Will it Fly?

[Alleya]

This is almost as dumb as the "a truck full of birds becomes magically lighter when all the birds fly at once" crap.

Mythbusters did a good job in busting this one.

I know another Mythbuster who busted this myth about 320 years before Jamie and Adam.

http://www.crystalinks.com/newton.jpg

[Jotaru]

.a treadmill doesnt apply much force against an object with wheels though,it just spins them faster.

This is the general idea; if the power is supplied through the wheels, as in the case of a car, it would indeed not move. However, with an outside force, it turns into a simple problem of force vs. resistance... the force in this case is the thrust of the turbofan engines, and the resistance is just the wheels spinning at twice whatever speed the plane is moving at, or the speed of the plane + the equal and opposite speed of the treadmill. As stated, frictional force on wheels with bearings allowed to spin freely is minimal.

[Skyylya]

.a treadmill doesnt apply much force against an object with wheels though,it just spins them faster.

This is the general idea; if the power is supplied through the wheels, as in the case of a car, it would indeed not move. However, with an outside force, it turns into a simple problem of force vs. resistance... the force in this case is the thrust of the turbofan engines, and the resistance is just the wheels spinning at twice whatever speed the plane is moving at, or the speed of the plane + the equal and opposite speed of the treadmill. As stated, frictional force on wheels with bearings allowed to spin freely is minimal.

I see exactly what you're saying in your previous post about the force being supplied by the engine and not the wheels, but the whole idea is still ludicrous in itself. Because the treadmill is really inconsequential. It's akin to if you were running on the treadmill and essentially going nowhere and I came up and pushed you from behind. Did you move forward off the treadmill, yes, but not from your own momentum of the legs but from me pushing you, similar to the process of a jet engine, it pushes the plane.

If a plane were sitting on a treadmill with it's jet's off and wheel's turning due to the treadmill running below it, nothing would happen it would sit still. If you then turned on the jets the plane would no longer be on the treadmill, regardless of the wheels turning similar to if i pushed you while running on it. So no, a plane cannot take off while it is on a treadmill, because any time you apply the jet pressure the treadmill would become inconsequential and the plane would then be taking off due to it's forward momentum and actual forward movement.

[Venture]

I know another Mythbuster who busted this myth about 320 years before Jamie and Adam.

http://www.crystalinks.com/newton.jpg

It would have been more entertaining for it to be busted by Isaac Newton, if we got to watch him get hit on the head by a apple on Discovery channel.

[divisortheory]

It's akin to if you were running on the treadmill and essentially going nowhere and I came up and pushed you from behind. Did you move forward off the treadmill, yes, but not from your own momentum of the legs but from me pushing you, similar to the process of a jet engine, it pushes the plane.

Not saying you're wrong because like I said I'm bad at Physics, but was my explanation wrong above that showed that the plane would still be moving forward? Your entire argument is based around the idea that the plane is stationary.

[Skyylya]

I don't think you're necessarily wrong, it's just that the example of a plane on a treadmill is too flawed to really give a serious discussion because the treadmill is completely inconsequential in regards to the movement of the plane.

Implying that the treadmill has counteracceleration to the planes forward acceleration would imply that anything is actually moving in regards to the wheelbase. The concept of a treadmill is to restrict forward movement while still applying force. The problem with this is that a planes forward movement has absolutely nothing to do with it's connection at the base where the treadmill is.

The only way for a plane to maintain it's position on a treadmill is if the jets of the plane are not pushing the plane forward. It is completely separate. My example of him running on the treadmill and me pushing him is the same. He can be running 100 mph on a treadmill using all the force of his body to try and accelerate but is not able to produce forward momentum. If i were to then push him even a little, he would go flying off the treadmill. If you put a plane on a treadmill and started it running at any speed the plane would sit still, grounded because all of the acceleration is taking place at the base, which has nothing to do with a planes ability to fly. If the planes jets were then turned on, even a little bit, the plane would go flying forward off the treadmill (not flying as in the air, but move forward) because it is being pushed by a separate mechanism that provides force not at the wheelbase and therefore has nothing to do with the wheels being turned by the treadmill.

A better discussion would be, if you tied the rear of a plane to something stationary to restrict it's forward movement but still allow the jets to thrust the plane forward would it fly but not be able to move forward.

[Jotaru]

The concept of a treadmill is to restrict forward movement while still applying force. The problem with this is that a planes forward movement has absolutely nothing to do with it's connection at the base where the treadmill is.

You're right, and that's exactly the point Many many people feel that isn't the case however and that the plane will not move, and that it won't generate lift etc etc. That's why I was bleh at the first answers trying to tell me how lift works... I understand that air has to move over the wings, that's why you have to think outside the box a bit to figure this one out The Treadmill is just a diversion, think of it as if instead of a treadmill, you were taking off on ice. Same thing, it will accelerate, and THEN air will be going over the wings (I didn't forget about you, first few posters! You were right, in a way, but not thinking it all the way through is all, which is why I urged you to think about it more That is why I was pretty stubborn about this not just being a simple 'no need lift etc lawl' problem.)

