Elasto-Hydraulic « hybrid » Lead-Lag Damper

Lead-Lag dampers are broadly used in helicopter rotor-heads as a major component for the dynamic control of the blades motions and to insure aircraft in flight stability. Particularly, these devices reduce the risk of ground-resonance which can be detrimental to the aircraft and its occupants.

Elastomeric and Fluid dampers are broadly used to fulfill this function but both technologies have their own advantages – performance, reliability - and drawbacks – limited performance in specific conditions, maintenance & repair cost,... The “hybrid” elasto-hydraulic dampers, such as this damper, combine advantages and overcome weaknesses of each technology.

On one hand, the outer structure of such a damper integrates an elastomeric element allowing large motions between fixed and moving parts. This resilient element is designed not only to bring the requested elastic spring rates but also to provide a natural sealing suppressing all need for traditional dynamic seals, this is known to be source of reliability problems in fluid dampers. On the other hand, a fluid cell is encapsulated inside this elastomeric envelope to provide enhanced damping performances.

The innovations here are, first, the design of the hydraulic cell to achieve enhanced performances and then, the overall design allowing simultaneously to accommodate with the environment and to achieve reliability targets. The operating conditions of a part installed on a main rotor-head are very specific and challenging due to the complex vibration environment: A lead-lag damper has to perform at high and low temperature.
The hydraulic stage consists in this application of two fluid cells of different nature working in parallel providing enhanced performances on a broad range of amplitudes. Furthermore, the encapsulated system integrates a fluid volume variation compensation system which allows this system to operate efficiently on a broad range of temperature that military helicopters may have to face.

To conclude, this innovation proposes not only a system with enhanced characteristics supporting the requested flight envelop but also a device with higher reliability compared to fluid dampers, with lower maintenance and thus reduced operating cost.