Research On Symmetrical Quad-rotor Biplane Tail-sitter Unmanned Aerial Vehicle System

With the drastically increased potential use for unmanned aerial vehicles(UAV)in the military and civil fields,the traditional fixed-wing UAVs and rotary UAVs can no longer meet the task of increasing complexity.The tail-sitter aircrafts have become a research hotspot in the fields of UAV because these aircrafts integrate the advantages of those two types of UAVs above and simplify the flight mode transition.To solve the problems of the traditional tail-sitter aircraft,such as low accurate attitude and big changes of height in transition mode,a symmetrical quad-rotor biplane tail-sitter aircraft has been designed from the structure,power system and control system.This aircraft has the characteristics of highly accurate attitude,strong robustness in hovering mode and rapid bidirectional flight mode transition.This aircraft achieves high accuracy in the attitude control and smooth flight mode transition with four rotors rather than the conventional vertical take-off and landing UAVs using control surfaces.The proposal of angled rotor mounting is adopted to address the issue of insufficient yaw control authority.The layout of symmetrically mounted fixed wings makes the aircraft have capability of rapid bidirectional flight mode transition to improve maneuverability.The PIDsliding mode controller is adopted in hovering mode to improve the robustness of the system.The minimum time with constant altitude optimal strategy is used in transition flight mode to solve the problem of big change of altitude in transition.In order to improving the accuracy of the attitude measurement,the attitude measurement sensors are corrected.The raw data is through the digital low-pass filter and is fused to get an accurate attitude.To validate the performance of the aircraft,simulation and flight experiments are both implemented.The results show that the aircraft has a rapid yaw response under condition of the stable attitude control.In comparative experiment,it is shown that the aircraft is more flexible than other similar configuration of aircrafts.