Improving Receiver Station-keeping In Aerial Refueling By Formulating Tanker Motion As Disturbance
Elliott, Christopher Michael
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During aerial refueling operations, the receiver aircraft should hold position within a “refueling box” to maintain the boom-receptacle connection while the tanker aircraft flies in a racetrack maneuver. Prior research work shows, especially in turns, significant difficulty resides in meeting y-deviation requirements, i.e., to stay within the box in the lateral direction. This observation indicates tanker motion as “the biggest disturbance” in turn. The nonlinear equations of motion for the receiver aircraft used in this work are developed in terms of position and orientation states relative to the tanker. Linearization results in a set of equations with tanker motion clearly quantified as disturbance. The linearized state-space equation has an additional term with a disturbance matrix representing how tanker motion affects the relative motion. In this research work, a disturbance rejection method, based on these linearized equations, is employed to develop a new control law to reduce the effect of the tanker turning maneuver on the station-keeping performance of the receiver. This would lead to proactive (feed-forward) control action in addition to reactive (feedback) control. Practical implementation of this approach will require the communication of tanker states (velocity, attitude, angular rates, etc.) to the receiver controller. Research findings conclude the new control law offers significant potential to improve the receiver station-keeping performance in the presence of a disturbance where the improvement potential appears directly proportional to the fidelity of the disturbance model.