Airplane and Conveyor Belt Debate

[FredGarvin]

Board searches are pretty fickle. If you do a search on "conveyor" you will get this thread (which links back to some of the original threads)

https://www.physicsforums.com/showthread.php?t=112124&highlight=conveyor

Please, someone go out into the ether and beg that this topic die a horrible death that it so rightly deserves and smote the boards that started it...amen.

BTW...what board is it that has had this raging debate going on for so long?

 

[ZapperZ]

This question is fast becoming the Most Annoying Question (MAQ).

Zz.

 

[P.G]

Debate

Hey people. I have a problem that I don't know the answer to, but you guys could probably help. Its quite a hot topic on other forums. Anyways, here it is.

A plane is standing on a runway that can move (some sort of conveyer belt). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction).

Can the plane take off?

I say no personally but I've been told it can help!

 

[chroot]

This same question has been answered many, many times already, largely by people like you, P.G, who have come here from another forum. This question is no longer welcome here. Use the search function to find previous discussion on it.

- Warren

 

[userjayson]

plane landing on giant conveyor belt

What would happen if a plane was approaching a runway at 200 mph and the runway (conveyor belt) was moving at 200 mph in the opposite direction. I think if your wheels could take the sudden jolt, they would start turning at 400 mph. Since the plane is being thrusted buy a jet not attached to the wheels, it would continue to go its original 200 mph until the jet was shut off. Once that happens, at what rate do you slow the conveyor belt down so the that the plane is not forced of the back end of the belt. I can't get my mind around this one.. I heard a radio talk show host talking about this one day and was wondering if were possible.

 

[Integral]

Please use the search function. Airplane or conveyer ought to get what you are looking for.

 

[Kastey]

Airplane. Fly up or not?

i have a some trouble in solution of this problem:
Airplane is standing on conveyer. Rate of movement of this conveyer automatically (without delay) concide with rate of movement wheels of undercarriage. Conveyer move to side reverse of course fly up airplane. This system is switch on. Question: airplane fly up or not?

 

[Astronuc]

Need more information. Each aircraft has a take-off speed based on the lift and weight of the aircraft.

Student is expected to show work (equations and computation) when asking for assistance.

 

[Kastey]

I think, what in order to this problem weight of this aircraft absolutely unimportant. This aircraft be able to fly up from usual landing strip. question:
can it fly up from conveyer?

 

[Gokul43201]

Read the guidelines.

We can not help you with schoolwork unless you show what effort you have made.

 

[dav2008]

This isn't homework. This is the airplane on a treadmill question that has been discussed ad nauseam.

Do a search for "treadmill" on the forums. You should find at least 10 other threads on this subject.

It looks like this is the longest thread on the subject: https://www.physicsforums.com/showthread.php?t=101259

 

[DaveC426913]

The very short answer:

An airplane's ability to take off has nothing to do with the movement of the ground under its wheels and everything to do with the movement of air over its wings.

 

[Astronuc]

This isn't homework. This is the airplane on a treadmill question that has been discussed ad nauseam.

Do a search for "treadmill" on the forums. You should find at least 10 other threads on this subject.

It looks like this is the longest thread on the subject: https://www.physicsforums.com/showthread.php?t=101259

I wondered about that as soon as I saw "conveyor".

And as DaveC426913 has indicated, the solution has to do with the airspeed (airflow) over the wings. The air provides lift via the wings, which must be greater than the weight of the aircraft in order for the aircraft to 'takeoff'!

However, if the thrust of the engines are not increased to offset the force of the conveyor (once the aircraft lifs), then the aircraft will simply reduce speed due to drag and fall downward to the ground/conveyor. It's simple physics.

The question is ill posed and describes a physically unstable system.

 

[Gokul43201]

This isn't homework. This is the airplane on a treadmill question that has been discussed ad nauseam.

I'm more than aware of the letter, but certainly not as sure as you about the former.

If some teacher decided to pose this question to a class (heaven forbid), then we're violating the Homework Help guidelines by responding to a query that includes no original work.

