Accessory drive

[2] Power for the accessory drive is taken from the central shaft linking the turbine and compressor sections of the engine.

The design of the internal gearbox is complicated by the heat and small space available in which to connect the driveshaft.

The drive and accessory gearboxes may also be split in two, one driven from each engine shaft, so as to distribute their loads.

Helical gears are sometimes used for the high-torque drives, typically the starter, as these give smoother running.

However helical gears also generate an end-thrust, which then requires a more complicated thrust bearing to support them.

[8] In some engines, bleed air is also tapped to provide power for accessories, as well as a mechanical shaft drive.

Klimov TV3-117 turboshaft engine. The accessory drive is the large casting on the top.
Turbomeca Adour , with the accessory drive mounted beneath. The accessories are removed and their mounting flanges covered by bright red blanking plugs.
Internal gearbox of the Rolls-Royce Pegasus
de Havilland Goblin
Separate accessory drives are taken from the nose cone, above and below the engine core.
Sectioned accessory drive on top of a Rolls-Royce Pegasus