Research On Control Law Reconfiguration For Civil Aircraft With Asymmetric Thrust

Engine-Out is the main reason causing civil aircraft accidents, especially in the phases of approaching and landing. Thrust asymmetry, caused by the outboard engine in one side out of work, results in abnormal attitude and the aircraft deviates from the ideal direction. To deal with the dynamic characteristics changing of the aircraft with engine inoperative, control law reconfiguration is an effective method for safe flight. The technology of control law configuration for flight control system of the aircraft with asymmetric thrust is mainly studied in this thesis.The longitudinal and lateral mathematic models of A300 in the phases of approach and landing are established firstly. Base on classic control theory, normal control laws including pitch attitude control law, altitude control law, airspeed keeping control law, roll attitude control law, heading control law and lateral bias control law are designed. Numerical simulation results show that the control laws designed work effectively in normal flight condition.Then,the dynamic characteristics of aircraft with asymmetric thrust are analyzed theoretically. The feasibility that constant disturbance forces and moments can be introduced to simulate the thrust asymmetry is demonstrated by numerical simulation. The controllability conditions and balanced flight attitude in the case of thrust asymmetry are studied based on flight dynamics. Simulation results indicate that normal control laws perform badly due to static error in the thrust asymmetry flight condition and flight attitude of the aircraft is unsuitable for landing.Finally, in the case of asymmetric thrust, reconfigured control laws are designed. Numerical simulation results demonstrate that the reconfigured control laws have good control effect. The method to suppress transient, which can ensure the smooth switching from normal control laws to reconfigured control laws, is studied and proved effective by simulation.