Robust time-varying formation control for tail-sitters in flight mode transitions

This paper mainly addresses the formation control problem for a group of tail-sitters in transition flight between forward and vertical flight. A robust formation control method is proposed to achieve the aggressive time-varying formation subject to nonlinear dynamics and uncertainties. For each tail-sitter, the proposed control method results in a composite controller that includes a trajectory tracking controller and an attitude controller to achieve the translational and rotational motion control, respectively. It is proven that tracking errors of the proposed global closed-loop system can converge to a given neighborhood around the origin in a finite time. Finally, the simulation studies for multiple tail-sitters to accomplish the time-varying formation in transition flight are presented to show the effectiveness of the proposed control strategy.