What Myth would you want to see busted?

Voltjunkie said:
Friction from wheel bearings isn't quite the same as the rotational force applied to a helicopter body though hence the possibly confusion :)
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It is effectively the same. When you realise the body is effectively the wheel and the propshafts bearings are the wheel bearings.
 
Alphane said:
Same reason there is no movement relative to the world on a 'rolling road'
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Very bad example.

Where does a planes power and propulsion come from? The engine, which uses a prop to move air.
A rolling road does not stop the engine from turning, which means it doesn't stop the prop from turning, which means you still have air movement from the rotating prop. Which means you get forward movement, at no point is a rolling road and planes engine linked. This is the key difference.

A car on a rolling road. The road is in direct contact with tyres, which is in direct contact with propshaft, which is in direct contact with internals of engine. So it all cancels out neatly.
 
Glaucus said:
And your not belittling either.

Come on simple question, how is turntable force transferred to propshaft. Please explain and show how.
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I'm jumping in on this with the not fly camp. Imagine this...

Helecopter with engine not running is rotated on a turntable anti clockwise at 1000rpm. By your argument the blades would remain stationary? As you state "the turntable force cannot be transferred to the propshaft".

In reality the whole heli would be rotating anticlockwise, blades included at 1000 rpm. Now lets start the engine and rev the blades up to 1000rpm clockwise. The engine is designed to drive the blades relative to the body of the heli. Heli rotating anti clockwise at 1000rpm, blades being driven by engine 1000rpm clockwise relative to the heli = blades not moving relative to the air.
 
neodude said:
I'm jumping in on this with the not fly camp. Imagine this...

Helecopter with engine not running is rotated on a turntable anti clockwise at 1000rpm. By your argument the blades would remain stationary? As you state "the turntable force cannot be transferred to the propshaft".

In reality the whole heli would be rotating anticlockwise, blades included at 1000 rpm. Now lets start the engine and rev the blades up to 1000rpm clockwise. The engine is designed to drive the blades relative to the body of the heli. Heli rotating anti clockwise at 1000rpm, blades being driven by engine 1000rpm clockwise relative to the heli = blades not moving relative to the air.
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Totally different scenario, which have totally different set of instructions. As such is irrelevant.
What the blades would do in that scenario would depend on many things. But is irrelevant and not at all the same to the original question.

And no the blades rotate in relation to what the internals of the engine are doing. Not what the body is doing.

So the pistons in a car engine suddenly stop reciprricating when you go round a corner.
 
Glaucus said:
Very bad example.

Where does a planes power and propulsion come from? The engine, which uses a prop to move air.
A rolling road does not stop the engine from turning, which means it doesn't stop the prop from turning, which means you still have air movement from the rotating prop. Which means you get forward movement, at no point is a rolling road and planes engine linked. This is the key difference.

A car on a rolling road. The road is in direct contact with tyres, which is in direct contact with propshaft, which is in direct contact with internals of engine. So it all cancels out neatly.
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It doesn't matter how you achieve the forward momentum to 'roll' the tires if what the tyres are rolling on (the conveyor belt) is rolling the same speed the opposite way the forces WILL cancel out regardless.
 
Alphane said:
It doesn't matter how you achieve the forward momentum to 'roll' the tires if what the tyres are rolling on (the conveyor belt) is rolling the same speed the opposite way the forces WILL cancel out regardless.
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No, the rolling road in the planes case, makes no difference. The plane speeds is independent from the rolling road.
All which happens is the wheels turn at 200mph. As the planes moving forward at 100mph and the road is moving back at 100mph.

 
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The whole point is that the movement of the blades has no direct effect on the movement of the helicopter. The helicopter would not be spinning at the same speed as the blades if it wasn't on a turntable.

It'd fly, basically. It would spiral madly out of control, but it would take off.
 
Reaper 392 said:
glacius, im quite happy to admit i dont know a lot about helicopters, but im saying you are wrong if the following assumptions are made:
- the engine of the helicopter cannot rotate relative to the body of the helicopter
- the engine of the helicopter is directly linked to the blades through a gearbox of some sort
- the maximum speed that the blades can go is limited by the maximum RPM of the engine
- no damage will occur to the helicopter in this experiment

if this were true, and you spun the helicopter around at the maximum RPM that the engine could spin the blades in the opposite direction, then held the blades still, the engine would be doing its maximum RPM in the forwards direction. this is because the blades are rotating relative to the helicopter at their maximum speed. since the helicopter is rotating at the blades and engines maximum speed in the opposite direction the engine will be exactly countering this action

now, what i would like you to do is tell me, in the real world, where my assumptions fall down (excluding the helicopter falling apart, or anything that stops the engine from working like centrifugal force on the fuel).
is it that the blades are not limited by the maximum speed of the engine, but by air resistance, and the engine will happily spin more than twice as fast given no blades to push through the air.

