A controllable-pitch propeller (constant speed) permits the pilot to select the blade angle that will result in the most efficient performance given the flight conditions. A low blade angle and a decreased pitch reduces the propeller drage and allows more engine RPM (power) for takeoffs. After airspeed is attained during cruising flight, the propeller blade is changed to a higher angle to increase pitch. The blade takes a larger bite of air at a lower RPM and consequently increases the efficiency of the flight. This process is similar to shifting gears in an automobile from low to high hear.
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