Terrain-Based Hierarchical Trajectory Planning for Low-Altitude Flight of Fixed-Wing Aircrafts

For the complex low-altitude flight mission of fixed-wing aircrafts, this paper proposes a terrain-based trajectory generation method based on hierarchical planning framework. The sampling-based path planning algorithm, rapidly-exploring random tree (RRT*), is modified to search collision-free low-altitude path according to the terrain information. Since the generated path by RRT is not dynamically feasible, the subsequent trajectory optimization step is introduced to refine the non-smooth path. In this step, an advanced numerical optimization method is used to achieve spatial optimization subject to the flight performance of fixed-wing aircrafts, which can improve the trajectory smoothness and dynamic feasibility effectively. Numerical simulations on complex terrains are conducted, and the results validate the effectiveness and efficiency of the proposed method.