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Aviation History
1951
1951 - 0896.PDF
II May 1951 Bristol Theseus turboprop with heat exchanger. turbojet version known as the Adder, gives 1,050 lb static thrust at sea level, and has a dry weight of 580 lb, whilst the second—given the name Viper—is a short-life experimental version of the Adder, but with an annular combustion chamber, and in which the static thrust output has been increased to 1,500 lb. The latest, largest and, so far as internal details are concerned, still-secret Armstrong Siddeley turbojet is the Sapphire. Developed from an original design by Metropolitan-Vickers, Ltd., the Sapphire has an axial-flow com- pressor and an annular combustion chamber, and completed the 150-hour Service type test at a sea level static thrust rating of 7,220 lb, with a specific consumption of 0.916 lb/hr/lb. These figures make the Sapphire the most powerful turbojet engine in the world yet to have flown, and the low specific fuel consumption speaks volumes for the efficiency of the design as a whole. The Bristol Aeroplane Co., Ltd., first released details of their Theseus turboprop towards the end of 1945. This unit aroused considerable interest, for it bristled with unusual features. A nine-stage axial compressor delivered into a final centrifugal stage, giving an overall compression ratio of 5:1. Flow from the compressor was delivered to a matrix-type heat-exchanger before passing to the combustion chambers, and a three-stage duplex turbine was used, the two-stage first turbine powering the com- pressor and auxiliaries, whilst the single-stage second turbine—of so-called "free" type—drove the airscrew through an epicyclic priate airscrew is stopped and feathered, whereas in the "coupled" (Proteus) instance, the remaining live engine takes over the duty of both and drives the airscrew by itself. In short, the doubled installation employs two airscrews mounted one behind the other and rotating in opposite directions, whereas the coupled installa- tion drives a single airscrew made up of two banks of contra- rotating blades. Two new turbo jets are now engaging the attention of the Bristol Engine Division, one of them being the Olympus, a high-powered unit which embodies twin axial-flow compressors, and which is designed to operate at a very low fuel consumption. Beyond this, however, nothing else may be mentioned of the projects. The de Havilland Engine Co., Ltd., early in 1941, began considering the design of a turbojet for use with the Vampire fighter. Sixteen months later, the unit, which was given the name Goblin, was ready for testing, and by June, 1942, had been operated at its full designed thrust of 3,000 lb. Just as Armstrong Siddeleys have consistently advocated the axial-flow design, so de Havillands have equally consistently held to the centrifugal (Above) Bristol Proteus turboprop. reduction gear. A free-turbine obviates airscrew starting drag. Experience gained with the Theseus was put to good use in the development of the Proteus. In fundamental layout, the units differ appreciably, the Proteus having a reverse-flow compressor/ combustion system, although as before, an axial compressor delivering through a final centrifugal stage is utilized. Again, a three-stage duplex turbine is used, but, in the Proteus, the first two turbine stages (which drive the compressor) are individual wheels splined to a common shaft instead of following Theseus practice in employing two rows of blades on a common disc. The third stage (airscrew-driving) turbine is a "free" unit. A preliminary turbojet version of the Proteus was developed by the company, and served as a research unit. Given the name Phoebus, it produced 2,540 lb static thrust at 10,000 r.p.m. In coupled form, the Proteus will power the second prototype Brabazon, and the Saunders-Roe Princess. In this connection, it should be emphasized that the power installation differs fundamentally from that of, for example, the Double Mamba in that, whereas each unit of the Double Mamba drives its own airscrew, both units of the coupled Proteus commonly drive a contra-rotating airscrew. The basic difference shows up in the fact that, if one of the twin units fails, in the case of the "double" (Mamba) installation, the appro- (Below) de Havilland Goblin turbojet.
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