Is it just me or are people fucking thick?

[Mir Nyet]

The answer does unfortunately have a lot to do with the method of measuring and application of the retardation. If the planes thrust can be completely negated, then of course, the plane will not lift, regardless of cross winds, or dirty air from the engines, or rolling road etc etc etc. If the thrust is only dampened, then if the engines can provide enough thrust to overwhelm this dampening force and propell the plane to its take off speed, then it will fly.

For me, the riddle suggests that the thrust of the engine is completely negated and the plane remains stationary. This is a riddle to question peoples perception of why and how planes fly, the knee jerk reaction is -- duh, its not a car, the wheels do nothing, the plane flys because the engines are on . Regardless of how the thrust is negated, if the plane is stationary (or below its take off speed), it does not lift even if the engines are banging away at full thrust.

[kalmar]

Hm, not really. The article doesn't say anything about "negating the force of the engine" or the wheels or anything like that, it just proposes the scenario and asks if the plane will fly or not. So you have to try to work out what's happening.
You keep saying "if the plane doesn't move then it can't fly". Yeah, we get that. Nobody is arguing (outside of a few examples involving headwinds and high lift/drag coefficients). But that's not the question.

[gravy]

This is what I reckon.

How fast the plane moves forward depends on the bearings in the wheels, not between the wheels and the conveyer belt.

If they were completely frictionless the plane would move forward at the same speed however fast the conveyer was moving, not at all or infinity.

There will be friction in the bearings which will turn into drag and how much drag will be dependant on both the friction in the bearings and the friction between the wheels and the conveyer.

So that means the answer is "it depends"

If the drag created by the conveyer belt moving doesn't allow the plane to reach take off speed by the end of the converyer it won't take off.

[Mir Nyet]

Hm, not really. The article doesn't say anything about "negating the force of the engine" or the wheels or anything like that, it just proposes the scenario and asks if the plane will fly or not. So you have to try to work out what's happening.
You keep saying "if the plane doesn't move then it can't fly". Yeah, we get that. Nobody is arguing (outside of a few examples involving headwinds and high lift/drag coefficients). But that's not the question.

The article mentions a pushing force on the place (the rolling road), this not an attempt to make the wheel spin fast and make a nice sound , is an attempt to negate the thrust of the engine.

[aureole]

Right, so in the second plane there's a goat on a treadmill, so if you choose that plane, then you're guaranteed to not get the plane with snakes in, but the thing is, right, if they're survivors, then they wouldn't be dead and so couldn't be buried, even if the doctor was really the captain's mother, who was on the plane because she travelled south, then due east and north to get back to the South Pole, although polar bears really come from the North Pole and then when they got back on the plane the snowman they built melted leaving the coal and a carrot.

[piku]

Planes don't need thrust to fly. All they require is airflow over their wings. They don't need to move, they don't need any engines.

How else do kites work? It's a wing on a string and the moving air keeps it flying.

Its the same as kayak surfers surfing on a wave. You can either catch a wave and ride it to the beach (you moving over the water) or you can find a stationary wave and surf it without moving (water moving underneath you, you stay still). For a real live demonstration of this, go and watch kayakers on the sea, and then watch them on a river.

So there. Replace the kayak with an aeroplane, replace the water with air and you have the same model. Physics is consistent like that.

[Mir Nyet]

Out of interest, just how much thrust does a plane (normal plane, not an SR-71 ) have in hand when it is taking off? It is my understanding that a plane is pretty much maxed out on thrust during take off?

If this is the case, then surely the rolling road would not need to provide that much of a dampening force to keep the plane below its take off speed...

[fred_zen]

The article mentions a pushing force on the place (the rolling road), this not an attempt to make the wheel spin fast and make a nice sound , is an attempt to negate the thrust of the engine.

The rolling road doesn't attempt anything, it just does its thing. And yes, it makes the wheel spin fast. The hypothetical makers of the hypothetical road may well have intended for something else to happen, but that's too bad for them.

Come to think of it: what happens it the plane's motion is not exactly parallel to the road's motion? Does the road topple the plane?

[Mir Nyet]

The article mentions a pushing force on the place (the rolling road), this not an attempt to make the wheel spin fast and make a nice sound , is an attempt to negate the thrust of the engine.

The rolling road doesn't attempt anything, it just does its thing. And yes, it makes the wheel spin fast. The hypothetical makers of the hypothetical road may well have intended for something else to happen, but that's too bad for them.

Come to think of it: what happens it the plane's motion is not exactly parallel to the road's motion? Does the road topple the plane?

