Plane

[Voyager EMH]

In Pope vs Galileo who won?

One defended words as reality.
The other described observed reality.

Initially the Pope won. He had majority view, authority and law on his side and Galileo was under house arrest for the rest of his life.
Galileo did win, but after his death.
He was not wrong.

A minority can be right.
This can include a minority of one.

 

[Golf is fun]

The engines produce a force that wants to move the airframe forwards. The point of least resistance with the ground (Or the conveyor belt) are the planes wheels therefore the airframe moves forward as the wheels turn. In such a theoretical exercise we have to take certain conditions as reasonable (The wheels are able to turn and support the airframe at any speed etc).
The conveyor belt is setup such that it's rotation in the opposite direction to the wheels match their speed exactly. In this case the two rotations cancel eachother, therefore whatever the thrust of the engines the forward rotation of the wheels are offset by the rearward rotation of the conveyor. The airframe remains stationary with respect to the space around it, there will not be sufficient air passing over the wing to create lift, the plane will not take off.

There are 2 important things to be aware of here:

1) Watch a car moving forwards, the top surface of the wheel moves in the direction of travel, the bottom surface of the wheel (that touching the road) moves in the opposite direction of travel, it is actually trying to push the road backwards, the road pushes the wheel forwards with an equal and opposite force (Newtons 3rd law at work), and the car moves forward when that force is big enough to cause it to do so, because the force needed to move the car is reached before the force needed to move the earth. The key point here is really the direction of the wheel, the bottom surface moves opposite the direction of travel, so a conveyor overcoming that would have to move in the direction of travel, hence it would move the aircraft forward.

2) The engines are not connected to the wheels, they are just there as rollers as on a normal runway a wheel provides less resistance than a skid. To picture this imagine trying to rollerskate the wrong way on a travelator, it would be tricky because you are pushing against the ground, however if the travelator had fixed handrails you could pull yourself along with your arms, this is because the interaction between the wheels and the ground is not what is propelling you, it's your arms pulling the rails. The aircraft is the same, the wheels are rollerskates and the engines are your arms with fixed handrails. Hopefully this way of visualising it makes it easier to understand.

 

[RichA]

Counteracting their rotation - this wording can not be used to justify an impossibility that becomes "a thing that actually does happen". The impossibility does not happen.

The rotation of the wheels is not an act of the wheels. The wheels are not active. They are passively responding when they rotate.
If the wheels start to rotate, then the conveyor moves at the same speed. This is the conveyor countering.

The conveyor IS countering the wheels, by matching their speed of rotation.
But this countering action of the conveyor does not prevent the plane from taking off.
The conveyor does not counter or oppose the jet engines.

Arguing that the wording or the phrasing describes an impossibility that is happening, or can happen, seems a very pointless exercise.
It will never be a "winning" argument.

If the wording has produced vagueness or an ambiguity, this does not change reality.
Such a conveyor, as we know the realms of reality allow, will not prevent the plane from taking off.

All true.
But if the plane has managed to move forwards 2 miles then one of two things has to have happened.

Either

The plane wheels have rotated 2 miles further than the conveyor belt (impossible due to perfect speed matching)

Or

The tyres are skidding.
They aren't locked; they are still rotating perfectly opposite the belt but they are skidding.
But their surface, which is designed for grip on a runway to allow braking after landing, is rubbing against the conveyor belt at the rate of whatever the plane's speed is at it tries to take off (up to ~180mph).

Friction, heat.

The new question for me is how much friction and heat can a 747 tyre take before it fails. They certainly aren't designed to be abrading a runway surface at 180mph.

 

[Beezerk]

Exactly! The question is badly worded, but if we take the question so literally that some laws of physics don't apply and replaced by some mysterious unexplained phenomenon, the question becomes impossible to answer, as there is no point applying any other physical laws to the situation, why not just replace them with unexplained phenomena too?

As much as I agree with this and following the laws of physics the plane will take off, under the wording of the question though it can’t take off. That’s the whole point of it, it’s so badly worded that it causes arguments and division.
If a plane is at the far end of a massive conveyor runway which starts to turn away from the nose of the plane at 180mph it moves the plane backwards, once the plane reaches 180mph (backwards) the pilot chucks on the engines and the plane will eventually start moving forward and reach 180mph and take off but, the wheels are turning at 360mph which means it doesn’t fit the original question.
We need Harry Potters magic to change the question so the plane can take off

 

[Golf is fun]

All true.
But if the plane has managed to move forwards 2 miles then one of two things has to have happened.

Either

The plane wheels have rotated 2 miles further than the conveyor belt (impossible due to perfect speed matching)

Or

The tyres are skidding.
They aren't locked; they are still rotating perfectly opposite the belt but they are skidding.
But their surface, which is designed for grip on a runway to allow braking after landing, is rubbing against the conveyor belt at the rate of whatever the plane's speed is at it tries to take off (up to ~180mph).

