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Aviation History
1961
1961 - 0066.PDF
Turboprop T64s are being run in the new cell at Lynn referred to in the accompanying text; the -4 is shown on test, but there is also a -8 with propeller shaft above the centreline instead of below. On the right, engineers at Lynn are assembling a fully instrumented gas-generator T64 . . . single and twinned configurations, all using the same gas generator.This is unique. There was never any doubt in the company's mind that thefree turbine is safer than the single-shaft formula, and for shaft- drive units they regard it as essential that the power turbine andall portions of the compressor should be completely disengaged. Such an arrangement increases the flexibility of the propulsionsystem, and enables optimum engine and rotor (or propeller) r.p.m. to be matched at all times. In planning the turbineassembly of the T64 care was taken to achieve a fairly flat effi- ciency curve over an adequate range of rotational speeds. A cyclewas then picked which permitted the 2 + 2 type of turbine. With regard to the combustion system, the company had pre-viously achieved success with truly annular designs on the T58 and J85 and regarded such chambers as essentially sound. In theT64 the inner liner and flame-tube consist of upper and lower halves, either of which may be removed without disturbing thehot end of the engine. The split combustion chamber was not pan of the original scheme, but was incorporated in a secondbatch of test engines. Already liners have been dismantled with- out removing the engine from the stand. This is one of numerous instances in which the detail engineer-ing has been planned to give the engine maximum accessibility and ease of maintenance. For example, even when the engine isinstalled, the compressor casing can be unbuttoned and any required blade may be slid from the casing or rotor withoutfurther ado. Another example of this practice is found in the turbine section, where again the casings are split. During develop-ment this has been found a great asset, in that it permits the diaphragm openings for a given set of wheels to be optimizedwhile the engine remains in situ. Having established the design of the gas-generator, GE wenton to evolve gearbox systems for the turboshaft and turboprop versions. In both cases the boxes are self-contained assemblieswhich may be replaced with minimum disturbance to the front end of the gas-generator. In the turboprop version the gearboxis carried remote from the intake in an arrangement superficially similar to that adopted by Allison for the Model 501. Engineaccessories are hung beneath the compressor and driven from the front end of the gas-generator, and the aircraft units areattached around the rear of the reduction gearbox. Provision is made for electric or other means of shaft-power starting, but atthe present time it appears likely that most carrier-based aircraft using the T64 will have an air-impingement starter operatingon the first-stage turbine. Use of such a starter has been found a great help during the development of the gas-generator, sincethe latter can be motored gently on the air blast alone. GE have with their own funds constructed a unique test standat Lynn, in which is being conducted the development of the T64-4 turboprop. It is constructed from corrugated steel conduit,without any subsidiary structure; in previous test cells of this nature corrugated sheets have been employed only as a formefor a reinforced-concrete cell. The new construction is still partly experimental, but it is working well and seems to have cost roughlyhalf as much as the previous method. As the left-hand photograph above shows, the turboprop is suspended from the roof and allfeed and instrumentation lines are grouped in an axial trunk along the upper part of the cell. The cell orifice is mounted on a track,and orifices of different sizes permit this parameter to be matched to the size of the propeller employed. At present a 14ft HamiltonStandard propeller is being used, with four blades. During early runs strain-gauges were fitted to an average of two blades in each stage of the compressor. By this means "live" blades couldbe tracked down before the blade settings were frozen. This work was first conducted on the T64-2 turboshaft engine, and wasthen transferred to the -4 to investigate the effect of the propeller upstream of the intake. Although the qualification date for the turboshaft engine isahead of that of the turboprop, the latter ran first, in January 1959, the output power being absorbed by a dynamometer. The-2 followed in March, and the guaranteed powers and s.f.c. have both been surpassed, as the data tables show. An unusual contractrequirement is a stipulation for endurance testing. GE will have completed 10,000hr of cell running before the first engines areshipped in a few weeks' time. Sheer hours mean little, since excessive consumption of this commodity during certificationtesting may merely reflect the incompetence of the manufacturer; GE feel that any contractor worth his salt should pass all 150hrqualification tests on a new engine well inside the 10,000hr mark. Included in the contract is finance for "a substantial number"of development engines—certainly more than 30. Some of these have been selected for repeated l,000hr endurance testing. Otherengines are running with inlet ducts from two airframe manu- facturers, with excellent results. One T64 has spent two winterson Mount Washington ingesting up to 2.1gm/m3 of water at 5°F while preventing ice formation—even at ground idle—withouttapping more than 0.7 per cent of bleed air. Last September an engine started environmental tests at the Navy engine laboratoryin Philadelphia. All running has been on JP.4 or JP.5. First delivery is scheduled for early this year, when a pair ofYT64-GE-4 turboprops are due to be shipped on a 50hr basis to de Havilland Aircraft of Canada for installation in a Caribou.This aeroplane is regarded by GE as an ideal test-bed for the fixed-wing T64s. Only one firm application of the engine has sofar been announced: Sikorsky have stated that a switch to the T64 in the S-60 twin-engined crane helicopter will permit thepayload to be increased by two-and-a-half times. But this does not mean GE have backed the wrong horse; a recent check showedthat American airframe manufacturers have, as active projects: T64-powered cargo helicopters, an assault helicopter, a crane (theS-60/64 series), VTOL vehicles, STOL assault transports, carrier- based ASW vehicles, executive transports, "long-endurance air-craft" and ground-effect vehicles. W.T.G. T64 DATA Compressor stages Turbine stages Max. mass flow ... Max. pressure ratio Max. compressor r.p.m.Max. output shaft r.p.m. Reduction gear ratio Max. output r.p.m. LengthHeight Weight Guaranteed military s.h.p. s.f.c.Achieved military s.h.p. ,. s.f.c. Guaranteed 85"O rated s.h.p. . s.f.c. . Achieved 85",, rated s.h.p. s.f.c.= irst official run ... 50hr prelim, flight rating 150hr qualification 14 (four variable stators) 2 + 224.5lb/sec (original figure, 25) 12.6 : T64-2 turboshaft 2.61 : 1 5.200 91 in30in 854lb 2,650 0.5062,780 0.490 1,897 0.552 2,065 0.537 Mar. 1959 April 1960 Aug. 1961f 1 (original figure 12.5) 17,00013,600 T64-4 turboprop 11.8 : 1 1,160 113in36in 1 079lb2,700* 0.4952,760* 0.483 1,982* 0.530 2,150* 0.513 Jan.1959 May 1960 Dec. 1961f T64-6A direct drive 13,600 68m 30in 700lb 2,650 0.5062,780 0.490 1,897 0.552 2,065 0.537 Mar. 1959 April 1960 Aug. 1961 + * e.h.p.; f contract date (other dates were two months ahead of contract).
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