The amount of friction the road could and would apply to the wheels would increase with the angle of difference.

[fred_zen]

If this is the case, then surely the rolling road would not need to provide that much of a dampening force to keep the plane below its take off speed...

That's true but it can't provide much of a dampening force, too, because the wheels are free-spinning.

[Mir Nyet]

If this is the case, then surely the rolling road would not need to provide that much of a dampening force to keep the plane below its take off speed...

That's true but it can't provide much of a dampening force, too, because the wheels are free-spinning.

But not perfect, there is resistance.

[kalmar]

The article mentions a pushing force on the place (the rolling road), this not an attempt to make the wheel spin fast and make a nice sound , is an attempt to negate the thrust of the engine.

The rolling road isn't "pushing" on the plane directly, it's pushing on the part of the tyre in contact with the road. Forcing it to rotate about its axle. This is what it does anyway. Rolling resistance in the tyre (usually 1-2% of the tractive effort in cars) will cause a backward force on the plane. The disc brake drag will have a similar effect (although much less). Finally the bearing loss will have a minescule effect also.

So overall, at normal speeds (up to takeoff speeds) you have a tiny, negligible fraction of the engine's power being consumed by these losses: the plane still takes off. On the hypothetical rolling road, if it causes the wheels to go twice as fast, there will be 2*negligible losses. If the rolling road goes 10 times as fast, the tyres will explode before you get very far at all.

[Mir Nyet]

The article mentions a pushing force on the place (the rolling road), this not an attempt to make the wheel spin fast and make a nice sound , is an attempt to negate the thrust of the engine.

The rolling road isn't "pushing" on the plane directly, it's pushing on the part of the tyre in contact with the road. Forcing it to rotate about its axle. This is what it does anyway. Rolling resistance in the tyre (usually 1-2% of the tractive effort in cars) will cause a backward force on the plane. The disc brake drag will have a similar effect (although much less). Finally the bearing loss will have a minescule effect also.

So overall, at normal speeds (up to takeoff speeds) you have a tiny, negligible fraction of the engine's power being consumed by these losses: the plane still takes off. On the hypothetical rolling road, if it causes the wheels to go twice as fast, there will be 2*negligible losses. If the rolling road goes 10 times as fast, the tyres will explode before you get very far at all.

More than likely, but if you can construct a rolling road the size of an airstrip, then you can most likely construct a tire that can take the heat of a rolling road doing mach 2

[kalmar]

Out of interest, just how much thrust does a plane (normal plane, not an SR-71 ) have in hand when it is taking off? It is my understanding that a plane is pretty much maxed out on thrust during take off?

If this is the case, then surely the rolling road would not need to provide that much of a dampening force to keep the plane below its take off speed...

No no no. See, this is why you're making things more confusing, because you're not understanding the basic concepts. No offence.

ALL* of the engine power at the end of the runway is going into accelerating the mass of the plane, countering wind resistance (and providing lift).

The plane does not accelerate noticeably quicker when the tyres have just left the runway, does it? (hypothetical question - answer is no). This demonstrates that the drag due to the wheels on tarmac, bearings etc is a negligible force at take-off speed.

* At a conservative guess I'd say better than 95%

[Mir Nyet]

Out of interest, just how much thrust does a plane (normal plane, not an SR-71 ) have in hand when it is taking off? It is my understanding that a plane is pretty much maxed out on thrust during take off?

If this is the case, then surely the rolling road would not need to provide that much of a dampening force to keep the plane below its take off speed...

No no no. See, this is why you're making things more confusing, because you're not understanding the basic concepts. No offence.

ALL* of the engine power at the end of the runway is going into two things: A) accelerating the mass of the plane and B) countering wind resistance.

The plane does not accellerate noticeably quicker when the tyres have just left the runway, does it? (hypothetical question - answer is no). This demonstrates that the losses due to the wheels on tarmac, bearings etc is a negligible force at normal speeds.

* At a conservative guess I'd say better than 95%

Completely agree.

Most of the engine thrust is being spend counteracting the resistance of the air (both on the ground, and in the air, which is why there is no noticable change in speed) once the plane has countered its own inital inertia... As you say, in normal curcumstances the ground plays almost no part in this equation as the friction is for the most part meaningless...

But suppose we actually put the ground into the equation by increasing the grounds resistance via the rolling road. Admittedly the force that can realistically be expected to be transfered into the plane is not huge, but over the span off all the wheels of the plane, could it all add up to just enough to tip the balance and stop the plane reaching its take off speed.


(no offence taken by the way, as I said, this is fun)