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Aviation History
1953
1953 - 0866.PDF
22 FLIGHT THE A.F.I.T.A. CONGRESS 100,000 50,000 1/5 § 20,000 Z 2 IO.OOO < ' 5,000 1,000 ^ "^•^ s H CTAklKiOn Fl^UTFP A g "*« ~~- **«• LIGHT FIGHTER^ ~«., 2 5 IO 20 SO IOO 200 500 IOOO NUMBER OF AIRCRAFT 7 6 ~5 c 0 =4 2 2 1 _ STANDARD FIGHTER -'LIGHT -FIGHTER ^s «iUU 4UU OUU OUU NUMBER OF AIRCRAFT 10OO 12C machines in the two contracts was £21,000 and £5,350 respectively. When cumulative total costs were plotted against numbers (see Fig. 4) it was seen that, for the £6 million, one could obtain either 215 of the large machines or 900 of the smaller type. The remark able conclusion was that, although the large aircraft was three times the weight of the smaller one, it was possible to produce for the same outlay of man-hours five times as many of the small aircraft as of the larger aircraft. In terms of total cost, the ratio would still be more than four to one. It might be asked, however, how it was possible while achieving an equal performance to carry an effective useful load in so small a machine. An analysis of the weight distribution, however, showed that the useful load carried (i.e., fuel and military load) was approximately 42 per cent for the small machine against 33 per cent for the larger aircraft. This striking conclusion could be attributed to three important factors, namely, the structure, the engine and miscellaneous services, all of which could be lighter for the small machine without sacrifice of performance or strength. The structure, weight and complexity of the light aircraft considered showed considerable reductions over the larger aircraft, particularly in the wing design. For instance, the under carriage could be retracted into the fuselage, thus avoiding dis continuity in the main load-carrying part of the wing structure (that had made so many wing designs so difficult and heavy), and it Fig. 5. Adequate strength and stiffness for the light fighter wing can be provided by this simple type of construction. Using separate stiffeners, production is cheaper and easier than by means of integral stiffeners, used in larger wings. Fig. 6. Pressed sheet metal parts can be used in the light fighter in place of built-up assemblies embodying castings and forgings. An example is this frame, a basic one-piece metal item supporting t/ie front wing attachment. Fig. 3. (Left) Production comparison, showing man-hours required per aircraft for both types of fighter, for production numbers up to 200 and 1,000 respectively. Fig. 4 (Above) Cumulative total costs (including material) of the standard and light fighters (airframes only). For £6 million, 215 standard or 900 light machines could be built. was found that adequate space was available in the fuselage for the required fuel stowage. Hence, the only discontinuity from tip to tip was the inevitable change of direction due to sweep-back. Adequate strength and stiffness could be provided by a wing construction in which skins were stiffened by separate stiffeners, a much cheaper and easier method than those involving the integral structures now used for larger wings. A considerable sav ing in manufacturing man-hours could be achieved by replacing sub-assemblies by single parts. It was obvious that the reduction in size made the application of this principle much easier. Because of these and similar simplifications, it had been found possible to design a structure weight of 30 per cent compared with almost 35 per cent on the large machine. It was undoubtedly possible to produce a light-weight engine, that is, one having a very high thrust/weight ratio with somewhat less emphasis on consumption, in the small size, and a figure of 5 lb of thrust to 1 lb weight was realizable with a reasonably long hfe. An improvement on the present figures of approximately 3 lb of thrust per lb of weight for the large engine was also possible, although perhaps not to the same extent, but the great cost of developing such large engines made it inevitable that a compromise solution be produced. Were full advantage taken of this power-plant gain, the difference in power-plant weight would be greater than that between 16.5 per cent and 20 per cent as at present shown. It had been proved that a high compression ratio, necessary for long endurance, was not essential in fighters and, equally impor tant, the extremely low cost which could be realized when very large numbers of engines were made had been demonstrated. A cost ratio of 1: 10 was not unusual. Finally, the small machine could benefit from a more than proportional simplification of its services, i.e., the hydraulic, electric and other systems which were an ever-increasing burden on a large machine, not only in manufacture, but also in servicing. Comprehensive examples of the simpler hydraulic, fuel and pressure cabin systems of the small aircraft were then given by Mr. Petter. Concerning equipment, he said that one would, of course, like to reduce the amount of equipment proportionately with the size of the machine, but since the object of the fighter was to fight, there was a limit below which further reduction of equip ment could not be performed. This limit would comprise two 20- or 30-mm guns, or four 0.5-in guns with reasonable ammunition, adequate wide-range radio facilities, some form of navigational aid, and possibly provision for radar gun ranging as an overload. It was agreed also that an ejector seat would be necessary, although even here substantial weight-saving could be achieved compared with what had been common practice, firstly, by good engineering design, and secondly by the use of a reasonable ejection velocity suitable for fighters, rather than a general-purpose high-velocity which might be necessary for larger machines. A useful load of some 1,000 kilos (2,200 lb)—about 40 per cent of the all-up weight—would cover all the above essential military load, including the pilot, together with a good internal fuel allowance, and we were led to the surprising conclusion that the small machine was a better carrier of useful load than the larger aircraft. Admittedly, this derived in part from the employment of a more up-to-date—or at least specialized—engine, which, how ever, economics and time would probably prevent from being available in a larger size for the large fighter. Mr. Petter con cluded : "It is hoped we have shown that a major contribution to a reduction of cost can be achieved, and at the same time a practical fighting weapon can be designed which will meet, if not all, a great many of the requirements for the operational functions of a day fighter. "We found that four or five times as many machines can be produced for a given cost, which makes possible efficient produc tion in many countries which might otherwise not be able to con tribute to their own and NATO defence."
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