Page 75 - The Jet Engine

7: Accessory drives

Contents Page

Introduction 65
Gearboxes and drives 65

Internal gearbox
Radial driveshaft
Direct drive
Gear train drive
Intermediate gearbox
External gearbox
Auxiliary gearbox
Construction and materials 69

Gears
Gearbox sealing
Materials

GEARBOXES AND DRIVES

Internal gearbox
3. The location of the internal gearbox within the
core of an engine is dictated by the difficulties of
bringing a driveshaft radially outwards and the space
available within the engine core.
INTRODUCTION
4. Thermal fatigue and a reduction in engine
1. Accessory units provide the power for aircraft performance, due to the radial driveshaft disturbing
hydraulic, pneumatic and electrical systems in the gasflow, create greater problems within the
addition to providing various pumps and control turbine area than the compressor area. For any
systems for efficient engine operation. The high level given engine, which incorporates an axial-flow
of dependence upon these units requires an compressor, the turbine area is smaller than that
extremely reliable drive system. containing the compressor and therefore makes it
physically easier to mount the gearbox within the
2. The drive for the accessory units is typically compressor section. Centrifugal compressor engines
taken from a rotating engine shaft, via an internal can have limited available space, so the internal
gearbox, to an external gearbox which provides a gearbox may be located within a static nose cone or,
mount for the accessories and distributes the in the case of a turbo-propeller engine, behind the
appropriate geared drive to each accessory unit. A propeller reduction gear as shown in fig. 7-1.
starter may also be fitted to provide an input torque
to the engine. An accessory drive system on a high 5. On multi-shaft engines, the choice of which
by-pass engine takes between 400 and 500 compressor shaft is used to drive the internal
horsepower from the engine. gearbox is primarily dependent upon the ease of

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