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Aviation History
1953
1953 - 0485.PDF
17 April 1953 481 an engine (or anything else, for that matter), the question of personnel was of the first importance; and the exercise of benevolent control by a minimum of Ministry staff was possible only if experienced individuals were available. Practically all the technical and scientific staff in the aircraft and engine directorates of the M.o.S. were civil servants, although there was a sprinkling of Service officers heading some of the directorates and sections. There were Royal Navy and R.A.F. officers on the staff, whose duties were to supplement the normal contacts with the Services and to keep in touch with their respective Services regarding behaviour of the equipment in the field. This group also included a U.S.A.F. officer, who was attached to the directorate on the exchange basis now operating between the two countries. A. Cdre. Banks favoured a hard core and a high proportion of civilian technical staff in these directorates, since their individual and aggregate experience was considerable; and they were able to guide and advise any officer personnel who might head a directorate from time to time, but whose tour of duty (usually three years) was hardly sufficient, without some previous background of experience, to permit the exercise of balanced judgment without such advice. He did not believe in putting civil servants in uniform and, therefore, rendering them subject or sub servient to military law and discipline, except for their own protection in a theatre of war. Gas Turbine Development.—Under the heading of "Engine Development" A. Cdre. Banks gave it as his opinion that there were only a few firms in the world today who really understood the art of developing and building a successful aviation engine and who could carry the whole effort through effectively and expeditiously. While the aviation gas turbine was taking the place of the piston engine for most, if not all, important aircraft applications, and responded more readily than the latter to theoretical treatment in the design stages and prior to prototype manufacture, it was not until it got into the hands of the legitimate aviation-engine manufacturer that it really progressed. In fact, it was due to the accumulated experience of the aviation piston engine in the last 30 years that the gas turbine had progressed so rapidly. The industrial engineering firms had been the first to be introduced to the aviation gas turbine because they alone had had any sort of turbine experience, which was thought (wrongly) to be needed for this engine's successful future development. The war, and their own prejudices, prevented or delayed the acceptance of this new prime mover by the legitimate aviation-engine builders. The industrial firms did, however, make one or two good attempts to design and build a workable turbojet engine. These concerns, with many years' experience in the manufacture of massive steam-turbines and electrical generating plant for public utility purposes and for ship propulsion, could hardly have been expected, almost overnight, to get down to such a lightweight piece of mechanism as the aviation engine. Since little or no restriction was placed upon the weight of ground plant, it was not necessary to obtain the absolute maxi mum output or to reduce scantlings. Indeed, it would have been quite uneconomic to to so. These conditions had always governed and enforced conservative practices in the industrial field, and it was surprising that any progress was made at all with the aviation gas turbine by the industrial engine firms. But, in the lecturer's opinion, it would take another ten years for those industrial organizations remaining in this very specialized business to master the design technique and development of the aviation engine— and then only if they were willing to learn by bitter experience. And where would the successful aviation engine firms have progressed by that time ? He had underlined the word "successful" since some of the legitimates in the aviation industry had "fallen flat on their faces" and nearly to ruin, due to lack of a sound engineering policy and good technical control; or as the result of being overridden by bankers and accountants, who came in at the top due to previous bad management, and then tried to dictate technical policy. The Time Factor.—A. Cdre. Banks continued by saying that con trary to optimistic prognostications of six or eight years ago, when it was thought that the turbojet could be designed, built and type-tested within two years, the modern axial engine took about the same time to brine to the type-test stage as did the larger and more complex piston engine. But the gas turbine, whatever its type, got through the flight-test stages and into actual service much more quickly than the piston engine— principally due to the considerably reduced mechanical and installational problems and the almost complete lack of cooling requirements. The day-to-day inspection and maintenance of the gas turbine in military and in airline service absorbed far fewer man-hours than did piston engine inspection. On the subject of engines for civil use, the Air Commodore said that since the last-war military requirement had not always included the par ticular engine types wanted for airline operation, and in certain cases it had been necessary to design and build engines (propeller turbines) specifically for civil purposes. This had meant the introduction of engines having no previous flight background, the accumulation of which then fell upon the aircraft manufacturer and the airline operator. Of the rapidity with which gas turbines could be put into regular flight service, the lecturer said that in only nine months of scheduled airline operation, the Ghost engines in the Comet had shown a failure rate of 0.49 per thousand hours flying, which was superior to that (0.60) of two well-tried air-cooled radial piston engines. It was also of interest that, on January 22nd last, de Havilland's chief test pilot completed 1,000 hours of test flying in the Comet without any serious mishap. The time factor in engine development, assuming an axial turbojet of 8,000 to 10,000 lb thrust, was estimated as follows: design about one year; building of first prototype a further twelve or more months; during the following three years 8,000 to 10,000 hours of engine bench running and 2,000 hours of flight testing; 3,000 to 4,000 engine hours bench running was a good yearly figure in the fourth and fifth years. The lecturer said he had thought that with great accumulated knowledge of the axial compressor it would have been possible to see a reduction in this four- or five-year period, but there was still a number of problems to be mastered, and the same old troubles of compressor stall, blade vibration and flutter remained. Designers were, however, in a better position to overcome these troubles more quickly than was the case a few years ago. Skilled Apprentices and Design Staff.