Airplane on a treadmill

[Scn64]

The Airplane on a Treadmill is a type of physics riddle that usually results in two groups of people taking different sides and calling each other idiots for hours at a time. None the less it’s a fun thought puzzle and worth taking a look at.

The Set Up:

Let’s say that we have a jet airplane (like a 747 for example) trying to take off on a giant runway sized treadmill. The treadmill, which turns in the opposite direction that the plane is facing, is capable of precisely matching the speed of the airplane. Here’s a visual to bring it all together (not drawn to scale obviously )

The Question: Can the airplane take off under these conditions?

 

[tonksy]

Neil Boortz discussed this for hours the other day. His verdict was yes and I agree with the physics of his arguement...basically the extra thrust from the force of the lifting air overrides the inertia of the airplane...I dunno if I am wording that correctly but to dumb it down:
All that air kicked up by the engines lifts the plane off the treadmill and away it goes.

 

[Dave]

but how does the plane get lift if there is no air flowing over the wing surface? if the treadmill is matching the planes speed, it is essentially standing still.

 

[tonksy]

The engines are running. That creates air flow through the intake....and if the plane is a prop job then it is definitely a no brainer.

 

[Luis G]

I'm with Dave, unless the airplane gets the right speed it will not fly. It would be like turning on the turbines and having some guys spinning the airplane's wheels while it is standing still. Airplanes are not helicopters.

Unless of course, the treadmill is going really fast and then stops, making the airplane actually move of its position.

 

[unclehobart]

I say its a bunch of croc for the same reason that the former Mr. Spot said. There is no airflow over the wing surfaces. There is no pressure differential lift, nor is there any impact lift. Just because the wheels are going spin-spin-spin, it simply doesn't mean anything. If the wheels going spin-spin-spin meant anything, then cars would be flying all over the place once they hit 100mph.

Air may be flowing through the intake, but its not gathering compression with speed. A prop and a jet can develop pulling power and accelerate... but the treadmill is keeping up with that pull. It still essentialy means zero windflow over the wings.

 

[unclehobart]

http://en.wikipedia.org/wiki/Lift_(force)

 

[tonksy]

Guys...this is not a car. Aircraft engine create force and lift. Lift will be what aids it in take off in this case. For example...an aircraft carrier is moving quickly yet an aircraft can take off from it...and before you say that they have catapult assistance this is not true in all cases - just in cases where an aircrafts weight requires more accumulative force for take off.

 

[BeardofPants]

I'm thinking ... not. Unless as said earlier, the treadmill stops. The key thing is that the treadmill is MATCHING the speed of the plane.

 

[chcr]

Yup, engine thrust relates to flight only in that it propels the plane through the air. If there's no airflow over (and under) the wing, there's no lift. There are vehicles that lift by thrust alone, they're called rockets. Why do you suppose airplanes have wings if they don't need them. Wings and the lift they generate are the only reason an airplane can fly. Even the propellers on a prop plane generate far less wind over the wing than required for takeoff. Hence runways.

You could approach the speed of sound, hell the speed of light but you still wouldn't be generating lift and it's the lift that's important.

 

[chcr]

That wasn't clear enough. lift is not created under the wing. The shape of the wing makes air flow over the top of the wing faster than it flows under the bottom of the wing. This creates a net vacuum above the wing, generating lift. Look it up anywhere. Boortz is wrong. It's how an airplane works and it's the only way it will work, speed through the air. Sorry to disappoint.

 

[unclehobart]

But, as a cavet to what Tonks said, there are a good many aircraft built to piss that can self generate either rocket grade spontaneous force if required (F-15), a specific designed VTOL (Harrier), or a prop plane of insane overforce dragging so much air over the wing that it can make an unstable bunny hop off of the treadmill and possibly shoot forward enough to make a stable air envelope and generate enough lift to make it up.

