Gas Turbine Engine Gearboxes

GEARBOXES systems  in addition to ~ Gearboxes  provide the power for aircraft hydraulic, pneumatic and electrical systems  providing various pumps and control systems for efficient engine operation. ~ The drive for the gearbox is typically taken from a rotating engine shaft, usually the HP shaft , via an internal gearbox, to an external gearbox that gearbox that provides a mount for the accessories and distributes the appropriate geared drive to each accessory. ~ An accessory drive system sys tem on a high by-pass engine takes between 400 4 00 and 500 horsepower hor sepower from the engine.

INTERNAL GEARBOX ~ The location of the internal gearbox within the core of an engine is dictated by the difficulties of outwards (tower shaft) and the space available within the engine core. bringing a driveshaft a driveshaft radially outwards (tower RADIAL DRIVESHAFT (Tower shaft) gearbox to an accessory unit or ~ The purpose of a radial driveshaft driveshaft is to transmit the drive from the internal gearbox the external gearbox. ~ It also serves to transmit the high torque from the starter   to rotate the high pressure system for engine starting purposes. INTERMEDIATE GEARBOX (Transfer gearbox)  )) (T  ransfer gearbox ~ Intermediate gearboxes are employed when it is not possible to directly align the radial driveshaft with the external gearbox. ~ To overcome overc ome this problem an intermediate gearbox is mounted on the high pressure p ressure external gearbox. gearbox. compressor case and  redirects the drive, through bevel gears, to the external

GEARBOXES (contd.)  ACCESSORY GEARBOX (External gearbox)  ACCESSORY GEARBOX ~ The accessory drive is usually arranged as a curved casing , so that the various accessories accessories are mounted close to the engine. ~ Separate machined mounting pads are provided for each accessory. ~ Accessories are arranged on both sides of the driveshaft entry, in reducing order of their speed . gears, running in roller bearings. ~ The gears are usually plain usually  plain spur gears, in  roller bearings. ~ Idler gears are commonly used between them, to increase the spacing between accessories. ~ Helical gears are sometimes used for the high-torque drives, drives, typically the starter, as these give smoother running . ~ However helical However  helical gears also generate an end-thrust , which then requires a more complicated thrust bearing to support them.

COMBINING GEARBOX ~ for coupling engines together  (dual  (dual engine drive systems) ~ keeps power outputs balanced