Rotor-Body Coupled Vibration Analysis of a High-Speed Lift Offset Coaxial Rotor

A rotor-body coupled vibration analysis is performed for a coaxial compound lift offset (LO) helicopter. The vehicle is featured by two-bladed counterrotating rotors, main wing, and auxiliary propulsions installed at each wing tip. The fuselage analysis model is constructed considering the existing designs of conventional helicopters and tilt rotors, while the blade structural design is established modifying the original platform of XH-59A blades. As many as 17 free vibrating modes are used to represent the airframe motions after conducting a convergence test on the vibration behavior of the rotor. An in-house structural design optimization framework based on the evolutionary algorithm is employed to systematically search the best suited combinations of the objective function while meeting all the design constraints set from the static and structural dynamics perspectives. The resulting property values of the optimized configuration are correlated with those by XH-59A. The predicted results on the performance show in good agreement with the flight test data of XH-59A. The trim, loads and vibration responses are examined using either isolated coaxial LO or compound coaxial LO rotors. Key results showing the beneficial effects of LO rotor in both configurations are discussed with the shaft-fixed or shaft-free conditions of the compound helicopter in high speed flights.