直升机单发失效后自转着陆轨迹优化

Trajectory Optimization of Helicopter Autorotation Landing After One Engine Failure

建立了直升机单发失效后增广的纵向三维刚体飞行动力学模型,通过选择合适的目标函数、路径约束和边界约束,将自转着陆问题表示成非线性最优控制问题,使用非线性规划方法求解得到自转着陆的最优轨迹和操纵。以UH-60直升机为例,首先计算了自转着陆距离最短的最优解,并与二维点质量模型进行对比。结果表明三维刚体模型在旋翼转速、旋翼拉力系数和下降率的时间历程与二维点质量模型一致的情况下,能提供直升机自转过程中的姿态变化,且纵向操纵更符合实际。然后考虑驾驶员反应滞后的实际情况,研究了自转着陆速度最小的最优轨迹和操纵,发现可以获得更小的下降率和更柔和的操纵,而着陆所需的末端时间和自转着陆距离会明显增加。

This paper studies the trajectory optimization of helicopter autorotation landing in the event of one engine failure by applying the nonlinear optimal control theory. An augmented longitudinal three-dimensional rigid-body flight dynamic model of a helicopter is first presented. By selecting the appropriate objective function, path constraints and boundary con- straints, the trajectory optimization problem of helicopter autorotation landing is then formulated into a nonlinear optimal con- trol problem, which is further transcribed into a discrete nonlinear programming problem. Finally, the optimal trajectories and controls are obtained by solving the nonlinear programming problem. Using helicopter UH-60 as the sample helicopter, the optimal solutions are calculated to minimize autorotation landing distance, and these solutions are compared with those obtained using a 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 show great correlation, and that the optimal solutions obtained using the three-dimen- sional rigid-body model furthermore include pitch rate, pitch attitude, and more realistic longitudinal cyclic pitch control. Then the trajectory optimization problem of helicopter autorotation landing is solved to minimize the velocity at touchdown with 1 second constant-control pilot delay. The resulting optimal trajectories and controls show safer sink-rate and slower pitch control rates while the final time and autorotation landing distance also increase considerably.