This old chestnut

[mike os]

The ground and convey make no difference to the body’s speed, the wheels are not the means of propulsion

 

[Munkul]

Why will the wheels and conveyor move at infinite speed? Once the areoplane has lifted there is no longer contact.

How does the plane lift without getting to its takeoff speed? That is the whole question... DOES the plane get to its takeoff speed?
And again, if you read the original question with the original set of conditions, it is mathematically impossible.

 

[mike os]

How does the plane lift without getting to its takeoff speed?

The wheels still do not provide propulsion …

 

[Seadog]

See my previous post.

 

[Pete.]

incorrect assumption

Pretty much the whole basis of debate about this topic. People are forced to make assumptions

 

[daleyd]

I can see where you are coming from. 99% of people would read it as the wheel surface speed. The possible confusion would be about the MOVEMENT of the wheel as a whole (ie the plane speed), not the surface speed.

Rotational speed is an incorrect assumption because revolutions or angular speed cannot equal surface speed, it's a non starter.

It's not an incorrect assumption any more than an assumption that it's referring to the forward speed. If you put a car on blocks, put it in gear and put your foot on the throttle you will get an indicated speed of say 50mph. Because the car isn't going forward does that mean the wheel rotational (Or circumference speed more precisely) speed of the wheel is zero? Of course not.

 

[Munkul]

It's not an incorrect assumption any more than an assumption that it's referring to the forward speed. If you put a car on blocks, put it in gear and put your foot on the throttle you will get an indicated speed of say 50mph. Because the car isn't going forward does that mean the wheel rotational (Or circumference speed more precisely) speed of the wheel is zero? Of course not.

Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the rotating surface speed of the wheels, moving in the opposite direction.

Does that make things any clearer? that is how it should be read from my point of view.

As Pete says, the whole question leads to incorrect assumptions regardless of wording

 

[daleyd]

Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the rotating surface speed of the wheels, moving in the opposite direction.

Does that make things any clearer? that is how it should be read from my point of view.

As Pete says, the whole question leads to incorrect assumptions regardless of wording

So they would be stationary then

 

[Munkul]

So they would be stationary then

Actually i see your point now, clever clogs It's an assumption which had never occurred to me. Whether you choose to go off the top dead centre of the wheel surface going forwards, or the bottom dead centre which is going backwards.

 

[Munkul]

The wheels still do not provide propulsion …

This is elementary.

 

[daleyd]

No! The wheels would only be stationary if the conveyor went the same way as the wheels.

You're going off the top surface direction of the wheels, not the bottom surface in contact with the conveyor. Why you are choosing to do this, i don't know. It's obvious that you use the surface in contact with the conveyor

Actually i see your point now, clever clogs It's an assumption which had never occurred to me.

No - the plane moves forwards in the air - the bottom of the wheels (in contact with the conveyor) rotate rearwards. The conveyor has to move forwards (as that is opposite to rearward) at the same speed as the wheels - so they would stay stationary.

The top of the wheel rotate in a forward direction when the plane is going forward.

 

[Munkul]

See my previous post.

If you totally ignore the wheels and conveyor, of course the plane is propelled forward. The trick in the question is in the fact that the entire scenario as a whole including the wheels/conveyor is impossible.

See my previous posts with the 2nd scenario which is possible, and was also proved on mythbusters et al

 

[Munkul]

No - the plane moves forwards in the air - the bottom of the wheels (in contact with the conveyor) rotate rearwards. The conveyor has to move forwards (as that is opposite to rearward) at the same speed as the wheels - so they would stay stationary.

The top of the wheel rotate in a forward direction when the plane is going forward.

Sorry mate i see your point, I edited my post

 

[daleyd]

Actually i see your point now, clever clogs It's an assumption which had never occurred to me. Whether you choose to go off the top dead centre of the wheel surface going forwards, or the bottom dead centre which is going backwards.

You can tie yourself up in knots all day thinking about this And I still don’t know that I’m right, just that I “think” what I’m saying makes sense to me (at least!!)

 

[Cobbler]

115 posts on this question, there is only one way to prove it. Let’s get building

 

[Munkul]

You can tie yourself up in knots all day thinking about this And I still don’t know that I’m right, just that I “think” what I’m saying makes sense to me (at least!!)

The person who came up with this question was either an evil genius, or just as simple as the rest of us and didn't realise how open to interpretation is is

 

[bricol]

The person who came up with this question was either an evil genius, or just as simple as the rest of us and didn't realise how open to interpretation is is

Whoever came up with it wasn't asking you to design the system to do it, just what would happen if you could. And that answer is easy. You're in for some time of the flippin kid behind twatting the back of your seat . . .

 

[RWD3M]

I must look and see the speedometer the next time I pilot a Jumbo. Surely they use speed sensors not speedometers.

Well yes, of course, hence hiding behind the sofa!

At the moment, though I have been out of the arena for a couple of years, most military and commercial aircraft use simple, axle mounted transducers to send wheel speeds to an anti skid controller.

Some older stuff use maxaret units which were also used on the Jensen Interceptor FF!

 

[Olderisbetter]

Once you put anything on the conveyor belt that is not luggage the baggage handlers will go on strike and that is the end off take offs.

 

[Maker]

Imagine holding a bike on a treadmill, as long as you hold it still, the surface speed of the wheel must be exactly the same as the belt speed (Assuming it's not skidding or anything). If you push the bike forward a little, while the bike is moving, the wheel is turning slightly faster than the belt. If the belt speed matches the wheel speed, bike cannot move forward. It doesn't matter how fast (Or even which direction) the belt is moving, if the wheel's speed matches it, the bike is stationary.

Reasoning it like that, the question essentially becomes "What happens if you push something that can't move?", which is easy, it doesn't move.