You have a plane and a conveyor belt.

[JujuFish]

Tom, are you just going to ignore what I've been saying?

 

[PurdueRy]

Originally posted by: Tom
"if you simply stand on a treadmill and don't walk forwards you would move backwards too "


Wouldn't you agree with me that actually you would not be moving, relative to the treadmill, pretty obvious you would since you even say you are standing still.

I still think the big problem some people(not you) have is they can't grasp that motion is RELATIVE, not absolute.


The plane can be going like the blazes, relative to the conveyor, but standing still relative to everything else, including the air needed for lift.

You still have yet to find a scientific way to refute either of the practical examples presented here. Tell me how the car rolls down the treadmill in the toy car case, and how the rollerblader is pulled towards the wall in the rollerblade example. Don't tell me again that its not fair because there is a stationary wall...draw the FBD and SHOW me how they are different

 

[iamwiz82]

Originally posted by: Fraggable
Oh come on people, this makes no sense. The plane would have to take off.

The belt is powered by itself - some lawnmower engine, whatever I don't care.

The plane is providing its own thrust - it is using air's inertia or resistance to change in sped to move forward.

When the plane's wheels begin to roll, the belt speeds up to match that speed in the opposite direction. Let's say the belt can travel infinitely fast.

Eventually, the plane will begin to move forward. the belt will continue to match the speed of the wheels, but the belt cannot keep the plane from moving forward, as it has no influence over on the plane's method of thrust.

The plane WILL move forward and take off normally, because the belt cannot slow its forward motion.

The belt compensates for the rotation of the wheels in reverse, as in the belt moves in reverse exactly as fast as the wheels move forward.

The belt will always go as fast as the plane is, in the opposite direction.

 

[PurdueRy]

Originally posted by: JujuFish
Tom, are you just going to ignore what I've been saying?

Originally posted by: PurdueRy

Originally posted by: PurdueRy

The plane is stationary no matter how fast the treadmill goes with the engines off. This is stationary relative to the stationary air...not the treadmill. Now create a unopposed force...your telling me nothing happens? The treadmill is already going much faster than the planes wheel speed...so its already matched that. Where does this new force factor in then? Acceleration...and this is acceleration relative to the AIR, not the treadmill.

Think about this Tom and respond to it directly.

G'night

He ignored that...so probably...

 

[Fraggable]

Originally posted by: iamwiz82

Originally posted by: Fraggable
Oh come on people, this makes no sense. The plane would have to take off.

The belt is powered by itself - some lawnmower engine, whatever I don't care.

The plane is providing its own thrust - it is using air's inertia or resistance to change in sped to move forward.

When the plane's wheels begin to roll, the belt speeds up to match that speed in the opposite direction. Let's say the belt can travel infinitely fast.

Eventually, the plane will begin to move forward. the belt will continue to match the speed of the wheels, but the belt cannot keep the plane from moving forward, as it has no influence over on the plane's method of thrust.

The plane WILL move forward and take off normally, because the belt cannot slow its forward motion.

The belt compensates for the rotation of the wheels in reverse, as in the belt moves in reverse exactly as fast as the wheels move forward.

The belt will always go as fast as the plane is, in the opposite direction.

It can go that fast, but the belt will not stay in contact with the plane, and still will have no influence on its forward motion.

 

[Tom]

Originally posted by: Fraggable
Oh come on people, this makes no sense. The plane would have to take off.

The belt is powered by itself - some lawnmower engine, whatever I don't care.

The plane is providing its own thrust - it is using air's inertia or resistance to change in sped to move forward.

When the plane's wheels begin to roll, the belt speeds up to match that speed in the opposite direction. Let's say the belt can travel infinitely fast.

Eventually, the plane will begin to move forward. the belt will continue to match the speed of the wheels, but the belt cannot keep the plane from moving forward, as it has no influence over on the plane's method of thrust.

The plane WILL move forward and take off normally, because the belt cannot slow its forward motion.

The conveyor isn't doing anything to restrict the planes motion, the plane can go infinitely fast.

What the conveyor does is restrict what that motion is relative to. The belt can and does also go infintely fast, in the opposite direction.

The net movement of the plane relative to the rest of the world is zero.

 

[KK]

Originally posted by: Tom

Originally posted by: dawks

Originally posted by: BriGy86

Originally posted by: Citrix

Originally posted by: dug777
I don't get why you are arguing?

No air movement=no lift=no flight.

exactly, if the plane stays in one spot i dont care how much thrust it has if there is no AIR SPEED over the wings its not flying.

i don't see how it can be put any simpler than this

people have made the arguement that wheels do not drive the plane

like planes with ski's or pontoons

well is doesn't really matter, in all cases the plane is moving forward to get air under the wings

lift has to do with air going under the wings, if you are stationary and its not a windy day how can there be air going under the wings to provide lift?

