Differential flatness based trajectory generation for time-optimal helicopter shipboard landing

In this paper, a time-optimal trajectory generation algorithm is proposed for helicopter shipboard landing. The algorithm utilizes a simplified model of the helicopter's dynamics and exploits the differential flatness of the model to formulate a nonlinear programming problem, whose solution provides time-optimal reference approach/landing trajectories. The trajectories are then tracked by an inner-loop linear dynamic inversion (LDI) controller to generate the actual inputs that steer the full-state nonlinear helicopter model. The proposed algorithm reduces approach/landing flight time and enables a higher degree of maneuverability (such as obstacle avoidance and large heading angle change) in comparison to typical state of the art methods of trajectory generation. Because of its computational efficiency, the path planner can also be used in real-time, i.e., through iterative recalculation of the remaining trajectory to account for deviations from the planned flight path. High fidelity simulations have been conducted on a verified UH-60A Black Hawk model, which show the effectiveness of the proposed method.