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Aviation History
1940
1940 - 0360.PDF
FEBRUARY 8, 1940 various directions. As a rule, one seldom got enough of any individual fitting to make it worth while using dies, so most of them were roughed out in a nibbling machine and then finished by hand. Much of the labour one had to use was described, apparently by- courtesy, as semi-skilled, and they wanted very care- ful watching if the percentage of scrap was not to rise to abnormal proportions. It is always so difficult to induce the inexperienced to realise the importance of a dimension. But after this type of man had been work- ing in the shops for some time, and had realised exactly what was wanted, he really did very well and often turned out work quicker than men who were fully skilled. The latter, being expert workmen, often spent time over little refinements which were not at all necessary. Bolts we usually bought "out," though there were certain special ones which we had to make ourselves. Turned parts generally did not give much trouble; a good battery of capstans and a few auto- matics dealt with them satisfactorily. Women Workers Later on in the war we used female labour extensively for the simpler jobs, not only at the bench but for simple wood work and for gluing small parts. Once they got the idea of what was wanted, they were quite efficient, but there were occasionally unexpected troubles. I remember particularly the female indignation among our dope room workers when they first discovered the effect of splashes of aeroplane dope on artificial silk stockings ! Design was much simpler than it is to-day. Spars were often designed by the simple three-moments formula, compression loads being dealt with by Perry's method. There were few complications ; the only one used then which does not occur to-day is probably the case of '' shot-away factors.'' For the calculation of these it was assumed that any one of the streamline wires might be cut by a bullet, and that the structure must be made safe under these conditions, though with reduced factors. The people of the technical depart- ment of the Air Ministry then existing were very easy to work with, and decisions on doubtful points came through very quickly. If we had known as much as we know to-day about stresses in aeroplane structures, I suppose these crude methods of stressing would not have been permitted, but, after all, the proof of the pudding is in the eating, and structural failures were almost unheard of, in spite of our ignorance. Looking at a modern aeroplane, the progress made is most impressive. Metal construction has made pos- sible many types which could not possibly have been designed in wood, but it has also brought with it many troubles of its own. Among these I would instance the extreme complication of the stressing methods which have to be used, and the fact that many of the parts can only be made on complicated, bulky and expensive machines, such as draw benders. I shall expect to see in the future a simplification of metal construction, the use of fewer parts of simpler form, and some methods of cutting down the immense number of rivets. As experience with light alloys grows, it is possible that many parts will in future be cast, and this method is far more flexible with regard to form than rolling or extruding. Some of the early cast-iron road or railway bridges or roofs, still fairly common in this country, might well repay study by the modern aeroplane designer. But the chief difference between now and then must reside in the necessity for the sub-contractor to possess complicated machinery. No longer is the possession of a band saw sufficient for important help, but presses, lathes or machine tools generally become necessary. Sub-contractors owning such tools as draw benches are not likely to be found. But' the production of any part, wood or metal, is necessarily dependent on the existence of the right machine, and in this sense wood has an important advantage, as wood-working machin- ery is generally so much simpler and cheaper. But it is always possible that the modern impregnated woods may be used extensively in the future. Conservative Designers One of the features which must strike the unprejudiced observer of aircraft practice would probably be its innate conservatism. It is true that it has advanced, is ad- vancing now and will continue to advance, but once the designer has been taught to think in terms of metal construction for a few types, he tends to think in the same way for all. Structures of normal wood, or of impregnated wood, can be made for special types which are probably lighter and cheaper than any metal job, and the advantage of wood should always be considered by the designer of a new type. In many cases it will be obvious after investigation that metal construction is the only type possible, but in others wood will be clearly the best. The idea which one hears, not infre- quently, that metal is the only material out of which a good aeroplane can be made, should be exploded. It would seem that the problems of production must be very different now than they were in the last war. Then the chief problems were to find firms which had tools which could be used, and there were quite a lot of them ; now the problem must be largely to find the tool and to find somewhere to put it, complete with all its complicated accessories. I fancy this problem must be the more difficult of the two. B.S.I. Plywood Specification ""PHE British Standards Institution announces that a revised -»- edition of the B.S. Specification 4 V.3 for plywood for structurally important parts of aircraft has just been issued by the British Standards Institution. The timber is limited to birch 'European or sweet or yellow) and rock maple. Under the provisions relating to the manufacture of the plywood, boards TO inches wide and under must have both faces free from edge joins in the veneers. In the case of wider boards the number of edge joins in the veneers in any ply must not exceed the width of the board divided by 8. The joins must have a stagger of at least 1 inch. End grain joins in the veneers are not permitted in boards up to and including 60 inches in length. Longer boards may have one such join in each face. The joins are to be not less than 12 inches from either end of the board and to have a stagger of not less than 12 inches. End grain joins through the thickness of the boards are not permitted unless specified in the contract, and if so specified they must be scarfed in an approved manner and in the position specified in the contract. The adhesive is to be a paper film glue or other resin glue of approved manufacture. The methods of determining the moisture content, tensile strength, bending properties, adhesion of plies and resistance to water of the finished plywood are fully described. Copies of this revised British Standard Aircraft Specification (5 V.3) may be had from the British Standards Institution, 28, Victoria Street, London. S.W.T. price is. each (is. 2d. post free). 125 Octane AT a meeting of the Institute of Petroleum recently Pro-fessor A. W. Nash, president of the Institute, said that , fuel of 125 octane number had been produced experimentally in laboratories, but the cost was about £10 per gallon. We remember the time when fuel of 87 octane number >vas pretty expensive. But the production was placed on a commercial basis, and then came the 100 octane fuel, also expensive. History seems to show that what is a laboratory process to-day becomes the commercial process of to-morrbw, so perhaps some day we shall have 125 octane fuel—and the engines to use it.
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