Semi-Active Linear Stroke Magnetorheological Fluid-Elastic Helicopter Lag Damper

Abstract

A semi-active linear stroke magnetorheological fluid-elastic lag damper is proposed as a retrofit to an existing elastomeric helicopter lag damper. A flow mode magnetorheological valve is incorporated into the inner chamber of the elastomeric damper. Consistent with sinusoidal loading conditions for a helicopter lag damper, single frequency (lag/rev) and dual frequency (lag/rev and 1/rev) sinusoidal excitations are applied to the magnetorheological fluid-elastic damper. Complex modulus and equivalent damping are used to compare the characteristics of the magnetorheological fluid-elastic damper with the passive elastomeric damper. Based on our measurements, the field-off magnetorheological fluid-elastic characteristics are similar to the passive elastomeric damping. Controllable magnetorheological damping is also observed as the applied current is varied in the magnetorheological valve. The experimental damping characteristics of the magnetorheological fluid-elastic damper are consistent with the analytical results obtained from the Bingham plastic analysis of the magnetorheological valve. A time domain magnetorheological fluid-elastic damper model is introduced to describe the nonlinear behavior of the magnetorheological fluid-elastic damper. Good correlation between the model and experimental data demonstrates the feasibility of the magnetorheological fluid-elastic model for future magnetorheological fluid-elastic damper applications. Significantly, this paper provides key insights into the practical design of semi-active linear stroke helicopter lag dampers.