ThinAirDesigns wrote:

@ The Natural Philosopher
Kinetic energy extractable from the air is a function of
the *relative* velocity between the machine extracting
the energy, and the air.

This is true for a device extracting energy through a turbine
mechanism, but not for a device extracting energy from the air using a
propeller.

There's something wrong with that assertion.

First, let?s summarize the difference between a prop and a turbine:
In short and simplistic terms, a turbine slows air down relative to
itself, and uses that extracted energy to provide an *output torque*
on the rotor shaft. A propeller requires an *input torque* at its
shaft, and uses that input torque to accelerate air relative to
itself.

Exactly, and this means that unlike the turbine, a propeller does not
*extract* energy from the air, it *imparts* energy to it.