Modeling, development, and testing of fluidic flexible matrix composite blade dampers

Currently existing lead-lag dampers are complex and maintenance-intensive parts of the rotor hub, and they are ineffective solutions for stiff-inplane rotors which experience very small deformation at the blade root. This paper introduces a new class of rotor blade dampers that use Fluidic Flexible Matrix Composite (F²MC) tubes connected to fluidic circuits. Models are developed that couple the blade, F²MC tube, and fluidic circuit dynamics in order to assess the performance of the proposed solutions. In this paper, two different devices are proposed for augmenting the damping of hingeless and articulated rotors. The first device is a compact F²MC damped vibration absorber intended for stiff-inplane rotor applications. Simulation results predict that an F²MC absorber placed at the root of a representative stiff-inplane hingeless rotor blade can increase the blade damping ratio from 2% to over 6%. The second device provides lag damping in an articulated rotor blade by harnessing the blade lag motion to strain an F²MC tube that pumps fluid through an orifice into an accumulator. Damping ratios as high as 25% critical damping are predicted for a representative articulated blade, although the F²MC damper effectiveness varies greatly depending on the blade operating lag angle. As a precursor to future rotor testing, a prototype articulated blade F²MC damper is built and tested on a 4.85-foot radius rotor blade. Using this device, blade damping ratios of up to 14.3% are achieved on benchtop experiments which include simulated centrifugal loading.