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Aviation History
1949
1949 - 1868.PDF
634 IN SEARCH of PROOF Research and Test Facilities at the English Electric Aircraft Division UNTIL the Canberra, so far our only jet bomber, burstupon the aeronautical scene a few months ago,relatively few people had much knowledge of the air- craft activities of the English Electric Co., Ltd. As noted in our May 26th issue, however, the aviation history of the company extends back to pre-1914-18 war years, and although from 1926 until 1938 the aviation department was closed, aeronautical work was resumed with the recent war, and Hampdens, Halifaxes and Vampires in their scores and hundreds were produced in the Preston factories of the company. Thus the idea that a superlative new war machine is the product of a newcomer to the aircraft woria—a sugges- tion more than once mooted—is seen to be quite erroneous. Nevertheleless, the decision of the company to undertake the design and manufacture of their own aircraft rather than those of other manufacturers meant that the whole fabric of a design and technical staff had to be established. This was built up under the chief designer, Mr. W. E. W. Petter, and his chief production engineer, Mr. H. C. Harri- son, together with the chief stressman, Mr. F. W. Page, and the chief aerodynamicist, Mr. D. L. Ellis. As an adjunct to the office work, it was foreseen that test and development equipment would be desirable, and (one of the advantages of having available the enormous resources of such a firm as English Electric) work on the design and construction of the requisite equipment was put in hand. At the Warton airfield establishment of the company— halfway between St. Anne's-on-Sea and Preston—three tunnels have been constructed; (i) a 9ft by 7ft low-speed wind tunnel, (ii) a jet-induced-flow high-speed tunnel, and (iii) a low-speed water tunnel. The gft by 7ft tunnel has been working since May last year, the jet tunnel since July last year, whilst the water tunnel was finished in March this year. It is both noteworthy and significant that the design and construction of these several pieces of equip- ment have been executed almost entirely by the company, the sundry small exceptions being such specialized com- ponents as, for example, the balance steelyards. In addi- tion to the three tunnels, a structural test frame has also been built at Warton and this, too, is of home design and construction ; it is by some measure the largest test frame possessed by any aircraft manufacturer in this country, being, in fact, somewhat larger than the "Abbey," and only a little smaller than the "Cathedral " test frames at the Royal Aircraft Establishment. It is generally agreed that the most useful all-round wind tunnel is one having a working section of between 50 and 100 sq ft, and a flow speed of between 200 and 300 ft/sec, in that Reynolds numbers high enough for reliable stability measurements can be attained in conjunction with models large enough for accuracy, yet of a convenient size to handle. In the basic design of the 9ft by 7ft tunnel the aim was to achieve a high standard of steadiness and evenness of flow with moderately low turbulence in a rea- sonable overall size. The salient points of design are: a contraction ratio of 5 :1; a maximum diffuser angle in any plane of 5 deg ; no expansion in first and second corners; 10 per cent expansion and Salter-type vanes in third and fourth corners; a settling length of 20ft; a constant net area through the fan section; a working-section length of 18ft; and provision for screens in the settling length. With no screens in place (there is no honeycomb) the maximum speed at 250 h.p. was just 200 ft/sec. One screen, of 30 mesh, 31 s.w.g. stainless steel, was then fitted, FLIGHT, 17 November 1949 J The 9ft by 7ft low-speed tunnel, the characteristics of which aim at steady, even flow with low turbulence. F, speed control ; G, working platform ;A, working-section with model onsix-component distant-recording auto- matic-balance ; 6, straightening vanes and nacelle Supports ; C, four-blade fan ; D, 250 h.p. driving motor ; E, concrete independent mounting for fan section ; H, independently mounted working section ; , J, balance recording console ; K, gauze screens ; L, cascade (at each corner). and this is the condition in which the tunnel is now run- ning, as it has not been found necessary to fit the second screen. The speed is now 187 ft/sec, and the velocity distribution varies less than ±0.3 per cent. The design of a satisfactory wind-tunnel drive sets a number of unusual problems for the electrical engineer, because an exceptionally high standard of steadiness and stability may be required over a speed range of up to 10:1, which corresponds to a power range of 1,000:1. The motor for the 9ft by 7ft tunnel has a normal rating of 200 h.p. with a two-hour overload of 250 h.p., and is supplied from a 350 h.p. synchronous motor-generator set. The arrange- ment adopted for supplying the generator field was deter- mined by the requirements of automatic control from a manometer operated by the tunnel pressure and having an accuracy of 0.15 per cent of top speed. A fully electronic system was designed to meet this requirement and was eventually developed to be sensitive to less than 0.1 per cent. Self-balancing steelyards are used in the six-component balance mechanism, the usual jockey weights being The low-speed water-turmel, minus viewing platform, showing glass-walled working-section above the circular-section screw- trunk in the return circuit. B 2
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