Design and model testing of helicopter rotor blade lag fluid elastic embedded chordwise inertial dampers

An embedded fluid elastic inertial damper is a small, single degree of freedom system that consists of a mass, rigidly connected to a fluid vessel, on an elastomeric spring located in the rotor blade cavity. The damper is tuned to a specific problem frequency and oscillates out-of-phase with the rotor blade resulting in an inertial moment about the lag hinge. This attenuates the lag motion of the rotor blade. The fluid elastic element gives the damper high static stiffness, which enables them to resist significant centrifugal forces, and low dynamic stiffness, which permits a low damper tuning frequency, necessary for the aeromechanical stability of the rotor system. Design guidelines for rotor blade lag damping using fluid elastic embedded chordwise inertial dampers were established. The design guidelines are intended to produce a device that is not only an effective damper but also light weight and compact. A design exercise for a full scale soft inplane rotor damper is conducted. Results of the design analysis indicate that a feasible device can generate 3% critical damping while satisfying constraints on weight, size, and stroke (static and dynamic). To validate this next generation of rotor blade lag dampers an embedded damper test facility was developed. The test facility consists of a rotor system with tubular segments in place of the airfoils. The purpose of the test stand is to simulate the centrifugal loads and rotor blade lag motions that the clamper would be subjected to when installed in an actual rotor blade cavity. Design analysis indicates 3-5% critical damping will be possible, depending on the lag flexure stiffness level. A prototype fluid elastic embedded chordwise inertial damper was designed for the embedded damper test facility from existing components and will provide rotor blade lag damping to the test stand rotor system while being proportionally light weight and exhibiting small damper amplitude. Final device testing is presently underway.