Page 250 - The Jet Engine

Manufacture

COMPOSITE MATERIALS AND SANDWICH for peripheral feature attachment on C.N.C.
CASINGS machining centres, which at one component load,
completely machine all required features. Examples
43. High power to weight ratio and low component of composite material applications are illustrated in
costs are very important considerations in the design fig. 22-14.
of any aircraft gas turbine engine, but when the
function of such an engine is to support a vertical 46. Conventional cast and fabricated casings and
take-off aircraft during transition, or as an auxiliary cowlings are also being replaced by casings of
power unit, then the power to weight ratio becomes sandwich construction which provide strength allied
extremely critical. with lightness and also act as a noise suppression
medium. Sandwich construction casings comprise a
44. In such engines, the advantage of composite honeycomb structure of aluminium or stainless steel
materials allows the designer to produce structures interposed between layers of dissimilar material. The
in which directional strengths can be varied by materials employed depend upon the environment in
directional lay-up of fibres according to the applied which they are used.
loads.
INSPECTION
45. Composite materials have and will continue to
replace casings which, in previous engines, would 47. During the process of manufacture, component
have been produced in steels or titanium. By-pass parts need to be inspected to ensure defect free
duct assemblies comprising of three casings are engines are produced. Using automated machinery
currently being produced up to 4ft-7in. in diameter and automated inspection, dimensional accuracy is
and 2ft-0in in length using pre-cured composite maintained by using multi-directional applied probes
materials for the casing fabric. Flanges and mounting that record sizes and position of features. The C.N.C.
bosses are added during the manufacturing process, inspection machine can inspect families of
which are then drilled for both location and machined components at pre-determined allotted intervals

Fig. 22-14 Some composite material applications.

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