it can happen

1/27/2008 10:30:34 PM

1/27/2008 10:38:52 PM

Planes are not propelled forward by the wheels. They are propelled by the engines, which will be entirely unaffected by the treadmill's movement if the wheels spin freely. If you think the plane does not take off, you either do not understand basic physics or you do not understand the scenario as it is presented.

1/27/2008 11:19:39 PM

it takes off.

1/27/2008 11:21:35 PM

It will take off. I used to think it wouldn't, but after watching that video, and thinking about it more it will take off. Imagine it this way....

You have a friend wearing rollerskates and he is standing on one of the moving sidewalks. You are standing to the side on stationary ground. You have your hand against his back and the moving sidewalk is going 5mph. Right now he is not going anywhere. He is staying in one spot and the wheels of the skates are rotating. If you walk forward pushing him with your hand, he is going to move forward also. Imagine at this time you are the jet engines. If the sidewalk increases to 15mph you are still going to be able to move him forward with the same amount of energy and you are also free to push him as fast as you want no matter if the moving sidewalk was even going 100mph.


Does this make more sense to those who think the plane will not take off?

1/27/2008 11:31:12 PM

^This assumes a frictionless environment, but considering rolling friction is negligible in this situation, that is a very good analogy. Hopefully people will be convinced.

1/27/2008 11:33:38 PM

^^ i thought the myth was that a plane on a belt, without the engines on, would take off. Many people believe this to be true. They think somehow that the plane taking off is related to the movement of the ground underneath it, which of course is not true. It's related to the movement of the air around the wings.

If the myth is that a plane on a belt fires up its jets and attempts to take off, obviously that is true. The wheels on the plane are just there basically so the belly of the plane is not sitting on the ground, but the rotation of the wheels relative to the ground have nothing to do with the plane taking flight.

1/27/2008 11:56:06 PM

ok...let's break this one down

plane on a belt, without the engines on, would take off

plane...without engines on, would take off

yeah, that's true

1/27/2008 11:58:14 PM

yeah, exactly. I don't think this is really a good myth for "MythBusters". This myth, unlike many of the ones they do, has an extremely simple scientific and physical explanation. If people do not understand the principles involved, that's their problem. Performing an experiment in this case will do nothing for proving or disproving the myth. All they need to do is bring on an aerospace engineer to explain how planes fly. It's not like they're going to put a plane on a belt (without the engines one) and all of the sudden it starts floating and Jamie and Adam are like "wtf, we just rewrote the laws of physics"

1/28/2008 12:01:32 AM

yeah, i think it will be good to illustrate the myth properly

i asked my friend who is in aerospace and he said the plane wouldn't take off

1/28/2008 12:04:29 AM

treadmill is basically negligable impact and irrelevent



my offer still stands to place bets against anyone who thinks it won't take off. I'll bet $50, $500, or $5000...whatever you want. It will take off, and I will take your money. Let me know if you're interested in taking this bet, and we'll try to make some arrangements.

1/28/2008 12:06:57 AM

this guy makes an important point
http://www.straightdope.com/columns/060203.html

the wording of the question makes a big difference. If the riddle/question is worded like this:
"The conveyer belt is designed to exactly match the speed of the wheels at any given time, moving in the opposite direction of rotation."
then that's a paradoxical question. If you have thrust from the plane's jets, that statement can never be true.

Quote :

"This language leads to a paradox: If the plane moves forward at 5 MPH, then its wheels will do likewise, and the treadmill will go 5 MPH backward. But if the treadmill is going 5 MPH backward, then the wheels are really turning 10 MPH forward. But if the wheels are going 10 MPH forward . . . Soon the foolish have persuaded themselves that the treadmill must operate at infinite speed. Nonsense. The question thus stated asks the impossible -- simply put, that A = A + 5 -- and so cannot be framed in this way. Everything clear now? Maybe not. But believe this: The plane takes off."

1/28/2008 12:21:24 AM

http://www.brentroad.com/message_topic.aspx?topic=499574

There are tons of videos in this thread of PLANES PHYSICALLY MOVING FORWARD ON A TREADMILL.

And yes, tons of pilots say it will take off.

I myself am an aerospace engineer for the NATIONAL AERONAUTICS AND SPACE ADMINISTRATION. It will take off. Everyone keeps saying "It won't take off, no air is moving over the wings". Why do you say no air is moving over the wings?

1/28/2008 12:22:20 AM

Quote :

"Everyone keeps saying "It won't take off, no air is moving over the wings". Why do you say no air is moving over the wings?"

