An internal gearbox,Direct drive

Fig. 7-3 An internal gearbox.

Direct drive

11. In some early engines, a radial driveshaft was used to drive each, or in some instances a pair, of

accessory units. Although this allowed each accessory unit to be located in any desirable location

around the engine and decreased the power transmitted through individual gears, it necessitated

a large internal gearbox. Additionally, numerous radial driveshafts had to be incorporated within the

design. This led to an excessive amount of time required for disassembly and assembly of the engine

for maintenance purposes.

12. In some instances the direct drive method may be used in conjunction with the external gearbox

system when it is impractical to take a drive from a particular area of the engine to the external gearbox.

For example, fig. 7-1 shows a turbo-propeller engine which requires accessories specific to the propeller

reduction drive, but has the external gearbox located away from this area to receive the drive from the

compressor shaft.