DRAG REDUCTION ANALYSIS IN CLOSE-FORMATION FLIGHT

Formation flight, especially the close-formation flight, can reduce the drag and increase the flight range by using the wake vortices in a beneficial way. Therefore, it is important to study the phenomenon of drag reduction of vortex flow in close-formation flight. In this paper, two flying-wings were chosen to form the close-formation, and the cruise aerodynamics of the close-formation were analyzed by changing the relative position of two aircrafts, and the reasons for these variations of aerodynamic characteristics were further analyzed. The study found that the lead aircraft in close-formation is almost unaffected by the tail aircraft, and the cruise drag reduction of tail aircraft mainly comes from its reduction of the cruise angle of attack because of the upwash flow of the wake vortices. The cruise drag is minimal when the lead aircraft and the tail aircraft overlap about 10% wing span; The violent increase or decrease of aerodynamic load deviation relative to the single air-craft due to wake vortices, especially in wing head aero, causes the violent decrease or increase of the pitching moment of the aircraft.