I think they are working the problem under the assumption that there is no friction, causing the plane's wheels to rotate atop the conveyor belt without moving the plane forward...

Anyway, since when did the problem ever involve a conveyor belt moving forward? I've ONLY heard it proposed as a conveyor belt moving in the opposite direction of the plane's thrust... in which case you either end up with a paradox (see someone's above post), or a plane that takes off because the belt does not influence the thrust of the engines.

[Edited on January 28, 2008 at 12:27 AM. Reason : .]

1/28/2008 12:26:51 AM

Quote :

"a plane that takes off because the belt does not influence the thrust of the engines."

Exactly.

1/28/2008 1:06:52 AM

...why does anybody give a shit?

1/28/2008 1:08:56 AM

Quote :

"i asked my friend who is in aerospace and he said the plane wouldn't take off "

Mills?

1/28/2008 1:13:04 AM

Quote :

"i thought the myth was that a plane on a belt, without the engines on, would take off. Many people believe this to be true. They think somehow that the plane taking off is related to the movement of the ground underneath it, which of course is not true. It's related to the movement of the air around the wings. "

I had never understood it to be with the engines off, and until know, I didn't know people thought it meant with engines off.

When I first heard the question, it was framed as a question on a test, not a "myth" so maybe that's why I didn't have this misunderstanding.

1/28/2008 2:02:08 AM

1/28/2008 3:06:09 AM

Quote :

"WHAT ABOUT A HELICOPTER ON A GIANT TURNTABLE????"

HAHAHAHAHAHAHAHAHA nice


you win the internet for today.


by the way,

Quote :

"This language leads to a paradox: If the plane moves forward at 5 MPH, then its wheels will do likewise, and the treadmill will go 5 MPH backward. But if the treadmill is going 5 MPH backward, then the wheels are really turning 10 MPH forward. But if the wheels are going 10 MPH forward . . . Soon the foolish have persuaded themselves that the treadmill must operate at infinite speed. Nonsense. The question thus stated asks the impossible -- simply put, that A = A + 5 -- and so cannot be framed in this way."

this is the argument of the 10th grade precal kid who thinks he's figured out math. if the plane is moving at 5mph forward, this means that the wheels are moving at 10mph. the argument stops there, why would the plane speed up just because the question is vague? stupid.

[Edited on January 28, 2008 at 3:22 AM. Reason : stupid.]

1/28/2008 3:18:10 AM

^He's saying that in the A = A+5 paradox (more accurately, A=2*A), A is the speed of the treadmill, not the speed of the wheels... turns out a lot people seem to misinterpreit this myth and the laws of physics such that they believe that the treadmill's speed will continuously double to compensate for the fact that the wheel's speed is twice that of the treadmill, and that the speed will increase infinitely to keep the plane from taking off.

Yes, it's stupid. But people think it.

1/28/2008 3:50:59 AM

I will not be convinced unless they use a real plane with a really big treadmill.

1/28/2008 4:08:28 AM

after watching the trailer for the show, it looks like the tarp will tear where it is attached to the pickup truck.

1/28/2008 6:15:08 AM

They should put this question on the FE.

1/28/2008 7:50:27 AM

I bet the guy who originally unleashed this scourge upon the Earth beats off every night thinking about how he mind-fucked so many people at the same time.

1/28/2008 8:43:34 AM

it still blows my mind that anyone with enough intelligence to post on the internet still thinks that, conceptually, the plane wouldn't take off


and how intelligent do you really have to be to post on the internet



my point exactly

1/28/2008 9:44:27 AM

Quote :

"I will not be convinced unless they use a real plane with a really big treadmill."

the scale doesn't matter, as long as the plane has wings that are capable of enough lift and an engine that is capable of enough thrust. Not to mention, it doesn't matter what it would take to convince you, since it's a simple matter of aerodynamics and physics. The outcome won't change based on scale or size or whether you believe in it enough.

as has been said a dozen times here already, the issue of the treadmill is irrelevant. It's just there to add confusion. It comes down to a fundamental difference between cars and planes, because most people try to think of this question in terms of how a car would act on a treadmill.

A car relies on its wheels to propel it forward, and nothing else. You can easily imagine the scenario where the wheels are on a belt or rollers, and as the wheels spin faster, the speed of the belt is turned up and the car goes nowhere, relative to the ground around it. You can see this in any bodyshop, actually, where they have rollers they can put a car on to test out the speedometer.

A plane, though, relies on its engines - via jet engines or propellers - to provide thrust through the air. The wheels are just free-spinning objects to help it move along the ground more easily. how fast the wheels are spinning in relation to the ground beneath them (the belt) or the ground surrounding the belt is irrelevant. As long as the engines are providing thrust against the surrounding air, the plane will take off regardless of what is happening to its wheels or the ground.


