Formulation of a helicopter rotor system damage detection methodology

A helicopter rotor-system damage detection methodology is formulated for an articulated rotor in hover, and in forward flight. Damages modeled are moisture absorption, loss of trim mass, misadjusted pitch-link, damaged trailing-edge nap, damaged pitch-control system and inoperative lag damper. These damages are represented by changes in mass, stiffness, damping and aerodynamic properties of the rotor blade. A rotor aeroelastic analysis based on finite element discretization in space and time, and capable of modeling dissimilar blades, is used to simulate the undamaged and the damaged rotor. Changes in rotor system behavior are identified for the selected faults and tables of rotor system diagnostics are compiled. Rotor faults detectable from blade tip response include moisture absorption, misadjusted pitch-link, damaged trailing-edge flap and damaged pitch-control system. Rotor faults detectable from vibratory hub forces include moisture absorption, loss of trim mass, damaged pitch-control system and damaged lag damper. Finally, rotor faults detectable from vibratory hub moments include misadjusted pitch-link, damaged trailing-edge flap and damaged pitch-control system.