SKF Products

Lead Lag Dampers

Lead lag dampers are required in fully articulated rotor systems (both main rotor and tail rotor) as described in the earlier section – fully articulated. Several technologies are utilised in the industry depending on the level of damping and the stroke (motion) that is required by the damper. The current technologies are pure orifice or shearing hydraulic dampers, visco-elastic (moulded silicone elastomer), and hybrid (both elastomeric and hydraulic components in a damping system). Damper systems consist of a damping device and a means of connecting that device to the rotor system. Linear dampers typically use rod ends for a two-axis freedom of motion interface with either the blade or the hub of the rotor. The rod ends used are consistent with the technologies discussed in the pitch link assembly section. Other configurations simply allow the damper to shear between two relative motion interfaces, creating a fixed interface on the damping device.

It is important to note that self-lubricating bearings are generally utilised at the attachment point between the damper and aircraft. In such locations, SKF self-lubricating bearings and rod end assemblies can be employed.

Typical solutions

SKF manufactures visco-elastic dampers using only SKF proprietary silicone elastomers. These dampers are typically configured in two ways; creating either a linear damper (canister configuration) or a shear damper (shear pad) depending on the rotor system.

Typical market constraints and customer preferences

The type of technology used for lead lag dampers is a function of the rotor system design, as each technology is limited by certain attributes. For the SKF product, the limiting factor is the available damping and maximum stroke (this is a factor of how much strain the elastomer will handle, which results in a very large damper given the length of stroke).

Lessons learned / best practices

SKF’s silicone blend is an industry – leading product in terms of the amount of damping it can produce. As such, SKF products can provide a safety margin for damping over a competitor product of comparable size, or can provide the customer with a smaller, weight – saving solution.

Damper design requires intensive consultation with the customer, as the dynamic performance and stability of the rotor system are affected by any change to the static and dynamic stiffness of the damper. Qualification of these products is typically done by SKF in terms of performance and life, but flight testing is always necessary in order to prove that aircraft stability is sufficient under all extreme conditions.
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