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Aviation History
1919
1919 - 0512.PDF
lem APRIL 17, 1919 DRAWING OFFICE DATA * By E. O. WILLIAMS, B.Sc.Eng. (Lond.), Assoc. M. Inst. Civil Engineers, Assoc. Fellow R.Ae.Soc.G.B. [ With the growth of the aviation industry the need for methodisation becomes increasingly important—methodisaiion in design and construction as well as in manufacture. With regard to the two first mentioned, as experience is extended the volume grows of data relating to construction and design, and unless a proper system is evolved for preserving and collating in suitable form such data, it is almost inevitable that confusion will ensue, or at any rate that full advantage cannot be taken of the experience and data collected in the past for the benefit of the future. Often it will be found that the work involved will be somewhat heavy, especially as regards design, but it will be found to pay " in the long-run.'' There is as yet a long way before we arrive at anything approaching standardisation, hence the number of lengthy calculations involved every time a new design is contemplated is prodigious. So long as each new machine differs to any considerable extent from the previous one-—and at present this would appear to be the case— all the calculations, aerodynamic as well as structural, have to be gone through afresh. It is not always possible to generalise owing to the difference in shape, size and material of component parts, but much may be done in this direction by making from the start calculations for all such sizes and shapes as may be reasonably expected to come useful for the next series of designs. It is particularly in this anticipation of the next requirements and in the methodical way of presenting them that the series 0/ articles by Mr. E. O. Williams, of which the first is published this iveek, are useful. The articles do not, except in one or two instances, introduce anything not already pretty generally knoivn, nor do we think that the author lays claim to disclosing any new discoveries in the bulk of the subjects treated. The articles arc, however, the outcome of an attempt to methodise the daily routine of the drawing office, and, given time, the tabulation of the various calculations would possibly occur to anyone. It is, however, just in this saving of time that these articles will, we feel sure, be found of great assistance. In regard to the tables, graphs, etc., it has not been possible, for reasons connected with publication, to make these all of a uniform size, but so far as has been possible we have endeavoured to do so, so that in the majority of cases readers who wish to do so will be able to tear out these pages and keep them in a loose-leaf pocket-book for easy reference. We regret that since writing this series of articles Mr. Williams has left the aviation industry and has turned his attention to a different branch of engineering. He is now devoting his energies to the restoration of our depleted tonnage—certainly a task of as vital importance as that of building aircraft-—but we hope that some day he may be persuaded to return to the aviation world. With these few words of introduction, we will leave our readers to the tender mercies of Mr. Williams.—ED.] I.—DRAWING OFFICE SYSTEM. (a) System of Numbering Drawings. THE successful production of complex repetition work, such as the aeroplane, is to a very great extent dependent on the efficiency of the drawing office. Errors in design or draughtsmanship are obviously fatal, but even if the general design is sound, there yet remains a great deal to be done in the drawing office, the quality of which goes a very long way towards making or marring the machine. When, as in pre-War days, only one or two machines of a new type were to be built, the drawings required were, of course, entirely different from those demanded when it comes to orders for large numbers, especially when parts or even complete machines are to be constructed at works other than those of the original designers. If only one machine were to be built, it would probably be convenient to mass together on one sheet the drawings for all the details referring to a complete unit such as the fuselage. For example, the fuselage drawing would then contain all details such as sizes of longerons, struts, wiring, cockpit, seating, padding, cowling, etc., and all trades would refer to the one sheet cf drawings. This procedure becomes impracticable when not one but 1,000 machines are to be built, with a consequent minute division of labour. The planning of the work is then facilitated if each part has a separate drawing. Also the work man is less liable to get confused if the drawing shows his work only, and he is not required to pick his job out of a multiplicity of other details. This is the basis of the " one part, one drawing " system. Important as is the method of having only one part on one drawing, the systematic numbering of drawings is no less so. The writer has evolved the following system to give effect to the above prin ciples : Each machine is given a distinctive number, and each assembled unit is given an alphabetical letter. For instance : A certain machine has been accepted for reproduction in quantities, and that particular type of machine has been given the works number 500. Then all sheets, and drawings * This article, which was written some time ago, has not been released for publication until recently. It has not, how ever, lost in interest during the interval. General arrangement complete machine Fuselage Wings Tail plane and ele vator Rudder and fin Landing gear Tail skid Tanks of a b c . d e f • g . h referring to this particular type will be provided with, firstly, the general number 500, and, secondly, with an alphabetical letter following the number and indicating to what part of the machine the drawing refers. The letter to follow the general number will depend on what system is chosen, and is not, perhaps, so very important so long as the particular system, once decided upon, is rigidly adhered to. The following lettering of drawings will, I think, be found convenient in practice :— Engine mountings and cowling ... j External wiring ... k External struts ... / Controls m Engine controls ... n Instrument board ... p Accessories q Parts lists r Stress diagrams ... s For example, if the general number of the machine is 500, the drawing of the landing gear will be numbered 500/. Detail drawings of the various component parts of the landing gear will then be numbered 500f-i, 500f-2, 500/-3, etc. Another important item as regards convenience and efficiency is the matter of size of drawings. Obviously, it is impossible to have all drawings of one size, irres pective of subject, while it is, of course, equally im practicable to have the different drawings of all sorts of different sizes. It is possible, however, by choosing suitable sizes to reduce the number of sizes to two, one for the general arrangement' drawings and one for detail drawings. The actual size of the drawings is, to a certain extent, a matter of personal opinion, large drawings being preferable in allowing of greater accuracy, while too great drawings become unwieldy to file and handle. In practice it will be found that for general arrangement tracings of machines, a convenient size will be 27 ins. x 50 ins. inside borders, with a f-in. border all around. For detail tracings, a good size is 28 ins. x 36 ins. inside borders, with a f-in. border all around. It will be found convenient to divide up the detail tracings as required to a standard size of 13\ ins. x 9 ins., or 512
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