It will take off.. I can't believe im going to do this again..

Imagine strapping on some roller skates and standing on a treatmill. Now if you grab on to the console at the front, and then turn on the treadmill, you will stay motionless with relativly little effort. Even if you increse the speed of the belt, it still takes very little effort to stay in one place, because the wheels compensate. Now grab a rope tied to the wall infront of you, and pull yourself forward. It CAN be done. Even if someone is speeding up the treadmill while you pull yourself forward, it CAN be done. The wheels on your skates will just speed up to compensate for the difference.

This is the basic idea of how a commercial 'jet' plane works. Its fan pulls air in the front and blows it out the back, using air, as the 'rope' to pull it forward.

The aircraft will move forward, and will generate lift under the wings as a result.

I've already refuted the rope and the wall scenario several times..

The engines acting on the air is not the same as a rope on the wall, unless the wall is mounted on wheels and is also on the conveyor belt.

The engines are part of the plane, the plane cannot pull itself off the conveyor belt by pushing against itself, if the conveyor belt functions the way the the original question describes it.

You haven't refuted a god damn thing. You are so hell bent on avoiding my questions.

Here is my previous post that I believe you couldn't answer.

Originally posted by: KK

Originally posted by: Tom

Originally posted by: KK
if the plane on this conveyor belt was hooked to a truck that was not on the conveyor belt, what would happen if the truck pulls the plane? Is the conveyor going to continue to match the wheel speed of the plane? Is this a magical conveyor belt, did the OP get this conveyor belt from the same place jack got his beans?

The truck pulling is going to exert(sp?) the same forces on the plane as the air is forcing on the plane going thru the engine.

No it isn't. When you put the truck off the conveyor belt you are no longer dealing with the same set of relative motions. You have completely done away with the special circumstance of the original question, rather than answer it.

As I've said umpteen times, i don't dispute the airplane's engines are going to exert a force that will cause the plane to move. The relevance is that the movement will be in relation to the conveyor belt, and as long as the conveyor belt moves as described in the original question, the motion of the plane relative to everythnig but the conveyor will be zero.

Yes you are dealing with the same set of motions, the air going thru the engine is going to exert the same force forward as the truck will. What will happen if this "conveyor belt" is matching the forward motion of the plane that is being pulled by the truck? You can not answer this because you know that if you answer it, this will totally fvck up your reasoning.

God, it's like arguing with a five year old.

For all you other dipsh1ts out there. The people saying that it will fly are also saying that the plane will actually be moving forward on the conveyor belt just as it would on regular ground. So there will be airflow over the plane causing the lift as usual.

 

[GuitarDaddy]

Originally posted by: KMDupont64
Soooo, you are in a seaplane aiming up river (against the current), you need 100 mph of airspeed to take off, the speed of the water is exactly whatever speed (in the opposite direction) you would be going if the water wasnt moving. (If you had enough thrust to go 50MPH, the water would move 50MPH the other direction).

How does the plane take off?

In this example the plane wouldn't take off. The difference in this example and the one in the OP is this plane has stationary pontoons that tranfer the force of the moving water to the plane. In the OP the plane has free spinning wheels, therefore the force of the conveyor belt is absorbed by the spinning wheels and not transfered to the plane.

 

[Tom]

Originally posted by: PurdueRy

Originally posted by: JujuFish
Tom, are you just going to ignore what I've been saying?

Originally posted by: PurdueRy

Originally posted by: PurdueRy

The plane is stationary no matter how fast the treadmill goes with the engines off. This is stationary relative to the stationary air...not the treadmill. Now create a unopposed force...your telling me nothing happens? The treadmill is already going much faster than the planes wheel speed...so its already matched that. Where does this new force factor in then? Acceleration...and this is acceleration relative to the AIR, not the treadmill.

Think about this Tom and respond to it directly.

G'night

He ignored that...so probably...

Probably, I went to bed !

First thing I posted today was that there is no unopposed force. The force acting on the plane is opposed by the force being applied to the conveyor belt that makes it move in the opposite direction.

 

[Fraggable]

Originally posted by: Tom

Originally posted by: Fraggable
Oh come on people, this makes no sense. The plane would have to take off.

The belt is powered by itself - some lawnmower engine, whatever I don't care.

The plane is providing its own thrust - it is using air's inertia or resistance to change in sped to move forward.

When the plane's wheels begin to roll, the belt speeds up to match that speed in the opposite direction. Let's say the belt can travel infinitely fast.

Eventually, the plane will begin to move forward. the belt will continue to match the speed of the wheels, but the belt cannot keep the plane from moving forward, as it has no influence over on the plane's method of thrust.

