Aircraft loss-of-coiitrol recovery strategy using high order sliding: Mode control based on optimal trim condition

Aircraft loss-of-control is one of the most fatal aviation accident types. Therefore, the mitigation of aircraft LOC is urgent and import. Aircraft loss-of-control is a very complex process, the definitions still remain vague in analytical terms, but it is generally associated with flight outside of the normal flight envelope, with nonlinear influences. Although human-beings have done a lot of loss-of-control research, most of them are focused on avoiding aircraft flying out of control, how to spot and expand the scope of safety, etc. In this paper, the controller is designed to recover the loss-of-control aircraft to a given safe flight condition which regards as the optimal trim condition. Firstly, an investigation of bifurcation phenomena is carried out to find a possible loss of control flight status of the aircraft. It addresses the connection of LOC with in fight bifurcation phenomenon which is ordinarily associated with upset fight vehicle. Such bifurcation points are not usually associated to a particular system failure of components, but once the fight condition near those points, it loses its ability to be regulated or tracked particular trajectory due to the occurrence of structurally unstable zero dynamics. Few research reports directly how to find the optimal safe trim condition, an optimal new trim state within the safety scope is found based on a bifurcation point winch corresponds to a dangerous flight state by using the optimization method, and this new trim state is regarded as the desired target safe flight condition. Finally, the high order sliding mode (HOSM) controller is designed for the loss-of-control recovery. The resulting controller would assist pilots during post LOC to steer the fight vehicle to the normal fight regime where safety requirements and flying qualities are ensured. The aircraft Generic Transport Model (GTM) is used for the study of the recovery process.