  Tail-sitters, with the advantages of both the fixed-wing unmanned aerial
vehicles (UAVs) and vertical take-off and landing UAVs, have been widely
designed and researched in recent years. With the change in modern UAV
application scenarios, it is required that UAVs have fast maneuverable
three-dimensional flight capabilities. Due to the highly nonlinear aerodynamics
produced by the fuselage and wings of the tail-sitter, how to quickly generate
a smooth and executable trajectory is a problem that needs to be solved
urgently. We constrain the speed of the tail-sitter, eliminate the differential
dynamics constraints in the trajectory generation process of the tail-sitter
through differential flatness, and allocate the time variable of the trajectory
through the state-of-the-art trajectory generation method named MINCO. By
discretizing the trajectory in time, we convert the speed constraint on the
vehicle into a soft constraint, thereby achieving the time-optimal trajectory
for the tail-sitter to fly through any given waypoints.
