Envelope Predicating And Protecting Control For The Post-stall Maneuver Of Fighters

The post-stall maneuver is the kernel method to strike enemy for the fourth fight. At the same time, the safety problem in the post-stall becomes an important field for further study which is closely related to the maneuverability of the flight. Quantifying the envelope of maneuverability in the present post-stall state and limiting the related states are prerequisite for accomplishing the post-stall maneuver and avoiding the disoperation caused by the pilot. Therefore, the problem on envelope predicating and protecting is a frontier and challenging subject. To research this problem, the definition and calculation method of envelope are proposed based on the aerodynamic model of fighters, moreover, the calculation, verification and protecting of envelope are illustrated by the cases of both the rolling maneuver around velocity vector and the pitching-rolling coupling maneuver in the post-stall. The main works are as follows:Firstly, a nonlinear flight mathematic model considering the unsteady aerodynamic for the advanced fighters is established. Afterwards, the related analyses are given for the construction, parameter setting, the zero input response of open-loop model, coupling characteristics of each channel, uncertainty and the interference characteristics of flight environment. Thus, the correctness of the established model which can be used as the foundation of predicating and protecting envelope is verified.Then, the method of predicating and protecting envelope is educed by analyzing on the loss-of-control(LOC) when rolling around the velocity vector in the post-stall, equipped with the dynamic inverse control laws. Inspired from the definition of flight envelope in the civilian aircraft, the traditional definition of flight boundary in the fighter is augmented to a new one and a universal algorithm for the envelope is also provided. In view of the dynamic envelope of the post-stall maneuver, the criterion of LOC is given with the acid of the attainable equilibrium sets, furthermore, the maneuverability under the constraint of the dynamic envelope can be obtained.Afterwards, according to the proposed criterion of LOC, the envelopes of the rolling maneuver around velocity vector and the pitching-rolling coupling maneuver are worked out with the help of dynamic trimming and attainable equilibrium sets, respectively. Furthermore, combined with the nonlinearity of the fighter, the correctness of these obtained envelopes can be verified in the physical mechanism. In addition, the deep post-stall is taken as one example to illustrate this algorithm.Finally, the control system for envelope protection consists of three parts, i.e. the inner-loop controller, outer-loop controller and protecting controller. In the second part, the compound protecting method which integrates the constraints of command signals and the control method under the constrained states, designed synthetically with the first part, is adopted. Thus, the robust model predictive control law based on feedback linearization is proposed and three kinds of typical post-stall maneuver are taken for examples to verify the feasibility of the proposed methods. On the other hand, the predictive algorithm under the constrained states based on the reachable sets is put forward to provide the future information of envelope. Further, some simulations in the rolling maneuver around velocity vector indicate that the envelope protection system has a good performance in the super maneuver of the fighter.