to achive lift and take off.

Disclaimer - I never read the original question

Doesn't it state that the treadmill will always move as fast as the wheels? Therefore, at 140mph, the wheels and treadmill both move at 140mph. If the throttle on the plane gets increased in order to overcome that and get some horizontal velocity, and starts going 150mph, the treadmill goes 150mph in the opposite direction. Repeat until explosion?

- M4H

wow.

Please see bolded, italicized, and highlighted line above.

- M4H

Well the thread is actually a 3+ x repost and its 20 pages long and im tired of trying to explain anything. Now all I can do is stare in awe.

The last 16 pages are full of people continually trying to explain why it takes off and other new people entering thread and restating things from the first few pages about why it doesnt take off. Its amazing.