Understanding High-Speed Aeroelastic Stability of a Hingeless Hub Proprotor

A 4.75-ft-diameter dynamically scaled hingeless-hub proprotor model was developed and tested for aeroelastic stability up to 200 kt–corresponding to 468 kt full scale. The model had interchangeable hubs, blades, and pylon center-of-gravity locations, allowing data acquisition for new parametric variations. This paper documents the design, assembly, wind tunnel testing, and comprehensive analysis of its stability and the insights gained from it. The key conclusion is that a hingeless hub, when equipped with swept-tip blades, will significantly increase aeroelastic stability compared with the state-of-the-art gimbaled hub with straight blades. The causes were determined to be the interaction of rotor regressive lag motion with wing–pylon modes and the perturbation of hub pitch and roll moments. The regressive lag was more important at lower speeds, whereas the hub moments were more important at higher speeds. The data shed light on high-speed tiltrotor flight and provided a unique database for validation of advanced rotor comprehensive analysis.