利用最优控制方法研究变转速旋翼直升机在遭遇单发失效时，旋翼转速对自转着陆低速回避区的影响。首先，以UH-60A直升机为样机，建立三维刚体飞行动力学模型，并分析低速范围内旋翼转速对直升机需用功率的影响。然后，在模型中加入单发失效后自转着陆阶段发动机输出功率以及旋翼转速变化方程，并利用直接多重打靶法将直升机单发失效后的自转着陆过程转换为非线性最优控制问题进行数值求解。最后，基于最小化回避区面积的思想，得到并分析直升机在不同旋翼转速下单发失效后的自转着陆低速回避区，以及回避区高悬停点、拐点和低悬停点对应的最优着陆轨迹和操纵过程。结果表明：随着旋翼转速的降低，直升机单发失效后的低速回避区首先会逐渐缩小，然后迅速增大。最小回避区对应的旋翼转速略高于最小需用功率对应的旋翼转速。适当降低旋翼转速不仅能有效降低直升机的需用功率，还有利于提高直升机单发失效后的自转着陆性能。
The optimal control method is used to study the effects of variable rotor speed on the helicopter low-speed Height-Velocity (H-V) diagram in the One Engine Inoperative (OEI) situation and the corresponding optimal autorotation landing procedure. First, a three-dimensional rigid body flight dynamics model for a UH-60A helicopter is established, and the effect of rotor speed on the helicopter required power in the low-speed range is analyzed. Then, equations for the engine output shaft power and rotor speed during autorotation landing in OEI are added into the flight dynamics model. The helicopter autorotation landing procedure in OEI is converted into a nonlinear optimal control problem by using the direct multiple shooting method, and solved numerically. Finally, based on the idea of minimizing the area of the avoidance zone, the H-V diagrams and the optimal autorotation landing procedures in OEI at three key points (high, knee and low) of the H-V diagrams with various operational rotor speeds are investigated. The results show that the reduction of operating rotor speed will cause gradual shrink of the H-V diagram area first and rapid expansion then. In addition, the rotor speed corresponding to the minimum H-V diagram is slightly higher than the rotor speed corresponding to the minimum required power. Properly reducing the rotor speed can effectively reduce the helicopter required power, and can also improve the autorotation landing performance in OEI.
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