Propeller Efficiency

Hi All,

I was thinking today about the fluid dynamics surrounding a propeller
as it moves in a circular motion.

It seems that, no matter what the blade angle, there would be a
significant amount of energy lost simply by turning the fluid. IOW,
even if there were no drag at any point on the aircraft, only a
fraction of the engine power would result in forward movement of the
aircraft. The remaining power would be lost in turning fluid in in a
vortex in the vicinity of the propeller.

Does anyone have any idea of the ratio between thrust power and churn
power?

TIA,

-Le Chaud Lapin-