An airplane on a treadmill: will it take off?

[ASB]

Is it a harrier ? Then it will.

[Menelaus]

Randall Munroe (xkcd) has an interesting and informed article on the subject...

http://blag.xkcd.com/2008/09/09/the-...amn-treadmill/

434 comments!

[Mich the Tester]

Is it a harrier ? Then it will.

Would it obliterate the treadmill first?

[Churchill]

Is it a harrier ? Then it will.

Ah but that is lift in the form of thrust from the Pegasus engine, not lift created by difference in air pressure created by the distance the air has to travel over the surface of a wing compared with that travelling under it.

[VectraMan]

The answer depends on how the question is interpreted. If the treadmill and plane are at rest wrt to each other (like a runner on a treadmill) and the question is will the plane generate lift (i.e. take off and fly away with a small increase in engine power) if the treadmill goes fast enough. Then the answer is no, there is no lift. If the plane can ignore its speed wrt the treadmill (unlike a runner on a treadmill except on people do the funniest things), in which case the treadmill is just a red herring except for a small amount of friction to overcome at the wheels, then the answer is yes.

No it isn't. The treadmill is always irrelevant. The real question is whether or not the aeroplane's engines are on, something which wasn't mentioned in the original post. The mistake is in thinking planes work like cars, or runners. They don't. Propulsion is nothing to do with the wheels.

I guess a plane on a treadmill with its brakes on would be moving the same direction as the treadmill, and if that was backwards it might take a bit longer for it to reach take off speed going forwards.

[Menelaus]

Would it obliterate the treadmill first?

Probably. The downblast from the nozzles on the Pegasus would be enough to make a bit of a mess of it, certainly.

[Churchill]

Probably. The downblast from the nozzles on the Pegasus would be enough to make a bit of a mess of it, certainly.

There is a story that when the Harrier was unveiled that a reporter asked if he could stand underneath it to take some photographs as it took off!

[original PM]

Vectra - if you replace the treadmill with a mythical treadmill which can be used to efficively keep the plane stationary then regardless of thrust generated by engines plane remains stationary wrt to the ground and the surrounding air thus no pressure differential around wings thus no lift.

but yes if you just put a plane on a rolling road/treadmill arrangement then it ignores it because as you say plane weels are not driven

[Churchill]

Vectra - if you replace the treadmill with a mythical treadmill which can be used to efficively keep the plane stationary then regardless of thrust generated by engines plane remains stationary wrt to the ground and the surrounding air thus no pressure differential around wings thus no lift.

but yes if you just put a plane on a rolling road/treadmill arrangement then it ignores it because as you say plane weels are not driven

You really are a project manager, aren't you?

Rearrange the following words...

"got f**king you clue a have not"

[Menelaus]

There is a story that when the Harrier was unveiled that a reporter asked if he could stand underneath it to take some photographs as it took off!

I'd heard that actually - I also saw a picture once from the late 1970s(?) of a Vulcan doing the flypast at a recruit passing off parade at RAF Swinderby which was so close to the top of the reviewing dais the reviewing officer lost his hat and assembled dignitaries etc were temporarily deafened. Big, big buggers.

Also: was at an airshow in Sussex in 2006(?) when the Harrier there was in the hover ~40ft AGL for waaaaaaaay longer than he was meant to, followed by a *crump* noise and a *pop* as it hit the deck and burst its tyres. I'd imagine a fair number of bottles of port would have to have been bought for the mess!