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Aviation History
1957
1957 - 1048.PDF
138 -: :~~ •>•-$£• FLIGHT AERO ENGINES 1957 ... The tip radius of this compressor tapers considerably from front torear, giving the engine a wasp-waisted appearance which provides useful installations! volume for accessories. The high-pressure spoolis untapered along its outer diameter and both compressors are built up from centreless discs and spacers, the blades being retained bysingle dovetail slots broached diagonally around the periphery of each disc. The annular combustion chamber contains eight flame tubesformed from spot-welded stacks of Inconel rings. Each flame-tube forms a small-scale annular combustion chamber into which fuel isinjected from six downstream-injection burners (of which there are thus a total of 48). The burners are fed by main and secondary fuellines, the secondary circuit being brought into action at a flow of more than 2,000 lb/hr. At lower flow rates the fuel in the secondary pipesis stationary, and to avoid coking in this condition the secondary pipes are run concentrically through the centres of the primary pipes. Several types of afterburner have been delivered for the J57, themajority giving reheat up to 2,000 deg K from multiple radial injection bars and three concentric gutter-type flame-holders, ignition usuallybeing of the "hot-streak" pattern. Some of the more recent afterburner systems incorporate an aerodynamic flame-holding arrangement, inwhich high-velocity jets of compressor-bleed air are directed upstream within the afterburner. These jets create local regions of relativelydead or turbulent air in which the afterburner combustion can be maintained comfortably; in the dry condition they have far less dragthan mechanical flame-holders. The propelling nozzle of afterburner- equipped J57s is usually of the two-position type. In the earliestversions, used in the F-100A, there were 24 sliding nozzle segments which were positioned by 24 separate hydraulic jacks. Current fighterengines have but eight segments hinged at their leading edges. For the F-101 aircraft a short afterburner giving a relatively low augmenta-tion-ratio was developed, this powerplant having a length of 200in. As a basic design the J57 is no longer representative of current Prattand Whitney practice. Nevertheless the engine has a record of economy and reliability which is acknowledged throughout America as a targetat which other companies should aim, and Pratt and Whitney's great effort with the engine has been rewarded handsomely. Current production involves many types of J57, the majority beingadvanced powerplants for the B-52 and KC-135, or afterburner engines for supersonic fighters. In nearly all cases the low-pressure compressoris now manufactured almost entirely of titanium, the change both reducing the weight of the engine and increasing the fatigue-life ofthe blading. Discs, spacers, blades, low-pressure and intermediate casings and inlet case are all fabricated from the new alloys, and con-siderable night-time has now been accumulated, particularly with alloys 150A, 140A and C-130AM. The latest engines incorporate thenew PWA682 (6 per cent Al, 4 per cent V), which is reckoned the optimum available at present. As an indication of the weight-savingswhich have been effected, the cut-weight of the forging for the first- stage compressor disc has been reduced from 120 to 75 lb, and theutilization ratio has been improved. Typical equipment of J57s in- cludes Holley or Bendix fuel control, Hydro-Aire pneumatic gate-valves and water-injection control, a pneumatic turbine starter and a saddle oil tank. Provisionis made for bleeding air at up to 300 lb/sq in at 750 deg F. _ During the past year the engine has flown atleast a million hours, the majority being logged by the octets of engines flying with the 180-oddB-52s now in operation. In this aircraft the engine has a good record, and one powerplantwas recently "pulled" after having been flown in a B-52 for 1,000 hr without removal. During thefirst year of B-52 operations with Strategic Air Command the powerplant overhaul time was500 hr. Castle was the first base to operate the engine, and between June 1955 and August 1956,in which the aircraft strength grew from 1 to 40 machines, 81,112 engine flight hours were loggedand 95 engines were removed prematurely. At the end of that period the mean achieved life was600 hr, the failure frequency 0.28 per 1,000 hr