[stephen f. polyak]

To achieve optimal operating performance, it’s necessary to vary propeller blade pitch angle with airspeed and flight condition. A low angle works best for high power takeoff and climb (at relatively low airspeeds), while a higher angle serves lower power cruise flight (at increased airspeeds) best. I suspect that the fixed pitch vanes on a Fw 189’s propeller spinner used associated aerodynamic forces (that varied with flight airspeed and/or engine speed) to rotate/turn the vaned spinner (independent of the propeller) and, via a joined mechanical advantage mechanism, regulate propeller pitch to "fit" the plane's airspeed/engine RPM. It appears a clever form of automatic pitch control.