The three-dimensional helicopter rotor inflow vibrating modes and rigid blade flapping motion coupled with unsteady wake
system have been studied through eigen-analysis. The Peters’ generalized dynamic inflow theory has been chosen as the unsteady
wake model. The three-dimensional inflow velocity vibrating mode shapes for node lines have been plotted in various skew
angles. The continuous motions of these mode shapes provide important information and insight into the physical phenomenon of
a helicopter rotor-wake aeroelastic system. The damping of axial flight flapping modes and the flapping divergent boundary in
forward flight have been compared with Su’s and Lowis’ rsults, respectively, to show the accuracy of our model. The results of
this work give us stability information about a rotor aeroelastic system and also reveal that the induced flow has a profound effect
on blade dynamics even at high advance ratios, The effect may cause an earlier unstable condition for a helicopter rotor system.