Autonomous Formation Flight – Design and Experiments

Formation flight has long been performed by many species of birds for its social and aerodynamic benefits. The traditional "V" shape formation flown by birds not only helped communication between individuals, but also decreased the induced drag for each trailing bird, and thus reduced the energy required for flying (Weimerskirch et al. 2001). The benefits of formation flight have also been evaluated for manned aircraft. However, due to the high level of risk, human-piloted close formations are rarely sustained for a long enough time to fully appreciate the aerodynamic benefits. Therefore, reliable autonomous formation control can be an attractive capability for both human-piloted aircraft and Unmanned Aerial Vehicles (UAVs). The formation control problem has been extensively discussed in recent years with numerous applications with ground mobile robots, aircraft systems, and space vehicles. In their survey paper, (Scharf et al. 2004) classified the spacecraft formation flight control algorithms into five architectures: • “Multiple-Input Multiple-Output, in which the formation is treated as a single multipleinput, multiple-output plan; • Leader/Follower, in which individual spacecraft controllers are connected hierarchically; • Virtual Structure, in which spacecraft are treated as rigid bodies embedded in an overall virtual structure; • Cyclic, in which individual spacecraft controllers are connected nonhierarchically; • Behavioral, in which multiple controllers for achieving different (and possibly competing) objectives are combined.” Similar classifications can be extended to the formation control of other types of vehicles. However, due to the complexity and non-linearity associated with the aircraft dynamics, the ‘leader-follower’ approach was by far the most popular method for aircraft formation flight control. The advantage of the ‘leader-follower’ approach lies in its conceptual simplicity, where the formation flight problem is reduced to a set of tracking problems that can be analyzed and solved using standard control techniques. In the early 1990s, a series of publications from D’Azzo and his colleagues (Dargan et al. 1992) (Buzogany et al. 1993) (Reyna et al. 1994) (Veth et al. 1995) outlined the foundation for the control of the ‘leader-follower’ formation flight using compensation-type controllers.