Coordinated Flight of Three Tail-Sitter UAVs: Sequential Traversal Through a Narrow Window

Tail-sitter UAVs, a class of VTOL fixed-wing aircraft, hold significant promise. However, the transition from hover to forward flight entails highly nonlinear aerodynamics, imposing stringent demands on trajectory generation and attitude control. The challenge intensifies in the multi-UAV setting, where the problem shifts from single-vehicle dynamic feasibility to a multi-body optimization with strongly coupled constraints. We study three tail-sitter UAVs initially aligned in a straight line that must traverse a narrow window admitting only one vehicle at a time. We employ a distributed trajectory-planning strategy that enables coordinated flight: the three UAVs depart simultaneously and, by modulating their speeds, sequentially pass through the window. The resulting trajectories are dynamically feasible and achieve near-minimum flight time.