[Closed] What is this aircraft on a conveyor belt that people often quote?

So if the belt is moving backwards at 1500kmH the plane will not be making any forward progress.
Of course at the tires will have exploded by that point, somewhat increasing the friction.

not sure about that, metal rims of the wheels probably have less drag on the ground than rubber would

not sure about that, metal rims of the wheels probably have less drag on the ground than rubber would

I'd go with that.

You also can't ignore the fact that you're talking about the tyres exploding, but overlooking the ability of this (incredibly theoretical!) conveyor belt to move at 1500kmh.

I must admit I was thinking commercial aircraft rather than light. But ok. I'll give you a slow clap, for the maths 🙂

Why, pose me a situation whereby a conveyor belt would stop a plane taking off?

If you could get the belt moving at the right speed then the boundary layer could result in the air flow on the underside of the wing being the same as on the top resulting in no lift being generated (I'm not doing the calculations to check this by the way).

Bruce! We did those maths! The viscosity of the air would have to be ~3 orders of magnitude higher than it is (at sea level) for the boundary layer to grow to the wing!

surely the rolling resistance is only relative to how good the bearings are? if you have super-duper 100% efficient bearings, the rolling resistance is irrelivent? Or am I missing something

You did the calculations in 2 1/2 minutes. I'm impressed!

OK, so a conveyor belt in a big pressurised dome. The no people were right all along!

surely the rolling resistance is only relative to how good the bearings are? if you have super-duper 100% efficient bearings, the rolling resistance is irrelivent? Or am I missing something

That would be largely true if you were dealing with something like a train where the wheels are to all intents non deformable. But with a pneumatic tyre it deforms, and this deformation requires force/energy that is not all returned in a useful manner. Generally speaking the lower the pressure in the tyre, the more it deforms, and the faster it rolls the quicker it deforms, so as speed increases so does the force required to deform the tyre.

That would be largely true if you were dealing with something like a train where the wheels are too all intents non deformable. But with a pneumatic tyre it deforms, and this deformation requires force/energy that is not returned in a useful manner. Generally speaking the lower the pressure in the tyre, the more it deforms, and the faster it rolls the quicker it deforms, so as speed increases so does the force required to deform the tyre.

but..

as speed increases, the force required to deform the tyre increases, would it ever get to a point where the inflexibility of the tyre stops it deforming? ie would (at 1000mph) the tyre start to kinda 'float' into a perfectly spherical shape? Centrifugal forces would push the rubber out into a spherical shape, and in addition, as the tyre is circular, there might not be enough accelleration to deform it. Above a certian speed, these forces would be strong enough to hold even a completely flat tyre in a complete circle?

This really is getting absurd now! Back to perfect spheres in a vacuum...

So the tyre would eventually grow enough to take the structure of the tyre or plane out...

I read this as you can't answer the question without further information.

So the tyre would eventually grow enough to take the structure of the tyre or plane out...

I don't think so, as the structure of the tyre would stop it from expanding too much. Obviously at infinate speed the centrifugal force would out-do even those forces and it'd expand more, but at that point it'd loose contact with the wheel and just roll off down the runway?

I don't think so, as the structure of the tyre would stop it from expanding too much. Obviously at infinate speed the centrifugal force would out-do even those forces and it'd expand more, but at that point it'd loose contact with the wheel and just roll off down the [s]runway[/s] conveyor?

FTFY 😉

What a larrf. We have two possible GCSE level questions intended to demonstrate the idea that airspeed isn't groundspeed, and most of you are arguing with someone answering the other question, and some of you are answering both at once. Backwards.

Can a plane take off at a standstill by running on a treadmill?
(No, because airspeed isn't groundspeed.)

Can a plane with a runway sized treadmill take off even if the treadmill runs against it?
(Yes, because airspeed isn't groundspeed.)

Thread over.

except its not, as described in the thread, if a treadmill's running fast enough, it creates air pressure which reduces lift on the wings, and drag on the tyres which would slow the aircraft down

Not at GCSE level it doesn't.

And in the real world if it's the treadmill that acclerates to match but oppose the plane's groundspeed, then it won't get nearly fast enough to do either.

And in the real world if it's the treadmill that acclerates to match but oppose the plane's groundspeed, then it won't get nearly fast enough to do either.

What gave you the idea we're talking about the real world?

So if the conveyer is running at such a speed that the rolling resistance of the wheels equals the thrust of the engines then the plane won't take off. Tick

But how would it ever reach this steady state? The only way to achieve this is if the rolling resistance of the tyres matches exactly the thrust of the engines as they are accelerated from a standstill.

So all you need is an aircraft engine that can accelerate faster than the conveyor and your plane will still take off, preventing the conveyor from reaching its speed of victory.

or you could just have the conveyer belt running full pelt the whole time, and the 'start' of the conveyer is against a wall to stop the plane falling off the back?

twoundred!

Why would you do this!? I'm now rereading the thread and becoming angered by the muppets who imagine the plane would stay still when you start the conveyor belt!