The actual problem WASN'T "Can a plane take off without moving" - it is a pseudo-trick question, formed in such a way to make people think critically. It is exactly the point for someone to say 'Hey, the treadmill is inconsequential'. Thus, continue your thinking Skylaa - if it were not a treadmill, just a runway that 'acted' as a treadmill (i.e. long enough for a plane to takeoff on) you can see that it would indeed take off. The question wasn't meant to be posed as 'If a plane is held stationary, can increasing wheelspeed make it fly' - that is why it was posed as it was Its a mixture of a critical thinking problem and sort of a trick question if you don't understand the question fully, which is quite easy because people aren't sure if the original poster means 'If it can't move forward' or 'Can it move forward enough to fly under these situations'

To the people above who instantly said noway, GTFO, please reread that last paragraph, as it is very important to understand why I said what I did earlier. Never was it stated that I intended the plane to not move - that was part of the overall question itself.

[Skyylya]

But still, a plane cannot fly while it is on a treadmill, because the only way for a plane to maintain it's position on a treadmill is to not apply force through the jet engines.

As soon as jet force was applied the plane would move forward off the treadmill, before ever gaining enough acceleration/speed to fly.

[Jotaru]

Hm... But original question states, its not a treadmill, its a full-length runway, just one with a treadmill effect. I see what you are saying however. Just forward that to a full-length runway situation.

Edit: The picture was a distraction, a poorly chosen one at that. Kinda just chose it to kinda relay the situation, but I think people take it too literally. Someone in another forum stated it couldn't take off cuz it couldn't fit through the handlebars, lol; ; The picture is just for looks and a very basic outline of whats going on, the runway is full size.

[Skyylya]

The size of the treadmill is equally irrelevant to the fact that it's there in the first place. Since there is absolutely no connection between the wheel's and the planes ability to fly. The fact that the treadmill's direction is counter to the planes direction is no different than if the ground were not moving at all.

Given the concept of a normal treadmill where it's size is relative to the object on it, my original point stands. If you want to expand the treadmill to an unreasonable size then you could say anything you want really. Why not rap the treadmill around the whole planet then you could say that a plane is always able to fly on one.

[Jotaru]

As soon as jet force was applied the plane would move forward off the treadmill, before ever gaining enough acceleration/speed

to fly.

I guess my confusion stems from what I perceive to be a contradiction.. You're saying the plane could accelerate on the treadmill, but would jump right off so couldn't fly... so then make it longer... but then you say that it... still could not fly, due to the ground having no effect on the plane? That would be the reason that it DOES fly.. not sure what you're saying is all. As long as it has the potential to accelerate, it will take off eventually, if it is long enough (or if it transitions onto a regular surface after a certain distance, etc) due to it eventually accelerating past the point where it receives sufficient lift.

[Skyylya]

As soon as jet force was applied the plane would move forward off the treadmill, before ever gaining enough acceleration/speed

to fly.

I guess my confusion stems from what I perceive to be a contradiction.. You're saying the plane could accelerate on the treadmill, but would jump right off so couldn't fly... so then make it longer... but then you say that it... still could not fly, due to the ground having no effect on the plane? That would be the reason that it DOES fly.. not sure what you're saying is all. As long as it has the potential to accelerate, it will take off eventually, if it is long enough (or if it transitions onto a regular surface after a certain distance, etc) due to it eventually accelerating past the point where it receives sufficient lift.

I think I explain this in my last post. Given the concept of a standard treadmill which would be relative to the size of the plane, what I'm saying still is valid. The plane would move off the treadmill long before gaining the velocity to actually fly and therefore could not take off and fly while on a treadmill.

If you want to extend the length of the treadmill then you can really say anything you want in regards to whether or not it can fly on the treadmill since the planes ability to fly has nothing to do with the treadmill at all anyway.


saying that a plane can fly on a treadmill implies that it can stay stationary while the jets are providing thrust which just is not the case, again assuming that the general concept of a treadmill is maintained and not expanded in length to suit your argument.

[Osede]

The concept of a treadmill is to restrict forward movement while still applying force. The problem with this is that a planes forward movement has absolutely nothing to do with it's connection at the base where the treadmill is.

You're right, and that's exactly the point Many many people feel that isn't the case however and that the plane will not move, and that it won't generate lift etc etc. That's why I was bleh at the first answers trying to tell me how lift works... I understand that air has to move over the wings, that's why you have to think outside the box a bit to figure this one out The Treadmill is just a diversion, think of it as if instead of a treadmill, you were taking off on ice. Same thing, it will accelerate, and THEN air will be going over the wings (I didn't forget about you, first few posters! You were right, in a way, but not thinking it all the way through is all, which is why I urged you to think about it more That is why I was pretty stubborn about this not just being a simple 'no need lift etc lawl' problem.)

