Interesting physics/logic riddle

[SugrueNSX]

I went back through and read some more of your posts. You seem to go way outside the original question. The question is worded in a very trickey way. The wheels of the plane have nothing to do with forward motion.

What someone needs to do here is get a 1:18 car. Attach a model rocket engine to the car. Then get the car on a treadmill that is spinning fast enough that the car wheels are turning but the car is staying in place, then light the rocket engine. Record the whole thing and post the video in this thread.

As you say the original question is worded in a “tricky way” . Your own interpretation will dictate how the belt operator responds to the plane. Read it one way and the plane takes off. Read it the other and it does not.
But you and I are not discussing the original question so we don’t have to worry about that.
What you said in post #124 was “No matter how fast the belt moves the plane will still take off."
Do you stand by that statement after reading my post #89?

Regards,

Patrick

 

[AdnanVCS]

Aircraft do not derive their forward thrust at their wheels. If a plane is traveling at 250mph on a conveyor belt, and the conveyor belt is moving at 250mph in the opposite direction, the aircraft is still moving at 250mph. The wheels are spinning at 500mph. That's the only difference. The wheels provide NO momentum at all! The friction caused by the wheels touching the conveyor belt isn't nearly significant enough to slow the craft down whatsoever.

~~~~~~~~~~~~~~~~~

However if you wanted to play around with this, the universal answer is no.:biggrin: There is an elephant in the way. :tongue:

You forgot that the weight of the plain is pushing it down on it's wheels!

 

[KSXNSX]

Look, it is a poorly worded question but from what the author is trying to propose: the plane will NOT take off.

The key here is LIFT (air passing over and under the wings), like so many of my colleagues tried to stress. Wings are shaped so that the top is convex, and gradually tapers off from the nose of the plane to the tail, creating a decrease in pressure relative to the underside of the wing. This is what allows us to "take off" so to speak.

***Interesting sidenote: The same principle that guided wing design probably also guided the design for the side intake on the nsx body and other NACA ducts--Bernoulli's principle***

Yes, the thrust of the jet engines in a modern plane will create decreased pressure relative to the air in front of the engines and that pull some air over the wings but it is NOT enough to create the lift needed to lift any passenger plane.

It looks like some people just copied an answer posted from the link above--which itself was quite sophomoric. The whole rollerblade anology was just bs. Why are people talking about friction at the wheels. It was given from the proposed situation that everything was frictionless less the air.

LIFT is the key to taking off. This depends on air being deflected by the wing's airfoils. Forget about the thrust, the wheels, the friction of the conveyer belt. Forget about everything except how much air is passing over and under the wings and at what speed (and possibly if the airfoils are deflected downwards creating downwash).

So for a regular passenger jet--NO. Maybe if you strapped on some wind turbines in front of the wings and passed air over them (the amount that a regular plane would pass when taking off not on a conveyer belt in a stupid logic riddle).

 

[Daedalus]

Does the fact it's on a treadmill change the amount of thrust an airplane gets from its engines? Of course not. If a 747 can create 200,000 lbs of thrust on a normal runway, how is that different if the plane is on a moving treadmill? The thrust will push the plane forward, against the air around it, regardless of what the runway below it is doing.

 

[KSXNSX]

Does the fact it's on a treadmill change the amount of thrust an airplane gets from its engines? Of course not. If a 747 can create 200,000 lbs of thrust on a normal runway, how is that different if the plane is on a moving treadmill? The thrust will push the plane forward, against the air around it, regardless of what the runway below it is doing.

The whole point of the proposed "treadmill" is to say: "This plane is not moving relative to the ground the treadmill is sitting on." Otherwise, there is no point in said treadmill and no riddle. I mean, why ask such a blatantly obvious question. If the plane can move forward relative to the ground--and more importantly, relative to the air around it--then it can take off given it reaches a certain speed (i.e. that is passes through enough air--like it would on a normal runway takeoff).

 

[steveny]

If the speed of the wheels on a plane determined the speed of the plane I am sure there would be no way to ever land a plane. What is the speed of the wheels just before landing? Why doesn't the plane stop dead when the wheels hit the runway? The wheels aren't moving, but the plane is still flying.

 

[12AMNSX]

I think we have reduced this issue down to one point - will the plane move forward. If the plane can move forward, it will fly. It seems that we all agree that the plane cannot fly unless it is moving forward through the air.

One group says no, the plane cannot move forward because the belt is counteracting any forward movement.

The other group says that despite the belt moving backward, the plane will still go forward due to thrust.

