Aerodynamic analysis of RQ-2 fixed-wing UAVs in close formation flight

Control and precision navigation advancements have renewed interest in formation flying for commercial and unmanned aerial vehicles (UAVs). Most of the research in this area has focussed on extended formation flying, which is unsuitable and less effective for UAVs. Various bioinspired formation patterns, including the echelon, normal V, and inverted V patterns, have been proposed for research and use in the aviation industry. The optimal separation distance is maintained for maximum aerodynamic benefits of flying. Formation controllers, in conjunction with wake and vortex tracking sensors, can be used to achieve this and maintain the preferred formation pattern and structure. This research examined the effects of close formation flying on the lift, induced drag, and, consequently, the overall range of UAVs. The aerodynamic benefits of flying UAVs in coordinated formation patterns included reduced drag and increased lift by positioning the trailing UAVs at optimal longitudinal, lateral, and vertical separation distances behind the leading UAVs. A lift/drag ratio increase of 25.6% and 52.4% were achieved in the inverted V and the normal V pattern, respectively. This corresponded to an average increase of 8.5% and 17.4% in the capable range of the UAV. The typical V-formation pattern proved better than the inverted V pattern due to the reduced induced adverse rolling effect on the trailing UAV on the former formation pattern.