The actual problem WASN'T "Can a plane take off without moving" - it is a pseudo-trick question, formed in such a way to make people think critically. It is exactly the point for someone to say 'Hey, the treadmill is inconsequential'. Thus, continue your thinking Skylaa - if it were not a treadmill, just a runway that 'acted' as a treadmill (i.e. long enough for a plane to takeoff on) you can see that it would indeed take off. The question wasn't meant to be posed as 'If a plane is held stationary, can increasing wheelspeed make it fly' - that is why it was posed as it was Its a mixture of a critical thinking problem and sort of a trick question if you don't understand the question fully, which is quite easy because people aren't sure if the original poster means 'If it can't move forward' or 'Can it move forward enough to fly under these situations'

To the people above who instantly said noway, GTFO, please reread that last paragraph, as it is very important to understand why I said what I did earlier. Never was it stated that I intended the plane to not move - that was part of the overall question itself.

answer still no. Forget about the treadmill. you forgot the relative velocity between the aircraft and a specific position.

let say:

<---threadmill direction

aircraft ---> moving direction
--A-----------------B-------------------------C-----------------------------D

let the aircraft initial position at "A". So, when the trust applied by engine and the aircraft start moving, but at the same time, the threadmill also apply the same velocity at the opposite direction. So in the end, the aircraft still stay at position "A", and the relative velocity of aircraft respect to point "A" is zero. Or assume the controller so the threadmill got .5sec delay, still the relative velocity of the aircraft respect to point "A" still very small. (OP said that there is no control error)

so, does airflow occur? No.

no airflow = no life = no take off.


oh, the only condition it might take off if assume the controller for threadmill is at least 1 sec delay. And the aircraft got 140mph/s (or 140km/hr/s is the require take off speed? i've forgot ; . acceleration.

[Skyylya]

The concept of a treadmill is to restrict forward movement while still applying force. The problem with this is that a planes forward movement has absolutely nothing to do with it's connection at the base where the treadmill is.

You're right, and that's exactly the point Many many people feel that isn't the case however and that the plane will not move, and that it won't generate lift etc etc. That's why I was bleh at the first answers trying to tell me how lift works... I understand that air has to move over the wings, that's why you have to think outside the box a bit to figure this one out The Treadmill is just a diversion, think of it as if instead of a treadmill, you were taking off on ice. Same thing, it will accelerate, and THEN air will be going over the wings (I didn't forget about you, first few posters! You were right, in a way, but not thinking it all the way through is all, which is why I urged you to think about it more That is why I was pretty stubborn about this not just being a simple 'no need lift etc lawl' problem.)

The actual problem WASN'T "Can a plane take off without moving" - it is a pseudo-trick question, formed in such a way to make people think critically. It is exactly the point for someone to say 'Hey, the treadmill is inconsequential'. Thus, continue your thinking Skylaa - if it were not a treadmill, just a runway that 'acted' as a treadmill (i.e. long enough for a plane to takeoff on) you can see that it would indeed take off. The question wasn't meant to be posed as 'If a plane is held stationary, can increasing wheelspeed make it fly' - that is why it was posed as it was Its a mixture of a critical thinking problem and sort of a trick question if you don't understand the question fully, which is quite easy because people aren't sure if the original poster means 'If it can't move forward' or 'Can it move forward enough to fly under these situations'

To the people above who instantly said noway, GTFO, please reread that last paragraph, as it is very important to understand why I said what I did earlier. Never was it stated that I intended the plane to not move - that was part of the overall question itself.

answer still no. Forget about the treadmill. you forgot the relative velocity between the aircraft and a specific position.

let say:

<---threadmill direction

aircraft ---> moving direction
--A-----------------B-------------------------C-----------------------------D

let the aircraft initial position at "A". So, when the trust applied by engine and the aircraft start moving, but at the same time, the threadmill also apply the same velocity at the opposite direction. So in the end, the aircraft still stay at position "A", and the relative velocity of aircraft respect to point "A" is zero. Or assume the controller so the threadmill got .5sec delay, still the relative velocity of the aircraft respect to point "A" still very small. (OP said that there is no control error)

so, does airflow occur? No.

no airflow = no life = no take off.


oh, the only condition it might take off if assume the controller for threadmill is at least 1 sec delay. And the aircraft got 140mph/s (or 140km/hr/s is the require take off speed? i've forgot ; . acceleration.

This isn't really the case either. The direction and speed of the treadmill has absolutely nothing to do with, and has no effect on the planes ability to fly.

