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Aviation History
1956
1956 - 0018.PDF
. ANNULAR COMBUSTION 53) CHAMBER 18 FLIGHT Armstrong Siddeley Sapphire ASSo.6 turbojet. Overall diameter, J7.4in; overall length as shown. 134m; dry weight including anti-icing, high-energy igniter units and oil tank, 2,700 Ib; minimum internal jet-pipe diameter, 22.6in; rated thrust, 8,000 Ib at 8,600 r.p.m. with specific fuel consumption of 0.9; cruising s.f.c, 0.8S. Note: the similiar ASSa.12 is rated at 8,500 Ib thrust. ARMSTRONG S1DDELEY SAPPHIRE dove-tail slots into which the rotor blades were driven and sealed by Marco resin. This welded-drum form of compressor was retained in the Sa.2, but variable inlet guide vanes were incor- porated, the exhaust cone was modified and slight alterations were made to the combustion system. Meanwhile, in October 1948—the month in which running started at Coventry—the basic Sa.l passed its first M.o.S. accept- ance test, and running with these engines continued into 1949. In December, 1949, the Sa.2 also completed its acceptance test, at its design rating of 7380 lb, and this is believed to have been a record at this time (the much-larger General Electric J53 was not at a comparable state of development). The running of the Sa.2 was sufficiently encouraging for a flight-clearance test to be attempted, and achieved at the first try. Two Sa.2s were then mounted in the Lancastrian test bed VM 733 and this aircraft flew in January 1950. The following August a pair of Sa.2s were flown in Meteor 8 test bed WA 820, and on August 31st, 1951, this aircraft, flown by F/L. R. B. Prickett, reached an altitude of 12,000m (39,370ft) in a time of 3 min 7 sec from a standing start— a record which still stands. The third Sapphire-powered aircraft was a H.-mdley Page Hastings, in which two Sa.2s were fitted, chiefly to provide the firm responsible for the Victor with Sapphire experience. This aircraft was first flown by S/L. H. G. Hazleden on November 13th, 1950. Meanwhile, Armstrong Siddeley had been carrying out a con- siderable amount of redesign on the Sapphire, and the resulting ASSa.3 marked the first complete departure from Metrovick tradition and practice. There were three major alterations: the adoption of a vaporizing type of combustion chamber, the addi- tion of a centre bearing and redesign of the main rotating assembly to bring it more into line with previous Armstrong Siddeley practice. The new compressor rotor was built up from thin discs, two to each stage, with light-alloy blades riveted through each adjacent pair of discs. The discs were mounted on a drum driven by a conventional hollow shaft from the turbine. A spherical bearing was incorporated in the drive immediately to the rear of the centre bearing, the latter being a roller assembly carrying no axial load. This completely different arrangement for the main rotating assembly was subjected to extensive rig testing and was found to offer considerably more promise, at a lighter weight, than did the original, drum-like rotor, hung between two bearings. Initially the Sa.3 had a slightly lower rating than die Sa.2, the Sa.3 starting off some 300 lb under the 7,500 lb thrust eventually reached by the earlier unit. Nevertheless it was clearly a better engine mechanically, and it passed its accept- ance test in April 1950, and a full type test only three months later, the rated performance being 7,220 lb thrust with an s.f.c. of 0.916. These excellent figures are a tribute both to the Metro- vick design team and to the engineering ability of Armstrong Siddeley. At this stage the latter company could confidently foresee a bright future for the sparkling Sapphire, which was not only an outstanding performer but was singularly free from the surging, and other, troubles which were then being encountered by several axial programmes both in this country and abroad. Nevertheless, there were difficulties to be surmounted, and these were chiefly related to the compressor blading. As noted previously the Sa.3 introduced blading through-riveted to the compressor discs, and a certain amount of trouble was experi- enced as a result of fatigue across the rivet holes. A change was A longitudinal section of the original Metro- rick F.9 Sapphire as it was when Armstrong Siddeley first assumed responsibility in 7947.;
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