Nonlinear adaptive close formation control of unmanned aerial vehicles

This paper treats the question of formation flight control of multiple unmanned aerial vehicles (UAVs). In close formation the wing UAV motion is affected by the vortex of the adjacent lead aircraft. The forces produced by these vortices are complex functions of the relative position coordinates of the UAVs. In this paper, these forces are treated as unknown functions. For simplicity, it is assumed that the UAVs have autopilots for heading-, altitude-, and Mach-hold in the inner loops. An adaptive control law is derived for the position control of the wing aircraft based on a backstepping design technique. In the closed-loop system, commanded separation trajectories are asymptotically tracked by each wing aircraft while the lead UAV is maneuvering. It is seen that an overparametrization in the design is essential for the decentralization of the control system. These results are applied to formation flight control of two UAVs and simulation results are obtained. These results show that the wing UAV follows precisely the reference separation trajectories in spite of the uncertainties in the aerodynamic coefficients, while the lead aircraft maneuvers. (Author)