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Aviation History
1961
1961 - 0988.PDF
FLIGHT, 20 July 1961 AERO ENGINES 1961 . . . of boosting fighter-aircraft performance. Thrust was to be variable over a wide range up to 4,900lb at sea level. After taking a long look at nitric acid, it was decided to adopt HTP and JP-4, a decision which may well be gratifying to British workers in this field. Although work stopped in 1958, the specification was fully met, by an extremely simple pump-fed engine weighing 1651b dry. USA AIRESEARCH AiResearch Manufacturing Co, Division of The Garrett Corporation, Phoenix, Arizona. Long renowned for their very widely used series of small gas turbines employed for the provision of compressed air, shaft power or both, AiResearch were drawn into the aircraft-propulsion field in 1959 when McDonnell wanted are liable compressor to serve as prime mover in their Model 120 crane heli- copter. Even then AiResearch had delivered nearly 4,000 GTC.85 engines, and its reliability caused three to be fitted to the helicopter to feed the rotor tip jets. As a result AiResearch have been encouraged to develop the engine described below. Model 331 The GTP 331 is the first engine designed by the com- pany with aircraft propulsion as the primary objective. Its layout is exactly like a Dart RDa.7, with two tandem centrifugal compressors driven by a three-stage turbine; but the 331 is a notably compact little engine, with a direct annular intake, annular combustion chamber with ten high-pressure nozzles, turbine inlet temperature up to l,720°F on to 713C cast blades, and full provision for accessories (which are inclu- ded in the weight given in Table 2). Front or rear output can be pro- vided, and a reduction gearbox will be provided according to the air- craft requirement. Specific consumption is given as 0.64 at take-off power on the bench, and AiResearch have great hopes for the engine. It has already exceeded its design point specifications, and develop- ment should be completed by the end of 1962. ALLISON Allison Division of General Motors Corporation, Indiana- polis 6. Indiana. Although the T56 and Model 501 turboprops are performing satisfactorily in both military and commercial service in all parts of the world, the future of this programme appears to be a rela- tively limited one. Allison have for many months been negotiating with Rolls-Royce, on both technical and commercial grounds, and have even prodaced Americanized versions of such engines as the Spey and projected Conway 7, but it is now unlikely that any workable agreement is likely to benefit the two companies. In the aircraft- propulsion field the various types of Model 250 miy be the only now source of business, although the PD-37 Pyrodyne ramiet system may ultimately be manufactured in very great quantity for the propulsion of supersonic targets and drones. Allison have won substantial contracts for the manufacture of cases and nozzles for laige solid rocket motors, are heavily committed to research in the nuclear-rocket field for the USAF Systems Command, and recently announced a spacaflight auxiliary-power system using the Stirling cycle. Model 250 Sponsored jointly by the US Army and USAF, from 1958 onwards as the T63, this engine is unusual in several respects. The sheer size of General Motors has enabled the development pro- gramme to proceed methodically without ever being starved of funds, and the probable scale of future sales—which could run into tens of thousands of engines for air, ground and marine applications—is being carefully considered, and may enable a unit of advanced design to be sold for a price of less than $6,000. Allison have evolved a method by which complete compressor rotor stages are precision cast in an aluminium/cobalt alloy or reinforced plastic, the resulting assembly of disc and blades requiring virtually no machining and costing less than a third of an equivalent part produced by any other method. From the precision-cast centrifugal stage the air is delivered through a vaneless diffuser to a collector scroll, thence passing to the rear through lateral pipes to the single combustion cham- ber. The hot gases move forward through the gas-generator and power Fiat 4004 turbojet (exhibition mock-up) turbines, and are discharged through an exhaust hood projecting downwards. Backbone of the engine is the gearcase; the compressor is bolted on ths front, the combustion chamber to the rear, and inside is the train of spur gears which take the power to an upper output shaft turning at 6,000 r.p.m. From the latter, drives can be taken to front or rear, and in the turboprop version a planetary reduction gear provides a final output at 2,000 r.p.m. An additional train from the gas-generator assembly provides drives to the accessory pads on the front and rear faces of the gearcase. Ratings for the Model 250 given in Tables 3 and 4 do not make it clear that the flame temperature is deliberately restricted under normal conditions to less than l,760°F. As a result all versions of the powerplant can give their full output of 250 s.h.p. at up to 100°F ambient, the only effect on the engine being a rise in turbine-inlet temperature and specific consumption. No applications have been announced for the turboprop 250-B2 version, nor for the projected Model 252 powerplant consisting of a pair of power sections attached to a common gearcase. The turbo- shaft 250-C2, however, is specified as the powerplant in both the Hiller 1100 and Bell D-250 helicopters, which are the joint winners of the US Army's design competition for a new four-seat light observation helicopter; and many other applications are in prospect. Model 501/T56 Sharing essentially the same power section and remote-mounted propeller gearbox, the commercial 5O1-D13 and military T56 was the first family of turboprop engines developed in the US to achieve any degree of success, and well over 1,000 of each type of engine have now been delivered. As the powerplant of the Lockheed Electra, the 501-D13 entered service in January 1959 at an FAA- approved overhaul life of 800hr. Late in 1959 the engine became the only gas turbine not of British origin to achieve a genuine l,000hr overhaul life, without intermediate inspections. The time between overhauls has steadily climbed until earlier this month it was announced that the engines used by Pacific Southwest and Western Airlines have been cleared to the excellent figure of l,800hr. Braniff and Eastern are at 1,600, American and National at 1.400 and Northwest at l,200hr. By April of this year the 5O1-D13 had logged 2,300,000 flight hours in scheduled service. Production has ceased on the original military T56-1A and -9 engines installed in the Lockheed C-130A. In their place have come the T56-7, rated at 3,755 s.h.p. (4,050 e.h.p.) and driving a four-blade Aeroproducts propeller in the C-130B and C-130E, both of which are the subject of substantial production contracts. A similarly rated engine is the Navy T56-8, but the installation in the Grumman W2F Hawkeye is a complex one peculiar to the unusual requirements of this aircraft. The most powerful of all Allison turboprops is the T56-1OW. which incorporates a water-injection system and other detailed improvements to give a maximum rating of 4.585 e.h.p. It differs from all other military T56 engines in having the propeller gearbox mounted below the axis of the power section; this is because the engine is installed in the Lock- heed P3V-1 Orion, the ASW version of the Electra. Jurbomica Turmo 3D turboprop (exhibition mock-up)
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