Abstract: Nonlinear characteristics are observed in self-excitation of helicopter with elastomeric lag dampers implemented. In order to identify accurately the nonlinear equivalent damping levels of regressive lead-lag motion, a new method of damping identification is presented. Numerical multi-blade coordinate transformation (NMCT) performs transient decaying responses of regressive lead-lag motion in forms of cosine and sine components, which can directly perform the decaying envelope curves. The envelope curves can be applied to estimate the equivalent damping levels. The equivalent damping levels vary with regressive lag amplitude arising from nonlinear lag damper introduced. The present approach appears to exclude the influence of vibratory frequency on damping identifications, and therefore improves the equivalent damping accuracy. This method is successfully applied in regressive lead-lag equivalent damping identifications from helicopter ground resonance simulated responses.

Key words: helicopter dynamics, damping identification, self-excitation, nonlinear vibration