and the in-flight shut-down rate 0.29 per 1,000 hr.A further increase in overhaul time to 800 hr was made last October and the current figure isjust on 1,000. At present a major overhaul occupies about 850 man-hr (or 1,012 includingaccessories) and costs about $15,000. Current B-52 and KC-135 engines are similarto that shown in the diagram, and related units are used by the U.S. Navy in the A3D. After-burning fighter engines are generally operating on a 200-hr basis with a 15-per-cent premature-failure rate. These engines should reach a 460-hr cycle by the end of 1960. J58. Mindful of their lack of success with another turbojet maker, the U.S. Navy have recently been placing anincreasing amount of business with Pratt and Whitney. The com- pany's largest commitment to the Navy is the J58 turbojet, which isintended to fill the role for which G.E.'s advanced (high-energy fuel) engines are being planned for the U.S.A.F.. It has been reported inthe U.S.A. that the J58 is a high-airflow engine intended for operation at Mach 3 and sized to give 22,500 lb static thrust, conforming to theNewbury Memorandum requiring each new engine to exceed the previous generation's output by 50 per cent. Another report, how-ever, has claimed that the J58 is an 18,000-Ib engine, which would in effect make it a much lighter and more advanced unit in the thrust-classof the J75. Current J58s are designed to use conventional jet fuels, and their development and testing is being undertaken at the Prattand Whitney facility at West Palm Beach, Florida. J7S. In 1951 Pratt and Whitney received a U.S.A.F. developmentcontract for a scaled-up J57 with a mass flow of 250 lb/sec. The engine first ran in 1953 at about 14,000 lb static thrust, and was then ex-haustively tested in the Willgoos laboratory and flown from Rentschler Airport at the beginning of 1955, slung beneath a B-45 test-bed.During the past two years many thousands of hours of bench and flight time have been logged, and current versions already form a consider-able family for a range of applications. In its basic geometry the J75 is similar to the J57. Owing to its laterdesign its increase in thrust over the earlier engine is considerably greater than the proportional increase in weight, and today's J75 isa most competitive unit, particularly for long-range aircraft which have to be capable of supersonic speed. A considerable proportion oftitanium is employed in the construction of the compressor rotors and low-pressure and intermediate casings. Fighter powerplants have alarge afterburner with a multi-shutter con-di variable-area nozzle. Powerplants of the latter type are fitted to the F-105B and C,F-106A and B, and F-107, and are scheduled for the F8U-3. These large aircraft have peak level performances up to Mach 2.3, and thestatic thrust of their engines is approximately 24,000 lb with reheat. The J57 is about to be flown in a B-52 on endurance testing, but it is veryunlikely that it will ever power a version of this aircraft. The engine has, however, been chosen as the powerplant of the Martin P6M-2SeaMaster, which is now in production. Second-source production of the J75 is undertaken by Ford (q.v.) and the commercial variant is theJT4A below. J91. As one of the two prime powerplant contractors to the U.S.A.F.for the WS-125A nuclear bomber specification, Pratt and Whitney have established an exceedingly large ad hoc facility known as theConnecticut Aircraft Nuclear Engine Laboratory (CANEL). Stretch- ing for over two miles along the Connecticut river near Middletown,the plant is nearing completion and will ultimately be used as a pro- Pratt and Whitney J7S (JT4A is essentially similar). Split-compressor turbojet. The configuration of this engine is basically similar to that of the J57, described on the preceding page. Overall diameter, 58.5in; length, as depicted, 214in (basic length. 191in); dry weight. 5.300 Ib; mass flow, about 260 Ib/sec; pressure ratio, 12.5:1; maximum thrust, 17,2001b. With afterburner this engine gives a reheat thrust of about 24,500 Ib. The civil JT4A series have ratings from 15,500 to 16,800 Ib. A row of J57-P-12 afterburning engines in the Chance Vought factory at Dallas, Texas, await- ing installation in the F8U-I, fastest aeroplane in the U.S. Navy. One such engine recently operated at maximum-continuous rating for 3 hr 23 min while an F8U was setting up a new * American coast-to-coast record.
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