Grimly Curmudgeon wrote:
We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember ThinAirDesigns
saying something like:

Initially the wind merely starts blows the vehicle downwind. Once the
vehicle is moving the wheels provide the input torque to turn the
propeller. The propeller takes wind that was moving at say 10mph
across the ground and pushes back on it until it is only moving say
5mph across the ground. The energy removed from the wind when it is
slowed is the energy powering the vehicle.

Light dawns. If you'd mentioned pusher prop at the start...

My gut feeling is it would be heavily dependent on very low frictional
losses in the transmission of whatever type.
Permanent Magnet bearings? Air bearings need an input.

WD40?

Conceptually its easier to think of it like a air paddle steamer car

The wind blows the car along, which drives the paddles which move
backwards against the wind. Therefore the paddle blades are never in
still air when the car is travelling at windspeed. So they can still
extract energy.