However, imagine for a second that you had a plane that acted more like a car, in that it did not have any jets or propellers, and instead had powered wheels, like a car that were capable of propelling the plane to the speed it needs to take off. It is easy to see what would happen in this case. It would take off down the runway, propelled by the powered wheels, then as soon as it reached take-off speed, it would start to lift, then the wheels would lose contact with the ground, therefore the propulsion would end and drag would slow the plane down immediately and it would fall back to the ground. Then the wheels would start to propel it forward again, it would lift slightly again, then fall, etc etc. If you imagine this, it is easy to see what would happen on a treadmill - the plane would act exactly like a car - as the wheels turned and the belt went backwards, the plane would just sit there, generating zero lift, just like a car on rollers. Take away the powered wheels and add jets or propellers, though, and you have a whole different ballgame.

1/28/2008 9:45:11 AM

Quote :

"WHAT ABOUT A HELICOPTER ON A GIANT TURNTABLE????"

lol




and the plane will not take off.

1/28/2008 9:50:09 AM

at this point I'm assuming anyone that says it won't take off is a troll

1/28/2008 9:53:02 AM

i think you'd be giving them too much credit.

1/28/2008 10:02:31 AM

Lol@people thinking that engines cause planes to take off.

Thats why when you hit 88 mph on the highway, your car takes flight and goes back in time to save a hot Teacher...right..RIGHT?

1/28/2008 10:07:07 AM

The myth as i understand it is that the treadmill is providing the same force on the wheels in one direction as the jet/prop provides force in the other direction.

If you want to see what happens go grab a toy car or train or a pair of roller skates. Put the skates on a treadmill going whatever speed and then put your hand on the back of the car/train/skates so that it stays still on the treadmill relative to yourself.

The force you are exerting on the car/train/skate works the same as the force of the jet/propeller on the plane. Friction of the belt on the wheels forces the plane/car/train/skate backwards. Your hand/jet/propeller is an opposing force in the opposite direction. if the plane does not move relative to the ground/air it wont take off.

1/28/2008 10:11:23 AM

Quote :

"the treadmill is providing the same force on the wheels in one direction as the jet/prop provides force in the other direction. "

yeah, but that's impossible, because the treadmill is exerting a force on free-moving wheels, and the jets/prop are providing a force on the air. The treadmill has no effect on the air around and behind the engines and wings, therefore has no effect on the thrust of the plane.

1/28/2008 10:16:20 AM

Quote :

"The force you are exerting on the car/train/skate works the same as the force of the jet/propeller on the plane. Friction of the belt on the wheels forces the plane/car/train/skate backwards. Your hand/jet/propeller is an opposing force in the opposite direction. if the plane does not move relative to the ground/air it wont take off."

fine, but that's not the myth. The myth is that a plane can't take off.
If you account for rolling friction and and the weight of the plane, then yes, there is a certain amount of trust that would be necessary to keep the plane in one place, otherwise it would roll backwards with the belt. So, turn the jets on "low" so the thrust matches the drag generated by the belt, and the plane will sit there in one place with the wheels free-spinning beneath it.

But after that, push the throttle and the plane will begin to move forward relative to the air around it. Push it more, and eventually it will pick up enough speed to take off, just like it would on a normal runway.

1/28/2008 10:20:43 AM

No that clearly isn't the myth as nobody is going to build a treadmill the length of an runway.

And no, the length of a treadmill isn't long enough to provide lift.

[Edited on January 28, 2008 at 10:23 AM. Reason : >.<]

1/28/2008 10:22:54 AM

^^yea but thats not the myth

The myth is that the treadmill is generating the same force as the engines in opposing directions.

If i have a plane on a treadmill and the treadmill is doing 5mph against me and i throttle up to mach2 of course im going to take off. That would be a fucking stupid myth.

[Edited on January 28, 2008 at 10:25 AM. Reason : .]

1/28/2008 10:23:45 AM

ok, well whatever the "real myth" is is irrelevant. The whole thing is a thought experiment anyway, and if the question is framed properly, there are definitively correct and incorrect answers to it.

