wrote:
True that propeller research went away around WWII, but wind turbine
research is currently a hot topic and that's what the propeller
becomes when the engine stops.

True, but if the propeller airfoil has asymmetrical camber then when the
engine stops, the relative wind is inverted (coming from the wrong side -
similar to inverted flight.) So it wouldn't be terribly efficient and
attributes like prop stall angle differ from engine on versus engine off.