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Old January 30th, 2008, 05:55 PM   #151
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Apparently "Myth Busters" will be taking this little problem on so we'll finally get to see this setup in action. :-)

http://www.boingboing.net/2008/01/28...s-tackles.html

" the next episode of MythBusters (airing this Wednesday). It tackles the famous "plane on a conveyor belt problem," that has pitted brother against brother and friend against friend for years.

To get to the bottom of the thought-problem, Adam and Jamie used a real plane, in this case a 400-lb ultralight, and a large conveyor belt. Did the plane take off? You'll have to wait until Wednesday to find out, but Adam said even the pilot guessed wrong."
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Old January 30th, 2008, 07:15 PM   #152
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So, today's Wednesday.... a whole week to wait!

I would have thought that the plane would not take off, but since the airplane pilot guessed wrong.... who knows!
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Old January 30th, 2008, 07:20 PM   #153
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Several pilots on this thread have conflicting opinions. I'm a pilot, and I say it flies.
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Old January 30th, 2008, 07:43 PM   #154
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I figured they would get to this one at one point...... is that tonight....?
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Old January 30th, 2008, 07:59 PM   #155
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Watching it right now...here's what I've identified as a problem with this DVInfo thread:

The problem statement is incorrectly or ambiguously stated. The original problem statement (as far as I know):

Quote:
Imagine a plane is sitting on a massive conveyor belt, as wide and as long as a runway, and intends to take off. The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation.

Can the plane take off?
http://boards.straightdope.com/sdmb/...d.php?t=348452

Whereas the the way it is in this forum:

Quote:
If you have a large jet plane (747) sitting on a runway that was actually a giant conveyor belt (go with it). And there is also a device on the plane that communicates with the conveyor belt to tell it how fast the plane is traveling, which would then make the conveyor belt match the speed IN REVERSE.

Can the jet take off?
The difference is subtle but critical and I believe goes a long way to explain the vehement disagreement we have endured. The latter statement is ambiguous, leading to two very different interpretations.

I leave it to you to spot the difference!
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Old January 30th, 2008, 08:06 PM   #156
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I was one who said it wouldn't fly, but first test with came off showing it would, but I don't think they really matched speed with treadmill.
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Old January 30th, 2008, 08:22 PM   #157
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Did I miss it??? I thought it was next week! I assume it flew... VINDICATED!
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Old January 30th, 2008, 08:27 PM   #158
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Quote:
Originally Posted by Richard Alvarez View Post
Did I miss it??? I thought it was next week! I assume it flew... VINDICATED!
Yes, verily vindicated!

Though the way they did it was rather unscientific which doesn't suit my scientific (in)sensibilities but does suit my boys and their toys bent.

Oh - it was on at 9e, perhaps it will be on at 9p?
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Old January 30th, 2008, 08:35 PM   #159
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Cool it's on at eight pm here in California. Funny, they do a lot of their outdoor testing just up 101 from me, in the old Naval Yards.

I don't think the original statement here is 'wrong' or confusing. Even if you gave the treadmill a slight 'head start' - the plane would still accelerate independent of the speed of the treadmill.
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Old January 30th, 2008, 09:04 PM   #160
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I was hoping they'd get to this...did somebody here suggest it on their site, or was this just coincidence?

I have to agree that the question as posed in this thread is a bit confusing, only because of "And there is also a device on the plane that communicates with the conveyor belt to tell it how fast the plane is traveling". How fast the plane is traveling? That means it's moving. If it's moving forward fast enough, it can create the necessary lift to take off, so the entire point is moot, as you've just explained the thing is able to move. The more appropriate setup would be to match the speed of the wheels' rotation, as John pointed out, but that only changes the way the situation is stated, not the fundamental principles involved. The whole thing is difficult to imagine just from the question, as whether the belt matches the wheels or the body of the plane, it wouldn't have anything to match if there were not already motion, and once the plane gets moving, well, problem solved.

I think the biggest problem here is to get hung up, as I initially did, on the Bernoulli effect, and to focus on how wings generate lift, forgetting that you've already made the mistake of assuming the plane does not move forward. "Can a conveyor belt stop an aircraft from moving forward?" might be a better question, excluding of course helicopters and those pontoon-equipped dealies that land in water. Since the propulsion of the aircraft has absolutely, positively nothing to do with the wheels, I should say the answer is a definite 'no'. The wheels can spin as fast as they need to, the landing gear could snap off if it came to that, even skidding on its belly the thing would create lift if it had enough thrust behind it. I don't know if a jumbo jet is really built to overcome that kind of friction, even with four enormous engines, but you get the idea; unless this conveyor system is on the moon or underwater, there's plenty of air for the jets or propellors to send backward in the pursuit of thrust.
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Old January 30th, 2008, 09:25 PM   #161
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I think most people got hung up on the notion that wheels provide motive force for the aircraft's movement. The wings were not necessary for 'forward motion' - only for flight. You could just as easily say "If you put an airplane engine on a skateboard, and the treadmill moved in the opposite direction - would it move forward? The answer is still yes - the motive force is not connected to the ground or the wheels - it operates and applies thrust independent of wheel rotation speed.

Once its moving then the wings take over.

You could say "Moved in the opposite direction in response to wheel speed rotation" OR "Moved in the opposite direction in response to engine thrust" OR "Moved in the opposite direction in response to apparent motion as observed by a viewer off the treadmill" OR "Moved in the opposite direction in response to an airspeed indicator" OR "Moved in the opposite direction in response to a speedometer attached to the wheels" - The wheels provide no motive force, they are only there to eliminate (as much as possible) friction between the device and the ground.

EDIT - Man, its on and I think it's not the one. I must have missed an earlier showing.
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Old January 30th, 2008, 09:33 PM   #162
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Quote:
Originally Posted by Richard Alvarez View Post
EDIT - Man, its on and I think it's not the one. I must have missed an earlier showing.
They showed two episodes back-to-back here, the first at 8. The one of interest is the second one. Can't remember what the first one was about since I'd seen it before.
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Old January 30th, 2008, 09:35 PM   #163
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Hah! You're right they just showed the preview for it, two shows back to back.
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Old January 31st, 2008, 08:41 AM   #164
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Well I watched it last night, and it was fun to watch them deal with it. As smart as the guys are, sometimes they can be a little 'common sense' blind. It was obvious the treadmill was going to be too short for the model plane take off run for instance.

Still, good fun to see the myth busted.

The. Plane. Will. Fly.
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Old January 31st, 2008, 09:14 AM   #165
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Quote:
Originally Posted by Richard Alvarez View Post
...good fun to see the myth busted. The. Plane. Will. Fly.
Thanks for bringing this thread back to life and giving it proper closure, guys! Much appreciated,
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