1/28/2008 10:24:27 AM

Quote :

"The myth is that the treadmill is generating the same force as the engines in opposing directions."

which is impossible, because the treadmill is generating force against the wheels, and the plane engines are generating force against the air, which is completely decoupled from the treadmill and wheels.

whether the myth is true or not depends largely on how it is worded, and if it's worded such that the treadmill is generating the same force as the engines, or that the treadmill is moving the same speed in the opposite direction of the plane, then the whole myth is based on a false premise. In that case, it is impossible to say if the myth is true or false, because the basis of the myth itself is factually incorrect in and of itself.
Its like the fallacy where you ask someone "do you enjoy killing people?". That question presupposes the false premise that you do kill people, so no answer you give is "correct". If the airplane myth is built upon physical impossibilities, then if that myth is true or not is not relevant.

1/28/2008 10:42:09 AM

Quote :

"WHAT ABOUT A HELICOPTER ON A GIANT TURNTABLE????"

ftmfw



/thread

1/28/2008 10:50:15 AM

If I were I a high school physics teacher, I would put this on a test.


btw on that scaled test they were doing... I really don't think that treadmill they put it on is long enough for the plane to take off.

[Edited on January 28, 2008 at 11:20 AM. Reason : ]

1/28/2008 11:11:04 AM

Quote :

"it won't take off, why would anyone even try this? "

There must be lift generated by air flowing across the wings. The speed of the wheels have no relation to airspeed. Most small aircraft come up to full power with the brakes applied before setting off down the runway to takeoff. They do not leave the runway until they have built enough airspeed over the wings to create lift.

1/28/2008 11:28:04 AM

I seem to notice that everyone who says "It won't take off" either don't leave a valid explanation or don't respond when people refute their flawed logic.

1/28/2008 11:29:40 AM

i am not an engineer, i do not have a degree, i may one day finish my degree in business management... if it becomes financially smart homehow.

i like mythbusters, and i DVR it, and i'm sure i'll be watching this at some point this week. with the amount of dickbag know-it-alls on the internet, COMBINED with the fact that they love going above and beyond life-sized with their "mythbusting" then all i can comment on with certainty is that its gonna be big. and that no matter what there will still be unemployed know-it-alls saying that this and that were done wrong

but if i had to answer based ONLY on the opinions of people here. its lifting off. cause i'm a lot more inclined these days to go off credentials and life experience. if the guy that got in at nasa and all his friends say its going to go, and the guy who flies jets for a living says its gonna go, then its in my best interest to believe them. cause if they're the stupid ones, then i'm never flying again

1/28/2008 11:40:41 AM

Quote :

"I seem to notice that everyone who says "It won't take off" either don't leave a valid explanation or don't respond when people refute their flawed logic."

Quote :

" There must be lift generated by air flowing across the wings. The speed of the wheels have no relation to airspeed. Most small aircraft come up to full power with the brakes applied before setting off down the runway to takeoff. They do not leave the runway until they have built enough airspeed over the wings to create lift."

No wind over the wings = no lift = no flight. Doesnt get any easier than that.

[Edited on January 28, 2008 at 12:19 PM. Reason : ,]

1/28/2008 11:50:59 AM

Quote :

"the plane engines are generating force against the air, which is completely decoupled from the treadmill and wheels"

This would be true if there was no friction between the wheels and the treadmill.

[Edited on January 28, 2008 at 11:55 AM. Reason : or if it was a harrier]

1/28/2008 11:51:31 AM

Quote :

"If i have a plane on a treadmill and the treadmill is doing 5mph against me and i throttle up to mach2 of course im going to take off."

Engine speed irrelevant, Engines at full power still dont produce lift.

1/28/2008 11:56:50 AM

im just gonna argue that if you cant figure out the quote thing on tww then you probably shouldnt be in this debate

[Edited on January 28, 2008 at 12:04 PM. Reason : i skip words]

1/28/2008 12:03:58 PM

^^yes but with that force you'd overcome the treadmill easily and start moving.

[Edited on January 28, 2008 at 12:04 PM. Reason : .]

1/28/2008 12:04:16 PM

There is air going over the wings though. The plane is still moving forward. Say the treadmill had oil all over it and was completely frictionless. When it starts moving backwards, it is frictionless, so the plane stays still, right? So now the engines power up and the only force acting on the plane is the engines. If you take out the oil, it is the exact same situation because (in an ideal situation) you neglect the friction between the wheels and the treadmill.

1/28/2008 12:09:36 PM

Holy crap i cant believe people are still debating about this.

People are now to the point of arguing about the wording of the question, because it can be phrased incorrectly.

If i put you on roller skates, and strap a rocket to your ass, then put you on a treadmill, will you move forward?

Yes, you will (assuming the rocket is powerful enough to overcome the friction in the wheel bearings on the roller skates + some).

Same principle.

1/28/2008 12:09:41 PM