Aeromechanical stability investigation of a composite hingeless rotor in hover

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Aeromechanical stability investigation of a composite hingeless rotor in hover

Han, C.H. / Yun, C.Y. / Kim, S.J. / Jung, S.N.

An experimental and analytical investigation was carried out for improving the aeromechanical stability characteristics of a hingeless rotor helicopter. The rotor model tested was a four-bladed, Froude-scaled, soft-inplane, hingeless rotor with a diameter of 1.98 m. Five different rotor/body configurations were built and tested to examine the effects of various structural couplings and body inertias on the aeromechanical stability of a helicopter. A finite element formulation based on Hamilton's principle was used for the analysis of composite hingeless rotors. The fuselage was modeled as a rigid body undergoing pitch and roll motions. The agreement between analysis and experiment was seen to be excellent for the lag mode frequency while the lag mode damping showed some variations depending on the cases considered. The quantitative behavior of stability augmentation through different structural configurations was investigated. A maximum of 400% increase in the regressive lag mode damping was obtained when a flap-lag coupling was combined with a pitch-lag coupling. Experimental results were also provided showing that a helicopter system became less stable especially at the ground resonance region when the frequencies of body springs were similar in magnitude.