A deep stall maneuver enables a fixed-wind UAV to land in a small area because it allows the UAV to approach the landing site with a steep descent flight path angle. Depending on the wing-loading, the aircraft can descend slowly enough so that it can endure the impact to the ground at touch-down.
For a sustained deep stall maneuver the aircraft must have an all-moving horizontal tail-surface (instead of the conventional elevator) with a wide range of deflection angles. During a deep stall landing the vehicle descends with a very deep flight-path angle while the pitch attitude is maintained more or less horizontally, and the aircraft¡¯s main wing lies in a deep stall state beyond the stall angle-of-attack. However, the both the horizontal and vertical tail are not in the stall area. So, they can be used to control the flight path.
We have developed a control system for precision deep stall landing. We developed the full six degree-of-freedom dynamic model for deep stall. Wing strip theory was adopted to model the aerodynamics with a high angle-of-attack. Trim and stability analysis were conducted. Linear model was extraced to be used for control law design. Flight-path and heading angle controllers were designed using the classical controller design method.
Flight path planning and deep stall guidance technique was developed. For a given desired touch-down position, the deep stall starting position was calculated considering the wind effect. A virtual-target-following guidance method was developed to guide the vehicle to the desired touch-down location during deep stall under wind.
A series of flight tests was performed in the airfield at Korea Aerospace University, Goyang City, Korea. It was successfully demonstrated that the aircraft can be guided to a desired landing spot within a 10m accuracy from relatively high altitudes at various wind conditions in a controlled deep stall state.
