Controllable Magnetorheological Damping in Advanced Helicopter Rotors
Lag dampers are a critically important stability augmentation device in modern soft in-plane rotors that are used to mitigate mechanical instabilities such as ground resonance, as well as aeromechanical instabilities such as air resonance. The in-plane bending, or lead-lag, modes of helicopter rotor blades have very low aerodynamic damping levels, so that damping in these modes must be augmented using a mechanical damper. Typical dampers utilize flow of hydraulic fluids through an orifice, and/or direct shearing of elastomeric material, to achieve these augmented damping levels. In this chapter, an existing lag damper of the snubber type that employs both hydraulic flow through an orifice as well as direct shearing of elastomeric material is modified to provide controllable damping using magnetorheological fluids. The existing orifices in the snubber damper are modified in such a way that magnetic field can be applied to the magnetorheological fluids flowing through the orifice, in order to effect a change in apparent viscosity and, thus, a change in damping level.