Hybrid magnetorheological fluid–elastomeric lag dampers for helicopter stabilityaugmentation

Abstract

A laboratory demonstration of a hybrid magnetorheological fluid–elastomeric (MRFE)damper is investigated for adjustable or programmable lag mode damping in helicopters, sothat damping requirements can be varied as a function of different flight conditions. Thelaboratory demonstration of this hybrid MRFE lag damper consists of a double lap shearelastomeric damper in parallel with two magnetorheological (MR) flow mode dampers.This is compared to a damper where only elastomeric materials are implemented,i.e., a double lap shear specimen. The relationship between the output force andthe quasi-steady harmonic displacement input to a flow mode MR damper isexploited, where the output force can be adjusted as a function of applied magneticfield. Equivalent viscous damping is used to compare the damping characteristicsof the hybrid damper to a conventional elastomeric damper under steady-statesinusoidal displacement excitation. To demonstrate feasibility, a hybrid MRFEdamper test setup is designed, and single frequency (lag frequency or rotor in-planebending frequency) and dual frequency (lag frequency and rotor frequency) tests areconducted under different magnetic fields. The hybrid MRFE damper exhibitsamplitude-dependent damping behavior. However, with application of a magneticfield, the damping level is controlled to a specific damping level objective as afunction of displacement amplitude. Similarly, under dual frequency conditions,damping degradation at the lag frequency, because of lag motion at the rotorfrequency, can also be recovered by increasing magnetic field. A time-domainanalysis is developed to study the nonlinear dynamic behavior of the hybrid MRFEdamper. Using rate-dependent elasto-slides, the amplitude-dependent behavior ofthe hybrid MRFE damper is accurately reconstructed using both constant andcurrent-dependent (i.e. controllable) parameters. The analysis is physically motivated andcan be applied to the elastomer and MR fluid damper components separately.