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Aviation History
1961
1961 - 0994.PDF
94 FLIGHT, 20 July 1961 AERO ENGINES 1961 . . . GAM-77 Hound Dog air-launched missile, and for this purpose an entirely different version of the powerplant was developed, with a rating of 7,5001b without an afterburner and optimized for flight over a wide range of Mach numbers and altitudes. Control and accessory systems of the Hound Dog engine differ considerably from those re- quired for land aircraft, and unusual features of the installation are that a conical centrebody is mounted in the intake and a variable central plug in the propelling nozzle. In 1958 the J52-6 was funded by the Navy to power the Grumman A2F-1 Intruder attack aircraft, and a unique Pratt & Whitney J52-6 turbojet Pratt & Whitney JFTDI2 turboshaft feature of this engine is that its jetpipes can be hinged downwards through 23° to increase STOL ability. The J52-6 has been the subject of at least two production contracts, and some dozens of engines have now been completed. Now the wheel has turned full circle, and the J52 is back in its original application, the Skyhawk. In many ways based upon the defunct A4D-3, the all-weather A4D-5 has a J52-6 or -8, with a conventional fixed jetpipe. No fewer than 180 A4D-5s are inclu- ded in the Navy budget for the coming financial year (begun on July 1), far more than for any other type of aircraft. Components of the JT8 are employed in the JTF10 and have assisted in the development of the JT8D. JT8D Discussed at some length in our June 29 issue, this power- plant has been carefully optimized to provide the most efficient possible propulsion for short- and medium-range transports. As has previously been remarked, its basic design parameters are essentially similar to those established by Rolls-Royce, but it differs from the British engines in having a rather lower pressure ratio, considerably lower flame tem- perature and a turbine split 1 +3 instead of 2+2. It is instructive to compare the company cutaway drawings of this engine and the Rolls- Royce Spey which Flight has published.* The ruling materials throughout the JT8D-1 are steel and titanium, and their selection is claimed to minimize foreign-object damage and permit compressor- blade profiles which result in increased efficiency. All fan blading is of titanium; each blade is dovetailed into its disc and those Of the first stage are provided with an integral shroud on either side, at about 61 per cent span, abutting against those on the adjacent blades. The flame tubes are conventional assemblies built up by welding together succes- sive circular sections, the "bullet nose" contrasting with the unusual annular tubes disposed around the combustion chambers of the com- pany's earlier engines. Further proof of the fact that this engine is not just a converted turbojet is the manner in which engine accessories are hung on the outside of the fan duct, the latter leading to the rear to exit around the hot jet. To minimize specific consumption a Rolls- Royce type of hot/cold mixer is included, and a single reverser and suppressor can be fitted. The JT8D-1 was specially tailored to the Boeing 727, and United Aircraft's licensees, SNECMA, have designed a complete nacelle suitable for both this aircraft and the projected Cara- velle 10. The first JT8D drawings were released to experimental fabrica- tion last November and the first development engine ran in April. At least two other engines have now run, and total bench time is probably of the order of 200hr. The first flight will take place in October, with an engine slung beneath a B-45; prototype delivery is due next May and first production delivery in February 1963. Some of the data given in Table 2 have not been published previously. JTFIO This medium-sized turbofan was evolved directly from the original JT8, in 1958. All work on it has been passed across to SNECMA, the company's licensees in Europe (q.v.). JT11 Described by the company as "a turbojet in the 30,0001b thrust class, intended for operation at high altitudes and high Mach numbers" this family of powerplants began as the Navy-funded J58, the design of which was completed in 1957. All the development of this powerplant has been handled by the Florida Research & Development Center, where about 30 JTlls have been manufactured and tested under conditions simulating Mach numbers of up to 3. The JT11 is a single-shaft engine of "moderate" compression ratio, and is in some respects reminiscent of the much smaller JT12. Hamilton Standard, another United Aircraft division, have developed for it a very advanced control system which automatically governs the variable intake, peri- pheral compressor blow-off valves, fuel supply for engine and after- burner and the configuration of the very large convergent/divergent variable nozzle. When we discussed the JT11 in our 1960 review it was still primarily a military project, although its only likely applications were projected developments of the B-58 and to act as a back-up to the GE J93-3 for the B-70. Today, the JT11 is regarded principally as a national "workhorse" development unit for the investigation of struc- tures, control systems and complete propulsion installations for a 2,000 m.p.h. airliner. The afterburning ratings vary from 30,000 to almost 40,0001b (and far more at high forward speeds), but it is anticipated that the ultimate transport engine will not have an afterburner, in which case the dry rating will start at 23,0001b. JT12 Designed largely by Canadian Pratt & Whitney, this single- shaft turbojet is sized to achieve the best possible thrust/weight ratio, and its brochure performance and demonstrated reliability indicate that it has become hard to beat in the 3,0001b thrust class. The company state that it was conceived "specifically for executive aircraft use"; but the truth is that, when it was designed, military applications, both piloted and unmanned, appeared to offer as good a potential market. Its design is true Pratt & Whitney, the basic engineering being conserva- tive and amenable to considerable development. It was the first of the company's engines to revert to simple centre-injector flame tubes. Drawings were released in January 1958 and bench-testing began in May of that year. First flight took place in April 1959 beneath a B-45, a 50hr test was completed in August of that year and during 1960 the engine flew in the Canadair CL-41, JetStar, Fairchild SD-5 drone and T-39 Sabreliner, in that order. All guarantees have been handsomely exceeded, and—although the afterburning variant has no apparent * Rolls-Royce Spey, May 18, pp 670-1; JT8D-J, June 29, p 892.
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