Effects of Temperature on Magnetorheological Fluid Elastomeric Lag Dampers for Helicopter Rotors

Abstract

A snubber type magnetorheological fluid elastomeric (MRFE) lag damper was developed as a retrofit to a fluid-elastomeric (FE) lag damper to provide adaptive lead-lag damping augmentation for a hingeless helicopter rotor. This MRFE damper consists of a flexible cylindrical snubber body, a flexible elastomeric center wall fitted with two MR flow valves, through which MR fluid enclosed in the snubber body can pass through and be activated by a magnetic field in the MR valve. During normal operation, the MRFE damper is exposed to temperature variations due to ambient temperatures and in-service self-heating. To characterize performance at different operating temperatures, the MRFE damper was tested in the fixed frame under a helicopter rotor in-plane bending frequency (lag/rev) at temperatures varying from 20°C to 50°C. Complex modulus and equivalent viscous damping were used to compare the MRFE damper characteristics at varying temperatures with a baseline passive FE damper. The field-off MRFE damping was comparable to the baseline damping at all test temperatures. A significant controllable damping range was also observed as current was applied to magnetic valves in the MRFE damper at all temperature conditions. To account for the non-linear hysteresis behavior of the MRFE damper, a hydromechanical model was formulated based on lumped parameters. In the current study, the hydromechanical model accounts for performance variations due to damper operating temperatures. Model Parameters were established at each test temperature based on valve geometry, material property and measured data. The model was then applied to accurately simulate the force time history of the MRFE damper at lag/rev frequency.