Characterization of Magnetorheological Helicopter Lag Dampers
Abstract:Magnetorheological fluid dampers are attractive candidates for augmentation of lag mode damping in helicopter rotors, where additional damping is required to avert instabilities only during specific flight conditions. Magnetorheological (MR) fluids change properties dramatically with application of a magnetic field. This active damping component presents an advantage over passive elastomeric and fluid‐elastomeric dampers. An extensive comparative study of fluid‐elastomeric and MR dampers is presented. The study was conducted with four (a pair each) 1/6th Froude scale dampers. The MR dampers were tested with the magnetic field turned off (OFF condition) and with the magnetic field turned on (ON condition). The dampers were tested individually and in pairs, under different preloads, and under single and dual frequency excitation conditions. The fluid‐elastomeric and MR (OFF) damper behavior was linear, while the MR (ON) behavior was nonlinear with the stiffness and damping varying with the displacement amplitude. Under dual frequency conditions, the MR dampers (ON condition) showed a significant degradation in damping and stiffness as the dual frequency excitation was increased. The MR (OFF) dampers showed no change in properties. The fluid‐elastomeric dampers showed a mild degradation in stiffness and damping under dual frequency excitation conditions. The MR (ON) damper hysteresis was modeled using a nonlinear viscoelastic‐plastic model. The model captures the nonlinear behavior accurately. Using the single frequency parameters, the dual frequency hysteresis behavior was predicted, and it correlates well with experimental data.
Document Type: Research Article
Affiliations: Alfred Gessow Rotorcraft Center, Department of Aerospace Engineering, University of Maryland, College Park, MD 20742
Publication date: July 1, 1999
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