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Aviation History
1955
1955 - 1275.PDF
2 September 1955 Mamba. Although the history of this neatsingle-shaft turboprop can be traced back to World War 2, there is no major part of the presentengine remaining from the original design. Of the first series of Mambas the ultimate develop-ment is the ASM.5 rating, the power of which (1,590 e.h.p.) is 50 per cent greater than theoriginal design figure. This engine has a ten-stage light-alloy compressor, six tubular combustionchambers and a two-stage turbine. Considerable development has been expended upon the com-bustion system and the cans are now considerably simpler and more efficient than before; allMambas employ the Armstrong Siddeley type of vaporizing burner of "walking stick" shape. The engine illustrated drives a single 10ft four-blade Rotol airscrew. Other features of the instal- lation are the twin-breech Rotax cartridge starter,shown in the drawing on the port side, and the drive-shaft along the top of the engine which cantransmit power to a remote accessory gearbox. Later Mambas have an annular combustionchamber reminiscent of that used in the Viper (see next page) and are significantly more power-ful and efficient engines. The first of the new range is the ASM.6, and Mambas at this ratingwent into production during the last 12 months for the Seamcw. In spite of the large ventral oiltank, the complete engine-change unit is shallow enough to be accommodated entirely beneath thecockpit floor in this aircraft. Cartridge starting is provided, and engine thrust is varied by alter-ing airscrew pitch while maintaining r.p.m. con- stant at 15,000. By this means a very rapidresponse is achieved, suitable for the requirements of carrier operation. 389 Armstrong Siddalay Mamba ASM.5 single-shaft turboprop. Ten-stage axial compressor, six combustion chambers and two-stage turbine. Mass flow, 18.5 Ib/sec; pressure ratio. 5.35:1. Overall diameter. 33in; overall length, 88.2m; dry weight, 820 Ib; maximum power, 1,480 s.h.p. plus 300 Ib thrust (1,590 e.h.p.) at 15,000 r.p.m. with specific fuel consumption of 0.71 Ib/hr/e.h.p. Sapphire. Without doubt one of the mostimportant turbojets in the Western world, the Sapphire is being built in quantity at Brockworthin Gloucestershire and also in the U.S.A., where Curtiss Wright and Buick have already deliveredover 6,000 of an Americanized version, desig- nated J65. Details of the British Sapphire arerestricted, but the J65 is known to have a 13-stage axial compressor with steel blading, a truly annu-lar combustion chamber with 36 vaporizing burners, and a two-stage turbine. Progressive development culminated in 1953with the ASSa.6 type-test at 8,300 lb static thrust, and similar engines rated at 8,000 lb thrust haveentered service in large numbers during the past year in the Hunter 2 and 5. In service, theseengines have performed outstandingly well and are very popular. An up-rated Sapphire 6 isdesignated Sapphire 12 and this engine has been type-tested at 8,500 lb. A considerable amountof successful flying has also been achieved by a Canberra powered by two Sapphires fitted withafterburners. In the prototypes of the English Electric P.I, Sapphires have been flown at veryhigh Mach numbers, and supersonic afterburner trials will also be carried out in such aircraft. Two years ago a redesigned Sapphire wasevolved in order to provide a great increase in thrust. To achieve this alone would pose noinsuperable problem; the engine could be run hotter and would then give more power at theexpense of a rise in specific fuel consumption. It is noteworthy, therefore, that the Sa.7, the firstof the new series to be type-tested, provides 32 per cent more thrust, yet actually has an improveds.f .c. These Sapphires have increased mass-flow. Engines of this revised type have now goneinto production at a type-tested rating of 10,500 lb. The Sa.9 has also been run at greatthrust, and other engines are the Sa.4 (which gives 9,700 lb thrust) and the Sa.5 and 8, all of whichare undergoing development running. Armstrong Siddeley Sapphire ASSa.7 turbojet. Axial compressor, annular combustion chamber and multi-stage turbine. Mass flow and pressure ratio, not released: maximum diameter, including accessories, 37.4m: overall length, as ihown, 132in; dry weight (including anti-icing, turbostarter, high-energy igniters and oil tank), 3,075 Ib: maximum rated thrust, 10,500 Ib at 8,600 r.p.m. with specific fuel consumption of 0.885 Ib/hr/lb.
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