Comparison of flight data and analysis for hingeless rotor regressive inplane mode stability

During the development of the AH-56A, a considerable amount of analytical and experimental data was obtained on the stability of the regressive inplane mode, including coupling with other modes such as body roll and rotor plunge. The data were obtained on two distinctly different control systems; both gyro controlled, but one with feathering moment feedback and the other with direct flapping feedback. The paper presents a review of the analytical procedures employed in investigating the stability of this mode, a comparison of analytical and experimental data, a review of the effect of certain parameters, including blade droop, sweep, 63, tx I , vehicle roll inertia, inplane frequency, rpm and forward speed. It is shown that the stability of this mode is treatable by analysis and that adequate stability is achievable without recourse to auxiliary inplane damping devices.