plane on the treadmill

[Scotty]

A plane is standing on a runway that can move (like a giant conveyor
belt). 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).

Will the plane be able to take off?

[SilverSpoon]

So the plane is just in one spot the entire time?

[Scotty]

ya.

[SilverSpoon]

I don't think the rotation of its wheels will make it fly.

[Bill5461]

It might lose weight though

[PushMyButtons]

uhhhh why would anybody do this?

[Scotty]

Maybe the pilots got bored.

[Val]

I think this is more a logical question than in the practice.

[Blackmask]

This has come up before and it was insisted that the plane would take off. The idea being that the engines don't drive the wheels like a car, the wheels are just there to create a "frictionless" surface.

Despite all the explanation that was given, and a very questionable video simulation to demonstrate, I still don't see the plane taking off. The wheels are in contact with the ground and if the point of contact moves backwards then I don't see how the plane is going to move forward.

[MSFixR]

No the plane can not become airborne because it is not moving relative to the air around it only relative to the conveyer. It is the movement of the air over the surfaces of the wing that creates lift and hence flight.

[Blackmask]

That's how I see it, but there's others who disagree. I wonder if Vinny is still around to explain the why the plane will take off side.

The previous discussion in case anyone wants to read it. In the end there was still no agreement.

[Samson The Cat]

Yes, this topic came up before.

And there are more ways to interpret that line:

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).

1. The plane will move, just the belt will move in the other direction:
The plane will take off with the wheels will running at double speed.

2. The belt is designed, so that plane doesn't move: There's a fallacy in the question alone, unless, we want to transform all of the plane's energy, that it would normally use for acceleration into ratatory energy of the wheels. The converyer belt would have to accelerate extremly fast up to a point, where the tires blow to avoid the plane from moving.

[Samson The Cat]

Despite all the explanation that was given, and a very questionable video simulation to demonstrate

I'd rather watch a plane landing on a field.

The IL-62 rules! You don't to try doing that with a Boeing or an Airbus and their small wheels.

[open32]

You need forward motion to get lift. You get lift by wind under the wings and flaps, for for that you need speed.


I didnt get it untill I read Vinny's answer and the treadmill example.

if the point of contact moves backwards then I don't see how the plane is going to move forward.

I think it would have to be assumed that the wheels will spin in place and not push the plane backwards no matter how fast the conveyor moves.

[Blackmask]

This problem is a lot easier to consider in reverse. If you run a treadmill with a plane on it, then the wheels won't just spin underneath, the plane will move with the belt until it is thrown into a crumpled mess of metal at the back.

To avoid destroying the plane in such a fashion the plane needs to have a forward force on it to make it move at the same speed that the belt is trying to move it backwards.

To move the plane forward on the treadmill, which is needed to create the air flow, then it needs to be moving faster than the tread mill. The problem is "This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same".

[MSFixR]

It doesn't matter how fast or slow the plane/conveyer is moving. What matters is the plane's velocity relative to the air. Movement of air over the wing's surface creates lift due to unequal air pressure between the top and bottom of the wing. The top of the wing is curved more than the bottom, therefore the air has to travel a longer distance over it and hence is less dense creating an area of low pressure.

[open32]

If you run a treadmill with a plane on it, then the wheels won't just spin underneath, the plane will move with the belt until it is thrown into a crumpled mess of metal at the back.

How much force would be required to make the wheels spin in place rather then the whole plan moving backwards.

I dont know my physics well enough to know if this is true:
With it being such a heavy object, and the wheels very low friction, would the force required to make the wheels spin and the plane not movie be less.

Like the treadmill example, if you where standing on it with shoes, held the handlebars and turned it on, it would require a lot of force to prevent you from flying backwards.

Now with wheels on, rollerblades, all you would have to do is practically touch the handlebars with you pointer fingers and you would spin in place. Almost no force required at all.

[MSFixR]

Originally Posted by open32

How much force would be required to make the wheels spin in place rather then the whole plan moving backwards.

I dont know my physics well enough to know if this is true:
With it being such a heavy object, and the wheels very low friction, would the force required to make the wheels spin and the plane not movie be less.

Like the treadmill example, if you where standing on it with shoes, held the handlebars and turned it on, it would require a lot of force to prevent you from flying backwards.

Now with wheels on, rollerblades, all you would have to do is practically touch the handlebars with you pointer fingers and you would spin in place. Almost no force required at all.

True, but you need to overcome the initial friction of getting the wheels to turn. Once that is done then only a small amount of thrust, presumably from the engines would be needed to keep the plane moving in a direction opposite to that of the treadmill belt.

However the original question was "Will the plane be able to take off?" and the answer is still no.

[open32]

Why no, if the wheels where turning, the plane could still be moving forward. The wheels wuld just be be rolling backwards at a greater speed.

No lift, no flying. Simple.

Layman's terms: same speed forwards and backwards, you won't go anywhere. Unless you're a duck. Flap the wings-- !! !! we have liftoff.