Path Planner Based on Bidirectional Spline-RRT* for Fixed-Wing UAVs

This paper proposes a bidirectional spline-RRT* path planning algorithm for fixed-wing unmanned aerial vehicles (UAVs). The proposed algorithm combines the basic RRT* algorithm with the spline method to produce smooth paths, which are essential for fixed-wing UAVs. The proposed bidirectional spline-RRT* algorithm generates paths satisfying approach direction constraints on both start and goal points, which makes it significantly different from typical path planning algorithms. Further, the algorithm is asymptotically optimal as the cost of the path found decreases as the number of vertices increases, with the path found finally converging to the optimal path. The proposed algorithm also considers the aerodynamic characteristics of the target aircraft. As a result, the paths produced are within load factor and thrust-to-weight ratio limits, are geometrically and dynamically feasible, sub-optimal, and satisfy approach direction constraints. The results of several simulations conducted confirm these properties of the bidirectional spline-RRT* algorithm. In particular, the results of a nonlinear six degree-of-freedom simulation verify the aerodynamic characteristics for the target aircraft, and show that the proposed bidirectional spline-RRT* algorithm can be effectively utilized in path planning problems for fixed-wing UAVs.