Nonlinear stability region determination and safety manipulation strategies for icing aircraft

Icing will destroy the dynamic performance of the aircraft and cause the safety envelope shrink, which seriously affects the flight safety. It is of great significance to study the changes of nonlinear stability region of the icing aircraft for reducing flight accidents. In this paper, the NASA's GTM is taken as the object aircraft. First, the dynamic model of longitudinal channel under icing condition is established based on polynomial fitting of the aerodynamic parameters and the icing factor model. Then, the change of flight state under different icing conditions and control commands is studied by bifurcation analysis method which used to guide flight manipulation. Considering the limitation of bifurcation analysis method, the nonlinear stability region of flight system is determined by differential manifold theory. And the nonlinear stability region is regarded as flight safety boundary. Finally, considering the icing condition, the bifurcation analysis method and differential manifold theory are combined to guide manipulation. Furthermore, the time domain validation of the manipulation is carried out. The results show that icing will shrink the safety boundary, and a slight disturbance may contribute to flight state outside the safety boundary. Moreover, with the increasing degree of icing, the stability of the aircraft will even change and the flight state will be difficult to maintain within the original safety boundary. At this moment, the flight state can be brought to the new safety boundary by changing the pilot's manipulation instruction. The research results are helpful for flight safety manipulation and boundary protection.