Research On Several Control Issues In Maneuvering Process Of Vertical Or Short Takeoff And Landing Aircraft

Vertical/short-range takeoff and landing aircraft can fly at high speed and efficiency like fixed-wing aircraft,and can rely on its unique lift device and conversion mechanism to achieve vertical or short-range takeoff and landing,which has a very broad application prospect.However,the structure of V/STOL aircraft is more complicated than that of conventional aircraft,and the control problems faced by different flight modes are more complicated,the control is more difficult,and it is very challenging.This article takes thrust vector type V/STOL aircraft and tailsitter vertical takeoff and landing UAV as the research objects.Researches are carried out on the nonminimum phase control problem and the transition process control problem during the maneuvering process of V/STOL aircraft.When the thrust vector type V/STOL aircraft is hovering or flying at low speed,since the aircraft makes a lateral roll maneuver,non-minimum phase problems will occur due to the coupling between lateral thrust and roll torque.In response to this problem,this paper proposes a lateral roll maneuvering trajectory tracking controller.The system decomposition method is adopted to decompose the original system into a minimum phase subsystem and a non-minimum phase subsystem.A high gain controller is designed for the minimum phase subsystem to ensure external dynamic convergence;for the non-minimum phase subsystem,a method for solving the ideal internal model of the non-minimum phase system based on the center of the steadystate system and adopting the LQR controller to make the internal dynamics track the ideal internal model is proposed.which ensures that the internal dynamics are bounded.In the horizontal flight state,the vertical/short-range takeoff and landing aircraft will also produce non-minimum phase characteristics when using elevators to adjust the flight height.Its negative adjustment characteristics make the aircraft altitude response slower,and undesired height drops will occur in the initial stage.To solve this problem,a design method of PID controller combined with two-step parameter tuning based on the structure of the minimum phase predictor controller is proposed.By extending the design method of Smith predictive controller,the non-minimum phase system is transformed into the minimum phase system.The minimum phase predictive controller is designed to improve the dynamic response of the system.However,a faster response causes a larger negative adjustment.The PID controller combined with two parameter tuning can reduce the impact of negative tuning,thus taking into account the dynamic response speed of the system and the suppression of negative tuning characteristics.For the thrust vector-type V/STOL aircraft,a transition process control law based on the optimized trajectory is designed.The system takes into account the dynamic saturation conditions of the actuator and uses the steepest descent method to calculate the optimized transition process trajectory.On that basis,the optimized trajectory is used as a feedforward,and a feedback amount is given according to the actual state and the reference trajectory state.The feedback controller is designed to correct the current state in real-time to complete the tracking of the optimized trajectory.The designed controller makes the transition process of the thrust vector type vertical/short takeoff and landing aircraft have fast dynamic characteristics and better stability.Regarding the transition process control of the tailsitter vertical takeoff and landing UAV,because the control input is only thrust and pitch angle,the flight speed and altitude of the aircraft during the modal conversion process cannot be controlled at the same time.A total energy control method is used to generate coordinated pitch and thrust control commands,which solves the problem of coupling between flight altitude and speed in the transition phase,and realizes that the aircraft does not fall during the transition.In the cruising state of horizontal flight,this article is inspired by the flight mode of birds to propose an intermittent bionic flight trajectory strategy for tailsitter aircraft,which turns the long-term horizontal flight into an intermittent undulating motion in two stages of climb and gliding.Since this flight mode only consumes energy during the climb phase,it is more energy-efficient than the conventional horizontal flight mode and greatly improves the endurance of the aircraft.Finally,this paper has completed the flight experiment of the vertical/short takeoff and landing aircraft,and the thrust vectored vertical/short takeoff and landing aircraft completed the short takeoff-to-level flight experiment and the flat-flying to hover experiment.The tailstock vertical takeoff and landing aircraft completed the hovering and vertical flying experiments.