Whirl flutter and Rotor Hub center's motion image of tiltrotor aircraft

Based on the Johnson's classical model of tiltrotor aircraft, and considering the elastic connections between the nacelle and wing, an aeroelastic model of tiltrotor aircraft with eleven degrees of freedom for analysis of the whirl flutter of rotor/nacelle and instability of wing in forward flight has been established in this paper. By using the system parameters of experimental model, the modal frequencies and damping ratios changing with the flight speed were calculated to determine the critical instability speed of the system. The method for determining two kinds of dynamic instability forms of tiltrotor aircraft such as the whirl flutter of rotor/nacelle and the divergence of vertical motion of wing has been established. The motion images of rotor hub center in the conditions of whirl flutter and wing instability of tiltrotor aircraft were revealed, intuitively describing the motion patterns of rotor hub center when whirl flutter occurs.