The plane WILL move forward and take off normally, because the belt cannot slow its forward motion.

The conveyor isn't doing anything to restrict the planes motion, the plane can go infinitely fast.

What the conveyor does is restrict what that motion is relative to. The belt can and does also go infintely fast, in the opposite direction.

The net movement of the plane relative to the rest of the world is zero.

The fact that a plane could fly into a 600-mph gale and stay in the air while moving backwards means that the plane's method of thrust and motion have nothing to do with its wheels and ground speed.

 

[spidey07]

The general problem here is it isn't really a physics question, but a logic/relativity one.

I'll say again - if the plane moves forward (relative to world/air) then the conveyor did NOT move at the same speed as the wheels. If the plane moves forward in anyway shape or fashion the wheels somehow moved faster than the conveyor...which cannot happen. It cannot happen because of the stipulation that given in the original problem.

 

[PurdueRy]

Originally posted by: Tom

Originally posted by: PurdueRy

Originally posted by: JujuFish
Tom, are you just going to ignore what I've been saying?

Originally posted by: PurdueRy

Originally posted by: PurdueRy

The plane is stationary no matter how fast the treadmill goes with the engines off. This is stationary relative to the stationary air...not the treadmill. Now create a unopposed force...your telling me nothing happens? The treadmill is already going much faster than the planes wheel speed...so its already matched that. Where does this new force factor in then? Acceleration...and this is acceleration relative to the AIR, not the treadmill.

Think about this Tom and respond to it directly.

G'night

He ignored that...so probably...

Probably, I went to bed !

First thing I posted today was that there is no unopposed force. The force acting on the plane is opposed by the force being applied to the conveyor belt that makes it move in the opposite direction.

Tell me how that force is applied to the body of the plane. According to me FBD, all it can do is spin the wheels.

 

[iamwiz82]

Originally posted by: spidey07
The general problem here is it isn't really a physics question, but a logic/relativity one.

I'll say again - if the plane moves forward (relative to world/air) then the conveyor did NOT move at the same speed as the wheels. If the plane moves forward in anyway shape or fashion the wheels somehow moved faster than the conveyor...which cannot happen. It cannot happen because of the stipulation that given in the original problem.

Exactly.

People keep saying that since the plane has thrust it can go faster once applied, but the original post specifically says that the speeds will continue to be matched, so the plane will stay STATIONARY.

Stationary = no lift

 

[PurdueRy]

Originally posted by: spidey07
The general problem here is it isn't really a physics question, but a logic/relativity one.

I'll say again - if the plane moves forward (relative to world/air) then the conveyor did NOT move at the same speed as the wheels. If the plane moves forward in anyway shape or fashion the wheels somehow moved faster than the conveyor...which cannot happen. It cannot happen because of the stipulation that given in the original problem.

How does the toy car roll down the treadmill in my previous example if this is the case?

 

[LTC8K6]

You are correct given the facts you describe, but those facts are different than the original question.

To make your scenario like the original question, the treadmill would respond to the opening of the throttle by going faster in the opposite direction. (The original question doesn't have a "fixed speed" of 10 mph or any other fixed speed for the conveyor, in fact it is very definately not fixed.)

Which would result in no movement relative to the surroundings.

The speed of the conveyor is irrelevant. The only thing the engine has to overcome is the friction of the wheels and bearings, which is never very much. The only thing keeping you from moving forward is this friction.

You will be able to take off pretty much just as if you were on solid ground. The conveyor changes nothing much at all except it adds a slight bit of resistance to your forward motion, which is easily overcome by any engine powerful enough to let you fly in the first place.

Let's take a skateboard with a powerful rocket engine attached. You are holding the skateboard on a treadmill that is somehow set at 50mph.

What do we have?

A skateboard standing still with it's wheels screaming and smoking at 50mph due to the treadmill.

Light the pipe and the skateboard leaves the area like a bat out of hell. It won't even notice the treadmill.

A plane will do the same thing. It will take off normally even on a giant treadmill exactly the same size as the runway it normally uses. It will not be any different except for the slight friction of the wheel bearings. The plane will not act much different at all from being on a solid runway.

It will move forward pretty much just as quickly, reach V1 easily, and rotate just as quickly.

It will be like the conveyor belt is not even there.

 

[GuitarDaddy]

The original problem is flawed, and against the laws of physics


If you applied thrust, the wheels would spin faster than the conveyor and the plane would take off, period.

The entire premise that the wheels and conveyor would spin at the same speed regardless of the thrust applied is just wrong.

