Page 62 - The Jet Engine

Fig. 5-8 Typical nozzle guide vanes showing their shape and location.

14. The nozzle guide vanes are usually of hollow velocity reaches that required at exit to produce the
form and may be cooled by passing compressor required degree of reaction (para. 5).
delivery air through them to reduce the effects of high
thermal stresses and gas loads. For details of turbine 18. The actual area of each blade cross-section is
fixed by the permitted stress in the material used and
cooling, reference should be made to Part 9.
by the size of any holes which may be required for
15. Turbine discs are usually manufactured from a cooling purposes (Part 9). High efficiency demands
machined forging with an integral shaft or with a thin trailing edges to the sections, but a compromise
flange onto which the shaft may be bolted. The disc has to be made so as to prevent the blades cracking
due to the temperature changes during engine
also has, around its perimeter, provision for the operation.
attachment of the turbine blades.
19. The method of attaching the blades to the
16. To limit the effect of heat conduction from the turbine disc is of considerable importance, since the
turbine blades to the disc a flow of cooling air is stress in the disc around the fixing or in the blade
passed across both sides of each disc (Part 9). root has an important bearing on the limiting rim
speed. The blades on the early Whittle engine were
Turbine blades attached by the de Laval bulb root fixing, but this
17. The turbine blades are of an aerofoil shape, design was soon superseded by the 'fir-tree' fixing
designed to provide passages between adjacent that is now used in the majority of gas turbine
blades that give a steady acceleration of the flow up engines. This type of fixing involves very accurate
to the 'throat', where the area is smallest and the machining to ensure that the loading is shared by all

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