Simulation of helicopter rotor-system structural damage, blade mistracking, friction, and freeplay

Selected helicopter rotor faults are simulated by changes in stiffness, inertial, and aerodynamic properties of the damaged or mistracked blade(s), A rotor aeroelastic analysis based on finite elements in space and time and capable of modeling dissimilar blades is used to simulate the damaged rotor in forward flight. The various rotor faults modeled include chordwise imbalance, aerodynamic mistracking, localized cracks, distributed changes in blade stiffness properties modeling a stiffness defect and a manufacturing defect, friction and freeplay in the pitch-control system and the lag damper, and friction in the flap and lag hinge. Changes in blade tip response and rotor hub loads are identified for the selected faults and tables of rotor-system diagnostics are compiled.