—A. Cdre. Banks' next remarks will be of particular interest to Flight readers in view of recent articles on skilled manpower, opportunities and pay in the aircraft industry. He said that, in his opinion, there was one important difference between British and American practice as affecting the rapidity of proto type engine manufacture. Britain still had some good trade or craft apprentice schemes in her engine firms which produced skilled workmen (fitters and machinists), with the result that experimental engines could be built relatively quickly and with the minimum of jigging and tooling. Admittedly, we were at present short of skilled labour. This was due to the fact that the state of our national economy was such that there had been an almost barometric variation in the orders given to the aircraft industry, according to the state of world politics; and labour, particularly, was chary of an industry which only appeared to prosper in time of war or national emergency, and would rather remain in the more stable industries whose operations were relatively steady or less subject to violent change. There were also insufficient highly qualified men coming from the British universities and technical colleges, and already this deficiency was being felt. We did, however, appear to have a more stable condition in our design offices. He understood that, in the United States, the young man did not generally take kindly to the idea of spending some years engaged upon engineering design and could earn better promotion and money on the production floor or in the field. In Britain a designer was thought to have a quite promising pro fessional career ahead of him; and he could eventually become chief engineer of his firm, particularly if he had had previous experience in other departments before going to the design office. In any case, a young man should go through the plant (the machine shops, the experimental departments and, also, the servicing departments) before entering the design office, otherwise he was likely to perpetrate "quite impossible" designs. Later the lecturer repeated that it was the man that mattered rather than the machine. To get experienced aviation engine designers and development engineers it was necessary to pay them well, because one was buying "experience that is not in any book." "British Engines can be Produced."—A. Cdre. Banks next touched on a matter which needed airing before an American technical audience. He said that recent articles in the American Press had stated that the British-designed engines were difficult to produce in quantity. This was certainly not the case when considered in terms of production costs. All aviation engines were relatively difficult to produce, but there were none that he knew of which could not be produced in quantity with the facilities possessed in the United States, coupled with the great ability of its production specialists. When considering a licensed engine it was very important not to make any change from the original purely to facilitate production. In fact, a licensed engine should be a "Chinese copy" of the original, both in regard to materials and manufacture. Although the particular engine in question had already passed its type test it was still m the early develop ment stage and therefore vulnerable to engineering and material changes. It was quite natural, however, to acquire the licence in the early develop ment stage in order to ensure the most up-to-date product. It needed great caution and restraint on the part of the licensee firm in making engineering change, particularly for production reasons, where production might just be starting or already in full spate. If there were insufficient running hours behind the design change or modification, subsequent failure in production engines would lead to a chaotic state when dealing with large production rates common in the U.S. A. Cdre. Banks added that the engine he had in mind had less critical material in its make-up than existing engines, and was therefore all the more acceptable when considering wartime production. Cost: Axial versus Centrifugal.—A. Cdre. Banks next commented on the relative cost of centrifugal and axial engines. He said that the axials had practically all the advantages, but present experience of relatively small production quantities suggested the cost would be twice that of the centrifugal in terms of pounds sterling per pound weight. If, however, the centrifugal were designed for the same pressure ratio as some of the present axials, then it would probably cost more than the latter on the same costing basis. Limited Testing Facilities.—Before making his concluding remarks the lecturer referred to testing and calibration facilities. He said that, due to limited financial sources, individual British firms had not been able to provide all the facilities considered necessary for the performance- testing and calibration of turbojet engines, particularly at simulated altitude conditions. But by improvisation it had been possible to obtain surprisingly close agreement between component tests and performance of the full-scale engine in the air. He instanced the insufficiency of power for making compressor tests at full output and, as a result, the testing and calibration of compressors of all large engines with throttled air inlets. Turbine design had been proved and improved by running part-scale wheels with light-alloy blades on cold air; the results had read across very satisfactorily to the full-scale components. Cold-air testing permitted the use of light-alloy blades which could be easily and readily manufactured when a new blade form was required. Full-scale engines had been instrumented, strain-gauged and cali brated in fighter aircraft and two-way radio communication between the pilot and technical personnel on the ground had been used directly to report flight readings and to permit engine conditions to be altered and controlled as necessary. In this way the altitude characteristics of the compressor and other components had been confirmed. So far it had been possible to get by, and the absolute need for an altitude test-chamber for full-scale engine tests had not yet been felt. But while there were already available some limited testing facilities at the N.G.T.E., it was realized that additional and elaborate equipment must eventually be provided to meet engine altitude requirements for military aircraft—which were steadily increasing. Though the flying
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