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Aviation History
1917
1917 - 0176.PDF
[ft!GHT FEBRUARY 22, 1917. METAL IN AEROPLANE CONSTRUCTION. WHILE the last few years have witnessed great progress in the improvement of the aerodynamical qualities of the flying machine, there has not been any marked advancement in the methods of con- struction employed. From the engineering point of view practically all the improvement has been in the utilisation of more suitable materials and fittings which are better adapted both for their purpose and for rapid manufacture than the crude contraptions which had to do duty on the machines with which the pioneers experimented ten years ago. From time to time attempts have been made to employ metal for the main framework of machines, but owing largely to the lack of support, in the way of orders, accorded to manufacturers in the past very little has been accomplished in this direction. Now, however, when different conditions prevail, and having in mind the present restrictions with regard to timber, the question is again being forced to the front, and in the following article a few considerations in connection with the use of metal construction are •dealt with. In the early days, when orders were not forthcoming at all, or at best in twos or threes, wood construction did very well, was, in fact, the only practicable form. Alterations, which were many and frequent in those days, could be easily carried out, and in case of damage, a thing not totally unknown to the pioneers, repairs could be made almost by any one and, at a pinch, with any material at hand. As the industry grew everyone became so intent on improving the aerodynamical qualities of machines that the original construction was retained almost universally, and quite justly so, since it lent itself so well to experimental work. It was only on the outbreak of war that the question of reproduction began to have any real importance. Since then, however, the question of quantity reproduction has become quite as important as the military value of the machine to be reproduced, and ways and means will have to be found, which will not only speed up the output, but also render the aeroplane a better engineering proposition. If a parallel in another line of engineering were required, it would only be necessary to turn to the motor car. The early ones had wood frames, which were followed by reinforced wood frames, the latter being in turn supplanted by the channel steel frame. It is not necessarily suggested that the channel steel form will prove the solution of the problem in con- nection with aeroplanes as it did in the case of the motor car, but try to imagine a motor car built on present aeroplane constructional lines. . The idea makes one smile, yet it is quite conceivable that in the no distant future the idea of building aeroplanes of bits of wood and wire will seem quite as crude. But what about economy of production ? Surely a time like the present, when orders are being received for hundreds instead of pairs of machines, is favour- able for attempting forms of construction that not only lend themselves to mass reproduction, but may actually be preferable from an engineering point of view. Although there can be no doubt that the component parts of the aeroplane as built to-day are quickly and cheaply made, the question of erecting and assembling is a serious item, even when making the widest possible use of jigs and templates. Take, for instance, a. fuselage. The sawing out and spindling of longerons and struts is not a lengthy operation, it is true, but consider the number of man-hours con- sumed in erecting and trueing up the fuselage. In each bay there are two diagonal wires, each divided in two by the wire strainer, which latter has taken a certain amount of man-hours to make. In each bay the wires have to be cut approximately to length, eight loops must be made in them for the wiring plates and eyes of the strainers. Ferrules must be slipped over each of the eight bent wire ends, and the free ends bent back over the ferrule and cut off. Then there is still the tuning up, with the tightening of a wire here and the slacking of another there, before the strainers can actually be locked. The number of man-hours that go into the making of an ordinary fuselage is, to our way of thinking, unnecessarily great. As we have said, there are a few aeroplane builders who have turned to other materials than wood in their search for something better. Steel tube con- struction is, perhaps, the commonest of these. From the point of view of strength tubing is, of course, < suitable enough for many purposes, but in others it does not afford the best distribution of material, such as, for instance, in a beam where, in circular sections, much too great a proportion of the material is located near the neutral axis, where it is adding weight without adding materially to the strength. .For use in fuselage construction a tubular framework may be all that it should be as regards strength to weight ratio, but the brazing, welding or other forms of attaching the struts to the longerons are as cum- bersome as in wood construction, while the number of bracing wires and strainers with their attendant tuning up are in very much the same position. For mass reproduction, therefore, the tubular frame has little or no advantage over the wood girder. A form of girder very extensively employed in other branches of engineering and, in the aviation industry, by our enemies in their airship construction, is the lattice girder. After nearly 20 years of experimenting the Germans have, apparently, been unable to devise a better method, and although we are well aware that the stresses in a rigid airship of the Zeppelin type may be very different from those obtaining in an aeroplane, it does not necessarily follow that the lattice girder cannot be adapted, to meet the require- ments. If it can, and at the same time give the same strength to weight ratio as the wire braced wood girder, it appears to have much to recommend it from the point of view of production. The smaller component parts are stamped out in large quantities, therefore working out very economically as regards man-hours, which is, after all, the only standard by which to measure costs in times of war. If the assembling be done over jigs the erecting should not be a lengthy process if modern pneumatic riveting machines are employed, and, at the finish, we are convinced it would be found the number of man-hours required for the turning out of a complete fuselage had been more than halved. This may sound some- what optimistic, but we do not think it is far wrong. Reckon up the number of man-hours required in shaping and cutting to length the longerons and struts, in cutting out the wiring plates and welding sockets on to them, in drawing the bracing wires, in making the loops in them, in making the turnbuckles, in securing the wires to wiring plates and turnbuckles> and in the final trueing up. Against this must bg 176
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