Aspects of Control for a Parafoil and Payload System

A parafoil controlled by parafoil brake de ection offers a lightweight and space-efŽ cient control mechanism for autonomous placement of air-dropped payloads to speciŽ ed ground coordinates. The work reported here investigates control issues for a parafoil and payload system with left and right parafoil brakes used as the control mechanism.It is shown thatparafoilandpayloadsystems can exhibit two basicmodesof lateral control, namely,roll and skid steering. These twomodes of lateral steering generate lateral response in oppositedirections. For example, a roll steer conŽ guration turns left when the right parafoil brake is activated, whereas a skid steer conŽ guration turns right under the same control input. In transition between roll and skid lateral steering, the lateral response is zero, and the system becomes uncontrollable.Angle of incidence, canopy curvature of the parafoil, and magnitude of brake de ections are important design parameters for a controllable parafoil and payload system and greatly effect control response, including whether the basic lateral control mode is roll or skid steering. It is shown how the steering mode switches when fundamental design parameters are altered and as the magnitude of the brake de ection increases. The mode of directional control transitions toward roll steering as the canopy curvature decreases or the angle of incidence becomes more negative. The mode of directional control transitions away from the roll steering mode as the magnitude of the brake de ection increases, and for “large” brake de ections most parafoils will always skid steer.