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Aviation History
1928
1928 - 0509.PDF
June 21, 1928 Supplement to FLIGHT ENGINEERINGSECTION Edited by C. M. POULSEN June 21, 1928 CONTENTS PAGE Metal Construction Development. By H. J. Pollard, Wh.Ex., A.F.R.Ae.S 45 The Application of Aerodynamic Data to the Structural Design of Aircraft. By Frank Radcliffe, B.Sc. A.R.Ae.S 47 Technical Literature ... ... ... ... ... ... ... 5] EDITORIAL VIEWS In the previous instalment of his series of articles on Metal Construction Development. Mr. Pollard has dealt mainly with questions of design, discussing problems con- nected with efficient spar sections allowing a high percentage of the strength of the material used to be developed, forms of rib construction, methods of attachment of different members to each other, and so forth. Interesting as that subject undoubtedly is, we believe that the next few articles will be found by many of our readers even more so. Turning from the problems of design to those of manufacture, Mr. Pollard commences in the present issue a discussion of methods of production. Unfortunately, it has been neces- sary, owing to lack of space, to divide Mr. Pollard's article, with the result that the portion which appears this month is in the main introductory, and the reallv instructive section is still to come. That it will be found very instructive we are quite certain, especially to those who are just about to take up the manufacture of components for all-metal aircraft. Even in the present issue, however, the reader will find much to interest him. A formula is given for determining the radii of the final rolls and dies in order to allow for the right amount of spring-back, and although Mr. Pollard frankly admits that the formula is empirical, and that he can give no mathematical justification for it, we think that at the very least it may be accepted as a good starting point for those with little or no practical experience of forming corrugated sections from flat strip. Doubtless, as experience is gained, modifications will suggest themselves. On the subject of whether the user should employ strip which has already been heat treated by the manufacturer, or should do his forming of softened strip and heat treat subsequently, Mr. Pollard points out that there appears to be reasons to believe that both systems will have their special advantages, the former method relieving the user of a good deal of work and expense, and the latter being, probably, preferable where a very light structure is required, and where consequently it is desired to use steels with high values of proof stress. METAL CONSTRUCTION DEVELOPMENT. By H. J. POLLARD, Wh.Ex., A.F.R.Ae.S. (Continued from- page 41.) These articles have in the main had reference to strip construction of the structural members of aeroplanes. It is consequently appropriate that the following notes on workshop practice should begin with a description of one or two methods of forming sections. Rollins and drawing are common operations, and strip and sheet steel are frequently pressed to shape. An abundance of information is available regarding pressing and allied operations, and the student who has not had the advantage of tool-room experience is referred to the books on press-tool work. One such hook to which attention may be drawn is ""Die and Press Tool Work," by 15. W. Butler and E. J. Hall, published by Cnssell and do.. Ltd. Different and possibly better methods than that given below could no doubt be described by others engaged in metal construction. The method, however, which we will survey briefly, has always given good results, and probably improvements on it will lie in the direction of speed of production. In experimental aircraft, or for that matter in quantity production of such volume as is to be anticipated during the next few years, the method indicated is likely to give the required production. For example, two rolling mills and draw benches will produce from strip all the necessary sections for an output of five or six aeroplanes of average size per week. The procedure is, in general, to do a certain amount of rolling on every section ; in fact, where possible the completed section is formed by rolling. In cases where the finished section is bent to the equivalent of more than a semi-circle as in Fig. 8, major segment, p. l(i, or where spring-back necessitates the gap contour of the finishing tools having an arc greater than a semi-circle, the rolls will be followed by a die fixed to the draw bench for the purpose of the second and subsequent operations. Another method is to work dies in conjunction with rolls on the rolling mill, and so obtain the finished section at one pass ; another way is to put the strip through a progressive series of dies, thus obtaining the finished section in one pass. A third method is to fit the draw bench with rolls and dies, and so obtain the finished section at one draw. The last-mentioned way. a combination of rolls and dies on a draw bench, might be the most suitable for mass production. Satisfactory results may be obtained with all the above methods. Whichever way is chosen, it is necessary 464a E 2
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