Helicopter transmissions are very complex systems, comprising a great variety of bearing types.

Different transmission schematics can be classified according to various helicopter weight segments and rotor configurations. For a specific transmission configuration, it is possible to distinguish several sub-assemblies typically identified as main gearbox transmission (main gearbox), auxiliary/accessory gearbox transmission (AGB), intermediate gearbox transmission, tail gearbox transmission.

The primary transmission system takes combined power from the engines, reduces the revolutions per minute (r/min), and transfers the power to the main and tail rotors. The secondary transmission provides a drive for electrical and hydraulic power generation systems. Most systems also include an oil cooler, blower, and rotor brake system.

In this section, the typical positions of each transmission subset are discussed with reference to existing projects where SKF Aerospace has been directly involved.
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