It's not our job to speculate about whether or not this is coursework. The location of this thread determines its fate. If the OP has posted in error, s/he can correct that with a PM to a mentor.

 

[Kastey]

This questions are discussed on many many forums. On some of it this discussion last 3-4 years. Number of posts about this problem amount to 10 000. I simple want to know, what you think about it. Most of people incline to "The question is ill posed and describes a phyically unstable system."

 

[Astronuc]

This questions are discussed on many many forums. On some of it this discussion last 3-4 years. Number of posts about this problem amount to 10 000. I simple want to know, what you think about it. Most of people incline to "The question is ill posed and describes a phyically unstable system."

The problem as stated in the OP is ill-posed, i.e. it is too non-specific.

Replace conveyor or treadmill with catapult, and one has the situation on a naval aircraft carrier. Navies around the world have demonstrated that one can lauch an aircraft, but if the aircraft leaves the carrier deck without sufficient thrust, it crashes shortly after takeoff.

As soon the the force applied by the conveyor, treadmill or catapult is removed, the plane begins to decelerate because of drag and the lift (which is dependent on air speed over the wings) decreases as the forward velocity decreases and the plane descends.

This should not be hard to understand - and it certainly does not warrant 1000's of posts on countless websites.

 

[moose]

Astronuc, I can't seem to understand what you are saying. Are you saying that yes it will fly because the thrust has nothing to do with the ground, or are you saying no for some weird reason?

 

[Astronuc]

Astronuc, I can't seem to understand what you are saying. Are you saying that yes it will fly because the thrust has nothing to do with the ground, or are you saying no for some weird reason?

Under certain conditions, that being forward thrust >= drag, and lift >= weight, the aircraft will takeoff.

However, as soon as the aircraft 'takes off', i.e. loses the force from the conveyor, treadmill, or catapult, unless thrust (force) is produced by the aircraft to match drag, drag will cause a rapid deceleration, and resulting lift will decrease, and plane will come back down.

When flying (cruising) in air, there is a force balance. Lift = weight, and drag = forward thrust. If one cuts off (stopped) the engines in flight, the plane would immediately decelerate (forward) and that would cause a rapid decrease in lift, which would cause the plane to plumment. That is not flying as much as it is falling!

 

[Pengwuino]

Is there some sort of virus spreading around the internet that forces people to ask this same freaken question over and over and over? Does anyone know the source of this? Search the forum, it's been discussed beyond all reason.

 

[Astronuc]

Lock the thread! Please!

 

[chroot]

Please don't feed the trolls, Astronuc.

Kastey, this topic has indeed been discussed ad nauseum, mainly because people like you come here from other forums, don't bother to search, and post the same question again. It's not even an interesting physics problem -- the answer is definite and very clear, though the question is poorly worded.

Do not discuss this topic further here.

- Warren

 

[Brad117]

Question.

I wasn't really sure where this would go, and it seemed most sensable to place this question here since it wasn't a homework problem, just a random critical thinking problem. And with the anwser, could you also give a good explanation and proof.

A plane is sitting stationary on a runway. The runway is a giant conveyor belt that will instantly and inversely match the speed of the plane's wheels (wheels move at 10mph forward, runway moves 10mph in the opposite direction). As the plane accelerates the runway matches the planes speed.

Will the plane move? Will the plane take off?

 

[rcgldr]

This has been posted before. The plane isn't wheel driven, it's air driven by the propeller (or jet). The wheels just spin faster, might slow the rate of acceleration a tad, but the plane would still take off (assuming the belt doesn't move so fast to cause the tires to explode from fast rotation). So if the plane takes off at 100mph, the tires just spin at 200mph, as long as they don't explode, there's no problem.

 

[Hootenanny]

This has been posted before. The plane isn't wheel driven, it's air driven by the propeller (or jet). The wheels just spin faster, might slow the rate of acceleration a tad, but the plane would still take off (assuming the belt doesn't move so fast to cause the tires to explode from fast rotation).

