Riddle Me This.....Before My Brain Implodes!

[Sir_Brizz]

Alright, dead horse or not, this needs to end now.

Aircrafts work by having these things called Wings. Wings generate lift. Lift is generated by having gas (most likely the surrouding air) move across the foils. A pressure difference is created, and the wings "move" to fill the void.

Now, part two of this comes from another magical thing called relativity. If I was in a train that's moving at 20 m/s, and I walk 3 m/s towards the back of the train, an observer on the train would say that I'm moving at 3 m/s. However, a dude standing next to the train tracks would say that I'm moving at 17 m/s.

Same thing here. To the surrounding atmosphere (aka your source of wind), the plane is moving at 0 m/s. To an observer standing next to the conveyor, there is no forward velocity. Barring any hurricane or an already extremely windy day, there's no lift generated. A plane cannot magically lift up when its wheels are spinning fast enough. It needs to have a consistent amount of moving gas blowing across its wings, and moving very fast against a body of gas happens to be a great way of doing it. The engines/propellers alone do not generate the wind necessary to lift off, they only allow the plane to accumulate enough kinetic energy to allow the wings to generate lift.

I can't believe people are arguing against this.

If you think about the fact that in order for the plane to actually MOVE forward, the wheels would have to be going double the speed of the conveyor belt, in which case the conveyor belt would then double it's speed to match, you can see that in fact the plane cannot move forward, as the conveyor is always going exactly the opposite acceleration of the wheels friction upon it. It's absolutely ludicrous to say that the plane could actually lift off the ground.

 

[sid]

My apologies, sidgenex. I misunderstood your comment.
​

Apologies? no need

 

[Israphel]

Planes measure speed relative to airspeed, not wheel speed. This is so because sometimes there's a weird thing that happens that makes the air and the ground not going at the same speed. You might know this strange phenomenon from its common name: WIND.

The conveyor will simply make the wheels turn twice as fast as they would. The plane will accelerate the same (its engines aren't connected to the ground in any way or shape) and take off.

Next question.

Yup this is it exactly, everyone seems to have got bogged down with crap about the wheels moving and that this would be negated by the conveyer belt....but this has got nothing to do with it.
It would only be the case if there were traction, if the planes forward momentum were powered through the wheels...but its not, a plane's forward momentum is generated by thrust, which basically pushes against the air around it. As the air is stationary (kind of), the movement of the conveyor is irrelevent...the engines provide thrust against the surrounding air which generates forward movement, pushing air over the wings and the plane takes off.

If the plane were in a wind tunnel though, with a fan pushing air at exactly the same speed that the engines were generating thrust...now then it wouldn't be such a simple question

you can see that in fact the plane cannot move forward, as the conveyor is always going exactly the opposite acceleration of the wheels friction upon it. It's absolutely ludicrous to say that the plane could actually lift off the ground.

It's not ludicrous! A plane's forward movement is generated by thrust against the surrounding air. No matter how fast the conveyor belt moves, it has no effect on the air around the plane...and it is the air that the plane pushes against..the ground has nothing to do with it when no traction goes through the wheels.
In puzzle terms, it's what's commonly called a red herring

 

[Sir_Brizz]

Yup this is it exactly, everyone seems to have got bogged down with crap about the wheels moving and that this would be negated by the conveyer belt....but this has got nothing to do with it.
It would only be the case if there were traction, if the planes forward momentum were powered through the wheels...but its not, a planes forward momentum is generated by thrust, which basically pushes against the air around it. As the air is stationary (kind of), the movement of the conveyor is irrelevent...the engines provide thrust against the surrounding air which generates forward movement, pushing air over the wings and the plane takes off.

If the plane were in a wind tunnel though, with a fan pushing air at exacltly the same speed that the engines were generating thrust...now then it wouldn't be such a simple question

Not so.

The Conveyor is matching it's speed to the speed of the plane. The engine crreate thrust BEHIND the plane, where the air generated by thrust is NOT going to affect the wings which is ultimately what causes upward lift.

edit: in addition, the wheels are the mechanism of allowing the THRUST of the plane to coincide with the LIFT/DRAG of the plane which causes it to take off. Without a method of forcing air around the wings, planes cannot take off.

 

[G-Lite]

Given the size and weight of an airplane, and the length of the runway, I don't think such a conveyer belt will ever exist. Not because it cannot be done, but because it'd take too much in return for very little demand for such a product.

 

[namu]

If you think about the fact that in order for the plane to actually MOVE forward

would have nothing to do with its wheels at all.

Engines => push forward => plane accelerates forward.

Wheels/conveyor's total red herring.

 

[haarg]

If you think about the fact that in order for the plane to actually MOVE forward, the wheels would have to be going double the speed of the conveyor belt, in which case the conveyor belt would then double it's speed to match, you can see that in fact the plane cannot move forward, as the conveyor is always going exactly the opposite acceleration of the wheels friction upon it. It's absolutely ludicrous to say that the plane could actually lift off the ground.