Using your little diagram, if the treadmill is moving left, at any speed an the jets engines are off then the plane would remain stationary. As soon as the jets were turned on, they would push the plane forward completely ignoring whatever the ground condition is creating the necessary lift to fly. The fact that there is a treadmill or that the ground is moving, at any speed, opposite that of the plane is irrelevant because the force of the plane is not generated on the ground.


Edit: Picture a car on a treadmill with the wheels at a speed equal to the treadmills track speed with all power being generated by the treadmill. Essentially the wheels are turning at a speed of 55mph because the treadmill is moving at that speed to maintain the vehicles position at all times. If you were to then push the vehicle under your own power the vehicle would begin to move forward, regardless of how fast the wheels are turnin because the new source of force is coming from something not pertaining to the wheels.

[Osede]

Using your little diagram, if the treadmill is moving left, at any speed an the jets engines are off then the plane would remain stationary. As soon as the jets were turned on, they would push the plane forward completely ignoring whatever the ground condition is creating the necessary lift to fly. The fact that there is a treadmill or that the ground is moving, at any speed, opposite that of the plane is irrelevant because the force of the plane is not generated on the ground.

friction force...

[Tristam]

people that think this would work (the plane would fly)

If the jet pushed the plane forward, wouldn't the wheels move faster as well? And wouldn't it NOT MATTER since the treadmill, according to the OP, is in register with the speed of the PLANE not the WHEELS? If I push a car from behind, do not the wheels move? The only possible way this would work is if the jet produced enough thrust such that the wheels were spinning insanely fast and essentially started skidding across the treadmill, in which case yes, the plane would move forward. There must be something else here at work, or you need to reword the question.

[Jotaru]

Friction force on wheels = thrust from four jet engines?

If that's the case, how can airplanes take off at all?

The wheels have a minimal, negligent amount of friction. However, it is so small, you could just as easily replace the treadmill with a sheet of ice. The aircraft will accelerate, and eventually take flight.

To Skyylya, I think you may be taking it a bit personal.. I'm not expanding anything to 'suit' my argument, it was what was posted in the OP. Its not a 4 foot long treadmill, its a runway sized... runway... that simply has the potential to move in a treadmill-like fashion. As you stated, its irrelevant. As such, it accelerates as it would on pretty much any surface, and would eventually take flight. Sure, it might have to be a bit longer. But the idea is eventuality, would be kinda silly to make a question phrased as such and have the answer be 'no, cuz the runway is an inch too short' or something similar.

On that note however, it would take a longer runway roll, the friction force is very small, but it does add up. As such, wet-runway conditions (most notably on grass runways) require more length to takeoff as it causes extra friction.

Tristam - Yes, the wheels do move. But they act just as they would on a regular surface. If you are looking at it from the side, say the wheels are rotating clockwise - the plane is traveling to the right. Now move the surface its on to the left - it doesn't counteract the motion of the wheels, it would also make the wheels spin counterclockwise. They are additive.

[Tristam]

yo, if this is a frictionless surface between the wheels and the plane, then that is a COMPLETELY different question, in which case it would be impossible for the wheels to roll at all. You may as well have just said that "A plane is in space, and it's jets produce a thrust, will it move?"


edit: Further with the wheels,
- plane moves right, wheels move clockwise
- surface moves left at feedback response time, wheels move clockwise at a faster rate
- speed equalizes, wheels move clockwise at constant rate

...?

[Jotaru]

Its not frictionless. Its quite easy to see that the friction in wheels doesn't overpower the friction of four giant turbofan engines, however, go watch an airplane take off. The idea is that its inconsequential in this case because power comes from an outside source, not the wheels. Read: It doesn't matter if the wheels are spinning up down left right or sideways, so long as it keeps the plane off the ground.

[kuronosan]

There is counter-motion in the treadmill so the plane isn't really moving forward. If it's not moving forward it's not creating friction. If it's not creating friction, air isn't being pushed over its wings. If air isn't being pushed over its wings, it can't take off.

Seriously, for a simpler version of this... go running outside and feel the air pushing past your face. Then go run on a treadmill. You'll see significantly less air pushing on your face, if any at all, since the treadmill is counterbalancing your forward motion.

Edit: The only way this plane would create enough air-friction to take off would be if the treadmill was going slower than the forward movement of the plane. It's basic kinetics. The plane is too heavy and exerting too much of a downward force to be lifted off by the miniscule amount of air passing over the wings.

Edit #2: On the other hand, if the treadmill is not moving, the plane will eventually take off because there is no counter-motion - only increased friction. It would take a plane almost twice as long to take off on a stationary treadmill than on solid ground since the wheels would physically have to turn the treadmill before exerting any extra force required.

Either way, I would hate to be a person on that treadmill when the plane hits the threshold required to gain lift.