Reconfigurable Flight Control Law Design For Tiltrotor Aircraft

The flight dynamics of the tiltrotor aircraft are in general time-varying and nonlinear.Due to its control surface redundancy on each control channel,the control problem is intrinsically complicated.The control surface redundancy on the other hand provides the possibility to reconfigure the flight control law.To ensure flight safety,it is necessary to study the conversion mode control law reconfiguration of the tiltrotor aircraft.The 6-DoF nonlinear flight dynamics model is derived in this thesis.The nonlinear model is trimmed under the whole flight envelope.Control effects of the control surfaces are evaluated to determine the capacity of control law reconfiguration.In order to perform the whole-envelope flight simulation,redundant surfaces are combined and allocated under three flight modes.The whole-envelope flight control law is designed using the cascade inner/outer loop structure.The control law of the inner RCAH loop is designed with the nonlinear dynamic inversion to decouple the state variables of the faster loop.The intermediate/outer ACAH loops are designed using the cascade PID control.The aircraft under control is able to track the attitude and velocity command.The wholeenvelope flight controller is gain-scheduled in order to transit smoothly between operating points.The simulation is performed using a nonlinear model to verify the whole-envelop flight control law.The adaptive control law is designed based on the multiple model switching technique.The category of the actuator failure is analyzed and the fault reference model is derived with its corresponding controller.A proper performance index as well as a switching logic is chosen to identify the fault.The closed-loop system is stabilized under the adaptive controller designed,which is verified by the whole-envelope flight simulation.A two-layered-mixing direct adaptive control strategy is presented in this thesis.The outer layer of the adaptive controller is designed based on the concept of simple adaptive control.The inner layer is based on the multiple model technique.The inner layer is meant to deal with the foreseeable faults while the outer layer is to aim at the unforeseeable faults.A visualized flight simulation is performed under the whole flight envelope.A joint simulation environment of MATLAB/Simulink and FlightGear software is constructed to conduct the pilot-in-loop simulation to verify the control law of the helicopter mode.