Study on the lift and propulsive force shares to improve the flight performance of a compound helicopter

To investigate the effects of lift and propulsive force shares on flight performance, a compound helicopter model is derived. The model consists of a helicopter model, a wing model and a propeller model. At a low speed of 100 km/h, the Lift-to-Drag ratio (L/D) of the compound helicopter is improved when the wing provides 20.2% of the take-off weight. At high speeds, the L/D can be improved when the propeller provides the total propulsive force. Lowering the main rotor speed increases the wing lift share, however, the maximum L/D increases first and then decreases. The maximum L/D increases with decreasing the blade twist of the main rotor. Decreasing the blade twist from −16° to −8° increases the maximum L/D by 2.3%, and the wing lift share is increased from 65.0% to 74.7%. When the main rotor torque is balanced by the rudder, the maximum L/D is increased by 2.2% without changing the wing lift share. The wing should provide more lift as increasing the take-off weight, which reduces the induced power of the main rotor and increases the L/D. When increasing the take-off weight from 9500 kg to 11000 kg, the maximum L/D is increased by 6.5%, and the wing lift share is increased from 74.7% to 80.2%.