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Aviation History
1934
1934 - 1255.PDF
NOVEMBER 22, 1934. FLIGHT. 1259 THE LONG-RANGE FLYING BOAT Its Development and Characteristics : A Precis of a Lecture Delivered by Igor Sikorsky LECTURING before the Royal Aeronautical Society lastThursday, Mr. Igor Sikorsky, the designer of the—* S.42, explained at the outset how it had become obvious to him that the logical step needed to open up large areas for air transportation was an aeroplane capable of operating from land or water. He showed, how- ever, that such a machine was very difficult to design, as compared with the normal seaplane or landplane. The amphibian must take care of the extra weight and parasitic resistance resultant upon the attempt to combine the characteristics of both the landplane and the seaplane. It was, therefore, necessary to make use not only of highly efficient engines but also of equally efficient wings and con- trol surfaces, so that a wide margin of increased perform- ance would be obtained in order to compensate for the extra weight and resistance of the amphibian itself. By combining the requirements of Pan American Air- ways and those of people wishing to explore the hitherto inaccessible regions of Central and South America and Africa, the S.38 Sikorsky amphibian was evolved. The increasing business of P.A.A., however, outgrew the capa- city of their S.38S, and the three "Clipper" (S.40) boats were the outcome of their requests. From the very first the S.40 was a success, and, while it seemed to be a logical jump from the S.38, the Sikorsky staff had already started research with a view to developing a flying boat which would permit an even greater range and higher cruising speed than the S.40. It was when the first "Flying Clipper '' made its cruise from Miami to Colombia that Mr. Sikorsky, in conference with Col. Charles A. Lindbergh, technical adviser to Pan American Airways, laid down the requirements for the new type. The Evolution 0/ the S.42 In the evolution of this, the S.42, as it was to be known, two factors which helped to a great extent were the pro- duction of the new Pratt and Whitney 700 h.p. geared " Hornet" engines and of the Hamilton controllable pitch airscrew. The design work on this boat, which took into account everything like cost and operation maintenance, durability, and passenger comfort, was spread over another two years, and the rigid weight control resulted in the use- ful load of the finished boat being as high as 48 per cent, of the gross weight. In the S.42 the external outrigger type of bracing was not used, but the tail units were attached directly to the hull, while the one-piece wing, with heavily tapered tips, was also mounted directly on the top of the hull by means of a superstructure. Mr. Sikorsky, having got thus far, then went on with a very detailed description of this boat and its construction, but as these have already been given in Flight, it is un- necessary to repeat them here. It is as well, however, to recall one or two figures which show the great increase in efficiency achieved in the S.42 as compared with the S.40. The older machine, for example, with a gross weight of 34,000 lb and fuel for 1,000 miles range, had a payload of only 3,200 lb., while the S.42, under the same conditions, Britain's Municipal Aerodromes Twenty-two towns now have licensed aerodromes, and eight ™ Save, iu addition, purchased sites. When the number of towns which have merely " displayed interest in aerodromes " is con- this is not a very brilliant total, but the few are to .congratulated. I' is not reasonable to suppose that any out by iu. -,- will nr.Vnally pay for itself during the next few made quite cleat^o t authorities should see the necessity for structural defec^f Aiturc. where things have been definitely moving has a payload of 8,363 lb. Cruising speed at 1,000 ft. was 115 m.p.h. for the S.40, and is 157 m.p.h. for the S.42 ; and, as one would expect, the wing loading has increased from 19.5 lb. to 28.58 lb. per sq. ft. In this connection, however, it should be noted that the landing speed has, by means of flaps, been kept down to the same figure as that of the earlier boat, namely, 65 m.p.h. From an economical point of view, a comparison between the two is equally favourable to the S.42. Using the same h.p., with a fuel consumption per hour, for the S.42, of 144 galls., and for the S.40 of 140 galls., the S.40 does 0.82 miles per gallon and 1.35 ton-miles per gallon. The S.42, however, docs 1.0 miles per gallon, and has the greatly increased figure of 4.25 ton-miles per gallon. If the basis taken is that of ton-miles per flying hour, as is usual in the consideration of maintenance and operating costs, then the figures for the S.40 and S.42 are 169.75 and 616.25 ton- miles per hour respectively. Advantages of High Wing-loading r Referring to the parasitic resistance, Mr. Sikorsky said that the total resistance under this head of the S.42 flying at 160 m.p.h. is only 3,620 lb. He explained that much consideration had been given to the cantilever wing, but it was felt that the resistance would be increased, owing to the greater thickness of the centre section of the wing, and also that the structural weight of the cantilever wing would be greater. Another reason put forward for having a machine with a high wing loading was that good airworthi- ness in stormy weather was considered essential, as the boat was designed for high cruising speed and operation over long trans-oceanic routes, and it was evident that vertical air gusts become more violent in their effect as the wing loading decreases. This contention was more than proved in flight trials in very rough weather. The disadvantages of the heavy wing loading were overcome by the specially designed wing flap, which • produces an increase in lift of about 40 per cent. Mr. Sikorsky feels that the lessons learnt from building this boat allow him to say with certainty that very much larger boats, weighing hundreds of tons, are not only pos- sible, but practical, and he is confident that flying boats weighing 100,000 1b. or more, capable of non-stop ocean flights, and cruising at between 150 to 200 m.p.h., can be designed and be ready for service within two and a half to three years. He does not feel the size of the earth warrants greater speed than this, but air transportation will benefit more if designers give more attention to increasing passen- ger comfort and to ways and means of lowering transporta tion costs rather than to obtaining higher operational cruising speeds. Turning for a moment, in conclusion, to the question of altitude of flight, Mr. Sikorsky thought that the increase in structural weight, which would be necessitated by building an airtight cabin, if flights in the stratosphere were con- sidered, would probably limit the flying altitude of the commercial air liner to something between 12,000 and 20,000 ft. recently and sites have been inspected are York, Perth andGrimsby. Further developments will be keenly watched. A Japanese Airship Service? According tv d*a&L the Japanese Government has decidedthat a joint J&rau-MSilifjftikuo company shall be established in order to operate services Ibetween Tokyo and Singapore and theSouth Sea Islands, and between Japan and the U.S. The coni- ^ three rigid airships, and negotiations have-u with the Zeppelin Company. »r
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