Helicopter performance improvement by variable rotor speed and variable blade twist

Variable rotor speed and variable blade twist are combined to reduce rotor power and improve helicopter performance. Two modeling methods are respectively utilized. One is based on an empirical aerodynamic model and the other is based on CFD (computational fluid dynamics). The flight data of the UH-60A helicopter is used to validate the methods. The predictions of the rotor power by the empirical method are in good agreement with the test data and the CFD method, which verifies the application of present methods in analyzing helicopter performance. The analyses indicate that significant rotor power reduction can be achieved by decreasing rotor speed. It is not appropriate to decrease the rotor speed too much in high forward flight. More power reduction can be attained by varying rotor speed than by variable blade twist. The individual variation of rotor speed or blade twist can reduce the rotor power by 17.8% or 10.4%, at a forward speed of 250 km/h and weight coefficient of 0.0065. A combination of rotor speed reduction and blade twist can save 20.9%. The maximum power reduction increases with forward speed and then decreases. The optimal performance improvement occurs at the medium to high forward speed. With increasing takeoff weight, the benefit in power saving decreases. Variable blade twist has the potential in reducing blade loads introduced by variable rotor speed.