Parametric Investigation of the Flight Performance of a Variable Rotor Pitch X-Configuration Quadrotor Aircraft

To better understand and predict the flight performance of X-configuration quadrotor aircraft using variable rotor pitch and fixed rotor speed to control the aircraft, a flight performance tool including a rotor model, an aerodynamic interference model, and a new propulsive trim method is derived. The lifting rotors are modeled as circular fixed wings, and generate horseshoe vortices trailed from the retreating and advancing sides to affect the aerodynamics of the other rotors. The equilibrium equations of the aircraft are reduced by using symmetry. An iterative method by separately solving for the aircraft pitch and the collective rotor pitch is proposed to obtain the converged solution of the reduced equilibrium equations. The aerodynamic interference was found to be beneficial for the front rotors at low to medium speeds, because the nearby front rotors induced a larger upwash than the resultant downwash induced by the rear rotors. The interference is harmful to the rear rotors due to larger downwash induced by the rotors right ahead. The rotors can generate nose-up hub pitching moments, which can be used to counter the nose-down fuselage pitching moment, and decrease the thrust difference between the front and rear rotors. The effect of the fuselage pitching moment on the rotor power becomes pronounced at medium to high speeds. The vertical distance between the rotor plane and the center of mass of the aircraft can change the pitching moment acting on the aircraft, and its effect is similar to a change in the fuselage pitching moment. Reducing the fuselage drag can lead to larger rotor induced power due to the stronger aerodynamic interference, but the effect is relatively small, and fuselage drag reductions are desirable.