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# The planes engines
are pushing against the air to move the plane forward, it is not the wheels that provide the thrust. The wheels would just rotate faster than if the plane was travelling on a stationary runway. The plane would take off as normal.
(I helped save b3ta! Sammo, Mon 8 Jan 2007, 10:55, archived)
# so how would this help?
(I helped save b3ta! urbane legend i have known the inexorable sadness of pencils, Mon 8 Jan 2007, 13:34, archived)
# It doesnt help
It makes no diffrance
(I helped save b3ta! Letum Your Ad here £2.40, Mon 8 Jan 2007, 15:24, archived)
# There would be extra thrust needed
to counter the forces pulling against the wheels in the opposite direction.

If the treadmill was going the other way are you suggesting that would make no difference either?
(I helped save b3ta! .spanky is singing "PEANUTS!", Mon 8 Jan 2007, 16:00, archived)
# The treadmill
Will have no detectable difference to the take off.

The speed that the wheels are going round at is fairly irrelevant. Flight is based on airflow over the wings, not speed relative to the ground.

More effective would be a massive fan at the far end of the runway.
(fastandfurryous What was the question again?, Mon 8 Jan 2007, 16:37, archived)
# The speed relative to the ground does matter here,
because it's the same as the speed relative to the air.
The plane does move relative to the ground, and the air.

edit: aah, "the ground" meaning the surface of the treadmill, gotcha. That's irrelevant.
(I helped save b3ta! Newington, Mon 8 Jan 2007, 17:37, archived)
# but
if the plane was sat on the runway and they forgot to turn it off it'd end up wdged in a hanger.
(MrChimp previously Monsieur, Tue 9 Jan 2007, 1:43, archived)
# The speed relative to the ground
as in the actual ground, not the treadmill, is irrelevant too. The aircraft has to achieve a speed relative to the air to achieve flight.

Suppose the aircraft was a 747 with a rotate speed of 180kts. If there's a 30kts headwind, then it only needs to do 150kts relative to the runway for it to have 180kts of airflow over the wings, and thus fly.

This is why you always take off and land into wind.

It's also why an aircraft with a very low stall speed can fly backwards. A Tiger Moth has a stall of 35kts. If there's a 45kts wind down the runway it's entirely possible for it to have 40kts of airflow over the wings, but be moving backwards (relative to the ground) at 5kts.

/relative motion blog
(fastandfurryous What was the question again?, Tue 9 Jan 2007, 14:16, archived)
# The wheels wouldn't turn at all,
but the plane would move forwards and drag the treadmill round to match it. (So the treadmill in the animation is going the wrong way.)
(If the wheels and treadmill are both perfect, with no bearing friction and infinite friction between them.)
(I helped save b3ta! Newington, Mon 8 Jan 2007, 15:39, archived)
# It's not going the wrong way, it's illustrating a well known conundrum.
Have a read of www.straightdope.com/columns/060203.html for a concise explanation.
(I helped save b3ta! Paster of Muppets is an incredible screen name, Mon 8 Jan 2007, 16:35, archived)
# Yes, the conundrum is cool. I see that the plane definitely takes off.
I also thought that if the wheels and treadmill are 'perfect' (which they don't need to be) then the wheels don't spin, but the treadmill does, and it spins the other way than shown in this picture.

...which I now think is wrong, because there's no reason for only one of them to spin. They'd both spin, and both in the direction you'd expect, and the plane would still take off.
[I changed my mind again. The treadmill goes the wrong way.]


Thanks to tapeworm for introducing me to this!
(I helped save b3ta! Newington, Mon 8 Jan 2007, 17:20, archived)