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Aviation History
1951
1951 - 1275.PDF
12 FLIGHT, 6 July 1951 CONCERNING FLYING-BOATS . . . and water clearance considerations, had directed attention to the chassis, which, due to its length, had become a resistance-making component which could not be disregarded. Whilst some designers preferred to retain the braced type of chassis, others (of which Saunders-Roe was believed to be the first) had investigated and introduced a cantilever arrangement. The Saunders-Roe assembly (shown in Fig. 1) was designed to absorb lateral water loads by flexibility of the twin taper-gauge struts. This type of float suspension was applied to the Lerwick and Shetland, and, in addition to the general cleanness of the installation, the flexibility built into the chassis was found to be a marked improvement from the failure aspect; on at least one occasion in severe sea conditions the Lerwick had demonstrated the relative efficiency in no uncertain manner. The ultimate in resistance-reduction for a fixed float installation had probably been reached with this canti- lever arrangement, and retraction must be used if further aero- dynamic efficiency was required. Retracting float arrangements, like the landplane undercarriage, were invariably dictated by considerations of wing structure, stowage space or positional requirements. In Figs. 2, 3 and 4 various methods of float retraction were shown, Fig. 2 being a layout which had been intended for the Princess. In flight this arrangement would have presented the minimum of resistance. However, during the early stages of the Princess design re-assess- ment of the wing structure/float combination had indicated that in this particular application a weight penalty would have to be tolerated, and it was found that the wing geometry was being dictated by the float retraction requirements. Further investiga- tions and wind tunnel tests had shown that, by placing the float at the wing tip, an increase in wing efficiency was obtained which almost balanced the additional resistance of the exposed float. It had also been found that an efficient wing structure design could be achieved with the revised arrangement resulting in considerable weight saving. Fig. 3 showed the tip installation which had now been adopted for the Princess and reproduced for the Duchess project. Whilst the fully retracting float layout shown in Fig. 2 had been abandoned on the Princess, its possibilities might one day be further explored. A Saunders Patent of 1927 The tip arrangement was not a new approach to the problem, and it was interesting to record that the company was intimately concerned with the basic idea and a patent in the name of S. E. Saunders had been filed in 1927. This layout (Fig. 4) had been intended for the floats on a high-speed seaplane (designed for the Schneider Trophy contest). A float of excellent aerodynamic form was attached to the wing tip, the chassis being formed by a complete section of the wing. Apparently wing area and the hydro- dynamic performance of the floats had not been considered of the greatest importance ! A wing-tip float arrangement had also been adopted by Consolidated for their Catalina and Coronado series of flying-boats, and the robust form of chassis, unrestricted by aerodynamic considerations, had proved remarkably successful. Fig. 5 illustrated a fully retracting installation which had been used by Dornier on the D026. This arrangement had eliminated all resistance in flight, but had necessitated rather large wing "cutouts" and weight expenditure. A layout which had been suggested by Blohm and Voss was shown in Fig. 6, and it would be seen that the structural difficulties associated with this scheme were even more pronounced than with the Dornier layout. Fairchild had adopted a modification of the above scheme for an amphibian, and, using a symmetrical arrangement, had permitted half the float to project below the wing surface during flight. An installation which seemed to fall between the partial and fully retracting type was shown in Fig. 7 and was used on the Potez-CA.M.S.160 in 1938. In this layout the vertical retraction had been so arranged that the float had formed the rear fairing of the engine nacelle during flight; thus, the auxiliary buoyancy, required only when waterborne, had been put to good use in the air. This layout had required the floats to be positioned, when on the water, in close proximity to the airscrews, and it was suspecte"d that considerable spray interference had occurred. A method of retraction whereby the chassis and hydrodynamic portion of the float only was "buried" was shown in Fig. 8. This "inverted" arrangement was used for the Saunders-Roe S.R./A.i fighter, and although the thin wing precluded complete retraction in this project, the wing construction permitted the introduction of cutouts without excessive weight expenditure. A tip float installation had been investigated, but the possibility of fitting external droppable fuel tanks had suggested that the inboard arrangement should be used. It was thought that the foregoing covered the more interesting and practicable installations of the float type. Although the float and its varied methods of application had predominated through the years of flying-boat design, there were instances where designers