Close formation flight control

In this paper the close formation flight control problem is addressed. The formation consists of a lead and wing aircraft, where the wing flies in close formation with the lead, such that the lead's vortices produce aerodynamic coupling effects, and a reduction in the formation's drag is achieved. A controller, i.e., a formation-hold autopilot for the wing aircraft, is designed such that the formation's geometry is maintained in the face of lead aircraft maneuvers. In the formation flight control system, the wing and lead aircraft dynamics are coupled due to kinematic effects, and, in the case of close formations, additional aerodynamic coupling effects are introduced. In the paper these additional aerodynamic coupling effects are properly modeled. The most significant aerodynamic coupling effect introduced by close formation flight entails the coupling of the lateral/directional channel into the altitude-hold autopilot channel. It is shown that formation hold autopilots designed ignoring the aerodynamic coupling effects yield satisfactory performance in close formation flight.