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For those who are interested... [Oct. 12th, 2008|11:20 am]
John
An airplane on a treadmill *will* take off, because it's not the wheels that drive the plane forward.

Once the plane's propulsion method is pushing against the air, it moves forward in the air, and the wheels are just there to let it roll smoothly. (You don't want to drag a plane across the runway; it might scratch the paint!) If you tried to increase the speed of the treadmill, you'd make the wheels roll faster (air speed + treadmill speed), but you wouldn't slow the plane down significantly because the wheels aren't driving the plane, it's the push from the jets/propeller/whatever.

So the plane would move forward through the air, with some additional drag from the wheels, and eventually obtain enough airspeed to take off. (Herm. Assuming that the extra rotation on the wheels doesn't make the tires explode. But that's not the "real" question. :-) )

Now, if the wheels were powered, to throw the plane forward fast enough to let it take off, it would be a different story. The tires would be pushing against the treadmill, the treadmill would be rolling, the plane would stay in one place, and never gain airspeed.

This science lesson was brought to you by a long-haired weirdo who just felt like sharing; aren't you glad you have strange people on your friends list?
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Comments:
[User Picture]From: karenkay
2008-10-12 06:37 pm (UTC)
An airplane on a treadmill *will* take off, because it's not the wheels that drive the plane forward.

It would have to be a very small airplane, because most airplanes wouldn't fit on a treadmill.

:)
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[User Picture]From: jhetley
2008-10-12 06:56 pm (UTC)
Or really big treadmill?
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[User Picture]From: karenkay
2008-10-12 06:59 pm (UTC)
I would still fear the plane hanging up on the treadmill control panel.
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[User Picture]From: johnpalmer
2008-10-12 07:54 pm (UTC)
Well, not all treadmills have their controls on the front, and theoretical ones like this can have them anywhere they want to... even underground, where evil scientists who are trying to ground the world's air transport system can say "curses, foiled again!" never realizing that it's the simple laws of physics that are causing them problems.

Maybe that means I should call them "bad" scientists instead of "evil" ones.
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[User Picture]From: jhetley
2008-10-12 09:07 pm (UTC)
A really hot pilot ("right stuff") could handle it.
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[User Picture]From: anansi133
2008-10-12 08:26 pm (UTC)
When Mythbusters covered the question, they invented a kind of conveyer belt big enough to handle the airplane.
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[User Picture]From: karenkay
2008-10-12 08:44 pm (UTC)
Okay, this makes sense.
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[User Picture]From: jhetley
2008-10-12 06:56 pm (UTC)
I believe that technically, you aren't "pushing against the air" but working on throwing the exhaust gasses away as fast as you can. Action and equal-but-opposite reaction . . .

(Not a "rocket scientist" but willing to play nuisance on the Internet)
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[User Picture]From: johnpalmer
2008-10-12 07:53 pm (UTC)
I was thinking of propellers as well as jets, and that's why I was thinking "pushing against the air", but you're right... throwing mass backwards buys you thrust. (That's probably not scientifically or engineeringly accurate, but I think you know what I would have said if I was better educated :-).)
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[User Picture]From: wordweaverlynn
2008-10-12 07:52 pm (UTC)
I am fascinated.
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[User Picture]From: anansi133
2008-10-12 08:28 pm (UTC)
Well, yeah, of course! This is a lot like one of those shaggy dog math problems where they sneak a meaningless term into the equation and then invite the audience to find the missing dollar.

I didn't find the question interesting enough to think about that much. Now if we could examine this "Missing Mass" conundrum, I'd have attention for that.
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[User Picture]From: supergee
2008-10-13 12:18 am (UTC)
Very interesting. Thank you.
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