Short Landing Control Techniques Using Optimization of Flare Time Constant for High-Speed Fixed-Wing UAV

In recent years, the use of unmanned aerial vehicles (UAVs) has expanded in and across various fields, including agriculture, observation, and transportation. Generally, the landing distance of fixed-wing UAVs increases with speed. In particular, the landing distance in the flare phase is proportional to the flight speed. To expand the range of applications for missions by the UAV, it is necessary to develop a short-distance landing control technique. This study focuses on reducing the landing distance during the flare phase before touchdown. The flare path is dominated by the flare time constant. The smaller the flare time constant, the greater the curvature of the flight path and the shorter the horizontal distance. Therefore, we propose a method to determine the flare time constant by applying a nonlinear optimization in which the horizontal distance during the flare phase is used as the evaluation function. The method uses a motion model that incorporates both translational and rotational motion in the longitudinal direction, which is more comprehensive than a point mass model. After solving the nonlinear optimization problem to obtain the flare time constant, we first conduct longitudinal flight simulation to confirm both the accuracy of the optimal solution and the validity of the motion model used in the nonlinear optimization problem and, then, confirm the feasibility of the landing control technique with the optimized flare time constant using a six-degrees-of-freedom simulation.