Variable Pitch Propeller

A variable pitch propeller is an aircraft propeller whose blade angle can be adjusted in flight, letting a pilot or an automatic governor set the blades for maximum efficiency at different speeds and altitudes rather than being fixed at one angle. American engineer Frank Caldwell, working for Hamilton Standard, developed a practical controllable-pitch propeller design in the early 1930s, work recognized with the Collier Trophy in 1933 for its contribution to aviation safety and performance. Constant-speed propellers, which automatically adjust pitch to hold a set engine speed, followed soon after and became standard equipment on higher-performance piston aircraft.