Adaptive Magnetorheological Snubber Lag Damper (MRSLD) for Hingeless Helicopter Main Rotor Blades

摘要

A magnetorheological snubber lag damper (MRSLD) was developed to provide adaptive lead-lag damping control for a hingeless helicopter rotor. The MR snubber lag damper consists of a flow valve, a flexible snubber body, and a flexible center wall separating the body into two fluid chambers. MR fluid enclosed in the snubber body can flow from one fluid chamber to the other through the valve and its viscosity controlled via an electromagnetic coil in the valve. Based on a Bingham plastic constitutive relation and a steady state fluid flow model, valve design parameters were established, and analytical damping analysis was conducted and compared to the experimental results. The magnetic valve was designed using a magnetic circuit analysis tool and was validated by magnetic FEM analysis. Consistent with the loading conditions for a helicopter lag damper, the MRSLD was tested under single frequency (lag/rev) and dual frequency (lag/rev and 1/rev) sinusoidal excitation. The complex modulus method was used to compare the MRSLD damping characteristics with a baseline passive snubber type Fluidlastic® damper supplied by Lord Corporation. The field-off MRSLD damping was smaller than the baseline damping. A significant controllable damping range was also observed as current was applied to a magnetic valve in the MRSLD. The non-linear behavior of the MRSLD was not sufficiently modeled using the complex modulus method. To account for the hysteresis behavior of the MRSLD and estimate the damping force, a hydro-mechanical model was formulated based on lumped parameters. Parameters for the model were established using experimental data and a least-mean-square error minimization technique. The model was then applied to reconstruct the force time history under single frequency at lag/rev and 1/rev excitation frequencies. The average error between the predicted and measured damping forces was also evaluated to assess model accuracy.