I can't see how the plane would infact take off. If there is no air flow over the wings (because the plane is stationary relative to the air) then the wings generate no lift.

 

[Brad117]

This has been posted before. The plane isn't wheel driven, it's air driven by the propeller (or jet). The wheels just spin faster, might slow the rate of acceleration a tad, but the plane would still take off (assuming the belt doesn't move so fast to cause the tires to explode from fast rotation). So if the plane takes off at 100mph, the tires just spin at 200mph, as long as they don't explode, there's no problem.

yeah I don't quite get what you mean. I sort of thought of it as like a man running on a treadmill, and assuming that the man runs at a constant rate of 8mph and the treadmill is at 8mph also, then the man will stay stationary. But since this is an airplane, and there's no foward momentum...then your saying the airplane would vertically lift up in the air?

 

[rcgldr]

Once again, the plane starts off stationary, but doesn't remain that way once the propeller starts producing significant thrust. Again note that the plane isn't wheel driven, it gets its propulsion by accelerating the air backwards. As it does this, the plane accelerates forwards, the tires will rotate at twice the speed that the plane is moving forwards at, because of the rule you made about the conveyor belt. If take off speed is 100mph, then the tires will be rotating at 200mph when the plane takes off.

Now if it was a wheel driven vehicle, like a car, then the car wouldn't move, but your example is a plane which isn't wheel driven.

If it was a rocket powered motorcyle, like the one in this video, then the tires would rotate twice as fast at the motorcycle, but the bike will still accelerate forwards at a great rate. All of it's acceleration is due to acceleration of air backwards, not force applied to the wheels. Unless the tires exploded from the rotational speed, the bike would still accelerate very fast. Note this is a very short video, the bike is very quick:

rktbike.avi

 

[Hootenanny]

Ahh, makes sense now Jeff thank you. I've just read through the other thread loacted https://www.physicsforums.com/showthread.php?t=101259"

 

[Doc Al]

This has same question has been asked--and answered--many times already. Please look at the link that Hootenanny provided if you need more.

 

[cowmoo32]

Plane on a treadmill

Could it take off? I'm assuming yes because the wheels aren't what propel it forward. Once there was enough thrust to counteract the initial movement backward due to the friction of the wheels on the ground, it would be able to move forward. Am I correct in thinking this?

 

[Integral]

https://www.physicsforums.com/showthread.php?t=101259&highlight=treadmill" resulting from a search on "treadmill" There are more.

 

[david90]

airplane and conveyor belt

Can an airplane take off if it is traveling on a conveyor belt that travels in the opposite direction of the airplane and the conveyor belt speed = to the speed of the airplane?

 

[Doc Al]

Sorry, but this one's been done to death. Search the archives and you'll find several threads.

 

[mtaylor]

a jet plane on a large treadmill

This has been posted on other forums and has cause massive arguments

A plane (747 passenger jet) is sitting on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

The question is:

Will the plane (747 passenger jet) take off or not?

 

[leright]

This has been posted on other forums and has cause massive arguments

A plane (747 passenger jet) is sitting on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

The question is:

Will the plane (747 passenger jet) take off or not?

The control system is going to ensure that the plane's speed is always zero. If the plane is not moving, do you think it will take off?

errr...wait...no. the plane will take off. the moving tradmill will simple ensure the wheels of the plane move twice as fast.

 

[lufbrajames]

This has been posted on other forums and has cause massive arguments

A plane (747 passenger jet) is sitting on a runway that can move (some sort of band conveyor). The plane moves in one direction, while the conveyor moves in the opposite direction. This conveyor has a control system that tracks the planes speed and tunes the speed of the conveyor to be exactly the same (but in the opposite direction).

The question is:

Will the plane (747 passenger jet) take off or not?

I would say no, because to take of the plane needs to generate lift. And the lift is created by the airflow over the wings, if the plane is not moving, it means that there is no airflow, therefore it won't fly.

-James Hart
-Loughborough Uni, UK