Friction, heat.

The new question for me is how much friction and heat can a 747 tyre take before it fails. They certainly aren't designed to be abrading a runway surface at 180mph.

The key question to ask here is what has the plane moved forward relative to?

The wheels are freewheeling, the only way for the wheels not to turn it must be not moving relative to the conveyor, however for this to occur the conveyor must be moving the plane in a forward direction relative to the rest of the world.

 

[Deleted member 35927]

All true.
But if the plane has managed to move forwards 2 miles then one of two things has to have happened.

Either

The plane wheels have rotated 2 miles further than the conveyor belt (impossible due to perfect speed matching)

Or

The tyres are skidding.
They aren't locked; they are still rotating perfectly opposite the belt but they are skidding.
But their surface, which is designed for grip on a runway to allow braking after landing, is rubbing against the conveyor belt at the rate of whatever the plane's speed is at it tries to take off (up to ~180mph).

Friction, heat.

The new question for me is how much friction and heat can a 747 tyre take before it fails. They certainly aren't designed to be abrading a runway surface at 180mph.

Your obsessed with this perfect speed matching, how is it opposing the thrust of the planes engines , the wheels offer little resistance so how is it doing it.

 

[Golf is fun]

As much as I agree with this and following the laws of physics the plane will take off, under the wording of the question though it can’t take off. That’s the whole point of it, it’s so badly worded that it causes arguments and division.
If a plane is at the far end of a massive conveyor runway which starts to turn away from the nose of the plane at 180mph it moves the plane backwards, once the plane reaches 180mph (backwards) the pilot chucks on the engines and the plane will eventually start moving forward and reach 180mph and take off but, the wheels are turning at 360mph which means it doesn’t fit the original question.
We need Harry Potters magic to change the question so the plane can take off

The only way for the wheels to not turn in the real world is for the conveyor to move forwards, so the relative speed between aircraft and conveyor is 0. In this instance the plane will take off as the conveyor is moving it forwards.

If we take the question literally, there is no answer. It's like saying the red apple is blue, what colour is the purple orange? It's just nonsense, in the same way the conveyor cannot both move in the opposite direction to the wheels and counteract their rotation, they're completely opposite actions.

 

[Swango1980]

All true.
But if the plane has managed to move forwards 2 miles then one of two things has to have happened.

Either

The plane wheels have rotated 2 miles further than the conveyor belt (impossible due to perfect speed matching)

Or

The tyres are skidding.
They aren't locked; they are still rotating perfectly opposite the belt but they are skidding.
But their surface, which is designed for grip on a runway to allow braking after landing, is rubbing against the conveyor belt at the rate of whatever the plane's speed is at it tries to take off (up to ~180mph).

Friction, heat.

The new question for me is how much friction and heat can a 747 tyre take before it fails. They certainly aren't designed to be abrading a runway surface at 180mph.

These points are true, but the confusion lies into how you (not just you) are interpreting the OP. You have basically understood that the plane wheels will be going a speed forwards and the belt the same speed backwards. Like a regular treadmill with a person or car on it. Clearly the OP was written this way as it knew this is what many would jump to think. Including myself when I first read it.

But, I quickly realised that interpretation is impossible. You have concluded that yourself. It is impossible for a treadmill to stop the plane going forwards. So, if the treadmill goes backwards, even if the programmer tried to achieve matching up wheel speed and belt speed, it could never happen.

So, either the programmer was unsuccessful and plane took off anyway, or the OP meant the programmer was trying something else.

If they programmed the belt to match speed and direction of plane, then at any given point you could say it is matching speed of wheels in opposite direction. If plane was travelling 96mph forwards, wheels would be travelling 96mph backwards (against ground), so if it hit belt at this point the belt would need to go 96mph forwards to counter wheel rotation (effectively matching their speed in opposite direction). Obviously, we can assume plane is on belt at rest, so when it starts moving the belt will match the wheel speed straight away to counter the rotation, and belt will continue to speed up to match the speed they wish to move.

If you counter a wheel from rotating then it means it isn't rotating. So the belt must go forwards to do this. If it goes backwards, that part of the OP makes no sense, because the belt doesn't counter rotation, it aids it.

 

[Beezerk]

The only way for the wheels to not turn in the real world is for the conveyor to move forwards, so the relative speed between aircraft and conveyor is 0. In this instance the plane will take off as the conveyor is moving it forwards.

Exactly it’s purposely open to interpretation. For me it means it rolls the opposite way to the wheels for someone else it means the conveyor moves forward to try and stop the wheels rotating, I guess your reasoning in this depends on what you want the final answer to be. There are no right and wrong answers imo.

 

[RichA]

Your obsessed with this perfect speed matching, how is it opposing the thrust of the planes engines , the wheels offer little resistance so how is it doing it.

