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Aviation History
1926
1926 - 0791.PDF
OCTOBER 28, 1926 91 THE AIRCRAFT ENGINEER SUPPLEMENT TOFLIGHT (i.e., normalised), the section should be produced with an adequate radius in the corner, and should not be obtained "" sharp." In the construction of articles from Duralumin it is cus- tomary to rely upon riveted joints. It would, of course, be a particularly convenient thing under many circumstances if welded or soldered joints could be made in the metal and relied upon. The application of either of these two processes to Duralumin presents certain difficulties. The soldering of Duralumin suffers from all the disadvantages that are generalh' encountered in carrying out this operation on aluminium or light alloys. It can probably be said quite accurately that the difficulties of soldering Duralumin are scarcely different from those met with in the soldering of aluminium. It is known that aluminium can be soldered with more or less success, but that the soldered joint can only be used with satisfaction under certain definitely denned conditions. It is no good to expect the joint to be strong, and soldered joints in Duralumin should, therefore, be reinforced by riveting. Furthermore, those solders which are applied to the naked Duralumin are very frequently such as lead to ready and rapid corrosion. The welding of Duralumin follows somewhat on the same lilies, but there are certain features that are not met with in the welding of plain aluminium. Naturally, Duralumin that has to be welded must necessarily be heated to a high tempera- ture, sufficiently high to reduce the mechanical properties of the normalised Duralumin approximately to those of annealed Duralumin. This refers to the condition of the material at and in the vicinity of the weld. In the second place, a welded joint in Duralumin has the same characteristic as a weld in any other material—namely, that it is the result of what is more or less a casting operation. This necessarily means that the material at the weld has approximately the ductility of a cast metal. (The same remarks apply to welded steel structures. The material that is used for filling in is applied in the molten condition and, therefore, is to all intents and purposes cast into position. A welded-steel joint, therefore, is similar hi properties to a steel casting, and after normalising the joint is similar in properties and structure to those of a normalised steel casting.) It will be safe to infer, therefore, that welded Duralumin joints are only likely to become really useful when joints of sufficient excellence can be produced that the whole article can subsequently be submitted to the heat- treatment operation. This naturally limits very considerably the useful application of welding to Duralumin structures. In conclusion, it may not be out of place to make some remarks as to the sources of supplies of Duralumin. Naturally, the aircraft industry in particular is concerned to know whether Duralumin is likely to be available in adequate quantities in the event of a war, and more particularly in the event of a war of the magnitude of the last one. The only serious question which arises in this connection is whether there would be adequate supplies of the necessary raw materials for the production of Duralumin in the quantities that would be required. This narrows itself down to a con- sideration of the supply of aluminium, copper, manganese and magnesium. There is no need to enter into the question of the supply of copper and manganese, and the inquiry can, therefore, be narrowed down to magnesium and aluminium. Both of these materials are produced in this country in quantities. The quantity of magnesium required for the manufacture of Duralumin is not very large compared with that which would be consumed in other directions in warfare, and the existing capacity for its production in this country is quite equal to any demand that is likely to be made upon it by the aircraft industry and the others who would use Duralumin in wartime. Aluminium is being used every day in greatly increased quantities in various directions, and the British makers of aluminium are having to cope with a demand that is steadily growing. In the event of a war, of course, the output of these suppliers would naturally be concentrated upon satisfying the needs of the fighting services. At the present time the British suppliers are able to manufacture quite as much aluminium as would be likely to be required by the aircraft industry in a war of the same scale as the last, but they are, as is well known, increasing their capacity for production very considerably. and it is quite clear that the available supplies of aluminium will be more than equal to the aeronautical requirements of the country in the event of war. even taking into account the considerable quantity that would be employed in other branches of warfare. This is not the place in which to give the data that would prove this statement, but the facts, nevertheless, remain as stated. The only question that remains, therefore, is that of the availability of sufficient raw material from which aluminium manufacturers can produce the metal. In other words, the supply of ore must be quite adequate. As is well known, aluminium is produced from a mineral called bauxite. Various grades of this material exist, and in different qualities it is distributed very widely over the surface of the globe. Large quantities of bauxite, possibly the predominant proportion of the usefully workable supplies, are located in the British Empire, and are. therefore, available to this country in the event of a war, which might possibly remove the European supplies of the material from the British manufacturers. It is agreed that all these sources of supply arc not equal in quality, but there is certainly quite enough in the British Empire of the best quality to produce the requisite aluminium. Fortunately, ]>erhaps. bauxite has to undergo very special processes of purification before it can be reduced to aluminium, and as a result the aluminium manufacturers are bound to maintain a very large quantity of the ore at. or in the vicinity of. their reduction furnaces. This would mean that in the event of a sudden outbreak of war, resulting in a temporary dislocation of the merchant marine, the aluminium-producing companies would not be left short of the supplies of the necessary raw material. It appears to be quite safe to say that they would be able, to continue for many, many months without hindrance in the production of aluminium to their full capacity, even though not an ounce of bauxite reached these shores from the deposits overseas. It becomes plain, therefore, that in all the links of the chain the circumstances are such as would ensure a continuous supply of aluminium for the production of Duralumin. The other constituents of the alloy are available from home supplies, and. therefore, it is evident that in the event of a war, even of great magnitude, supplies of Duralumin would be quite adequate for the needs of the Air Ministry, even though this was based upon an '" all-Duralumin " programme. TECHNICAL LITERATURE. A.R.C. REPORTS. AN INVESTIGATION OF THE FLOW OF AIR AROUND AN AEROFOIL OF INFINITE SPAN.* By L. W. BRYANT, B.SC, A.R.C.SC, and 1). H. WILLIAMS, B.Sc, with an Appendix by G. 1. TAYLOR. F.R.S. R. and M. No. 989 (Ac. 200). (44 page?, 20 figures.) February, 1924. Price Is. <)<?. net, A great deal of attention has been directed of late years to the development of a rational theory of the aerofoil. Prof. L. Prandtl and others in Germany have applied the principles of th? hydrodynamics of a perfect fluid to the aero- foil with remarkable results, whilst investigators in this country have extended this work and have verified experi- mentally many of the deductions of the Prandtl theory. The assumptions underlying the work of Prandtl are, however, of uncertain validity, and it has become a matter of great importance to add to existing experimental evidence of the fundamental characteristics of the motion of a viscous fluid round an aerofoil. With this purpose in view an aerofoil section of fairly high lift coefficient was selected, and a model of it tested in the duplex tunnel at the National Physical Laboratory, the field of flow being thoroughly explored with a wind-velocity meter. At the same time the theoretical stream-lines corresponding to invisci 1 fluid flow were deter- mined experimentally, as described in Part II of this paper. * Royal Society, A., Vol. 225, November, 1925. 702e
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