Quote:
Originally Posted by AeroMcAeroFace
at wind speed, the wings on the propeller are still moving, and like the sail on a tacking boat, still providing thrust.
It doesn't require over-unity, because essentially the energy is coming from the difference between air speed and ground speed.
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The Second Law of thermodynamics doesn't allow for the energy transferred from the blades to the air to exceed the energy coming from the wheels and inertial/ momentum energy transfer from the vehicle/passenger.
The energy at the blade-air interface must be lower than that at the road-to-tire interface due to energy loss in the tire, gears, wheel bearings, lower sprocket, chain, upper sprocket, jack-shaft bearings, then the blades themselves.
Even if the blades were 100% efficient, there wouldn't be enough energy.
And a look at Abbott and Von Doenhoff's book, Theory of Wing Sections will disabuse you of any notion about high efficiencies under high lift conditions.