Propeller governor

A propeller governor or constant-speed unit (CSU) changes the blade pitch angle of a aircraft propeller to maintain a selected engine RPM regardless of the operational conditions of the aircraft.

Propeller governor PCU5000, made by Jihostroj a.s. company, fitted to an American Champion aircraft

History

In the history of the development of aircraft it became 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. If the propeller blade angle was 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 of an angle of attack. It was apparent that the blade angle needed 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 could obtain an acceptable amount of efficiency during all flight conditions. This device was the propeller governor, or propeller control unit.

Operation

Typically, constant-speed units on a single-engine aircraft use oil pressure to increase the pitch. If the CSU fails, the propeller will automatically return to fine pitch, allowing the aircraft to be operated at lower speeds. By contrast, on a multi-engine aircraft, the CSU will typically use oil pressure to decrease the pitch. That way, if the CSU fails, that propeller will automatically feather, reducing drag, while the aircraft continues to be flown on the good engine.[1] An unfeathering accumulator will enable such a propeller to return to fine pitch for an in-flight engine restart.

See also

References
  1. https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/airplane_handbook/media/14_afh_ch12.pdf Pg 12-4
  • Gunston, Bill. Development of Piston Aero Engines. Cambridge, England. Patrick Stephens Limited, 2006. ISBN 0-7509-4478-1
  • For more technical information on the first constant speed propeller governor mechanism invented by Elmer E. Woodward, see U.S. Patent 2,204,639
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