Rotor Design Options for Improving V-22 Whirl-Mode Stability

A CAMRAD II model of the V-22 Osprey tiltrotor was constructed for the purpose of analyzing high-speed aeroelastic instabilities (whirl flutter). The effects of different modeling options were examined, including single and dual load-path models of the blade root, swashplate coupling to the hub or transmission, compressible and incompressible rotor aerodynamics, and drive-train models with and without internal flexibility. Different amounts of blade sweep outboard of 0.8R were modeled with the intent of improving whirl-mode damping. Tip mass offsets were also examined. Appropriate combinations of blade sweep and tip mass offset greatly improved whirl-mode damping.