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Re: OT: FOAK Windmill Boat/Cart
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In autorotation gravity is powering the rotors and then for a short
period of time the momentum is.
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Gravity can't power the rotors: the airflow through them drives them.
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ROTFLMAO.
Gravity is providing the airflow! :-)
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No it ain't. See my other post on the matter.
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I can't find it.
The helicopter drops due to gravity. That drop creates a relative
airflow. Or can a stationary helicopter in a hanger spontaneously
autorotate?
Am I missing something?
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Yes, you've introduced gravity. Different kettle of Newtons.
A stationary helicopter, or more accurately one that is not moving
towards or away from the Earth, does not undergo a change in
gravitational potential energy (mgh stays constant, where m = mass in
Kg, g = 9.81 m/s^2 and h is height in metres).
An unsupported mass (let's say we just dropped a heli out of a C130,
007) will start to fall and in doing so mgh gets smaller. In the
absence of friction this gets turned into kinetic energy, ie. the mass
picks up speed (maybe more strictly velocity). This increase in speed
will go on indefinitely until the object hits the ground. In the more
realistic presence of friction, initially the majority of this energy
becomes kinetic energy, but as the speed increases the drag takes an
increasing proportion of the energy and the acceleration falls off
until the drag takes all the energy and the speed stabilizes. For
example, after about a dozen seconds or so a falling human in the
"spread stable" freefall position stabilizes at about 120mph.
Note that even if the object doesn't fall vertically, but say is
forced to move at an angle down a ramp, no matter what the angle,
provided the vertical drop remains the same then the final speed will
be the same, all other factors being equal. It will simply take longer
to get *to* that speed.
Back to the helicopter. Because it's now falling and has relative
airflow, the blades can now autorotate.
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Err no. Pressure differences are providing the airflow. Wind is caused
by air moving from areas of low pressure to areas of high pressure.
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Vice versa methinks.
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It tries but you mustn't forget the coriolis force.
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Irrelevant, it would still go from high to low but, tbf, the weather would
be err... somewhat different.
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I guess you haven't looked at a weather map recently.
You could try searching for Coriolis on Wikipedia....
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I guess you could try reading what I wrote and not what you think I wrote.
It goes *either* directly *or* indirectly. Whichever route, it *still goes*
high to low, hence my 'irrelevant' comment.
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I was doing well with that post wasn't I?
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I think you need to re-read the bits you quoted Phil. He's talking
about autogyros now, not boats.
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Err.. ah. Oh. Err. It was the kitten. He made me do it. Oh look - a
mushroom!
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Fine. Gravity is providing the airflow. If you want to work out how
fast the blades go and what the drag on them is, you need the airflow,
not the gravity.
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