Also take into account that a treadmill moving at 100mph would be generating a certain amount of airspeed to generate temp winglift or feed a jet engine into its higher performance windows.

 

[unclehobart]

Yup, engine thrust relates to flight only in that it propels the plane through the air. If there's no airflow over (and under) the wing, there's no lift. There are vehicles that lift by thrust alone, they're called rockets. Why do you suppose airplanes have wings if they don't need them. Wings and the lift they generate are the only reason an airplane can fly. Even the propellers on a prop plane generate far less wind over the wing than required for takeoff. Hence runways.

You could approach the speed of sound, hell the speed of light but you still wouldn't be generating lift and it's the lift that's important.

Navy A-7's essentially were rockets... the proverbial proof that bricks can fly. For them, wings are only good to make it turn where you need it to go.

 

[K62]

Guys...this is not a car. Aircraft engine create force and lift. Lift will be what aids it in take off in this case. For example...an aircraft carrier is moving quickly yet an aircraft can take off from it...and before you say that they have catapult assistance this is not true in all cases - just in cases where an aircrafts weight requires more accumulative force for take off.

Hmm I have to disagree here. Aircraft engines do notcreate lift. They create thrust. The thrust propels the aircraft forward causing air to flow around the wings to create lift. This is why airplanes have a stalling speed when they are not moving fast enough for the air flowing around the wings to generate enough lift. No enough air, not enough lift, no flyey.

Also why airplanes take off into the wind.

 

[tonksy]

But, as a cavet to what Tonks said, there are a good many aircraft built to piss that can self generate either rocket grade spontaneous force if required (F-15), a specific designed VTOL (Harrier), or a prop plane of insane overforce dragging so much air over the wing that it can make an unstable bunny hop off of the treadmill and possibly shoot forward enough to make a stable air envelope and generate enough lift to make it up.

Also take into account that a treadmill moving at 100mph would be generating a certain amount of airspeed to generate temp winglift or feed a jet engine into its higher performance windows.

When I was stationed at a squadron (VT-10) in the hangar next to the Blue Angel's we used to come running outside to watch Fat Albert take off (their cargo plane). Neatest thing to watch this big heavy motherfucker take off vertical using just a small patch of runway.

 

[unclehobart]

That wasn't clear enough. lift is not created under the wing. The shape of the wing makes air flow over the top of the wing faster than it flows under the bottom of the wing. This creates a net vacuum above the wing, generating lift. Look it up anywhere. Boortz is wrong. It's how an airplane works and it's the only way it will work, speed through the air. Sorry to disappoint.

You speak only of pressure differential lift. The treadmill wind would generate a buffer of impact lift to get its butt about 10 feet off the ground where it can hopefully jut forward enough to bring all aspects of lift into the game.

To me, it actually has a small bit of plausibility... but it sure as heck isnt stable and is most likely to crash and burn. An aircraft need to slipstream of air to keep its nose pointed in the right direction or else youre looking at a stall and possible tumble.

 

[tonksy]

Hmm I have to disagree here. Aircraft engines do notcreate lift. They create thrust. The thrust propels the aircraft forward causing air to flow around the wings to create lift. This is why airplanes have a stalling speed when they are not moving fast enough for the air flowing around the wings to generate enough lift. No enough air, not enough lift, no flyey.

Also why airplanes take off into the wind.

I think you are speaking only of larger aircraft. A lot of smaller planes (and vertical assist aircraft) create enough airflow through the engines to create lift.

 

[K62]

"an aircraft carrier is moving quickly yet an aircraft can take off from it"


When aircraft take off from carriers, they will sail into the wind. The reason for this is to increase the apparent airspeed for more lift..

 

[Dave]

A lot of smaller planes (and vertical assist aircraft) create enough airflow through the engines to create lift.

thats still just thrust.

 

[tonksy]

Okay...so maybe the treadmill is moving into the wind

I am not saying this is safe...I'm not saying this is a good idea. I just think it could happen with certain types of aircraft.