 

[Nyati13]

Originally posted by: NanoStuff

If the wheels have to be rotating faster than the conveyor belt to advance forward, how does the plane move forward if the belt doesn't allow for the wheels to rotate faster than the belt is moving backwards?

And that is where the complete failure of understanding is. An airplane does not apply any motive force to the ground through it's wheels. ( NONE WHATSOEVER) The aircraft will pull itself forward through the air by force of it's prop or jet and it will take off. It doesn't matter in the slightest if there is a conveyor belt under the plane or not.

 

[JujuFish]

Originally posted by: iamwiz82

Originally posted by: spidey07
The general problem here is it isn't really a physics question, but a logic/relativity one.

I'll say again - if the plane moves forward (relative to world/air) then the conveyor did NOT move at the same speed as the wheels. If the plane moves forward in anyway shape or fashion the wheels somehow moved faster than the conveyor...which cannot happen. It cannot happen because of the stipulation that given in the original problem.

Exactly.

People keep saying that since the plane has thrust it can go faster once applied, but the original post specifically says that the speeds will continue to be matched, so the plane will stay STATIONARY.

Stationary = no lift

Take the air as our reference point. Say the wheels and consequently the plane go at a speed of 50mph, which we'll call v. Accordingly, the treadmill moves at -50mph, or -v. The problem here is people are adding v and -v to get 0 in their mind, and that's just not the case. Relative to the air, they are both moving, but with opposite velocities. Relative to each other, they are moving at the change in v, or v - (-v), or 2v. In this case, 100mph. Nothing is stationary relative to anything else.

 

[LTC8K6]

The speed of the belt makes no difference. The plane will act like it is on solid ground except for the slight extra thrust needed to overcome the friction of the wheel bearings.

The plane will move forward. Air will flow over the wings. Lift will occur.

 

[spidey07]

Originally posted by: PurdueRy
The plane is stationary no matter how fast the treadmill goes with the engines off. This is stationary relative to the stationary air...not the treadmill. Now create a unopposed force...your telling me nothing happens? The treadmill is already going much faster than the planes wheel speed...so its already matched that. Where does this new force factor in then? Acceleration...and this is acceleration relative to the AIR, not the treadmill.

I'll respond.

In order for any acceleration to be involved in a linear line (plane moves forward relative to world/air) the wheels on the plane would have to move faster than the conveyor.

That is not allowed to happen from the original information given.

I know it sounds silly, but you can't think real world here. It is a hypothetical scenario which would be impossible to encounter in the real world.

 

[MrDingleDangle]

posted this on page one...will post it again...it does take off, here is another persons reasoning why, try and get it through your head...

if you put a car in neurtral on a conveyor belt it will start going backwards, but if you add a huge rocket to the top of the car and ignite it, the car will go forward, assuming that the rocket has more force then the friction between the wheels and belt...same as a plane...as long as the forward propulsion is greater then the friction between wheel and belt it will go forward and take off...



http://www.straightdope.com/columns/060203.html

 

[Jack Ryan]

Whatever

 

[PurdueRy]

Originally posted by: spidey07

Originally posted by: PurdueRy
The plane is stationary no matter how fast the treadmill goes with the engines off. This is stationary relative to the stationary air...not the treadmill. Now create a unopposed force...your telling me nothing happens? The treadmill is already going much faster than the planes wheel speed...so its already matched that. Where does this new force factor in then? Acceleration...and this is acceleration relative to the AIR, not the treadmill.

I'll respond.

In order for any acceleration to be involved in a linear line (plane moves forward relative to world/air) the wheels on the plane would have to move faster than the conveyor.

That is not allowed to happen from the original information given.

I know it sounds silly, but you can't think real world here. It is a hypothetical scenario which would be impossible to encounter in the real world.

This is where we disagree I think. The original problem states that the conveyor moves as fast backwards as the wheels are rolling forward...not the rotational speed of the wheels...although a little clearer wording would be nice.

Therefore, the wheels can be moving forward.

 

[LTC8K6]

The belt simply doesn't matter. As far as the plane is concerned, it's really not there, no matter how fast it's moving.

Even it were super conveyor going mach2, and the wheels could somehow stand that, it still wouldn't matter. The plane would take off pretty much just as if it were not on a treadmill.

 

[Nyati13]

Originally posted by: alien42

that is the entire point of the conveyor belt.

The only way to stop the aircraft from moving forward is if the wheels were clamped or locked to the ground, the rotating conveyor belt will NOT hold the aircraft stationary, the aircraft will be able to accellerate forward, which will move it's wings through the air, which will produce lift, which will lift the aircraft into the air. The conveyor belt means nothing.

For flight, groundspeed means NOTHING AT ALL. The conveyor belt is not altering airspeed, it is only altering groundspeed, therefore IT MEANS NOTHING.