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Aviation History
1959
1959 - 2360.PDF
Rotofs constant-speed drive—the G.E. design built under licence is particularly competitive on the score of weight ACCESSORY POWER English Electric ore to supply both constant-speed drives (the Sund- strand design) and A.C. generators for the VC.10. This is one of the first British-made drives, of which a number are now running SINCE electrical power has such an important function in themodern aeroplane, it was not surprising that a year or two ago a major technical battle should have developed within theindustry for the supply of equipment for the A.C electrical systems that were at that time proposed. Many firms entered thefield with A.C. generators or the constant-speed drives that were needed to rotate them. At least as far as the two major British civil transports are con-cerned, the battle now seems to have been resolved: English Electric are to supply at least a number of Sundstrand drives andA.C. generators for the VC.10 and H. M. Hobson and British Thomson-Houston respectively the constant-speed drives andalternators for the D.H.121. This is not to say that competition for the supply of units for these aeroplanes has now ceased. In thecase of the VC.10 the number of drives ordered is limited— possibly so that a competitors' unit could later be specified if itlooked promising—and orders for D.H.121 constant-speed drives have not yet been placed, although it is understood that theHobson unit will be fitted to the RB.163 engines for this aero- plane. Undoubtedly there is more actual operating experiencebehind the English Electric Sundstrand drive than with any British-designed equipment, and when English Electric say thattheir drives (which they are required to make to a comparable standard to that of U.S.-built Sundstrand units) will have aninitial overhaul period of 800 hr with quick development to 1,200 hr they can use actual American operating experience as aguide. In a few years time, they say, overhaul periods of 2,000 hr should be achieved. A small number of English Electric unitshave now been completed and some early experience should be obtained when the Boeing 707 goes into B.O.A.C. service, asEnglish Electric have a spares contract with the Corporation for 707 drives. In conjunction with their constant-speed drive, English Electrichave developed a 40 kVA A.C. brushless generator, designed to be driven at a constant speed of 6,000 r.p.m. This unit is still quitenew, but 3,000 hr running experience had been obtained by the start of the Show. This unit has a five minute overspeed rating of11,000 r.p.m., an overload rating of 60 kVA for five minutes and 80 kVA for five seconds. It weighs 86 lb. Both Hobson and B.T-H. have been affected by the recentchanges in the size of the D.H.121. Originally 30 kVA were required from the alternator and drive when this was matchedto the RB.141 engine. For the RB.163 the requirement is less, and both firms are producing new units which, in combination, wiltgive a 22| kVA supply. What this must mean in terms of delay in supply of equipment to the aircraft is not easy to assess, butHobson estimate that their development will be delayed by about six months and B.T-H. say that they hope to have the new22£ kVA unit running in February or March next year. It is quite clear that in both cases a considerable amount of work is requiredin the scaling-down process. Design of the 40 kVA B.T-H. self- exciting brushless alternator, for instance, took three months andmanufacture twice this time. Nevertheless, the development staff of both firms are naturally not dissatisfied that they can havesecond thoughts on these units so soon after completion of the first design, and there is every reason to suppose that betterunits should result. One major advantage in prospect is that for a drop in alternator output of 25 per cent, there will be a weightreduction of 30 per cent in the constant speed drive (from 94 1b to 661b with cooler) and 41 per cent in the alternator (from 85 to55 1b). Hobson have put a great deal of work into constant-speed drive development at Wolverhampton. Five experimental driveshave now been completed; delivered units should have a pre- This 30/40 kVA Hobson constant-speed drive is to be produced in 22V2 kVA form for the Airco D.H.121 liminary overhaul period of 1,000 hr with a rapid build-up to2,000 hr. Although the particular requirement for the D.H.121 haschanged, applications for 30 or 40 kVA alternator power still remain. Hobson and B.T-H. are hoping to find purchasers fortheir larger units in Vickers and English Electric for die TSR.2. Other companies in the British constant-speed drive field areRotol (who manufacture the General Electric unit under licence), Lucas (G.T.E.) and Messey. The first-na-ned now has anAmerican-built 40 kVA G.E. drive running at Gloucester and driving a B.T-H. alternator. The G.E. range includes 9, 20,30 and 40 kVA drives and one of these could well be first reserve for the D.H.121. The company also have hopes of being thesupplier for the TSR.2, either with a G.E. drive or possibly a turbo-alternator unit such as the Rotol unit fitted to the NA.39. As another supplier in the 30 kVA constant-speed drive range,Lucas displayed their hydraulic drive which weighs 70 1b. This unit has a normal output of 30.2 h.p. which may be temporarilyincreased to 80.2 h.p. A subsidiary company of Lucas, Rotax Ltd., produce a range of brushless alternators and a self-contained50 kVA bleed air turbo alternator, a high-speed machine which runs at 24,000 r.p.m. Rotor and turbine wheel are mounted on acommon shaft running at the governed speed and the unit is suitable for parallel operation of other similar alternators byaHHjng a small power-equalizing unit and a protection unit fitted with a synchronizing device. Another development of this com-pany is an environmental-free solid-rotor brushless alternator. There are a number of types in production at the momentdelivering outputs up to 20 kVA, but further design and develop- ment work should result in machines giving outputs of up to60 kVA at 8,000 r.p.m. The 20 kVA model weighs 47 lb. Ram air turbines were again much in evidence at the Show,
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