i guess also, the thrust of the jet engines forcing air behind the aircraft, will pull air across the wings, as the air being blown behind needs to be replaced.
hey presto..........lift.
hey presto..........lift.
Physics Puzzle
- Thread starter chilluk
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oh, and a fast moving conveyor belt will drag air back with it too.
lift again.
lift again.
Actually it's the opposite of what you think - the flow of air into, and combustion gases out of, the engine acts to counter the aerodymanic lift of the wing. However its counter-effect isn't sufficient to completely negate the lift.noseall said:
what i'm saying is, if you put an air craft in a wind tunnel and force air over the stationary plane the thing will eventually, when wind speed is sufficient, lift off the ground.
so, with the movement of conveyor and the planes thrust, they in turn create a certain amount of reverse wind speed, pulling air over the wings, creating lift.
the planes contact with the conveyor would eventually cease due to the planes lift.
so, with the movement of conveyor and the planes thrust, they in turn create a certain amount of reverse wind speed, pulling air over the wings, creating lift.
the planes contact with the conveyor would eventually cease due to the planes lift.
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When you used the word "eventually", you imply that time must pass - this is wrong because lift-off will occur as soon as the air speed is sufficient.noseall said:
That would be roughly correct for an engine mounted on top of a wing, but not for regular engines that are mounted underneath the wing.
Same comment about "eventually" - contact would immediately cease when the rear wheels lift off.
ok softus, maybe i'm not being as precise as you would like, but my point's still the same.
unless somebody below the conveyer belt is pushing the belt harder and harder against the plane's wheels, then i guess the experiment is duff.
after all when do you stop forcing the conveyor up?
when the plane is 100 feet up,
or.....airborne?
unless somebody below the conveyer belt is pushing the belt harder and harder against the plane's wheels, then i guess the experiment is duff.
after all when do you stop forcing the conveyor up?
when the plane is 100 feet up,
or.....airborne?
the original question asked that, could a conveyor belt counter the effects of "lift" as a result of forward jet propulsion by moving backwards in sync with the planes attempts at forward motion.
my argument is that, air movement over the wings caused by the movement of the conveyor and the jet engines, would give the aircraft lift causing the friction between the wheels and the conveyor to eventually cease.
my argument is that, air movement over the wings caused by the movement of the conveyor and the jet engines, would give the aircraft lift causing the friction between the wheels and the conveyor to eventually cease.
I think there's a fair bit of poetic license in the way that you're re-written the question, but the gist is there.noseall said:
I don't deny that the wheel friction will cease at the moment of lift-off, but my point on your theory is that the jet engines don't directly cause any air flow over the wings. The air flow, both over and under the wings, results from the movement of the plane through the air, and that movement results from the jet thrust, but equally could be produced by a nose-mounted propeller.
In case you didn't already know, air movement over a wing causes aerodynamic lift only by virtue of the difference in pressure between the upper and lower wing surfaces.
i have a basic grasp of aerodynamics.
a wings shape is such that air will move faster over the top of the wing than underneath. this is due to the thicker front and slimmer back of the wing and the way that the wing slopes front to back. this in turn makes the air travel faster over the top of the wing than underneath. hence the low air pressure above and high below.
i also iterated that the conveyor belt, travelling at speed, would create a backwards wind of its own.
this coupled with the residual wind left over from the jet suction (due to air displacement) would be sufficient to lift the aircraft off the ground.
a wings shape is such that air will move faster over the top of the wing than underneath. this is due to the thicker front and slimmer back of the wing and the way that the wing slopes front to back. this in turn makes the air travel faster over the top of the wing than underneath. hence the low air pressure above and high below.
i also iterated that the conveyor belt, travelling at speed, would create a backwards wind of its own.
this coupled with the residual wind left over from the jet suction (due to air displacement) would be sufficient to lift the aircraft off the ground.
Quite so.noseall said:
Er, no. The wing is shaped in that way to reduce its air resistance. The part of the shape that creates the air speed differential is the bulge on the upper surface, whereas the lower surface is pretty much flat. The upper surface is therefore 'longer', and the air has to travel a greater distance over the wing that underneath it. [Edit - although the outcome is correct, my assertion may be incorrect in the way that I've simplified the principle]
This is moot - even if the belt did create any significant wind, would it exceed the opposing wind created by the plane?
You keep coming back the to jet suction idea. My comment on this, which you seem to keep ignoring, is that any such suction, or blow, flow, draught, breeze or wind that the engine creates is under the wing, not over it. If the flow under the wing is so increased, then this will reduce the amount of aerodyamic lift, not increase it. Clearly, without a conveyor belt, this reduction is easily countered by the power of engine.
Additionally, propeller-powered airplanes are also capable of taking off, underlining my point that the jet suction (or blow etc) is completely irrelevant to the question posed at the beginning of this topic. It's only the thrust resulting from the jet engine principle (see the Newtonian laws of motion) that are relevant.
softus, im not sure of any thing i've said so far!
but, i am sure that, if an aerodynamic vehicle such as an air craft, applies a stack of energy into moving forwards and ultimately upwards, then i'm pretty sure a little conveyor belt ain't going to stop it.
what are your thoughts softus?
p.s can thrust be applied to a prop engine?
'cause the original question didn't differentiate, apart from the thrust thing, which engine was driving the aircraft. jet or otherwise. didn't say above or below the wing either.
but, i am sure that, if an aerodynamic vehicle such as an air craft, applies a stack of energy into moving forwards and ultimately upwards, then i'm pretty sure a little conveyor belt ain't going to stop it.
what are your thoughts softus?
p.s can thrust be applied to a prop engine?
'cause the original question didn't differentiate, apart from the thrust thing, which engine was driving the aircraft. jet or otherwise. didn't say above or below the wing either.
My thoughts are that it's both hot and late!noseall said:
You've hit the nail on the head when you point out that the jet engines are big, and therefore produce a large force, and the conveyor belt is little, and can do no more than double the frictional force at the wheels.
My opinion, as to which of these forces is bigger, is that the jet thrust is greater than twice the usual frictional force at the wheels. So, fundamentally I agree with you.
I think it was empip who produced some figures that illustrated the enormity of this difference.
I don't know. We could look it up, but I think it's irrelevant.noseall said:
You're absolutely correct - the question didn't specify. I made an assumption that the word "thrust" didn't apply to a prop engine. I deserve a slap.
Er, no, it didn't, but some assumptions are valid ones, like the fact that the engine is connected to the plane.
However, it matters not what type of engine is in use - the answer is that same.
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