独立桨距控制对直升机飞行性能的影响

为研究旋翼独立桨距控制对直升机飞行性能的影响，在已验证的直升机性能分析模型基础上，以UH-60A直升机为样例，通过输入不同阶次、幅值和相位角的独立桨距，分析直升机的需用功率和升阻比变化，在此基础上给出了旋翼桨盘内迎角和阻力系数的分布，探讨了独立桨距控制提升直升机性能的机理。分析结果表明：高速时，2阶和3阶的独立桨距控制可降低旋翼需用功率、提高直升机的升阻比，但提升效果有限，直升机起飞重量较大时，效果更明显；2阶耦合3阶的独立桨距控制对旋翼性能的提升效果比单独的2阶或3阶桨距输入更好，样例直升机的需用功率最多降低了4.5%，4阶的独立桨距输入则不利于提升旋翼性能；输入独立桨距后，旋翼桨盘迎角分布改善，后行侧迎角减小，有利于推迟失速，桨盘的后行侧的阻力系数减小，可有效降低旋翼的需用功率，提升直升机飞行性能。

Effect of individual blade pitch control on flight performance of helicopters

A verified model for prediction of helicopter performance is used to investigate the effect of individual blade pitch control on the flight performance of helicopters. The influence of the harmonic number, amplitude, and phase angle of the pitch control on the rotor power required and lift to drag ratio of the UH-60A helicopter is analyzed. The distribution of the angle of attack and drag coefficient over the rotor disk are shown to analyze the physical mechanism of performance improvement by individual blade pitch control. The results indicate that the second-and third-order harmonic individual blade pitch control can reduce the power required and increase the helicopter lift to drag ratio in high speed flight, but the effect is relatively limited. For the helicopter with larger take-off weight, the effect can be enhanced. The performance improvement achieved by the second-order harmonic coupled with the third-order harmonic individual blade pitch control is better than that by a single harmonic input, and the maximum power reduction is 4.5%. The fourth-order harmonic individual blade pitch control does not exhibit the potential in performance improvement. In high speed flight, the blade pitch control can reduce the angle of attack in the retreating side and delay the stall, and then the drag coefficient and rotor power required can be reduced to improve the flight performance of the helicopter.