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Alternatively, a constant-speed propeller is one where the pilot sets the desired engine speed , and the blade pitch is controlled automatically without the pilot's intervention so that the rotational speed remains constant. The device which controls the propeller pitch and thus speed is called a propeller governor or constant speed unit.
A 6-bladed Hamilton Standard 568F propeller on an ATR 72 short-haul airliner. Lowry [27] quotes a propeller efficiency of about 73.5% at cruise for a Cessna 172.This is derived from his "Bootstrap approach" for analyzing the performance of light general aviation aircraft using fixed pitch or constant speed propellers.
The momentum theory or disk actuator theory – a theory describing a mathematical model of an ideal propeller – was developed by W.J.M. Rankine (1865), Alfred George Greenhill (1888) and Robert Edmund Froude (1889). The propeller is modelled as an infinitely thin disc, inducing a constant velocity along the axis of rotation.
However, the actual propeller speed remains stable only if operational conditions (e.g., airspeed) do not change, otherwise the pilot has to constantly adjust the pitch to maintain the desired propeller speed. Constant-speed propeller control system simplifies this for the pilot by introducing a propeller governor, where the lever controls the ...
They introduced a twist in their blades to keep the angle of attack constant. Their blades were only 5% less efficient than those used 100 years later. [28] Understanding of low-speed propeller aerodynamics was complete by the 1920s, although increased power and smaller diameters added design constraints. [29]
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Power 100 hp (75 kW) at 2450 rpm, dry weight 236 lb (107 kg) Similar to O-235-C1 except ignition timing, lower rpm and power. Optional 2 position or automatic propeller governor drive. [2] O-235-C1B Power 115 hp (86 kW) at 2800 rpm, dry weight 245 lb (111 kg) Similar to O-235-C1 except with retard breaker magnetos. [2] O-235-C1C
For example, a common N p would be about 2200 RPM for a constant speed propeller. N 1 or N g refers to the RPM of the gas generator section. Each engine manufacturer will pick between those two abbreviations. N1 is also used for the fan speed on a turbofan, in which case N 2 is the gas generator speed (2 shaft