Since each group will not accept the position of the other, we are at an impasse. And it seems that each camp is going to defend their position until we have a thread as long as the "delete" thread.

Unless we can get some real professional help here, it's useless (but maybe fun?) to keep debating.

 

[KSXNSX]

I think we have reduced this issue down to one point - will the plane move forward. If the plane can move forward, it will fly. It seems that we all agree that the plane cannot fly unless it is moving forward through the air.

One group says no, the plane cannot move forward because the belt is counteracting any forward movement.

The other group says that despite the belt moving backward, the plane will still go forward due to thrust.

Since each group will not accept the position of the other, we are at an impasse. And it seems that each camp is going to defend their position until we have a thread as long as the "delete" thread.

Unless we can get some real professional help here, it's useless (but maybe fun?) to keep debating.

+1
Even if they plane can move forward, it has to move forward and pass the same amount of air at the same speed as a normal runway takeoff. If that were the case, then what is the point of the original riddle? Personally, I think the original author of the riddle (not necessarily the OP of the thread) meant that the plane was stationary relative to the ground that the treadmill sits on and the air around it.

 

[THE STIG]

+1
Even if they plane can move forward, it has to move forward and pass the same amount of air at the same speed as a normal runway takeoff. If that were the case, then what is the point of the original riddle? Personally, I think the original author of the riddle (not necessarily the OP of the thread) meant that the plane was stationary relative to the ground that the treadmill sits on and the air around it.

Whatever man.

You are an idiot.

Not only the plane will fly, it also will sing and dance.

 

[KSXNSX]

Whatever man.

You are an idiot.

Not only the plane will fly, it also will sing and dance.

Hahahaha. Not with a fat pilot in it.

 

[NSX-Stalker]

LOL, we have this one going around work now. It's quite the debate.

NSX-Stalker

 

[ShiftyBob]

NOOOOOOOOOOOOOOOOOOOO!!!!!!!

Please don't revive this thread!!!!

 

[nicholas421]

i've jumped ship. if the conveyor belt matches the wheel speed it will not take off. it will only take off if the the belt matches the plane's speed relative to a stationary object.

someone previously tried to explain this but i was too closed minded to listen. i apologize to whomever that was.

 

[Briank]

Airplanes move through the air, wheels are a necessary evil to allow the plane to move while in contact with the ground. The engine will move the plane through the air no matter which way the wheels are turning, forward, backwards or on at least on of my landings today forward and a little sideways at the same time. Also the plane flies even when the wheels are not turning so if the wheels had anything to do with the plane moving or flying they would be powered. :tongue:

 

[flaminio]

For those who still think that the plane won't fly, ask yourself: how does a seaplane take off?

 

[khappucino]

For those who still think that the plane won't fly, ask yourself: how does a seaplane take off?

sea planes dont take off.... the ocean moves down =)

 

[flaminio]

sea planes dont take off.... the ocean moves down =)

Oh yeah, forgot about that!

OK, try this experiment: Next time you go to the gym, bring a toy car with you -- one that has free spinning wheels. Place the car on one of the treadmills, and with the treadmill on, hold the car by the roof so that the wheels are spinning.

Now, using your arm, try to push the car forward. Can you do it? Try increasing the treadmill speed to maximum and see if you can push the car forward.

Obviously, no matter how fast the treadmill is going, you will still be able to push the car forward, because the wheels on the car are not providing any forward propulsion themselves. A plane works the same way, except instead of your arm it is the engines providing the forward propulsion.

 

[nicholas421]

Oh yeah, forgot about that!

OK, try this experiment: Next time you go to the gym, bring a toy car with you -- one that has free spinning wheels. Place the car on one of the treadmills, and with the treadmill on, hold the car by the roof so that the wheels are spinning.

Now, using your arm, try to push the car forward. Can you do it? Try increasing the treadmill speed to maximum and see if you can push the car forward.

Obviously, no matter how fast the treadmill is going, you will still be able to push the car forward, because the wheels on the car are not providing any forward propulsion themselves. A plane works the same way, except instead of your arm it is the engines providing the forward propulsion.

it is possible for the treadmill to accelerate at a rate at which you will not be able to push the car forward.

 

[Briank]

it is possible for the treadmill to accelerate at a rate at which you will not be able to push the car forward.

Maybe if you are pushing with a wet noddle. :tongue:

 

[SugrueNSX]

it is possible for the treadmill to accelerate at a rate at which you will not be able to push the car forward.

No! Surely not! In order for that to be true… I would have to use my imagination.

Regards,

Patrick

 

[nicholas421]