The question as stated says that the convayer will match the plane's velocity, which is not the same as it's wheel's rotational velocities.

 

[namu]

the wheels are the mechanism of allowing the THRUST of the plane to coincide with the LIFT/DRAG of the plane

Not.

The wheels only provide support for the plane, no horizontal force involved.

 

[Sir_Brizz]

would have nothing to do with its wheels at all.

Engines => push forward => plane accelerates forward.

Wheels/conveyor's total red herring.

That's exactly the conundrum. The engines force the plane into standing air, forcing the air to move around the wings which causes lift.

The conveyor belt is going exactly the same speed as the plane (not the wheels, but that's irrelevant). In essence, the plane is standing exactly still.

You could actually say this is such:

Imagine you are walking backwards on a conveyor belt so that you appear to be standing still. If you JUMP off the conveyor belt, will you move forward? If not then the plane gets no lift and cannot take off. How does a plane lift off?

Not.

The wheels only provide support for the plane, no horizontal force involved.

The wheels don't need to provide force. You could attach the turbine engines to the base of the landing gear and have the same effect, it makes no difference where the propulsion comes from. The fact is that without air pressure around the wings, the plane cannot take off. If it did, it would have to have some other mechanism of lifting off of the ground than what planes have now, which is forced air pressure.

 

[sid]

Yep Sir Brizz is cent percent right :tup:
Suppose there is no conveyer belt, it is a normal runway ..........its a no brainer, the plane will take off due to the the air being caught up in its wings when its is bueing pshed forward by the engines. But in this case, the push being generated by the engines is being nullified cause of the opposite force being applied by the conveyer belt so under normal windspeed conditions the plane will never take off (because the plane would never change its position and there will be no wind or air being caught up in the wings.....ultimately the wings would not serve their purpose).

 

[Raffi_B]

The question is phrased like this:

"As fast as the plane is moving forward, the conveyor belt is moving backwards"

In other words, the plane is moving forward. The plane cannot be stationary when the question specifically states that the plane is moving forward. Therefore, there is air moving under its wings. The plane will take off.

 

[namu]

That's exactly the conundrum. The engines force the plane into standing air, forcing the air to move around the wings which causes lift.

Yup.

The conveyor belt is going exactly the same speed as the plane (not the wheels, but that's irrelevant). In essence, the plane is standing exactly still.

Nonsense.
If the plane is moving, it cannot stand still. If it is standing still, the conveyor belt is standing still too.

The simple obvious thing is: the conveyor belt doesn't stop the plane from moving ! The wheels are free-turning. Whatever speed the conveyor belt is running at, has little impact on he plane's horizontal speed.

Imagine you are walking backwards on a conveyor belt so that you appear to be standing still. If you JUMP off the conveyor belt, will you move forward? If not then the plane gets no lift and cannot take off. How does a plane lift off?

Now imagine you have rollerskates on your feet, and are standning on a conveyor belt. Whatever way and speed the conveyor belt rolls, you're standing still. Now comes someone that shoves you forward. You fall off the conveyor belt forward.

Is that clear enough now ?

 

[Israphel]

Not so.

The Conveyor is matching it's speed to the speed of the plane.

The speed of the plane is relative to the air around it NOT the speed that it wheels move over the conveyor belt.
If the air is moving around the plane it will generate lift. The plane's engines will displace the air and move it forward. Imagine its a prop plane, it will pull the air towards it and that will in turn pull the plane through the air. How can a conveyer belt have any effect on that?
The conveyor belt has no effect on the air.

In puzzle terms, it's what's commonly called a red herring

I've said all I'm going to say. Either you get it or you don't...

Bet you kick yourself later though

 

[sid]

In other words, the plane is moving forward. Therefore, there is air moving under its wings. The plane will take off.

No, there is no air moving the plane is still.

 

[Raffi_B]

The question specifically states that the plane is moving forward:

The plane moves in one direction

If it were stationary, it wouldn't be moving would it?

This isn't a physics related question at all, which is kind of annoying... it's just the trickery in which the way the question is asked. Most people overlook the fact that the plane is explicitly described to be moving. If it is moving, there is air under its wings, and therefore it will take off.

 

[sid]

Read the question again there is no action being done the event of the plane moving forward is not taking place.

 

[Raffi_B]

Read this part:

The plane moves in one direction

The plane is moving.

 

[namu]

A plane is standing on a runway that can move (some sort of band conveyer). 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?

Quoted for obviousness.

 

[sid]

Okay think again what is the use of the conveyer if the plane is actually covering distance on the runway?

 

[Airmoran]

Oh great, okay, AGAIN, RELATIVITY.

If I was on the same damned train, running to the back at 20 m/s, a dude on the train would say that I'm running at 20 m/s, but a guy standing next to the tracks would say that I'm essentially not moving.

You can be both moving forward and standing still. It's called relativity and perspective.

Stating if the plane is "moving foward" probably meant relative to the conveyor. If not, the question is pathetically stated and I say we kill the thread starter for beginning the mess.