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Aviation History
1939
1939 - 1030.PDF
Arm 6, 1939 FLIGHT. 357 This photograph of an early Pegasus installation gives point to Mr. Nixon's observation on the sudden growth of accessory-drive complication a few years ago. hydraulics, first and foremost was the question of weight. The electric motor was heavy as compared with the hydraulic jack. The jack was dependent upon the amount of energy per stroke it was capable of handling and not upon the horse-power developed. Thus, a small jack of 1 in. bore by a 4m. stroke operating during part of its stroke at 2.2 h.p. (which was the horse-power developed by the Lockheed Mk. IV. hydraulic pump at 1,4001b./sq. in. at 1,300 r.p.m.) would weigh about 1.51b. whereas an electric motor with the same power would probably weigh I5lb. Where more or less continuous operation was required there was still a saving in favour of the hydraulic unit, since light and efficient hydraulic motors were now in existence. The lecturer next enlarged on some other advantages of hydraulic units, including their facilities for instantaneous stopping and starting, variation of gear ratio by modifying the bore and stroke of the jack and ease of limiting'the ANCILLARY POWER SERVICES M ORE than once in recent years Flight has criticised the ever-increasing complexity, cost and weight of ancillary power services in aircraft, and military aircraft particularly. It is a problem that would most certainly become a grave one in the event of war, for the intensive "plumbing" that is now customary might seriously hamper production. Aircraft and engine designers are thinking along the same lines, and last Thursday, in a joint paper before the Royal Aeronautical Society, two of them presented some ex tremely pertinent criticisms and suggestions. Mr. R. H. Chaplin, B.Sc, A.F.R.Ae.S. (assistant chief designer in the Hawker organisation), and Mr. F. Nixon, B.Sc, A.F.R.Ae.S., who for the past ten years has been engaged on engine development and design with the Bristol Company, put forward ideas, each from his own particular angle, and "their opinions suffered no loss of value by the fact that they were occasionally in conflict. As was to be expected, the subsequent discussion (which we hope to summarise in next week's issue) was an animated one. The following is a precis of the paper. Mr. Chaplin started by mentioning what might be called the earliest aircraft power service, the electrical system which derived its power from a windmill-driven generator. With the demand for more power and aerodynamically cleaner aircraft the windmill gave place to the engine- driven generator. The next step came with the introduc tion of pneumatic brakes, which were first fed from an air storage bottle. Ultimately an engine-driven compressor was added to keep the air bottle charged. More recent was the development of retractable under carriages and flaps, for which hydraulics met with imme diate and fairly general adoption and for which an engine- driven hydraulic pump was practically essential. Lastly, there was the modern tendency to use a vacuum pump to overcome the icing and other difficulties associated with the use of Venturis for driving instruments. Thus we had four main services, namely, electricity, compressed air, hydraulics and vacuum. These four ser vices were further complicated by the fact that each had its variations in matter of pressure. The first question was, "Are all these services essen tial?" The answer was, "They are not." Which ones could be eliminated? After outlining primary requirements of a comprehensive power service, Mr. Chaplin showed that the electrical service must obviously be retained and went on to argue that only one of the remaining three systems (compressed air, hydraulics and vacuum) need be retained. This was hydraulics and, using it together with electricity, they c °i'ld satisfactorily perform all necessary tasks. As regards reasons for supplementing electricity with Problems of Reducing the Present Complexity of Hydraulic, Pneumatic and Electric Equipment in Aircraft : R.Ae.S. Paper by R. H. Chaplin and F. Nixon force supplied to a mechanism by the provision of blow- off valves. Mr. Chaplin proceeded to question whether vacuum and compressed-air services could not be satisfactorily replaced by electricity and hydraulics. It was not im possible, he said, to obtain satisfactory results with elec trically driven gyros and there was at least one automatic pilot, the French Alkan, which was so operated. Passing to the third question—whether there was suffi cient justification to warrant the elimination of compressed air and vacuum, Mr. Chaplin said: — '' Some simplification and reduction in the number of services is essential for cheapness, standardisation and pro duction and it appears to me that the claims of vacuum and compressed air for retention are very small. From the aircraft designer's point of view it must be an advantage to effect so great a reduction in the number of types of services. Pipe systems, with their multiplicity of materials, gauges, couplings, valves, etc., would be considerably reduced, thus avoiding the necessity for specialisation in so many directions in a design staff. The stores and works problems must also be inevitably eased. Again, from the aspect of maintenance, this elimination of two services cannot fail to be an advantage both with regard to training and operation of personnel. Perhaps, however, as great a saving would be amongst the engine people and those in official authority whose business it is to approve the various accessories associated with these two apparently non essential services. "Although by no means a universal opinion, I find many people feel that for such-and-such an application the so- and-so service is ideal and that it will not be possible to design a mechanism so efficient as the present type if a particular form of power service is eliminated. This, I feel, is merely adopting a defeatist outlook, making any change from existing standards impossible. A certain lapse of time is, of course, necessary to develop new designs, but I do not think we should lose sight of the fact that small sacrifices, with regard to virtues of the old design, may be worth while if some simplification is achieved."
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