Research on Whirl‑Flutter Characteristics of Distributed Propulsive Rotorcraft

Aiming at the problem of whirl-flutter dynamics of distributed propulsion rotorcraft in high-speed forward flight state， this paper proposes a highly versatile， fast and efficient distributed multi-rotor/tilt-wing coupled aeroelastic dynamics analysis method. Based on the theory of moderately deformed beams， this method takes into account the elastic and inertial coupling between the rotors and the wings. By using the strip theory corrected by CFD， a distributed multi-rotor/tilt-wing aeroelastic dynamics analysis model is established to study its whirl-flutter characteristics in the forward flight state. After proving the accuracy of the analysis method， this paper also studies the influence of the dynamic parameters of the coupled system （such as the wings， nacelles and rotors， etc.） on the critical whirl-flutter speed of the aircraft. The results show that the system first experiences torsional instability and then in-plane bending instability. The torsional stiffness of the wings has the greatest influence on the critical flutter speed of the system， followed by the out-of-plane and in-plane bending stiffness. The three-dimensional effect of the flutter motion is obvious， presenting as the coupling of the torsional and in-plane and out-of-plane bending modes of the wings. Opening the lift rotors and increasing the number of rotors at low speeds can effectively increase the aeroelastic stability of the system. The flapping stiffness of the hinge-less blades has little influence on the critical flutter of the system. Increasing the rotor thrust and reducing the rotor speed are beneficial to increasing the critical flutter speed of the system， while increasing the height of the rotors and nacelles will reduce the critical flutter speed of the system.