the key word is ACCELERATE! if the treadmill is going at a constant speed, sure you can push the car at any speed. but if it's accelerating at the same rate you are pushing the car (ie, exactly match the speed of the wheel), than the car will not move forward. think about it before responding.

example:
you know those airplane rides you can take where you experience zero gravity? it's because the airplane is matching the acceleration of your freefall. even though there are 2 independent forces acting on the plane and the person, the person is not moving relative to the plane.

 

[flaminio]

the key word is ACCELERATE! if the treadmill is going at a constant speed, sure you can push the car at any speed. but if it's accelerating at the same rate you are pushing the car (ie, exactly match the speed of the wheel), than the car will not move forward. think about it before responding.

OK, I thought about it. And acceleration of the treadmill is irrelevant. It will only make the wheels spin faster -- if I'm holding the toy car, I can still push it forward. And if I can push a toy car forward on an accelerating treadmill, an airplane can push forward on a conveyor runway, and ultimately take off.

Note that I am disregarding certain real-world effects: eventually an accelerating treadmill would reach a speed where the machinery would fly apart, or spin the wheels of the toy car to destruction. If this is your point, do say so.

 

[SugrueNSX]

OK, I thought about it. And acceleration of the treadmill is irrelevant. It will only make the wheels spin faster -- if I'm holding the toy car, I can still push it forward. And if I can push a toy car forward on an accelerating treadmill, an airplane can push forward on a conveyor runway, and ultimately take off.

Note that I am disregarding certain real-world effects: eventually an accelerating treadmill would reach a speed where the machinery would fly apart, or spin the wheels of the toy car to destruction. If this is your point, do say so.

So looking at nicholas421 previous posts, I’m pretty sure he gets it but I think that most people are struggling to understand this and throwing in “Acceleration” is not going to help any. Please read my post # 89 to understand why you wont be able to push the toy car on the treadmill.
The point is that there is no upper limit on friction so if the belt operator is free to use any speed then however much force you can use to push the car can be balanced or even overcome with drag on the bearings in the opposite direction. As you pointed out in the real world the bearings might fail before we got there but then you still loose the battle due to even more friction

Regards,

Patrick

 

[nicholas421]

If this is your point, do say so.

it is not what I am saying at all. if the belt is going at a constant speed, the only resistance applied to the plane is the drag caused by the wheels.. which is not enough to prevent the plane from taking off. however, if the belt is accelerating it will produce greater resistance on the wheels. if the acceleration matches that of the wheels, it will be enough friction to keep the plane stationary.

 

[SugrueNSX]

Look, it is a poorly worded question but from what the author is trying to propose: the plane will NOT take off.

The key here is LIFT (air passing over and under the wings), like so many of my colleagues tried to stress. Wings are shaped so that the top is convex, and gradually tapers off from the nose of the plane to the tail, creating a decrease in pressure relative to the underside of the wing. This is what allows us to "take off" so to speak.

***Interesting sidenote: The same principle that guided wing design probably also guided the design for the side intake on the nsx body and other NACA ducts--Bernoulli's principle***

Yes, the thrust of the jet engines in a modern plane will create decreased pressure relative to the air in front of the engines and that pull some air over the wings but it is NOT enough to create the lift needed to lift any passenger plane.

It looks like some people just copied an answer posted from the link above--which itself was quite sophomoric. The whole rollerblade anology was just bs. Why are people talking about friction at the wheels. It was given from the proposed situation that everything was frictionless less the air.

LIFT is the key to taking off. This depends on air being deflected by the wing's airfoils. Forget about the thrust, the wheels, the friction of the conveyer belt. Forget about everything except how much air is passing over and under the wings and at what speed (and possibly if the airfoils are deflected downwards creating downwash).

So for a regular passenger jet--NO. Maybe if you strapped on some wind turbines in front of the wings and passed air over them (the amount that a regular plane would pass when taking off not on a conveyer belt in a stupid logic riddle).

What!?
Forget about the Thrust and the Friction?
That’s the whole puzzle right there. How about we forget about the plane as well and then we wont have to think about anything?
If we forget abut the thrust then of course the plane can never take off.
Providing we do have thrust and we forget about any friction associated with the wheels then the conveyer belt has no effect and of course the plane takes off.
Thanks for your wonderful diagram showing us all how an aerofoil produces lift. Given that… could you please tell us how planes fly inverted?

Regards,

Patrick