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Aviation History
1959
1959 - 0446.PDF
First illustration of the Orpheus BOr.12 ORPHEUS A VERSATILE AND LIGHTWEIGHT TURBOJET POLITICALLY the history of the Orpheus turbojet is unique.Planned as a private venture, it has now become virtually aworld standard in the 5,000 lb-thrust class, yet practically none of its development has been sponsored by the British Govern-ment. Few engines have developed as rapidly and achieved such universal success in such diverse-applications as supersonic inter-cepters, basic trainers, transports, research aircraft and ground attack machines, and in the years to come the Orpheus is certainto prove itself even more versatile. All design and development of the Orpheus has been handledby the great organization at Filton and Patchway which has suc- cessively been the Engine Division of the Bristol AeroplaneCompany, Bristol Aero-Engines Ltd. and the "Bristol portion of Bristol Siddeley Engines Ltd. After gaining experience withthe B.E.I7 pilotless-bomber engine, their first essay into the medium-thrust field evolved around the B.E.22 Saturn. During1952, however, the Ministry of Supply requirement for this engine lapsed and its development was accordingly abandoned. Thiswas a blow to Mr. W. E. W. Petter, managing director of Folland Aircraft, who had visualized the engine as the powerplant for hisGnat light fighter, then on the drawing boards. During 1953, therefore, Bristol's Engine Division and Folland Aircraft col-laborated in the design of a private-venture engine originally known as the B.E.26 and later given the name Orpheus. Like the Saturn, the Orpheus was planned as a single-spoolaxial unit of relatively low pressure-ratio. After choosing 4,850 lb as the design rating it was found possible to restrict the weightto an estimated figure of 850 lb, by employing only two bearings combined with novel structural principles and extreme simplicityin the overall design of the engine and its control and accessory systems. During 1953 the Supreme Headquarters Allied Powers Europeinstituted a specification for a lightweight fighter and ground attack aeroplane, to bedesigned, produced and operated as a standardtype among the NATO air forces. Virtually all thedesign studies prepared by the interested companieswere based upon the Bristol Orpheus, and as a resulta substantial contribution towards the cost of theinitial engine development was made available from theMutual Weapons Develop- ment Programme. During January 1954 thefirst drawings and manufac- turing instructions wereissued to the shops, and all detail drawings were clearedby the end of June. So rapid was the first-build that thecomplete engine was started and run on the bench onDecember 11, 1954 (prob- ably the first time in historythat a gas-turbine was designed and run in aS1ngle calendar year). To some extent the design was ORPHEU Aerfer Leone (Italy) Avro Ashton (G.B.) Breguet 1001 Taon (F.) Bristol 205 (G.B.) Canadair Sabre Dassault Etendard VI (F.)... Fiat G.91/91 A (Italy) Fiat G.91R (Italy) Fiat G.91S (Italy) Fiat G.91T (Italy) Folland Gnat Mk 1 (G.B.)... Folland Gnat Mk 2 (G.B.)... Folland GnatT.1 (G.B.) ... Fuji TIF-2 (Japan) Handley Page H.F 113 (G.B.) Hawker P.1127 (G.B.) Hindustan (India) HisDano HA-300 (Spain) ... Hunting H-107 (G.B.) Ikarus B-12 (Yugoslavia) ... Lockheed Jets tar (U.S.A.)... N.A.A. Model 249 (U.S.A.) Short SB.5 (G.B.) Sud Baroudeur (F.) S-POWERED AIRCRAFT Category Intercepter Test bed Tac. strike Transport Test bed Tac. strike Tac. strike Recce. Tac. strike Trainer Fighter/strike Fighter/strike Trainer Trainer Transport Tac. strike Fighter/trainer Fighter/trainer Transport Fighter Transport Trainer Research Tac. strike Engine BOr.12 Various 801 > 801/803 801/803 801/803 803 BOr.12 803 701 Reheat BOr.4 805 > BOr.12! BOr.12? l 701 TJ-37 BOr.4 802 BOr.12 Remark* Supersonic Orpheus pods under wing BOr.12SR in later version Four on rear fuselage Used by Bristol Siddeley Supersonic First aircraft to fly with Orpheus Supersonic Production engine is BOr.4 Two engines Orpheus fan derivative? Two engines? Probably Mk 703 initially Two engines Two engines; or four JT-12 Alternative powerplant to J34 Alternative to Atar hastened by employing a compressor very similar to the low-pressure spool of the B.E.25 Orion turboprop. By the end of 1954 Folland had completed a fair amount offlying with the Midge (geometrically similar to the Gnat but powered by an Armstrong Siddeley Viper), and the Orpheus wasurgently needed to enable the true Gnat to take the air the following year. It was accordingly decided that, as an initialtarget, the Orpheus should be cleared for flight at the restricted rating of 3,285 lb. A declared type test at this rating was success-fully completed in May 1955, and the engine first flew (as the powerplant of the Gnat) in July. Five Orpheus were running byApril 27 of that year and during the first six months of bench- testing over 2,000 hr were run without a single major problembeing encountered. It is particularly worth noting that these early engines weighed only 760 lb, some 90 lb under the originalestimate. Even at the reduced 3,285-lb rating the thrust/weight ratio was better than that of any other type-tested engine inthe world at that time. The original Orpheus carried the Ministry of Supply ratingdesignation BOr.l, and by January 1956 it had successfully com- pleted a declared type test at its design rating of 4,050 lb. Asdesigned for the Gnat, the fuel-flow requirements could be met by a single B-size pump and the accessory gear casing was tailoredaccordingly. At heights above about 12,000ft it was possible to achieve fuel flows—and hence thrust—-equal to the values requiredby the more powerful BOr.3, specified for the NATO strike aircraft. The BOr.3 however was designed to have a sea-levelrating of 4,850 lb and was therefore fitted with the larger D-size pump. In order to gain experience at the higher thrust it wasdecided to fit twin B-size pumps on an Orpheus 1, the additional pump being mounted on the hydraulic-pump attachment face.Throughout the early pan of 1956 ground-running of these engines was accomplished at the full brochure rating of 4,850 1b and the engine for the Gnat,the BOr.2 with a rating of 4,520 lb, began its flightdevelopment in pods mounted under the wingsof an Avro Ashton test bed. On August 9, 1956, the pro-totype Fiat G.91, the first of the NATO aircraft totake the air, flew for the first time on the reducedpower of a BOr.l. The next milestone was the full typetest of the BOr.2 in November 1956. Three BOr.ls were de-livered to Fiat during 1956 and additional engines weredelivered to Dassault, whose Etendard VI flew in January1957, and Breguet, whose Type 1001 Taon first flewin August 1957. Differences between the BOr.l and theproduction engines are slight. The most signifi-cant change was the intro- duction of a compressorincorporating blading which was redesigned to take
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