In the history of development of aircraft it became apparent that it is necessary to improve performance. One of the influential factors was the propeller design in relation to the most efficient blade angle. The first propellers were fixed pitch and if the propeller blade angle is set to give good take off and climb performance, the propeller would be inefficient in cruising flight because the blade would be at too low an angle. It was apparent, that the blade angle needs to be adjustable.
A constant-speed propeller was needed along with a device that would change the propeller blade angles according to varying flight conditions. Using this system of control an aircraft can obtain an acceptable amount of efficiency during all flight conditions. This device was the propeller governor, or a propeller control unit.