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Aviation History
1957
1957 - 1043.PDF
FLIGHT, 26 July 1957 133 General Electric J79-GE-1. Single-shaft, variable-stator turbojet. Seventeen-stage compressor with variable-incidence inlet guide vanes and succeeding six stator rows, annular combustion chamber with 12 injectors, three-stage turbine, and high-augmentation afterburner with convergent-divergent propelling nozzle of variable throat qnd orifice area. Overall diameter, 32.5in (36 at nozzle); length as depicted, 204in; dry weight, 3,1901b; mass flow, approximately 160lb/sec; pressure ratio, approximately 12:1; maximum thrust, about 17,000 Ib with reheat or 11,000 Ib dry. Powerplants of this general type are fitted to the B-58, F-104 and F11F-1F. AERO ENGINES 1957 . . . swallowed up by such massive programmes as the F-86 and B-47.Production of this engine is an outstanding instance of faulty logistics: the life of each unit was grossly underestimated, and the U.S.A.F. hadto cancel orders for some 6,000. As a result G.E. lost several hundred million dollars through making their product too reliable. Productionceased entirely more than a year ago. Non-afterburning engines in service with Strategic Air Commandtotal roughly 12,000, and their allowable overhaul time was raised to 1,700 hr in August 1956 and to 1,750 hr last February. Half of theengines which fail to achieve this theoretical figure are prey to foreign- body damage, and in a recent run of 4,715 overhauled only 15 hadsuffered corrosion. Fighter engines were still on a 400-hr basis at the end of 1956 and this figure produced a premature-failure rate of 15per cent. At the beginning of this year the J47 had logged a total of 13m flying hours, although it is doubtful if many individual J47s hadreached 2,500 hr. Hack engines are being widely used in research programmes. J73. When production ceased last year some 2,000 J73s had beenmanufactured, chiefly to meet the demands of the F-86H fighter/ bomber programme. Compared with the J47 the J73 compressor hub/tip ratio was reduced to increase the mass flow, and for the same reason the combustion system was changed to a can-annularconfiguration. Since 1954 J73s have been extensively used as basic thermodynamicvehicles in experiments intended to determine the optimum forms of advanced powerplant for future military service. These operations aredescribed under the sub-headings of WS-110A, WS-125A and WS-202A. J77. As far as one can determine, this big single-shaft turbojet isthe only descendant of the J53 of the 1950 era. Rated at some 25,000 Ib thrust, the J77 is a long-term programme financed by the U.S.A.F. Itis likely to be tied to the programmes for engines using high-energy or nuclear fuel. J79. By 1952 G.E. and the U.S.A.F. had recognized the future needfor a truly advanced turbojet capable of achieving good specific fuel consumption under subsonic cruise conditions at all altitudes, combinedwith very high thrust for supersonic propulsion while at the same time having minimum size and weight. In addition, the company hoped toutilize much past experience in increasing the reliability and ease of overhaul of the unit. Two teams were assigned the task of evaluating the most likely con-figurations for the compressor: two-spool (or, as G.E. term it, dual- rotor) and variable-stator. After reviewing the reports of these teamsthe company decided to choose the latter configuration. This decision was momentous and has given G.E. a family of engines with no counter-parts elsewhere. In order to achieve the required specific fuel con- sumption the new project required a compressor with 17 stages, and themaintenance of proper flow through a conventional compressor with such characteristics would have been impossible. Correct operationcould, however, be achieved by mounting several rows of stator blades on pivots and by adjusting their incidence to keep the blade/airflowangles correct. The company proposed to use such an arrangement in their new engine, and the Air Force agreed and later awarded adevelopment contract for an engine designated J79. To prove the variable-stator principle the company built a demon-strator engine, which, although not of J79 size or character, was of advanced high-flow and lightweight design. It successfully proved thepracticability of variable-stators, having been built in less than a year and going on the bench in 1953. At the beginning of that year actualdesign of the J79 began. Construction was made largely of steel, and titanium (with which the company had had unfavourable experience)was eliminated. As far as possible sheet was employed in place of cast members, to reduce both weight and cost. The intake is of very low hub/tip ratio to provide the maximumpossible airflow, and the struts and inlet guide vanes are heated by compressor-delivery air. The compressor itself has 17 stages forming asingle assembly carried on a roller bearing at the front and a ball thrust-bearing at the rear. Rotor construction is entirely of steel, withblades dove-tailed into thin webbed discs through-bolted together and separated by spacer rings. Stator blading is also steel. The casing isdivided into four sections, the top and bottom front casings being of magnesium alloy and the top and bottom rear casings being of steel.Like the inlet guide vanes, the first six stator rows have pivoted blades. Their incidence is changed by a linkage actuated by a ram fed—byR.700 flexible hose—with engine fuel at 3,000 lb/sq in. To ease access most of the engine casings are split into upper andlower halves, and