Is it just me or are people fucking thick?

[kalmar]

The treadmill exactly matches the rotation of the wheels when the plane is still, because it is also still. When the plane starts moving, the treadmill has to move to catch up, and then it immediately gets into a race with itself that it must always lose.

Even if the treadmill is capable of exceeding the maximum velocity created by the plane's engines?

It would have to exceed many many times the plane's maximum velocity. Even to resist "walking pace" levels of power the treadmill would probably have to be running at hundreds of miles per.

Even on a car, losses (at road speed) due to the wheels / bearings etc are almost negligible compared to the maximum output of the engine.

[phattslagg]

Even if the treadmill is capable of exceeding the maximum velocity created by the plane's engines?

In which case wouldn't we all be going on our holidays by treadmill rather than jetplane?

/troll

We'd all be a fucksight fitter if we did.

[Mir Nyet]

Simply connect a speedo to the planes wheels, link this to the rolling road, if the speed of the wheels is greater than the road thinks it should be, increase the speed of the road to address the issue. By constantly blipping the speed of the rolling road, any forward motion of the plane would be arrested, and the plane kept in place. There would need to be some form of lateral mounts fitted to the wheels to stop the plane drifting sideways on the rolling road, but other than this, the technology to do this for a small plane is quite old.


Magical means indeed

[Mir Nyet]

The treadmill exactly matches the rotation of the wheels when the plane is still, because it is also still. When the plane starts moving, the treadmill has to move to catch up, and then it immediately gets into a race with itself that it must always lose.

Even if the treadmill is capable of exceeding the maximum velocity created by the plane's engines?

It would have to exceed many many times the plane's maximum velocity. Even to resist "walking pace" levels of power the treadmill would probably have to be running at hundreds of miles per.

Even on a car, losses (at road speed) due to the wheels / bearings etc are almost negligible compared to the maximum output of the engine.

As I mentioned a little eariler, the rolling roads in F1 wind tunnels run at 200mph+ this is more than enough for a small plane.

[Mir Nyet]

If the treadmill was to match the wheels' rotation right from the start

No. The treadmill exactly matches the rotation of the wheels when the plane is still, because it is also still. When the plane starts moving, the treadmill has to move to catch up, and then it immediately gets into a race with itself that it must always lose.

Nah, phattslag has a different interpretation: the treadmill works like a treadmill, and can go so fast that the rolling resistance of the tyres equals the output of the engines.
You have to ignore that they would explode practically as soon as you open the throttle, but he's come up with an answer for it.

Err, so why do tires on a plane not explode when the plane is launching itself down a runway?

[fred_zen]

The treadmill exactly matches the rotation of the wheels when the plane is still, because it is also still. When the plane starts moving, the treadmill has to move to catch up, and then it immediately gets into a race with itself that it must always lose.

Even if the treadmill is capable of exceeding the maximum velocity created by the plane's engines?

It would have to exceed many many times the plane's maximum velocity. Even to resist "walking pace" levels of power the treadmill would probably have to be running at hundreds of miles per.

Even on a car, losses (at road speed) due to the wheels / bearings etc are almost negligible compared to the maximum output of the engine.

At that speed, wouldn't the treadmill also move the air above it, creating face-wind (and, thus, lift) for the plane?

[kalmar]

The treadmill exactly matches the rotation of the wheels when the plane is still, because it is also still. When the plane starts moving, the treadmill has to move to catch up, and then it immediately gets into a race with itself that it must always lose.

Even if the treadmill is capable of exceeding the maximum velocity created by the plane's engines?

It would have to exceed many many times the plane's maximum velocity. Even to resist "walking pace" levels of power the treadmill would probably have to be running at hundreds of miles per.

Even on a car, losses (at road speed) due to the wheels / bearings etc are almost negligible compared to the maximum output of the engine.

As I mentioned a little eariler, the rolling roads in F1 wind tunnels run at 200mph+ this is more than enough for a small plane.

OK, so you're on a rolling road at 200mph. Let's assume your plane tyres are good for 300mph. The plane will take off as normal.
There is no scenario that you can counteract the engine's power using only frictional losses in the wheels without immediately reaching ludicrous speeds, far above what any tyre can stand.

[zip accident]

kalmar wrote:

Nah, phattslag has a different interpretation: the treadmill works like a treadmill, and can go so fast that the rolling resistance of the tyres equals the output of the engines.

I thought that, but then he started talking about matching the speed of the wheels again.

phattslagg wrote:

Even if the treadmill is capable of exceeding the maximum velocity created by the plane's engines?

If the converyer is matching the speed of the wheels, then when the plane is making the wheels go at x, then the converyer is going at x in the other direction, which also makes the wheels go round by a factor of x. So the speed of rotation of the wheels is in fact 2x, at the time the plane is going at x. However, the conveyer is matching the speed of the wheels, so it needs to go at 2x, but when it does that, the wheels are going at 3x, because of what the conveyer has done. So the conveyer cannot, even in theory, match the wheels.

[tufty]

But isn't that the nub of it? If the treadmill was to match the wheels' rotation right from the start (and therein lies possibly the biggest problem of all) then the plane would never move. Nothing like the speed of light would be reached anyway, since the engines would max out much earlier than this.

This is, inded, the nub of it. It's the nub of where you are wrong.

