Analysis of Kinematic Constraints in Fixed-Wing UAV Formation Flying
Rise in autonomy has led to increase in usage of Unmanned Aerial Vehicles (UAVs) for various applications and has allowed the UAVs to perform complex and hazardous missions with ease. Formation of multiple UAVs finds applications in both military and civilian operations. Tasks like image mosaicking, mapping and target triangulation require multiple UAVs to maintain rigid formation while performing the mission. While maneuvering, rigid formation flying requires different speeds and bank angles from individual UAVs. However, fixed-wing UAVs have operational limits on bank-angle and speed. Bank angle and speed requirements for each UAV in formation depend essentially on the formation geometry and the maneuver. Relating to the maneuver capability of formation and the formation geometric configuration, this thesis presents a detailed analytical investigation of kinematic operating points (speed and bank angle) of fixed-wing UAVs flying in rigid formation. Represented in its speed and turn radius space, leader maneuver region is deduced abiding by kinematic constraints of all UAVs in the formation. In addition, the thesis also considers the converse problem of feasible follower configuration assignment for a given leader maneuver. The analysis derives a feasible spatial region around the leader instantaneous position defined by distance and bearing angle limits. Generating a given formation from arbitrary initial conditions and maintaining it presents another aspect in UAV formation flying. Addressing that the thesis considers a proportional-derivative control based guidance logics which command the follower heading and speed variation. Extensive validation studies are carried out using this guidance method providing insight into the dynamical nature of kinematic parameters as they vary in feasible and non-feasible formations. Considering time varying leader maneuvers and the need for smooth transition in follower kinematic parameters, the thesis proposes a virtual target based guidance methodology. Therein, the follower pursues a virtual target constructed around the desired position with respect to the leader. The proposed logic is based on constraining the virtual target’s position as a function of leader’s turning rate along an instantaneous circle centred at desired follower position, and governing the follower speed and heading direction to follow the virtual target. Engagement scenarios consider a variety of time varying leader maneuvers and present smooth variation in follower parameters with negligible errors in maintaining the formation.
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