Study On Lift-Drag Characteristics And Strength Analysis Of Unmanned Aerial Vehicle's Deformed Wing

Traditional fixed-wing unmanned aerial vehicle(UAV) can only guarantee the optimal performance of a certain flight condition, while deformed wing UAV can adapt to different flight conditions then make the flight performance best through changing the airfoil, wingspan and sweep. Thus the technology of UAV's deformed wing has caused great interest of scholars around the world, the related research of properties and structure deformed wing has become one of the hot topics in aerospace. This paper mainly studies lift-drag characteristics of UAV's deformed wing, propose a best way to deform and the corresponding deformation drive mechanism, did some strength analysis on them.According to the existing lift-drag characteristics theories, built a physical model and mathematical model of UAV's deformed wing, derived the subsonic lift-drag characteristics formula of deformed wing UAV, which contains multiple factors, such as Mach number, airfoil camber and thickness, angle of attack, aspect ratio, sweep angle and so on. We can get the best deformation shape of UAV's deformed wing in high and low altitude from the formula, and obtain the lift-drag coefficient equation and the maximum lift-drag ratio of the two best shape from the parameters.Analyzing the aerodynamic characteristics of eight deformed wing shape in high-altitude, low-speed and low-altitude, high-speed different situation through fluid dynamics analysis software CFX, comparing the lift-drag characteristics of different shape of deformed wing through the curve of lift-drag characteristic and maps of flow and pressure and come to the favorable shape in the different flight conditions. Then simulate the lift-drag characteristics of best shape in high and low altitude, compared with the theoretical results show that, because of the gas separation it makes a certain error between the value of the theoretical values and simulation in high-altitude, low-speed stage, it fits better in low- altitude, high-speed stage, the error is small.Based on the theoretical research and simulation analysis, the best deformation of a suitable switch from high-altitude, low-speed cruise to low- altitude, high-speed attack can be achieved. Through the shape memory alloy SMA spring actuator distributed within the wing to change the airfoil's camber and thickness, because of the large stiffness of the screw shaft nut mechanism, it can be used to change the wing aspect ratio, considering the merit of light weight, self-locking, synchronization, the incomplete symmetrical worm is a better way to change the sweep angle. Set the minimal volume of the incomplete worm gear as the objective function, optimize the design of the incomplete worm gear in the optimization toolbox in Matlab. And verify the strength and stiffness of the important components in the mechanism which used to change wingspan and sweep angle in ANSYS, the results satisfy the strength and stiffness requirement.