A semi-active linear stroke magnetorheological fluid-elastic (MRFE) lag damper is developed as a retrofit to an existing elastomeric helicopter lag damper. A flow mode magnetic 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 loadings are applied to the MRFE damper. Complex modulus and equivalent damping are used to compare the characteristics of the MRFE damper with the passive elastomeric damper. Based on our measurements, the Field-OFF MRFE characteristics are similar to the passive elastomeric damping. Controllable MR damping is also observed as the applied current varied in the MR valve. The experimental damping characteristics of the MRFE damper are consistent with the analytical results obtained from the Bingham plastic analysis of the MR valve. A time domain MRFE damper model is introduced to describe the nonlinear behavior of the MRFE damper. Good correlation between the model and experimental data demonstrates the feasibility of the MRFE model for future MRFE damper applications. Significantly, this paper provides a comprehensive insight into practical design of a semi-active linear stroke damper at full scale.
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