Mythbusters will finally test...

[photon]

Originally Posted by burn_this_city

It would work then... Similar to a glider being winched in the air.. If they locked the wheel of the plane and the treadmill slowly gained speed it should work..

The treadmill is going in the opposite direction.

[Frequitude]

Forward motion is caused by the propeller pushing air, not wheels turning against the ground like a car. The plane should take off if its engine is powerful enough.

Think Harrier jet.

[Locke]

I dont see this working just based on the principle of lift.

Air going under the wings provides lift, if the thing stays stationary then no lift is provided and it doesnt get off the ground.

Air speed and all that jazz.

Unless the propeller can generate enough all by itself.

[photon]

Originally Posted by Locke

I dont see this working just based on the principle of lift.

Air going under the wings provides lift, if the thing stays stationary then no lift is provided and it doesnt get off the ground.

Everything you say is right, except why would it stay stationary?

Unless the propeller can generate enough all by itself.

The propeller doesn't generate lift, but it does generate thrust

[FlamesAllTheWay]

Originally Posted by photon

Everything you say is right, except why would it stay stationary?

Well the plane itself will seem like it's moving, the instruments will all read a certain speed, wheels will be a turning, etc. That's all relative to the treadmill though. Relative to everything else, the plane is just sitting there (ideally, it'll probably move around a bit). I think it'd be like me running on a treadmill into the wind. I could be going as fast as I wanted on the treadmill and I'd still be going into the wind as though I was just standing there.

[Bobblehead]

But the wheels don't pull the plane forward, there is no gearing for that (only brakes, for stopping). the propeller will pull the plane forward through the air and generate airspeed until the wings create enough lift and it takes off. It doesn't matter if a treadmill underneath is causing the wheels to think they are going twice as fast as a plane, or not moving at all. The treadmill should be irrelevant.

Heck, remove the wheels entirely, get the treadmill to carry the plane to takeoff speed and it will still fly (although landing would be tricky).

[Locke]

Originally Posted by photon

Everything you say is right, except why would it stay stationary?

The propeller doesn't generate lift, but it does generate thrust

Right, but if the plane is going forwards, on a conveyor going backwards then its stationary assuming both speeds are equal right?

And yeah, the propeller generates thrust, but it also moves air from front to back for thrust, that still moves a little air under the wings, but hardly enough to lift the plane right?

[foofighter15]

I think before we can reach a decision we need to know what the purpose of the treadmill is. Is it to be the length of the plane, and the plane be stationary until take off...or is it going to be half a runway long and go at half the speed as the plane which then creates a shorter runway, and less space needed for the plane to take off

[worth]

edit, nevermind, misunderstood

[BlackArcher101]

It's impossible for the plane to stay stationary or go backwards.

Most people are thinking about this the wrong way, ie if the speed of the treadmill matches the wheel speed, then it will stay put. WRONG. If the plane's acceleration came from the wheels, such as a car, this would be true. However, thankfully it doesn't. Instead it's from thrust produced by the engines. This thrust will still move the plane forward and even if the treadmill matches the wheel speed (which by the way is creating the wheel speed) it will still take off since air is moving over the wings. Essentially, the only thing that will happen is the tire speed will be 2x faster than normal and the takeoff roll (distance) will be slightly longer due to extra rolling friction. This rolling friction is miniscule compared to the thrust of an engine.

If SOMEHOW mythbusters proves this myth debunked, then sadly their experiment was not set up correctly. It's simply physics, draw a force diagram if you remember how.

Think about it this way... a moving treadmill is to cars as is a headwind to aircraft. Wind is what can prevent an aircraft from moving, not the ground moving.

[Frequitude]

Is it a treadmill like in the gym, i.e. it is externally driven backward? Or just free-spinning like it were on ball bearings?

[BlackArcher101]

Originally Posted by FlamesAllTheWay

Well the plane itself will seem like it's moving, the instruments will all read a certain speed, wheels will be a turning, etc. That's all relative to the treadmill though. Relative to everything else, the plane is just sitting there (ideally, it'll probably move around a bit). I think it'd be like me running on a treadmill into the wind. I could be going as fast as I wanted on the treadmill and I'd still be going into the wind as though I was just standing there.

A planes instruments are relative to airspeed, not treadmill.

[photon]

Originally Posted by FlamesAllTheWay

That's all relative to the treadmill though. Relative to everything else, the plane is just sitting there (ideally, it'll probably move around a bit).

Why will it be relative to the treadmill though?

[photon]

Originally Posted by Locke

Right, but if the plane is going forwards, on a conveyor going backwards then its stationary assuming both speeds are equal right?

That's the assumption which gets people in this. Just because the conveyor goes backwards doesn't mean that will counteract the forward thrust of the engines.

And yeah, the propeller generates thrust, but it also moves air from front to back for thrust, that still moves a little air under the wings, but hardly enough to lift the plane right?

The thrust will push the airplane forward regardless of what the wheels are doing (assuming that there isn't enough friction to flip the plane or something like that).

[photon]

Originally Posted by foofighter15

I think before we can reach a decision we need to know what the purpose of the treadmill is. Is it to be the length of the plane, and the plane be stationary until take off...or is it going to be half a runway long and go at half the speed as the plane which then creates a shorter runway, and less space needed for the plane to take off

It's like a treadmill where it loops around so it's infinitely long.

And a plane can't be stationary until it takes off, unless it's got an engine that provides lift instead of wings (like a helicopter or harrier jet).

[photon]

Originally Posted by Frequitude

Is it a treadmill like in the gym, i.e. it is externally driven backward? Or just free-spinning like it were on ball bearings?

Like the gym, driven backwards.

[kdoir345]

Originally Posted by photon

Like the gym, driven backwards.

and how fast is the belt being driven, or did i miss something?

Because the plane shouldnt move until the propeller generates enough of a force to counter what the belt is doing to the plane. Say what you will about the wheels not driving the plane, but there is still going to be an element of friction there that the wheels cant over come completly

[BlackArcher101]

Originally Posted by kdoir345

and how fast is the belt being driven, or did i miss something?

Because the plane shouldnt move until the propeller generates enough of a force to counter what the belt is doing to the plane. Say what you will about the wheels not driving the plane, but there is still going to be an element of friction there that the wheels cant over come completly

Look at it this way... a float plane has a lot more friction on takeoff than the wheels will in this experiment. Wheels have bearings to avoid friction and even at 300 knots ground speed the friction will be negligible.

[Sparks]

I think the plane will be able to take off. The weight of the plane on its wheels will definitely make it difficult for the plane to get going, but if the engines are powerful enough, and it can generate enough lift to counteract this force, it should be able to accellerate fast enough to take off. I vote yes.

[kdoir345]

Originally Posted by BlackArcher101

Look at it this way... a float plane has a lot more friction on takeoff than the wheels will in this experiment. Wheels have bearings to avoid friction and even at 300 knots ground speed the friction will be negligible.

But what im saying is that will the belt not play any role in this whatsoever.

Would it not be like a racecar in a wind tunnel. They set those cars on belts and run them as if they were running full speed but they still have to generate the wind from a fan to get the realistic areodynamic info from the car. Does the forward motion of the plane not do anything, because if it is still does that not mean that there is no air speed?