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Aviation History
1956
1956 - 0017.PDF
A complete Sapphire power- plant ready tor installation in what can be deduced as a Gloster Javelin. Large numbers of generally similar engines, all tested at well over &JWO Ib thrust, have been delivered. ARMSTRONG SIDDELEY SAPPHIRE An Outstandingly Powerful and Efficient Single-shaft Turbojet ALTHOUGH in itself an engine of particularly straight-f\ forward design die Armstrong Siddeley Sapphire turbojet •L -*- has a history which is threaded with paradoxes. Designedby one famous British company it was entirely taken over, developed and put into production by another. A British engine,it is nevertheless flying in much greater numbers in the U.S.A., and it went into service in that country before it did in its ownland. And, although it combines high thrust, competitive specific consumption and easy handling to a marked degree, it is one ofthe simplest large gas turbines ever designed. Before writing of the Sapphire itself an outline should be givenof the work which led up to its original design. The Metro- politan-Vickers Electrical Co., Ltd., were the first non-Germancompany to work on axial gas turbines for aircraft propulsion. On behalf of, and in co-operation with, the Royal Aircraft Estab-lishment, this Manchester firm began research on axial-flow com- pressors in 1937, and the following year started bench tests on diefirst of a series of such units. In 1940 the R.A.E. invited Merrovick to build a turbojet to abasic design which had been formulated at Farnborough by a team working under Hayne Constant, the present director of theN.G.T.E. The compressor used was of an R.A.E. design which had been given the appellation "Freda," and the resulting enginewas accordingly designated Metropolitan-Vickers F.I. Various forms of F.I were built, the first being put on the bed late in1941. Later F.ls successfully completed special-category flight- clearance tests in 1942 and the first flight took place on June 29th,1943, the turbojet being mounted in the bomb bay of an Avro Lancaster. This was the first non-German axial engine to fly. Following the F.I came the F.2, also built in a number ofversions and one of the most advanced turbojets of its day. The original F.2/1 was rated at 1,800 lb thrust, and two of the firstflight engines were flown in Meteor DG 204/G on Novem- ber 13th, 1943, this being the first aircraft outside Germanyactually to be propelled by axial gas turbines. Progressive develop- ment brought forth die 3,500 lb-dirust F.2/4 which first ran in1945 (later named Beryl, in conformity widi die Metrovick policy of taking the names of precious stones), die F.3 ducted fan turbo-jet and the F.5 turbofan. Descriptions of these engines were published in our issues dated April 25th and November 28di, 1946. While long-term research and development was going aheadwith diese, and odier, units, die company began to investigate a high-thrust turbojet designated F.9. Throughout 1945 study ofthe F.9 project progressed, the work being purely of a research nature without Government support. In the following February,however, die company received a Ministry of Supply project con- tract, which was backed up by an order for prototypes in May1946. The F.9 design study was thus transformed into the Sapphire turbojet, with the first Ministry rating MVSa.l. Thefirst prototype ran in 1947. The small drawing overleaf depicts die MVSa.l as it was in that year. As might be expected it was a singularly straight-forward engine, with a 13-stage compressor, an annular com- bustion chamber and a two-stage turbine. Yet each componentwas significantly more advanced than current practice at that time. It is obvious mat the pressure ratio was considerably higherthan that of contemporary axial units, and the overall design of the combustion chamber—employing die typical Metrovicksystem of low-dispersion burners injecting upstream into a primary airflow—was also inherendy ahead of the can-typechambers of most gas turbines of 10 years ago. In spite of its advanced conception die Sapphire ran relativelywell from die outset. This reflects Metrovick's extensive axial experience and ability, and it could have placed die company in avery strong position in the aircraft gas-turbine field. Nevertheless the company decided in 1947 to cease their association with aeroengines entirely. It would have been tragic had so promising an engine as theSapphire been allowed to fade away; furthermore it was—at that time—die policy of the Engine Research and Development branchof die M.o.S. to sponsor two designs of engine to each major requirement, largely as an insurance. Rather than go throughall die uncertainties of ordering a completely new engine the M.o.S. decided to find a company capable of taking over theSapphire as a "going concern" so that, as an alternative to the Rolls-Royce Avon, it would remain a possible future engine forBritish military aircraft dien projected. The obvious choice for a company to take over the Sapphirewas Armstrong Siddeley Motors, Ltd., who were die only other firm in Britain with axial experience anything like comparable tothat of Metrovick, and who had the development capacity avail- able. Late in 1947, dierefore, diey agreed to accept responsibilityfor all future development of die new turbojet. At die Ministry, the designation MVSa.l changed to ASSa.l, and die Coventrycompany actually took over work at the beginning of 1948. As already stated, the original F.9 project was intendedprimarily as a research tool, and die Metrovick programme had not been aimed directly at producing an engine capable of enteringmilitary service. Nevertheless mere is no doubt that it was, when taken over by Armstrong Siddeley, one of die most promisinglarge turbojets in the world. It had already shown that it could develop something over 6,500 1b thrust with a low specific fuelconsumption and with remarkably easy and trouble-free running. Unfortunately it was impossible to avoid losing many monthsduring die change-over, and bench running did not start at Armstrong Siddeley until October 1948. Nevertheless die engine'snew masters had not been idle. By that month drawings had been issued for a considerably revised and cleaned-up version,designated ASSa.2, which, it was intended, would form a starting point for die development of future, operational versions. Indie original F.9 die compressor comprised discs welded togediei at their peripheries (as shown in detail on p. 20), each disc having
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