Dynamic Stability Analysis of a Flying Wing Considering the Rigid-Elastic Coupling Effects

The motion equation of a flexible aircraft have been derived based on the mean axes, which consider the rigid-body degrees of freedom as well as the elastic degrees of freedom of aircraft. The unsteady aerodynamics in time domain is computed by rational function approximation. The linear state-space model of the aircraft is then established based on the small disturbance theory, which could be used for flight dynamic stability analysis of the flexible aircrafts. For instance, the longitudinal stability analysis of a flying wing with large-aspect-ratio wings has been modeled and analyzed. The root locus indicates that an unsteady phenomenon called the free-body-flutter appears at a low speed, because the first structural bending mode will interact with the short-period mode, which means the structural flexibility will have a great influence on the flight stability of the flying wing, and that should be considered during the aircraft design procedure. Moreover, the effects by the number of elastic modes that have been used to establish the state-space model and the stiffness of the wing structure on the flight stability have also been studied. The result indicates that the stability critical speed of the flying wing will increase with the stiffness linearly. The frequency and damping of the short-period mode of the flying wing will also increase with the stiffness, if the velocity is frozen.