High-speed stability of tiltrotor was studied. The University of Maryland’s Maryland Tiltrotor Rig (MTR) was chosen for the analysis due to availability of properties and test data, and its interesting high-stability behavior observed in the Glenn L. Martin wind tunnel in August 2022. A Rotorcraft Comprehensive Analysis System (RCAS) model of the MTR gimbaled hub was built in addition to the University of Maryland Advanced Rotorcraft Code-II (UMARC-II) model from previous work. The objective is threefold: i) validate RCAS tiltrotor stability predictions, ii) shed light on the high-stability behavior of the MTR, and iii) find ways to lower the instability speed of the MTR for future wind tunnel tests. Trim collective for freewheeling and stability predictions were compared with wind tunnel test data up to 200 knots. RCAS and UMARC-II predictions showed good agreement with each other and the test data. Predictions show that MTR is stable up to 215 knots (490-knots full-scale flight) although the wing is only 18% thick (current technology is 23%). A parametric study was carried out. The impact of wing stiffness, pitch-flap coupling (${\delta }_3$ angle), lag stiffness, blade chord, number of blades, pylon mass, pylon center of gravity (c.g.), pylon location, and rotor speed was studied. MTR’s pylon c.g. is unconventionally behind the wing elastic axis. It was found that this significantly improved stability. This behavior is not specific to MTR; full-scale aircraft stability can also be improved by moving the pylon c.g. backward if wing beam is the least stable mode. A combination of forward pylon c.g., reduced rotor speed, and increased blade chord reduced the instability speed by more than 55 knots to near 160 knots, helping researchers obtain high-quality test data in the upcoming Glenn L. Martin wind tunnel tests.

对倾转旋翼机的高速稳定性进行了研究。由于性能和测试数据的可用性，以及 2022 年 8 月在 Glenn L. Martin 风洞中观察到的有趣的高稳定性行为，选择马里兰大学的马里兰倾转旋翼机 (MTR) 进行分析。旋翼机综合分析系统 (除了之前工作中的马里兰大学先进旋翼机代码 II (UMARC-II) 模型之外，还构建了 MTR 万向轮毂的 RCAS）模型。目标有三个：i) 验证 RCAS 倾转旋翼稳定性预测，ii) 揭示 MTR 的高稳定性行为，以及 iii) 找到降低 MTR 不稳定速度以用于未来风洞测试的方法。将惯性滑行和稳定性预测的纵倾总成与高达 200 节的风洞测试数据进行了比较。 RCAS 和 UMARC-II 的预测彼此之间以及测试数据都表现出良好的一致性。预测显示，尽管机翼厚度仅为 18%（当前技术为 23%），MTR 仍能稳定达到 215 节（全尺寸飞行 490 节）。进行了参数研究。机翼刚度、俯仰襟翼耦合的影响（${\delta }_3$研究了滞后刚度、叶片弦长、叶片数量、吊架质量、吊架重心 (cg)、吊架位置和转子速度。港铁的塔架重心非常规地位于机翼弹性轴的后面。结果发现，这显着提高了稳定性。这种行为并非港铁特有；如果机翼梁是最不稳定的模式，则通过向后移动吊架重心也可以提高全尺寸飞机的稳定性。前塔重心、降低旋翼速度和增加叶片弦长的结合将不稳定速度降低了 55 节以上，达到接近 160 节，帮助研究人员在即将进行的 Glenn L. Martin 风洞测试中获得高质量的测试数据。