dislibution is unlit- e. AEROMECHANICAL STABILITY OF A HINGELESS ROTOR IN HOVER AND FORWARD FLIGHT: ANALYSIS AND WIND TUNNEL TESTS

A research effort of analysis and testing has been conducted in the NASA-Langley Transonic Dynamics Tunnel to investigate the ground resonance phenomenon of a soft in-plane hingeless rotor. Experimental data were obtained using a 9 ft. (2.74 m) diameter model rotor in hover and forward flight. Eight model rotor configurations were investigated. Configura-tion parameters included pitch-flap coupling, blade sweep and droop, and precone of the blade feathering axis. An analysis based on a comprehensive analytical model of rotorcraft aero-dynamics and dynamics was used for this study. The moving-block method was used to experimentally determine the regress-ing lead-lag mode damping. Good agreement has been obtained between the analysis and test. Both analysis and experiment indicated ground resonance instability in hover. The pape