Study of helicopter autorotation landing following engine failure based on a six-degree-of-freedom rigid-body dynamic model

This paper focuses on the prediction of the safe autorotation landing operations of a helicopter following engine failure. The autorotation landing procedure is formulated as a nonlinear optimal control problem based on an augmented six-degree-of-freedom rigid-body flight dynamic model. First, the cost function and constraints are properly selected. The direct transcription approach is then employed to solve the optimal control problem. For a UH-60 helicopter, the optimal solutions with the rigid-body model are compared with those obtained using a two-dimensional point-mass model. It is found that the optimal solutions using the two different models show reasonably good agreement, and furthermore the optimal solutions using the rigid-body model involve the time histories of angular rates and attitudes, lateral velocity and position, as well as pitch controls. Finally the optimal control formulations with different cost functions are proposed for taking account of 1-s time delay and minimum touchdown speed. The calculated control strategies and trajectories are realistic.