Dynamic Analysis of Helicopter Bearingless Main Rotor With Hub Flexbeam Damage Configurations

Abstract : This report documents a dynamic analysis of a helicopter bearingless main rotor system with damaged hub flexbeam configurations. The analysis was performed using a comprehensive helicopter aeroelastic code based on finite element/blade element theory. The bearingless main rotor (BMR) system, including flexbeams, torque tubes, and main rotor blades, is modeled as a number of elastic beam finite elements, wherein each beam element undergoes flap bending, lag bending, elastic twist, and axial deflections. Aerodynamic forces on rotor blades are calculated using quasisteady aerodynamic theory with a linear in-flow model. Flexbeam ballistic damage is simulated by changes in the span-wise distribution of the mass, bending and torsional stiffness of flexbeam element. Results are first calculated for a soft in-plane, five-bladed, bearingless rotor, with an undamaged (baseline) configuration. Results are then calculated for this rotor system with damage representation. The effects of this damage on rotor and helicopter system performances are determined in terms of blade modal shapes and frequencies, rotor system aeroelastic response and loads variations. Ballistic damage to the hub flexbeam can significantly affect the dynamic behavior of the bearingless rotor system.