# Shafts

The shaft system transmits shaft power from the freewheel to the tail rotor gearbox and decreases the stress level in the shafts when the tailboom moves during flight. The system also pushes air through the oil cooler for the cooling of the engine and transmission oil.

The shaft system has the components that follow:

* [Forward driveshaft](#forward-driveshaft)
* [Fan shaft assembly](#fan-shaft-assembly)
* [Aft driveshaft](#aft-driveshaft)
* [Driveshaft segments](#driveshaft-segments)
* [Disc packs](#disc-packs)

## Forward driveshaft

The forward driveshaft is located under the engine, in the turbine section, and connects the freewheel to the fan shaft assembly. It is a steel alloy riveted assembly made of a shaft and two flange adapters.

## Fan shaft assembly

The fan shaft assembly is located above the tailboom attachment to the aft fuselage. It connects the forward driveshaft to the aft driveshaft and pushes air into the plenum and through the oil cooler for the cooling of the engine and transmission oil. The fan shaft assembly includes the subassemblies that follow:

* Shaft assembly and two flange adapters
* Impeller and housing
* Forward and aft bearing hangers

The shaft assembly is made of steel alloy and has a flange to attach the aluminum impeller. Two steel alloy flange adapters engage the splines on the end adapters of the shaft assembly and connect the forward and aft driveshafts. When the shaft assembly turns, it drives the impeller inside a housing which connects to the plenum. Cool air moves through the inlet of the housing and then flows to the oil cooler. The forward and aft hangers attach the shaft assembly to the truss assembly and have provisions for alignment of the bearing inside with the adjacent driveshaft. The bearings are permanently sealed units that have four 0.080 inch (2 mm) holes on each side of the seal for lubrication.

## Aft driveshaft

The aft driveshaft is located above the tailboom and connects the fan shaft assembly to the driveshaft segments. It is an aluminum riveted assembly made of a shaft and two flange adapters.

## Driveshaft segments

The driveshaft segments are located along the top of the tailboom. There are five driveshaft segments that connect the aft driveshaft to the tail rotor gearbox. The driveshaft segments are all the same. Thus, they are fully interchangeable units. Each driveshaft segment includes the subassemblies that follow:

* Shaft assembly and two flange adapters
* Bearing hanger

The shaft assembly is an aluminum riveted assembly made of a shaft and one flange adapter. The other flange adapter engages the splines on the opposite end of the shaft assembly and connects the adjacent driveshaft segment. The hanger attaches the driveshaft segment to the tailboom and has provisions for alignment of the bearing inside with the adjacent driveshaft segments. The bearing is a permanently sealed unit that has four 0.080 inch (2 mm) holes on each side of the seal for lubrication.

## Disc packs

The disc packs, or Thomas couplings, are located along the tail rotor driveshafts. There are nine disc packs that connect the shafts and their segments together, to the freewheel and to the tail rotor gearbox. Together, the disc packs absorb the movement of the tailboom during flight to prevent concentration of stress in the shafts.

Each disc pack is made of 9 to 12 stainless steel discs stacked together. Each disc has two index flats parallel to the grain of the disc. These index flats are visual aids to make sure the discs are correctly installed.
