Flight Control Research For Full-Wing Unmanned Aerial Vehicle

The solar powered UAV can complete communication,relay,patrol and reconnaissance missions instead of satellites,so it has vast application prospect in both civil and military fields.High aspect ratio full-wings,which have a higher lift-drag ratio at low speed,simpler structure but a more complete solar-cell laying area than conventional configuration,are one of the most important configurations for solar-powered UAVs.The full-wing UAV researched in this paper has some defects,such as,low airspeed,minimal longitudinal damping and marginal yaw stability,so it is sensitive to wind field disturbances during its flight.In order to reduce weight,the high aspect ratio full-wing UAV usually has no rudders and front wheel steering system.Meanwhile,in order to avoid aileron reversal and maintain the integrity of the upper surface of the wings,the full-wing UAV usually has no ailerons.Therefore,the full-wing UAV researched in this paper only has two propellers and an elevator as the control outputs,which prevents the drone from directly generating the rolling control moment.Still worse,longitudinal and lateral control coupling may occur during landing.To solve the problems mentioned above,the paper does research on the full-wing UAV control method through simulations and flight tests.The research work includes the following aspects.(1)A full-wing UAV dynamic mathematical model is established for on-ground and flight simulations.The test device for the propeller thrust and a small servo are designed respectively.The mathematical model of the propeller thrust and servo are improved through experimental data and specific parameters are identified.In order to solve the problem of long flight test cycle and high cost,an experimental test bed is designed,which consists of a small high aspect ratio full-wing UAV and a small autopilot,which greatly shortens the period of modifying the control law and accelerates the experimental cycle.The experimental test bed is the base for later flight tests.(2)To solve the lateral-directional control problem of the high aspect ratio full-wing UAV without an aileron and rudder,a control method is proposed which uses the differential thrust of propellers as the control output based on the nonlinear dynamic inversion(NDI)and active disturbance rejection control(ADRC)theories.After fully considering the cross-navigation characteristics of the full-wing UAV and the observation capabilities for total disturbances of the ADRC theory,the lateral-directional control designed in the paper can be used both in sliding and flight process.(3)With poor longitudinal static stability,minimal longitudinal damping and short longitudinal control moment,the full-wing UAV has poor control effects of in flight tests.To solve these problems,a longitudinal attitude control law is established based on the NDI and ADRC theories after fully considering the control influence caused by dynamic characteristics of second-order link and time delay of elevator servo.The simulation and experiment results show the control method has a good control effect,and disturbance rejection ability,completely meeting the requirements of practical application.(4)To solve the trajectory control problem of the UAV,a horizontal trajectory control law and a vertical trajectory control law are established respectively.As for the former,the control effects of different path following methods(L1 path following method,carrot chasing method and vector field path following method)are compared with simulations and experiment tests.The simulation and experiment results show that vector field path following method has better control efficiency.For the latter,research is done on the height tracking and height control methods of the full-wing UAV.The simulation and experiment results show that although the height control method has a better control precision,the pitch angle of the height tracking method is more stable in the control process,which is more friendly to the wing load.(5)To solve the take-off and landing problem of the full-wing UAV,control methods are proposed for the drone’s taking off and landing.First,considering the speed limit of the drone is easily exceeded during takeoff,a speed control strategy which uses the pitch angle as the control output is proposed based on the ADRC theory.The strategy can not only control the flight speed effectively,but it can also automatically adjust the climb rate.Second,a control method using propeller thrust reverse is designed to solve the problem that the full-wing UAV needs a long time and distance to land because of its high lift-drag ratio and the control coupling of the longitudinal and lateral.Third,a control law that uses crab crosswind landing method is established to solve the problem that the full-wing UAV tends to be off its runway when affected by the crosswind.Then the control law is improved by adding course angle during landing,making it effectively increase the lateral accuracy of the landing process.