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Aviation History
1957
1957 - 1076.PDF
\, * During development, this six-stage com- pressor was tested at C.A. Parsons, Ltd. G YRO N . . . of suitably lightweight design might have deformed under engineloads during extreme aircraft manoeuvres, and a very light but strong casing was therefore designed, using a double-wail boxsection—a splendid example of foundry art by Sterling Metals, Ltd. Coring problems are eased by welding plates over accesscavities after the sand has been removed and the casting cleaned. Effective use of the cavity between the walls is made by dividingit transversely into three separate compartments. One of these, with a liquid capacity of three gallons, carries the engine lubricat-ing oil and the remaining two duct hot compressor-delivery air to die compressor inlet guide vanes and to the leading edge of theintake struts for de-icing purposes. The latter flow of air is also ducted through to the double-walled nose bullet. An extension shaft from the front of the compressor rotor pro-vides a drive through a bevel gearbox and a quill shaft to the engine accessories mounted on the underside of the intake andcompressor casing. Carried in the rear of the intake casing are the compressorvariable-incidence inlet guide vanes. These vanes, which are solid forgings in S.96 steel, will ultimately be fabricated as hollowunits in order to pass de-icing air. Each is provided at its inner ends with a short swivel extension arm located in a sphericalbush in a circular actuator ring carried in the rear face of the intake centre housing. In the automatic control mechanism initially developed for theI.G.V.s the actuator ring was rotated by means of a pair of hydraulic jacks rather inaccessibly located at a near-tangentialangle within the actuator ring itself. In the present control mechanism a hydraulically operated push/pull rod passingthrough one of the lower intake struts is provided with a crank to rotate a small quadrant geared to the actuator ring. Movement ofthe rod, and consequent change in vane incidence, is automatically determined by the I.G.V. fuel-pressure-controlled hydraulicsystem, which in turn is responsive to a selected engine operating parameter. Attached to the rear of the intake casing is the longitudinallyand transversely split compressor casing. The front pair of cas- ings are machined from castings in R.R.58 aluminium alloy; andthe rear pair, where the compressor air temperature rise is com- paratively high, are machined from castings in Samuel FoxFortiweld high-tensile welding steel. August 19<7 The forward entry duct is extended rear- wards to carry the main rear bearing. All blading in the compressor is machined from forgings inS.62 stainless steel, chosen for—among other desirable qualities —its good vibration-damping. The stator blades are carried indovetail grooves machined directly in the compressor casing. At their inner end the stator blades are fully shrouded, the relatedshroud-rings carrying brass labyrinth seals on their inner faces. These are individually machined to run with a specified (but notover-fine) clearance relative to the compressor rotor drum. A very simple form of construction is used for the compressorrotor. With the exception of the first and seventh stages each of the S.97 high-tensile alloy steel thin-wall discs has a thin-walleddrum machined integral with its rear face by which it is attached to the adjacent disc. Integrally with its front face the first disccarries a stub shaft on which the front of the rotative assembly is supported. A similar shaft is formed integrally with the rearface of the disc. This is bolted to the centre of the second-stage disc, additional support being provided by a thin-wall cone. Aseparate drum joins the peripheries of the first two discs. For the seventh-stage rotor, a separate drum is provided whichjoins the disc at its periphery to an eighth disc. This latter disc, carrying the compressor-rotor air seal, is attached to the frontperiphery of the main turbine shaft. Aluminium spacer sleeves are fitted at the centre to obviate lateral vibration. A large triple-race bearing carried in a housing in the rear of theintake casing supports the front end of die rotative assembly. The bearing comprises a double ballrace (designed to transmitboth forward and rearward thrust loads from the rotor) and a single roller bearing to absorb the journal loads. On the basis of information available at the time of the designstage of the Gyron it was decided to utilize a single-pin swivel fitting for the compressor rotor blades. This allows for a limiteddegree of tip rock in the plane of rotation and so assists in damping out critical modes of vibration. Each blade has a pair of tangsmachined integrally with its root, and these straddle die rim of the relevant rotor disc; the blades are located by means of a hardenedhollow steel pin. This form of blade mounting has proved particularly successful. To prevent the escape of compressor seventh-stage air betweenthe combustion system inner casing and die main turbine shaft, a labyrinth seal is carried on the eighth compressor rotor disc.The large diameter at which the seal occurs involves high sealing velocities. Because of this, and of the need to provide for manu-facturing and assembly eccentricities, it was decided to incor- porate a carbon ring as the stationary portion of die seal. Carbon The inner and (right) outer flame-tubes. Closely spaced "wriggle strips" admit cool- ing air to the inner faces of the tubes. Air is ducted to the 17 swirlers in their perforated platforms.
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