The lifting rotor inflow mode shapes and blade flapping vibration system eigen-analysis Original Research Article

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 Petersʹ 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 Suʹs and Lowisʹ 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.