had made an effort to meet the require- ments in an entirely different way, and had attempted to utilize the auxiliary flotation, necessary for waterborne conditions, when the aircraft was airborne. An early attempt in this direction had been made in the English Electric Ayr flying-boat produced in i925- The layout of this aircraft, a biplane configuration with a heavily dihedraled lower wing of fairly highly tapered plan-form, was shown in Fig. 9. The relatively thick wing roots had been watertight and so positioned with respect to the waterline that sufficient auxiliary flotation had been provided for static stability. However, the directional stability of the hull had been below accepted standards during the take-off run; considerable wallowing had occurred, and it had been found that the positioning of the wing roots relative to the waterline was a critical factor in the arrangement, particularly under dynamic conditions. Reference to a Dornier patent specification filed in 1917 showed a layout similar to that of Fig. 9 applied to a triplane, the lower wing being used to provide the necessary flotation as on the Ayr. The idea of designing the waterborne stability installation so that it performed some useful function in flight had apparently been very much in Dornier's mind, for practically all of his flying-boats, ranging from the small Libelle to the Do X, had had aerodynamic- ally designed auxiliary flotation. Dornier's preference for the high-wing monoplane had enabled him to utilize a small span wing, usually of constant section, to obtain lateral stability without introducing excessive aerodynamic interference effects. This truncated wing, or "sponson," as it was termed, was illustrated in Fig. 10. It had been highly effective in providing lateral stability on the water : in flight it had contributed some lift. It had provided fuel tankage, and had formed a useful platform for passenger access to the aircraft. A similar arrangement had been used by Martin and Boeing on their transport flying-boats of 1935 and 1937, and in the original application a highly tapered plan form and thickness had been used. The reduction of buoyancy at the outboard sections had been too drastic, however, and it had been necessary, on the Boeing aircraft in particular, to introduce additional buoyancy at the tips to obtain the required stability and to prevent severe wallowing at low water speeds. It had been mentioned that the positioning of this type of stabilizer with respect to the water was critical. In 1936, Saunders- Roe had equipped a Cloud flying-boat with a series of sponson configurations in order to carry out research on this aspect, provision being made for vertical, horizontal and incidence adjustment. From these tests the arrangement for a large military flying-boat had been determined, and the aircraft had been equipped with sponsons of tapered section and with a large sweep- back angle at the leading edge. The layout had proved to be satisfactory and no trouble had been experienced with the fuel tankage, which was an integral part of the sponsons. The only other use of this layout in Britain had been on the Supermarine Air Yacht in 1929. Whilst the sponson method for lateral stability had some good features, the requirements of high speed and weight reduction had shown that the arrangement was inefficient and, except for amphibian applications, where the sponson might provide a useful wheel stowage, it had probably had its day. The Italian Savoia Company had obtained lateral stability by an entirely different method in the Savoia-Marchetti S.55 flying- boat, and had used a twin-hulled arrangement which had provided inherent stability without the need for additional flotation. This layout obviously had a higher overall aerodynamic resistance than the single-hull type, but, from the accommodation and water handling aspects, it was an interesting layout and might yet have a place for certain duties. It would be remembered that a large formation of these aircraft had flown the Atlantic in 1933. MAINTENANCE AND MYSTICISM "Round the Bend," by Nevil Shute. Wm. Heinemann and Co., Ltd., 99 Great Russell Street, London, W.C.I. Price 12s. 6d. "VfEVIL SHUTE'S new novel unquestionably starts well with J-^ the author at his down-to-earth, readable best. There follows a description of the development of an air-charter concern centred upon Bahrein and of many of the flights undertaken. At times there is a suggestion of the travel guide, but it is nevertheless well- worth reading, and carries the story along, particularly for anyone who shares the hero's enthusiasm for flying, and even without the aid of the additional homely narrative or the mystic religious thread which develops. Readers with no particular interest in aviation, one feels, might find some of the chapters dull. The central figure, Tom Cutter, first introduced as an airstruck, working-class youth, is a quite likely type, but his fellow- enthusiast—an Asiatic with a "wonderful smile"—named Connie Shaklin (or Shak Lin), is a most improbable individual—a chief ground-engineer-cum-prophet, in fact—who is reluctant to take positive form in the reader's mind. Under his guidance aircraft serviceability seems to be 100 per cent, and languages, race and religions become one.
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