constant angle of attack propeller via aerodynamics

[amorrison]

What has been developed to AERODYNAMICALLY maintain the highest L/D from a propeller under all conditions?

Example: allow the propeller airfoil to rotate on an internal support pipe to get the best L/D.
An archery arrow (c/w tailfeathers) lashed perpendicular to the blade radius would rotate the blade to maintain constant angle of attack or best L/D . ? ?

 

[GraviMan]

Or even mild tip sweepback. There was a boat propeller developed along these lines, but I don't have a link.

Mart

 

[crazywgl]

Flex fans in cars is an extension of the feathers back,
but the tip speeds on most airplanes approaching speed of sound start to create drag, and are used to prevent pilots redlining engines.

(So the tip sweep really reduces drag, and allows more power to be turned to thrust at speed.)

I experimented on a car fan, and did a 45 degree cut on a crumby fiberglass fan on the car, and got an increase of about 1,000 rpm (25 percent) climbing uphill with a low powered truck. (Also significantly reduced the sound)