page_title: Constant-speed propeller
section_title: Constant-speed units
hierarchical_section_title: Constant-speed propeller / Constant-speed units
caption_attribution_description: English: Pitch Change Forces on a Constant-Speed Propellor
context_page_description: A constant-speed propeller is a variable-pitch aircraft propeller that automatically changes its blade pitch in order to maintain a chosen rotational speed. The power delivered is proportional to the arithmetic product of rotational speed and torque, and the propeller operation places emphasis on torque. The operation better suits modern engines, particularly supercharged and gas turbine types.
context_section_description: A constant-speed unit (CSU) or propeller governor is the device fitted to one of these propellers to automatically change its pitch so as to attempt to keep engine speed constant. Most engines produce their maximum power in a narrow speed band. The CSU can be said to be to an aircraft what the CVT is to the motorcar:  the engine can be kept running at its optimum speed, no matter at what speed the aircraft is flying through the air. The advent of the CSU had another benefit:  it allowed the designers of aircraft engines to keep ignition systems simple; the automatic spark advance seen in motor vehicle engines is simplified in aircraft engines.
  Three methods are used to vary the pitch.  Engine oil pressure is the usual mechanism used in commercial aircraft and the Continental and Lycoming engines fitted to light aircraft.  Alternatively, or additionally, centrifugal weights may be attached directly to the propeller as in the Yakovlev Yak-52.  Small, modern engines with a CSU, such as the Rotax 912, may use either the traditional hydraulic method or an electrical pitch control mechanism. A pilot requires some additional training and, in most jurisdictions, a formal signoff before being allowed to fly aircraft fitted with a CSU.  CSUs are not allowed to be fitted to aircraft certified under light-sport aircraft regulations in the United States.
caption: Pitch-change forces on a constant speed propeller.
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