Investigation of Helicopter Autorotation Landing after One Engine Failure

This paper studies the trajectory optimization of helicopter autorotation landing and the prediction of the height-velocity (H-V) diagram in the event of one engine failure using the nonlinear optimal control theory. An augmented longitudinal three-dimensional rigid-body flight dynamic model of a helicopter is employed. For UH-60 helicopter, the optimal solutions are calculated to minimize autorotation landing distance, and the solutions are compared with those obtained using the two-dimensional point-mass model. It is found that the time histories of rotor speed, thrust coefficient and sink-rate using the two different models have a good agreement; however the optimal solutions using the three-dimensional rigid-body model can obtain pitch rate, pitch attitude, and more realistic longitudinal cyclic pitch control. Furthermore, with 1 second delay of pilot reaction to engine failure withappropriate performance index, the optimal trajectories and controls show safer sink-rate and slower pitch control rates. Finally, the low speed H-V diagrams with 1-second time delay are predicted at three different gross weights.