Passively Adaptive Variable Rotor Diameter to Improve the Flight Performance of Variable-speed Rotors.

A passively adaptive variable rotor diameter is proposed to improve the flight performance of variable-speed rotors. A validated helicopter model to predict rotor performance is utilized. The analyses focus on three typical flight states (i.e., hover, cruise, high speed) to explore the potential of the passively adaptive variable rotor diameter in reducing rotor power. During hover, the variable rotor diameter can optimize the distribution of lift and then reduce the rotor power, especially at lower rotor speeds. At a cruise speed of 150 km/h, the variable rotor diameter can delay stalling and reduce the rotor power, especially at lower rotor speeds. At a high speed of 300km/h, the rotor speed needs to be increased, and the reduced rotor diameter is beneficial reducing power. The reduced power comes from decreasing the parasitic power of the fuselage due to decreasing its longitudinal tilt, and the rotor profile power and induced power increase with relatively small magnitudes. The passively adaptive variable rotor diameter is more suitable for larger take-off weights, and can effectively delay stalling at lower rotor speeds. The strategy of varying the rotor diameter can be designed according to the performance improvement requirements. [ABSTRACT FROM AUTHOR]