Equivalent linear damping model of nonlinear hydraulic damper for helicopter rotor

An equivalent linear damping model is developed for forward flight condition, with the flap/lag/pitch kinematics and nonlinear characteristics of hydraulic damper taken into account. Damper axial velocity is analyzed from the velocities of the damper‐to‐blade attachment point in time domain. For the case of blade lead‐lag oscillations without forced excitation and kinematics, the equivalent linear damping is calculated from transient response with energy balance method, Fourier series based moving block analysis and Hilbert transform based technology, respectively. Results indicate that equivalent linear damping decreases significantly with lead‐lag forced excitation and flap/lag/pitch kinematics, especially with the latter in flight condition.