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Aviation History
1962
1962 - 2041.PDF
440 FLIGHT International, 13 September 1962 ROUND THE STANDS • DannnnnnnnnDDDnnnnnnnannnnnnnnnnnnnnD —-4 CUT-OUT U rn CONTROL I PROTECTION UNIT GENERATOR CONTROL SWITCH LOAD BUSBAR T l2kW 30V d.c. generator developed by English Electric The same company's brushless d.c. generator system (upper diagram) offers great simplifica tion in comparison with a conventional d.c. system (lower) AIRBORNE SYSTEMS ELECTRICS IN aircraft electrical power supply systems, probably the most interesting trend as seen at Farnborough this year is the increased attention paid to traditional 28V d.c. supplies, which are still almost universal for the smaller types of transport aircraft such as the Herald, Avro 748, and their future developments and counter parts. The 12kW 30V brushless d.c. generator shown by the English Electric Co Ltd is the result of three years of development. It comprises a full-wave silicon rectifier bridge integrated with a two-stage a.c. generator, the voltage regulator being transistorized. The brushless d.c. generating system offers a great simplification over conventional d.c. power systems, because it does not need a reverse-current circuit breaker, main contactor or a differential relay. In fact the system requires only three units: the generator; control and protection panel incorporating voltage regulator and protection circuits; and line diode. It is claimed that the elimination of brushes and moving parts (other than rotor bearings) gives a threefold increase in life between overhauls. A generator of this type is installed on the Rolls-Royce Dart Ambassador, and has completed nearly 800hr of trouble-free service. Although it was not on view at the Show we were told of another English Electric development, in alternating-current supplies, that is now emerging from the "bread-board"' stage and should be born commercially early next year. This development, variable speed constant frequency (VSCF), is attracting considerable interest from the German and French aircraft industries, representatives of which have recently been visiting the Bradford works to investigate progress. VSCF is a completely new method of achieving a static constant-frequency output, using semiconductor techniques. Meanwhile English Electric, in common with most other electric power supply manufacturers, are increasing their range of constant- speed drives, and showed two new private-venture hydromechanical drives for a 10kVA system, both rated at 16 h.p. and intended for helicopters and fixed-wing aircraft. One (type D. 14500) has an integral pump and motor for use where the aircraft hydraulic system is not suitable for supplying a c.s.d. The other, type D.14501, is for aircraft with large-capacity hydraulic systems. Another English Electric development shown for the first time was a 50kVA homopolar (solid-rotor) a.c. generator which, because it has no rotating windings, is capable of operating at the high ambient temperatures encountered in supersonic flight. The high temperature capability and greater reliability of the solid rotor involves some weight penalty—1321b as compared with 871b for conventional blast-air-cooled brushless alternators and 1031b for oil-cooled brushless alternators of the same output. On the Buccaneer and Lightning aircraft, compressor bleed air is used to provide a constant-speed turbo drive for the alternator. One of these 12-15 h.p. units was on view on the Dowty Group stand, sectioned to show the adjustable inlet blading, the angular setting of which is automatically governed to regulate the airflow so as to maintain constant turbine speed. Static inverters continue to increase their range of applications, because of their ability to achieve stable operating conditions almost instantaneously and to provide a closely controlled sine-wave out put from a 20-30V d.c. input, coupled with low maintenance requirements. Among several firms showing new versions were Rotax Ltd with a 300VA inverter using silicon-controlled rectifiers to produce a single-phase 115V 400 cyc/sec output. Weighing 151b. this unit is estimated to be some 25 per cent lighter than a rotary inverter for similar duties, and has outstanding ability for main taining wave form. The new 700VA single-phase inverter demon strated by the Plessey Co (UK) Ltd is to be used to power a wind screen de-icing system for an aircraft under development in India. The de Havilland Aircraft Co Ltd have developed a range of static- inverters, from 100VA to lkVA single-phase, and from 250VA to 3.5kVA three-phase. Four of these were on view, three for the first time: 100VA and 400VA single-phase units (the latter on BE A Argosies and Tridents) and 750VA and 1.5kVA three-phase units destined for the Belfast. These larger units incorporate silicon- controlled rectifiers. One of the advantages claimed by de Havilland for the three-phase range is a high overload facility for sub-circuit fuse-blowing in short-circuit conditions. Equipment installed in new transport aircraft formed one of the overriding themes of this year's static show. AEI Ltd, for example, showed schematically the layout of the components of one of the three channels of the Trident electrical system, which is claimed to be the first civil all-British constant-frequency aircraft a.c. power system. The system uses brushless, self-excited a.c. generators driven through H. M. Hobson Ltd constant-speed drives. The control equipment makes extensive use of static and semiconductor devices to give the maximum reliability in service. The magnetic-amplifier control unit contains no moving parts, and with the use of silicon rectifiers and a "potting" technique is completely free from adverse effects introduced by changes of
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