Perfect speed matching is the premise of the problem.
If the conveyor and the wheels are stationary the plane will skid forward with locked wheels due to the thrust.
If the conveyor and wheels are both moving at 1000mph and the plane is moving forward relative to the ground and stationary air at 100mph then the tread is the tyres is rubbing forward against the conveyer belt at 100mph.

The wheels may not be driven, but if their speed is always identical to the conveyor belt's speed and there is perfect traction then the plane can't go forward. That's how cogged gears operate.

 

[Swango1980]

The problem in the OP is only "does the plane takes off?".

So, even if you think belt goes backwards and wheels move same speed forwards (and ignore the part in OP about the rotation being countered), you could just say the plane takes off whilst wheels skid on runway (for a reason unknown, and nothing the programmer could control). Thus wheels are rotating at same speed they would have done on a static runway, skidding enough not to rotate more by the belt working backwards underneath

But, you can still answer the question, plane takes off.

 

[Voyager EMH]

All true.
But if the plane has managed to move forwards 2 miles then one of two things has to have happened.

Either

The plane wheels have rotated 2 miles further than the conveyor belt (impossible due to perfect speed matching)

This is the bit that needs a change of perception.
We are not observing a constant speed conveyor, but one that speeds up as the wheel rotation speeds up.

An observer, from a distance, sees the plane taking off as normal - travelling 2 miles and taking off.
What length of conveyor belt has passed beneath the plane during that observation will equal circumference of a wheel multiplied by the number of rotations made.
Whether that is 1 mile more than 2, 2 miles more than 2 or 8 miles more than 2, does not cause problems to or prevent takeoff.

If the observer was watching another plane taking off alongside on a normal runway, the plane's speeds would be similar, but the rotations of wheels would be more/faster for the one on the conveyor.
Because they are more/faster, that is how it is "keeping up" with the other plane.
The wheels "don't have to do anything" to achieve this, because they merely respond passively.

 

[Beezerk]

The problem in the OP is only "does the plane takes off?".

So, even if you think belt goes backwards and wheels move same speed forwards (and ignore the part in OP about the rotation being countered), you could just say the plane takes off whilst wheels skid on runway (for a reason unknown, and nothing the programmer could control). Thus wheels are rotating at same speed they would have done on a static runway, skidding enough not to rotate more by the belt working backwards underneath

But, you can still answer the question, plane takes off.

What if the pilot has the engine power output just enough to match the rotation of the conveyor? You’re assuming he’s on full blast and wanting to take off.

 

[RichA]

If you counter a wheel from rotating then it means it isn't rotating. So the belt must go forwards to do this. If it goes backwards, that part of the OP makes no sense, because the belt doesn't counter rotation, it aids it.

The conveyor belt is programmed to match the speed of the plane's wheels.
If you have it that the wheel is prevented from rotating then the conveyor isn't moving either.

 

[Deleted member 35927]

What if the pilot has the engine power output just enough to match the rotation of the conveyor? You’re assuming he’s on full blast and wanting to take off.

Yes you could do this I suppose , but thats a different question.

 

[Deleted member 35927]

The conveyor belt is programmed to match the speed of the plane's wheels.
If you have it that the wheel is prevented from rotating then the conveyor isn't moving either.

And back we go, the wheels are not powered, it's the movement of the plane through the air the belt needs to counter.

 

[Beezerk]

Yes of course you could do this, but thats a different question.

Not really, the question mentions the wheels and conveyor speed match so maybe the pilots remit is to try and do this and see what happens.

 

[RichA]

This is the bit that needs a change of perception.
We are not observing a constant speed conveyor, but one that speeds up as the wheel rotation speeds up.

An observer, from a distance, sees the plane taking off as normal - travelling 2 miles and taking off.
What length of conveyor belt has passed beneath the plane during that observation will equal circumference of a wheel multiplied by the number of rotations made.
Whether that is 1 mile more than 2, 2 miles more than 2 or 8 miles more than 2, does not cause problems to or prevent takeoff.

If the observer was watching another plane taking off alongside on a normal runway, the plane's speeds would be similar, but the rotations of wheels would be more/faster for the one on the conveyor.
Because they are more/faster, that is how it is "keeping up" with the other plane.
The wheels "don't have to do anything" to achieve this, because they merely respond passively.

This bit isn't about perception, it's about mechanics and maths. Regardless of whether conveyor belt speed is constant or variable, if the plane moves forwards on the belt either it's wheels are moving faster than the belt or it is skidding.

 

[Deleted member 35927]

This bit isn't about perception, it's about mechanics and maths. Regardless of whether conveyor belt speed is constant or variable, if the plane moves forwards on the belt either it's wheels are moving faster than the belt or it is skidding.

Well it's about the laws of motion and what you think is happening overrides those.

 

[Deleted member 35927]

Not really, the question mentions the wheels and conveyor speed match so maybe the pilots remit is to try and do this and see what happens.

And maybe there isn't a pilot at all.
We can all make stuff up and go off on irrelevant tangents. It's part of the reason the thread is still rolling on.