Consider a vehicle that is driven along the ground using its wheels. If we match the wheel's speed by moving the surface under the wheels at the same speed, yes, the vehicle will stay in the same place.

Now consider an aeroplane. It is not driven by its wheels, but, instead, by the reaction caused by applying forces to the air around it, one way or another (either by a jet engine, or a propellor). The wheels only rotate whilst it is on the ground because there is a speed differential between the two surfaces. The only way some "magic treadmill" could cause a plane not to take off would be to apply enough rolling resistance to stop the plane moving (very, very, unlikely, given that it would have to somehow apply that resistance through a set of relatively free-moving bearings), or by somehow applying enough force to the air surrounding the airplane in order to keep it under the plane's stall speed relative to the airplane's ground/treadmill speed.

The first of these is highly unlikely, and the second is not stated as being a function of the "magic treadmill", although there would likely be a certain amount of "entrainment" of the air due to the moving treadmill surface itself, the question then becomes "if we run the treadmill in the same direction as the aircraft, will it entrain enough air and fast enough to make it difficult for the plane to take off, and will that near-negligible entrainment be counteracted by the near-negligible accelerative effect of the frictional forces generated by running the wheels faster than they should go?"

So yes, the aircraft would take off.

simon

[kalmar]

At that speed, wouldn't the treadmill also move the air above it, creating face-wind (and, thus, lift) for the plane?

Very good point

[Mir Nyet]

The treadmill exactly matches the rotation of the wheels when the plane is still, because it is also still. When the plane starts moving, the treadmill has to move to catch up, and then it immediately gets into a race with itself that it must always lose.

Even if the treadmill is capable of exceeding the maximum velocity created by the plane's engines?

It would have to exceed many many times the plane's maximum velocity. Even to resist "walking pace" levels of power the treadmill would probably have to be running at hundreds of miles per.

Even on a car, losses (at road speed) due to the wheels / bearings etc are almost negligible compared to the maximum output of the engine.

As I mentioned a little eariler, the rolling roads in F1 wind tunnels run at 200mph+ this is more than enough for a small plane.

OK, so you're on a rolling road at 200mph. Let's assume your plane tyres are good for 300mph. The plane will take off as normal.
There is no scenario that you can counteract the engine's power using only frictional losses in the wheels without immediately reaching ludicrous speeds, far above what any tyre can stand.

How can the plane take off if it is effectively standing still? Only the wheels of the plane are in motion, all the forward thrust from the engines is being negated by the rolling road

Yes, I agree than the tires would be under huge stress, but the plane would be stationary... No air being accelerated over the winds means no lift...

End of story.

[Mir Nyet]

At that speed, wouldn't the treadmill also move the air above it, creating face-wind (and, thus, lift) for the plane?

Very good point

Made me smile this one, it is the air being accelerated OVER the wings that creates lift.

[kalmar]

At that speed, wouldn't the treadmill also move the air above it, creating face-wind (and, thus, lift) for the plane?

Very good point

Made me smile this one, it is the air being accelerated OVER the wings that creates lift.

No it isn't It's angle of attack.

[Mir Nyet]

But isn't that the nub of it? If the treadmill was to match the wheels' rotation right from the start (and therein lies possibly the biggest problem of all) then the plane would never move. Nothing like the speed of light would be reached anyway, since the engines would max out much earlier than this.

This is, inded, the nub of it. It's the nub of where you are wrong.

Consider a vehicle that is driven along the ground using its wheels. If we match the wheel's speed by moving the surface under the wheels at the same speed, yes, the vehicle will stay in the same place.

Now consider an aeroplane. It is not driven by its wheels, but, instead, by the reaction caused by applying forces to the air around it, one way or another (either by a jet engine, or a propellor). The wheels only rotate whilst it is on the ground because there is a speed differential between the two surfaces. The only way some "magic treadmill" could cause a plane not to take off would be to apply enough rolling resistance to stop the plane moving (very, very, unlikely, given that it would have to somehow apply that resistance through a set of relatively free-moving bearings), or by somehow applying enough force to the air surrounding the airplane in order to keep it under the plane's stall speed relative to the airplane's ground/treadmill speed.

The first of these is highly unlikely, and the second is not stated as being a function of the "magic treadmill", although there would likely be a certain amount of "entrainment" of the air due to the moving treadmill surface itself, the question then becomes "if we run the treadmill in the same direction as the aircraft, will it entrain enough air and fast enough to make it difficult for the plane to take off, and will that near-negligible entrainment be counteracted by the near-negligible accelerative effect of the frictional forces generated by running the wheels faster than they should go?"

So yes, the aircraft would take off.

simon

This falls over because the wheels are not independant of the plane, if the rolling road presents more force to the wheels pushing backwards than the engines generate pushing forward, then the plane is going nowhere...

The plane is not driven by its wheels, but it is certainly not independant of them either. Because the plane freewheels, the road would have to push a load of force through the wheels to negate the engine thrust, but it is doable.

[kalmar]

Yes, I agree than the tires would be under huge stress, but the plane would be stationary... No air being accelerated over the winds means no lift...

Yes, do try to keep up! But this is a silly and impossible scenario, just like the original question. And while we're here, it's just been pointed out that the draught from the magical rolling road going at nearly infinity miles per hour would allow the plane to lift anyway.