the combustion chamber is constructed in this manner. The chamber itself comprises an annular transition section togetherwith ten flame-tubes each served by a single injector, interior surfaces being lined with Incoloy T (a ni-cr-ti alloy). Combustion has to bemaintained over an extreme range of conditions, and relighting diffi- culties following flame-outs—a problem which once grounded theF-104 fighter—has been cured by a new design of G.E. dual ignition, applied to F-104 engines as an emergency modification. The turbinecasings and shrouds are fabricated from precision-welded sheet-steel assemblies. The turbine has three stages and is mounted on a conicalshaft splined to the rear of the compressor at the mid-point of the engine. A ball bearing is provided behind the turbine. If an afterburner is fitted, this takes the form of an advanced high-velocity unit incorporating a new form of aerodynamic flame-holding which gives minimum drag in the dry condition. The final nozzle hasmultiple segments actuated through rods from four remote jacks, and in supersonic installations the area of the convergent-divergent throatcan also be varied by injecting ram air through circumferential guid- ance passages around the periphery of the tailpipe. Augmentationratio from the afterburner is claimed to be greater than that ever pre- viously achieved. The automatic control system provides for single-lever operation andis divided into "main" and "afterburner" fuel systems. Both are flow- controlling units sensitive to turbine-inlet temperature and r.p.m.The main system is integrated with the variable-stator control and much of the flight operation of the engine is conducted at constantr.p.m. Fighter engines have an additional emergency system and all supersonic J79s have a separate system controlling nozzle area. Basicallythe controls are hydro-mechanical with electrical trim, power for these functions being supplied by the engine. The J79 is designed to supplyconsiderable quantities of bleed-air, and shaft drives are provided for accessories on forward and rear gearboxes, both of which are driventhrough a power take-off at the front of the engine. Development of the J79 has been rapid, and it took less than fouryears to reach full production from the start of design. The engine first ran in 1954 and flew in the summer of the following year, com-pleting its first 50-hr test at the same time with a total bench time of but 1,600 hr. Early flying was undertaken with the unit slung belowa B-45 from the G.E. air test station at Schenectady. Behaviour and reliability were so good that in December 1955 the engine was flown ina Douglas XF4D, the first time that a U.S. military engine had powered a single-engine aircraft in advance of delivery to an airframemanufacturer. The first 150-hr test was completed last August when running time had reached 6,500 hr. The engine entered full produc-tion late last year when bench and flight hours had reached 12,000, an impressive record of development which reflects the intensity of theefforts of the company and the U.S.A.F. to get the engine cleared for service. Its first production application concerned the F-104 A supersonicfighter, which first flew in February 1956 powered with the J79-GE-3. This aircraft has taken the engine to speeds higher than Mach 2.Two other applications are the B-58 and F11F-1F, which have respec- tively achieved sustained flight at Mach 1.9 and an altitude under powerof more than 76,000ft. New families of J79 are specified for the A3J and A4H of the U.S. Navy, and for several other aircraft as well asthe Regulus II missile. Particular interest attaches to the powerplant of the B-58 since it was the first gas-turbine installation intended forsustained supersonic propulsion. Each engine occupies a large nacelle of oval section, the space beneath the engine housing ducts for verylarge cooling airflows. The intake has a centre-body, the axial position of which is adjusted by a ball-screw ram controlled by a Minneapolis-Honeywell shock-sensing system. Supplementary intakes and heat exchangers are also provided for operation at various forward speeds. So far the U.S.A.F. have little experience with the engine. In spiteof the manufacturer's efforts to the contrary, overhauls have so far required some 2,400 man-hr; it has been reported that inspection ofcombustion chambers takes 40 man-hr and replacement and calibra- tion of the main fuel control requires 80. In addition, metal bellowsin the external fluid lines have been found to fail extremely frequently. At the beginning of the year engines operating on a 160-hr basis wererecording a premature-failure rate as high as 50 per cent. By the end of 1960 the J79 should be on a 400 hr, 15 per cent basis, and thetime should reach 1,000 hr by 1965. J8S. This extremely neat single-shaft turbojet stems from a U.S.A.F.competition early in 1954 which G.E. won. A development contract was awarded on December 14 of that year to the Small Aircraft EngineDepartment who have developed the engine rapidly and with high priority. Initially there are two main families, one for piloted aircraft andthe other for drone targets and missiles. Non-afterburning variants for aircraft have ratings from 2,300 to 2,500 lb, and weigh from 280 to298 lb dry. Basic transport/trainer J85s have been selected for the four-engine configuration combat-readiness transports such as theSabreliner and CL-329. Afterburning variants will be used in the Northrop T-38 supersonic combat and multi-purpose trainer. Missile
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