Aggressive Formation Flying of Fixed-Wing UAVs with Differential Geometric Guidance.

A nonlinear differential geometric guidance scheme is presented in this paper for aggressive autonomous formation flying of fixed-wing unmanned aerial vehicles (UAVs) in the leader-follower framework. It is assumed that the desired location of the followers are known in the velocity frame of the leader. It is also assumed that the followers can also access the position, velocity and acceleration parameters of the leader as necessary auxiliary information. By utilizing this information and manipulating their own dynamics, the proposed logic autonomously guides the followers to their respective desired positions. Depending on the leader's velocity and acceleration information as well as the intended relative location, the formulation also ensures an appropriate direction of the velocity vectors of the followers at the desired relative locations, including its rate of change if any. This leads to minimal transient effects while maintaining the formation even under maneuvering conditions. Usage of quaternions and other innovations ensure that the formulation is singularity-free and hence formation flying is ensured even under aggressive maneuvers of the leader without any restriction on its velocity vector direction. The desired thrust, angle of attack and bank angle are generated using a nonlinear point mass model of a vehicle. The generated guidance commands are then realized using a nonlinear six-DOF model, making the formulation practically more relevant. Extensive simulation studies demonstrate that the proposed approach is capable of bringing the UAVs from arbitrary initial locations to the desired formation and then maintaining the formation even under highly agile motion of the leader.