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Aviation History
1954
1954 - 0979.PDF
9 April 1954 447 considerably developed to give twice its design power of 1,000 h.p. A feature introduced for the first time is a vaporizing fuel burner, unique to Armstrong Siddeley engines, which gives very good combustion with a low supply pressure. Early in its career the mass flow of the Mamba was increased by taking off the three last compressor stages and adding three larger rows at the front; there has also been considerable modification to other parts of the engine. For some years, the ASM.3 was the standard engine, giving 1,475 e.s.h.p., and fitted with six combustion chambers, a torque- meter, and a reverse-torque switch for auto-feathering. This engine, which is illustrated, forms the basis for the Double Mamba ASMD.l. The ASM.5 is a considerably revised engine with an annular combustion chamber; it does not exist in single form, and serves as a development engine for the ASMD.3. The most important Mamba is the ASM.6, which is still largely secret. It can, however, be said that it will be the most powerful and efficient of all Mambas and a unit of this class may power the production Seamew. Flight trials will soon begin in the company's Dakota. Double Mamba. Initially developed for the Gannet, this remarkable engine is formed by attaching the power sections of two Mambas to a common gearbox driving two separate co-axial airscrews. Each power section retains its own fuel, oil and control system, and can be shut down independendy of the other to permit extended economical cruising. Each drive includes a free-wheel, and the 100 s.h.p. accessory gearbox drive takes power from which ever engine is running the faster, although both sections can be synchronized. Carrier operations have caused the Double Mamba to be developed as a constant-speed engine, running at 14,500 r.p.m. (except at take-off) with a very powerful airscrew control system, thus making full power almost immediately available for overshooting; the same type of work is responsible for the fact that the engine can run on a variety of fuels, including marine diesel oil. The Double Mamba ASMD.l has already been delivered in some quantity; this engine consists broadly of two ASM.3s, the characteristics of which are given above, with a drawing. If desired the engine may be mounted on a pair of tracks along which it can be slid forwards for removal; equipment includes a Rotol accessory gearbox and a separate Rotax or B.T.H. cartridge starter for each power section. The newer ASMD.3, which is illustrated, consists of two annular-chamber ASM.5s, and is a more powerful and efficient engine than the ASMD.l; this engine is a stepping-stone to the powerful ASMD.4, about which nothing may yet be said. It may be noted that the Double Mamba may satisfy the A.R.B.'s twin-engine safety rules, and the English Electric company are reported to have an interesting civil transport on the drawing boards using this engine. Python. The Python turboprop had passed acceptance trials in 1945, but a lot of work was needed before it could be used as a fully developed power plant. Many of these troubles stemmed from the difficult application of the engine—the Wyvern carrier- based strike aircraft. The early design of the Python is reflected in almost every pan of the engine, and it is much bigger than would be a present-day engine of the same power. It is a reverse- flow engine, with the air flowing forwards through the compressor and back again through the eleven cans which hide the compressor from view. The most common type of Python is the ASP.3, which has a compressed-air starter jet which spins the turbines; an airscrew brake is another fitting, which slows down the engine in about 11 seconds for carrier "striking down." The Python may be replaced by completely new engines, but development is proceed ing to produce an exceptionally refined unit capable of long, trouble-free life, a typical example of this work being progressive cooling of the turbine discs. The engine is still in production, the latest models being re-stressed for a turbine starter. Sapphire. When first taken over by Armstrong Siddeley in 1948—as described above—the Sapphire was the largest turbojet then running anywhere in the world (we believe) and, although in need of much development, it offered great promise. During the first few years, Armstrong Siddeley made and broke various Sapphires, and had them flying in a Lancastrian in 1949. There is today very little Metrovick design left in the engine; the com pressor and turbines are noticeably different, the structure has been revised, and the combustion chamber has been completely revised with the Armstrong Siddeley vaporizing burner system; photographs show six fuel pipes each split into six, making a total of 36 burners in all. Sapphires are made by Armstrong Siddeley and at the Gloucestershire factory of Brockworth Engineering. The ASSa.l flew in the Lancastrian; the Sa.2 flew in a Meteor (rate-of-climb record) and Hastings at about 7,250 lb thrust; the Sa.3 introduced the vaporizing combustion and other features and was air-tested at 8,300 r.p.m. and 7,500 lb; the Sa.6, the latest Sapphire which can be illustrated, has a type-tested rating of 8,300 lb at higher r.p.m., and is in quantity production. The Sapphires 4, 5 and 7 cannot be discussed in detail, but they Armstrong Siddeley Python ASP.3 single-shaft, reverse-flow turboprop. Fourteen-stage compressor, eleven combustion chambers and two-stage turbine. Mass flow, 52.5 lb/sec with pressure ratio 5.35:1. Overall diameter, 54m; length, 123.2in; dry weight, 3,450 lb; maximum power, 3,670 s.h.p. +1,180 lb thrust (4,110 e.s.h.p.^at sea level at 8,000 r.p.m. with s.f.c. of 0.805 Ib/hr/e.s.h.p. Armstrong Siddeley Sapphire ASSa.6 turbojet. Axial compressor, annular combustion chamber with vaporizing burners and two-stage turbine. Overall diameter, 37.4in; length, 134in; dry weight, 2,600 lb; maximum thrust, 8,300 lb at sea level at 8,600 r.p.m. with s.f.c. of 0.85 Ib/hr/lb thrust. Armstrong Siddeley Snarler ASSn.1 rocket. Dry weight of basic engine, as shown, 215 lb; maximum thrust, 2,000 lb; specific fuel consumption, 20 Ib/hr/lb. If «^x n i jVlAJ L.J. PI hi *A [ ' Armstrong Siddeley Viper ASV.3 turbojet. Seven-stage compressor, annular combustion chamber and single-stage turbine. Mass flow, 30 lb/sec with pressure ratio 3.5:1. Overall diameter, 24.7in; length, 65.4in; dry weight, 375 lb; maximum thrust, 1,640 lb at 13,400 r.p.m. with s.f.c. of 1.09 Ib/hr/lb. Armstrong Siddeley Viper ASV.5 turbojet. Seven-stage compressor, annular combustion chamber and single-stage turbine. Mass flow, 31 lb/sec. Overall diameter, 28in; length, 65.83in; dry weight, 465 lb; maximum thrust as for ASV.3.
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