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When the vehicle is moving at low speed or the propeller is rotating at high speed, the advance ratio is a low number. The advance ratio is a useful non-dimensional quantity in helicopter and propeller theory, since propellers and rotors will experience the same angle of attack on every blade airfoil section at the same advance ratio regardless ...
where is propulsive efficiency (typically 0.65 for wooden propellers, 0.75 metal fixed pitch and up to 0.85 for constant-speed propellers), hp is the engine's shaft horsepower, and is true airspeed in feet per second, weight is in lbs. The metric formula is:
Similarly to jet engines, matching the exhaust speed and the vehicle speed gives optimum efficiency, in theory. However, in practice, this results in a very low specific impulse, causing much greater losses due to the need for exponentially larger masses of propellant. Unlike ducted engines, rockets give thrust even when the two speeds are equal.
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.
The minimum control speed is the airspeed below which the force the rudder or ailerons can apply to the aircraft is not large enough to counteract the asymmetrical thrust at a maximum power setting. Above this speed it should be possible to maintain control of the aircraft and maintain straight flight with asymmetrical thrust. [4]
Rotor solidity is a dimensionless quantity used in design and analysis of rotorcraft, propellers and wind turbines.Rotor solidity is a function of the aspect ratio and number of blades in the rotor and is widely used as a parameter for ensuring geometric similarity in rotorcraft experiments.
A propeller speed reduction unit is a gearbox or a belt and pulley device used to reduce the output revolutions per minute (rpm) from the higher input rpm of the powerplant. [1] This allows the use of small displacement internal combustion engines to turn aircraft propellers within an efficient speed range.
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.