Wind tunnel testing of a 6-ft diameter Mach-scale rotor was performed in the Glenn L. Martin Wind Tunnel at the University of Maryland up to an advance ratio of 1.2. Performance and vibratory hub loads measurements were taken at a range of reduced rotor speeds, motivated by the requirement of slowed rotors for high-speed flight of compound helicopters. Advance ratios from 0.3 to 1.2 were tested with rotor speeds from 100% down to 25% and tunnel speeds up to 175 kts. Collective-thrust reversal was observed at high advance ratio as well as a drag-based autorotation due to trim settings and reverse flow. 4/rev vertical hub loads were found to increase severely at low RPM, despite the low mean thrust levels. 4/rev vertical hub load was found to be more strongly correlated with collective setting than mean thrust level at high advance ratios. Mean thrust and vibratory hub loads actually showed a negative correlation at these conditions. Finally, operating condition tradeoffs for efficient performance and low vibrations were identified.
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机译：在马里兰大学的Glenn L. Martin风洞中进行了直径为6英尺的马赫规模转子的风洞测试，推进比为1.2。性能和振动轮毂负载的测量是在一系列降低的旋翼速度下进行的，这是由于复合直升机的高速飞行对减速旋翼的需求所致。测试了从0.3到1.2的推进比，转子转速从100％降低到25％，隧道速度高达175 kts。由于修整设置和反向流动，在高进给率以及基于阻力的自转下，观察到了集体推力反向。尽管平均推力水平较低，但在低RPM时，发现4 / rev垂直轮毂载荷会急剧增加。发现4 / rev垂直轮毂载荷与集体设定的相关性比高推进比下的平均推力水平高。在这些条件下，平均推力和振动轮毂载荷实际上显示出负相关。最终，确定了有效性能和低振动的运行条件折衷方案。
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