Comparison between Gimballed and Hingeless Tiltrotor Whirl Flutter Stability with Multibody Dynamics Analyses

The tiltrotor whirl flutter stability of a gimballed hub and a hingeless hub are investigated using multibody dynamics simulations. A semi-span wind tunnel tiltrotor model are developed using the multibody dynamics code: Dymore. CAMRAD II predictions are used to correlate the Dymore predictions of the baseline tiltrotor characteristics. The rotor structural frequencies of the gimballed tiltrotor and the hingeless tiltrotor are compared between Dymore and CAMRAD II predictions with good agreements. CAMRAD II model of the baseline TRAST gimballed tiltrotor is used for correlating the whirl flutter stability with that of the Dymore model. Overall good agreements are shown for both the frequencies and damping ratios of all three wing modes. The effects of key design variables, such as blade stiffness, rotor RPM, and ƍ3 on tiltrotor whirl flutter stability of both hubs are studied.