Robust Autonomous Landing of Fixed-Wing UAVs in Wind

Abstract: Fixed-wing UAVs are today used in many different areas, from agriculture to search and rescue operations. Through various research efforts, they are becoming more and more autonomous. However, the procedure of landing a fixed-wing UAV remains a challenging task, which requires manual input from an experienced pilot. This work proposes a novel method which autonomously performs such landings. The main focus is on small and light-weight UAVs, for which the wind acts as a major disturbance and has to be taken into account. Robustness to other disturbances, such as variations in environmental factors or measurement errors, has also been prioritized during the development of this method.The main contribution of this work consists of a framework in which der\-iva\-tive-free optimization is used to calculate a set of waypoints, which are feasible to use in different wind speeds and directions, for a selected UAV model. These waypoints are then combined online using motion planning techniques, to create a trajectory which safely brings the UAV to a position where the landing descent can be initiated. To ensure a safe descent in a predefined area, another nonlinear optimization problem is formulated and solved. Finally, the proposed method is implemented on a real UAV platform. A number of simulations in different wind conditions are performed, and data from a real flight experiment is presented. The results indicate that the method successfully calculates feasible landing sequences in different scenarios, and that it is applicable in a real-world landing.