i know full well that no one would be stupid enough to make a helicopter where the engine has no direct link to the helicopter because then you'd waste a load of the power just spinning the entire engine round and round uselessly in the opposite direction to the blades
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But relative to the observer the blades are spinning and spinning is what causes the helicopter to fly. Not, as you might think, through pushing air downwards but more by the centripetal force acting outwards from the wings which counteracts the force on the mass of the helicopter due to mavity. That force doesn't suddenly stop acting when you turn the whole craft round.
 
Glaucus said:
Totally different scenario, which have totally different set of instructions. As such is irrelevant.
What the blades would do in that scenario would depend on many things. But is irrelevant and not at all the same to the original question.

And no the blades rotate in relation to what the internals of the engine are doing. Not what the body is doing.

So the pistons in a car engine suddenly stop reciprricating when you go round a corner.
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First point: How is it a different scenario?

Second point: So if I rotate a whole helicopter with engine off at 1000rpm the blades will stay still because the engine internals aren't running? You think that sounds plausable.

Third point: I fail to see your point with the car on the corner.
 
Surely somebody has got a remote control helicopter and a record deck.
My money is on the helicopter taking off.
There are You Tube videos but they are all stationary turntables.
 
neodude said:
First point: How is it a different scenario?

Second point: So if I rotate a whole helicopter with engine off at 1000rpm the blades will stay still because the engine internals aren't running? You think that sounds plausable.

.
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This is getting far more complicate than the original questions remit.

It's not the same. As the engine is off, when a engine is off, it has huge amount resistance. So assuming no clutch to disengage the engine and all that resistance the blade would turn. This is becuase there is ow a direct link between turntable and blades, thanks to the engines massive resistance when switched off. Same can not be said if the engine was on, or a clutch was engaged. If the clutch was 100% resistance free, the blade would not rotate, there's no forc being transmitted, so no movement.
 
Also - with regards to the OP, religion. Or rather, the myth that some all mighty cosmic being who also happens to be white and have a beard created everything just 'for the crack'. Thankfully that seems to be happening on it's own, albeit a bit slowly. But you couldn't expect people to believe that something that silly was actually true forever. It doesn't even answer the question it set out to answer, it just moves it around in such a way that gives those that created it a position of relative power.
 
Glaucus said:
This is getting far more complicate than the original questions remit.

It's not the same. As the engine is off, when a engine is off, it has huge amount resistance. So assuming no clutch to disengage the engine and all that resistance the blade would turn. This is becuase there is ow a direct link between turntable and blades, thanks to the engines massive resistance when switched off. Same can not be said if the engine was on, or a clutch was engaged.
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That huge amount of resistance doesn't magically dissapear when the engine is turned on, it's still there, albeit lessened slightly thanks to oil. The engine overcomes this resistance to drive the blades relative to the body of the aircraft.

Or to simplify matters the engine is turning the propshaft relative to the body of the engine, yes? If the body of the engine itself is being rotated the opposite way at the same rpm then the propshaft, relative to the outside world, is not rotating.
 
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w11tho said:
0.999999.... < 1 (or is it?!?!)
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0.99... is by mathematical definition equal to 1

1/3 = 0.33...
3(1/3) = 3(0.33...)
1 = 0.99...

or

x = 0.99...
10x = 9.99...

10x - x = 9.99... - 0.99...
9x = 9
x = 1
1 = 0.99...

or

1/9 = 0.11...
2/9 = 0.22...
.
.
.
9/9 = 0.99...
1 = 0.99...

You have to remember the decimal system works in base 10 so isn't suited for all numbers, especially not irrational numbers.
 
neodude said:
That huge amount of resistance doesn't magically dissapear when the engine is turned on, it's still there, albeit lessened slightly thanks to oil. The engine overcomes this resistance to drive the blades relative to the body of the aircraft.
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Yes it does. Argghhh this is insane.

When an engine is off, you have to compress the air, suck in air and all that yourself. Hence the huge resistance. When engine is on, you have explosions that not only do all that work for you, but gives a massive amount of extra energy out.

So you couldn't be more wrong.
 
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