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Aviation History
1949
1949 - 1428.PDF
192 FLIGHT left). The fabricated air intake has apertures which permit it to dear the gas conduits. (Above) Assembled rotor of axial compressor. Bristol Proteus length and are cut down to appropriate lengths for the various stages. All are given a rubbing relief at the tip. The same material and method of production is used for the stator blades which have rectangular roots of a seg- mental dovetail section. These blades are fitted in circum- ferential grooves in the stiffly proportioned, divided com- pressor casing. In each half the blades are retained by steel strips bolted to the casing at the parting line and each row is clamped by two radially-positioned taper bolts. The stator casing also carries a row of entry guide blades to direct the incoming air to the correct angle of attack for the first-stage rotor blades. On the Theseus the last axial stage delivers directly to the entry vanes of the centrifugal impeller but on the Proteus the two components are axially spaced and the air passes from one to the other by way of an annular trunk in the intermediate casing. In the trunk are eight stream- lined guide-vanes which serve to support the centre section housing the two ball-bearings carrying the front end of the compressor shaft. In view of the high speed of rotation and the temperature-rise in the air in the axial compressor, the double-shrouded centrifugal impeller is milled from a forging of S.96 steel. It is registered and bolted to a hub splined on the rotor shaft and is furnished on each side with labyrinth seals to prevent the highly compressed air escap- ing to either the intermediate casing or the accessories gear casing. The ring of curved entry vanes, also of steel, is produced separately and bolted to the impeller. To the necked diffuser casing of the centrifugal com* pressor are directly attached the eight "straight-flow" combustion chambers arranged compactly around the axial compressor casing. Chambers are somewhat longer than are contemporary units, to ensure thorough dilution and even temperature of the gases before reaching the turbines; otherwise they are of conventional design, with the outer casing of S.84 mild steel and the flame-tube of Nimonic 75 nickel-chrome alloy. Following what has now become almost common practice, the combustion air enters a small swirl casing through a metering orifice and the flame is fed by primary and secondary series of holes in the tube. Radial pins in the casing position the flame-tube upstream while the downstream end is fitted with a spacing ring and is free to slide to permit expansion. The air space is con- tinued in the junction pipe connecting the end of the cham- ber to the turbine entry. Chambers are interconnected by the usual pressure balance pipes which also serve for the propagation of flame when starting up. Only two cham- bers are fitted with igniter plugs. So-called "manacle" joints, comprising divided, V-section clamping rings, replace (Left) Eight-branched delivery duct of the centrifugal compressor. \ (Right) Fully shrouded impeller, with attached entry vanes, moun- ted in the diffuser casing.
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