A Minimum Snap Flight Transition Strategy for Quadrotor Tail-Sitter UAVs: Altitude-Hold Transition

This study examines the altitude-hold flight mode transition problem for tail-sitter unmanned aerial vehicles (UAVs) between hovering and level flight. The problem is significantly challenging because of the complicated nonlinear aerodynamics of tail-sitter UAVs during the transition process. To address this problem, this article proposes a minimum snap trajectory generation method and a model predictive control (MPC)-based tracking strategy. First, the generated trajectories are highly applicable, satisfying the dynamic constraint. Second, MPC tracks full states by solving a finite-horizon optimization problem at each step, yielding the optimal future behavior based on the system model. A numerical simulation was conducted in which the altitude changed by less than 1.4 m during the entire transition process.