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Aviation History
1935
1935 - 0574.PDF
282 FLIGHT. MARCH 14, 1^. FLYING-BOATS of 134 TONS? AFASCINATING glimpse of the future was af forded members of the North-East Coast Institution of Shipbuilders and Engineers in the paper read to them last Friday by Mr. Arthur Gouge, whose sub ject was " Flying-boats and their Possible Development." Mr. Gouge is, as most Flight readers will know, general manager of Short Brothers, and, as he was chief designer of that firm before becoming general manager, his views obviously carry a very great deal of weight, backed as they are by many years of experi ence in the design and construction of flying-boats. Thus, when Mr. Gouge speaks of the future, one may be sure that the opinions he expresses were formed on solid facts and not en problematical surmises and assumptions. After tracing briefly the development of flying-boats since their inception—for which, incidentally, he gave full credit to the Curtiss Company of America—the lecturer discussed the water characteristics of present-da v hulls, and showed typical curves of resistance, attitude and the effect of ap plied moments for a flying-boat of about 40,000 lb. weight. Engines were also dealt with briefly, and Mr. Gouge gave his reasons for believing that the petrol engine will hold its own against the compression-ignition engine for some time to come; Turning his attention to the subject of what we may reasonably expect in the not too distant future, Mr. Gouge examined the main factors which affect flying-boat size. As this part of his paper was of unusual interest, we give it in full. A Practical Qiant At the present moment it should be possible to start the design and construction of a flying-boat to be produced, say, in the year 1937 or 1938 weighing approximately 220,000 lb. This prediction is, of course, based entirely on what has been done in the past, and while this method of prediction is very sound as regards the total all-up weight, it gives no indication whatever how this total weight is made up, and it is con ceivable that while you can build a flying-boat weighing 220,000 lb., or even more, it is possible that all the weight would be expended in building the hull, wings, etc., and in installing the engines, leaving nothing at all for load or range. It is necessary, therefore, before assuming that the larger boat predicted from the curve of growth is a boat of practical application and not just a theoretical conception, that we attempt to analyse the component parts with particular regard to weight. Considering first the question of the hull for boats of vary ing all-up weight, it is easily proved that the beam of a fly ing-boat hull vaties directly as the cube root of the total weight. Also, within small errors the fore-body and after body planing surfaces vary in the same manner. If, there fore, one can assume that the depth of the hull and the top side width of the hull are proportional to- the beam (this assumption is, in general, a good approximation, but not necessarily strictly true), the surface areas of similar boats are No Size Limit in Sight : Struc ture Weight can be Kept Down : A Well-known Designer's Signifi cant Views proportional to the ratio of the total weights to the two-thirds power. The weights of simi lar flying-boat hulls will there fore, be proportional to the ratio of total weights to the two-thirds power multiplied by some quantity which repre- sents the skin thickness of the hull, when the skin thickness is taken to include any frames or stiffeners. If one now considers the stresses set up in the skin of the hull due to, say, a special landing case, that is, hitting the water surface at a fine angle, it is easy to arrive at a variation of this quantity which I have called skin thickness for similar hulls. This thickness is found to vary in the ratio of total weight to the two-thirds power; therefore, around the centre section of the hull the weight of the hull will vary as the ratio of the total weights to the four-thirds. This is always assuming that no greater stresses can be developed in the thick-skinned large hull than on the thin-skinned small hull. Actually, of course, a greater skin stress can be developed with the thicker plates; therefore, although theoretical considerations lead to the conclusion that the weight of centre sections of flying-boat hulls varies as the all-up weight to the four-thirds, the actual increase in weight will be less than indicated here for the reason mentioned above. Component Weights For the purposes of this Paper I propose to assume that it is required to design a flying-boat of, say, 300,000 lb. all-up weight, and the remainder of the Paper will be an attempl to forecast the weights of the various components and what could be reasonably expected from such a boat in the way of performance and pay load. For the hull there is no doubt that the centre portion will increase in weight slightly less than that given by the ratio of the total weights to the four- thirds power, and this ratio will hold over about half the area of a flying-boat hull surface. The other half of the surface area will probably not need increasing in thickness over the thicknesses existing on present-size hulls where the skin thick nesses are determined more from practical considerations than by any calculated stresses. If the above assumption can be considered reasonable, and I am of the opinion that it is, then it can easily be seen that the weight of the hull tor a flying-boat of 300,000 lb. weight will be in the neighbournooa of 134 per cent, of the total all-up weight, as compared witn about 12 per cent, for a boat weighing 60,000 lb. One of the graphs shows the percentage weight ol a ra hull plotted against the all-up weight for boats of wilicn have personal knowledge, and while these ranges and weign^ are limited to an all-up weight of 68,000 lb., of the boats opinion that the extrapolation of this curve to heavier is not an under-estimation of the hull weight. The- » I> of existing flying-boat hulls and the extrapolation tne are based on the use of aluminium alloy material throug ^ the construction of the hull, both for skin sheeting ai structural members. This material has a 0.1 per• cea • ^^ stress of 15 tons/sq. in. A<- the present time it is V ~ fl[ to obtain aluminium alloy with a 0.1 per cent. Pr00tjes equal r7 tons per sq in. having corrosion-resisting Pr0Pe.. sn0ws to that of the lower strength material. The dotted ua ^ the estimated weights of large flving-boat hulls us, WING I WING 2. WINS 3. WING 4. Plan form of wings for various wing loadings All wings have a 20 per cent, camber at the root and a 10 per at the tip.
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