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Aviation History
1961
1961 - 0990.PDF
90 FLIGHT, 20 July 1961 A///son Model 250 turboshaft AERO ENGINES 1961 . . . new powerplant being produced in turboshaft and turboprop versions. Although the words "entirely new" are deliberate, Continental have assembled the engine largely from proven components of the earlier production model: the compressor is that of the J69-29; the combustion chamber is common to that of most Continental turbines; the two-stage compressor turbine is that of the mass-produced Model 141 air com- pressor; and the single-stage power turbine is that of the J69-25 and -29. The basic unit is the USAF-sponsored T72-T-2 turboshaft unit with a 6,000 r.p.m. output. Around the intake diffuser is an accessory gear- train enclosed in a casing providing on its rear face drive pads for a wide range of equipment and the three engine mounting faces. Com- ponents of this engine have been on test for many months and at least one complete engine is now running on the bench. The entire design is regarded as conservative, suggesting that there will be no difficulty in providing the promised qualified flight-test engines early next year. Minor aerodynamic changes will permit early qualification at the increased rating of 600 h.p., and more extensive alterations will permit an increase in power to 850 h.p. without changing the engine frame size. Continental are also developing, with their own money, the Model 217-6A turboprop, with a maximum propeller speed of 2,100 r.p.m. GENERAL ELECTRIC General Electric Co, Flight Propulsion Divi- sion, Cincinnati 15, Ohio. This vast company studied gas turbines in 1895, built the first American (Whittle-derived) turbojet in 1941 and have now delivered more than 33,000 turbojets, more than any other manufacturer in the world. Today, the Large Jet Engine Department at Evendale (Cincinnati) is in quantity production with the military J79 afterburning turbojet, its commercial variant the CJ-805 and the aft- fan CJ-805-23. At one time the Flight Propulsion Division were one of the two prime contractors to the US Air Force for aircraft nuclear Removal of an Allison 50I-DI3 after 1,000br on Eastern Air Lines propulsion, but their X-211 direct-cycle powerplant was terminated by the President's decision to abandon all work in this field by June 30. Nevertheless, immense development effort is being applied to the J93 powerplant for the B-70 long-range bomber, and modest effort is also being applied to the military J79 aft-fan derivatives. The Small Aircraft Engine Department at Lynn, Massachusetts, are in quantity produc- tion with the T58 turboshaft and commercial CT-58, and the J85 turbo- jet both with and without afterburner. Development has reached an advanced stage with the CJ-610 turbojet, CF-700 turbofan and all forms of the T64 shaft turbine. The Flight Propulsion Division has also evolved from their aircraft powerplants a range of industrial and marine free-turbine units, ranging from the Model 720/722 of 900 s.h.p. up to the model 240 (derived from the J79) rated at 20,000 s.h.p. The model 240 will serve as primary propulsion for the Grumman hydrofoil, and is being offered in a 48ft airportable electric generator plant. J79 In 1952 studies were initiated to determine the design of a new military engine to follow the mass-produced J47 and J73. Primary objectives were efficient performance at M0.9 cruise, the ability to provide propulsion at more than M2 and the desirability of reducing specific weight and specific consumption. The requirement for low s.f.c. during subsonic cruise implied a high pressure-ratio, and it was finally decided to adopt a single-shaft configuration and employ vari- able stators throughout the early part of the compressor to regulate airflow during off-design conditions. The intake guide vanes and first six stator rows are all mounted in rotary bearings and actuated by a ram pressurized with fuel automatically scheduled as a function of inlet air temperature and engine r.p.m. New lightweight constructional methods were adopted throughout the engine, outstanding examples being the wide use of thin steel sheet fabricated by precision welding and the conical turbine shaft which transmits 70,000 h.p. at peak r.p.m. The J79 first flew beneath a B-45 in December 1955 and the J79GE-1 passed its 150hr qualification test and went into production in 1957. The first major production variant was the J79-3A, for the Lockheed F-104 A and B. Later models are listed in Table 1, and even more advanced versions are scheduled to go into production in the Fiscal Year 1963. This basic powerplant has served as the progenitor of the CJ-805 commercial turbojet and of various aft-fan aircraft and free- turbine industrial engines. The J79-11 is being licence-built in Canada, Germany, Italy, Belgium and Japan, for use in the F-104G,'F-104 J and CF-104. J85 The Small Aircraft Engine Department began the MX-2273 lightweight turbojet in 1955 under a USAF contract to meet a require- ment for a simple engine to power target drones and missiles. The demise of the competing Fairchild J83 increased GE's willingness to put money into the engine, and it has now materialized as a very succsss- ful military powerplant and as the basis for a civil turbojet and aft- fan engine. In its dry version (J85-7) the engine is in production for the Green Quail decoy missile, while the J85-5 with afterburner is in production for the Northrop T-38 Talon now operational with the USAF Air Training Command. More than 28,000hr of bench testing (incidentally, this is more than four times the current flight experience) have demonstrated that the engine can exceed its design specifications. The thrust/weight ratio of 7.5 is better than that of any other non-after- burning engine (excluding specialized lift engines), yet the SJI32 engine now on test achieves the remarkable figure of 10.5, increased flame temperature raising the thrust to 3,0501b and a number of structural modifications reducing the weight to about 2971b (2701b without fuel pump and control unit). The afterburning -5 engine has already demon- strated a thrust exceeding 4,1001b on maximum reheat, and on standard fuel has demonstrated numerous starts and protracted operations at ambient temperatures from —65° to 130°F at altitudes in excess]of 30,000ft. J93 Security restrictions still prevent the publication of details of this excellent single-shaft engine, six of which fit the propulsion bay of the North American B-70 Valkyrie long-range bomber. GE them- selves are merely allowed to list the following facts: design objectives were low s.f.c. at M3 cruise condition, low weight and high airflow and thrust at M3 cruise condition; the compressor has a relatively small number of stages, with variable stators, and handles an extremely high airflow per unit frontal area; a convergent/divergent nozzle is used, with infinite variation to suit changing flight conditions; stainless-steel honeycomb sandwich (and other unusual manufacturing principles) are employed to reduce weight; and all accessories are contained in a controlled-environment pod mounted beneath the compressor and removable for maintenance as a single unit. Termination of the high- energy fuel programme two years ago did not affect the J93-3 variant selected to power the B-70, and a considerable number of development engines have logged something like 5,000hr on the bench and in a ram test facility at Evendale capable of simulating all conditions up to 2,000 m.p.h. at 90,000ft. Flight-testing up to M2.2 at 70,000ft is being accomplished with engines mounted in a self-contained and fully instrumented nacelle attached beneath a B-58A. Although it is not possible to duplicate the B-70 installation, the B-58 pod incorporates the same Hamilton Standard variable-intake control system. CF-700 The Small Aircraft Engine Department have with com- pany money developed this commercial aft-fan engine from the J85 turbojet. Since it is a commercial engine, the gas-generator is that of
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