Aeroplane

The purpose of this book is to give some indication of the principles and methods of construction of modern aeroplanes, as distinct from those considerations pertaining purely to design, although occasional references to various elementary principles of aerodynamics have been found necessary to illustrate the why and wherefore of certain constructional details.

To many the aeroplane is a structure of appalling flimsiness, yet the principle which it exemplifies, that of obtaining the maximum strength for a minimum of weight, constitutes a problem of which the solving is not only an unceasing labour, but one demanding the observance of the best engineering procedure. The whole future of aviation, commercially or otherwise, may be said to be indissolubly bound up with the development of efficiency; and whether this is to be attained in improvements in aerodynamical qualities, by the discovery of a material giving a greatly enhanced strength to weight ratio, or by progress in the arrangement of the various members of the complete structure of the aeroplane, is a matter upon which some diversity of opinion exists. However, it is certain that the very great developments of the last few years are clue more to refinements in design rather than construction; and it is questionable whether the constructional work of the modern aeroplane has developed equally with design, so that, even taking for granted the oft-repeated, but very doubtful, statement that we are approaching the limitations of design, there irf certainly plenty of scope for experiment and improvement in the constructional principles of the modern aeroplane.

Standardization of Details.
Whatever may be said for the standardization of aeroplane types, a scheme which should effect a considerable saving in labour and material, and which offers chances of success, would consist in the standardization of metal fittings and wood components generally, for in this direction there is certainly great need for improvement. Taking as a hypothesis the various makes of scouting machines, we find hardly any two details the same. This means that if in this country there are six firms producing machines of their own design (these figures, of course, being purely suppositionary), there will be six sets of detail drawings, six sets of jigs, templates, and press tools, and sundry special machine tools. There seems no valid reason why many of the fittings for all machines within certain dimensions should not be of standard design, and a brief review of the various details which could be standardized without detracting in the least from aerodynamical efficiency will indicate the extent to which the con- serving of labour could be carried. In the construction of the fuselage, the clips fastening the longerons and cross struts could easily be of one design, whatever the make of the machine. At present we find some clips are bent up from a stamping and attached to the longeron without the drilling of the latter; some built up from various parts, such as washer-plates, duralumin pressings, and bolted through the longeron; while some combine advantages and others the disadvantages of both. In some cases the longerons of spruce are spindled out for lightening; in others no spindling occurs; while in a few instances hickory or ash, with or without channelling, is used. There are the interplane strut attachments, stern-post fittings, control-surface hinges, and under- carriage attachments, all showing great variations, and in all of which the design could be brought within reasonable limits.
As indicating how unnecessary a good deal of the variation is, one may instance the fact that for the swaged streamline, or R.A.F. wires, there are at least three different terminals in use. Although more difficult of achievement, there is scope for improvement in the different arrangements for the fixed gun mounting, while a standard instrument board would benefit the pilot.

Methods of Manufacture,
It is fairly well known that the output of some firms is considerably better than others, although the machines are of the same design. Although a good many factors may contribute to this result, it seems fairly certain that in some cases the methods of manufacture must be superior, which calls for some system of standardizing the broad principles pertaining to manufacturing procedure. Under this arrangement a much better estimate of probable output could be made. It is also necessary by the fact that some firms have been developed through the exigencies of war, and not as a result of any great manufacturing ability, whereas in peace time the spur of competition would force the adoption of the most rapid methods of production. The creation of a central or universal office for the design of the various jigs used in the manufacture of aircraft, with power to decide the process of manufacture, although a somewhat far-reaching reform, would certainly eliminate a number of useless experiments made by the individual constructors, and would also greatly improve the interchangeability of the various components. In addition, fresh firms to the aviation industry would be at once acquainted with the general methods of manufacture, which should be of considerable assistance in expediting initial output. Of course, this system would tend rather to destroy individual initiative, in that much that is now left to the skill and experience of the workman would be predetermined, although this would be more than compensated for by the increased benefits accruing to the State. Jigs designed to produce the same work in different works often differ in detail considerably, and this, of course, often influences the rate of production. As an instance, in some works elaborate benches are considered necessary for the erection of fuselages, while in others a pair of trestles suffices. With this system of unified manufacturing procedure extreme regard would have to be paid, in the design of various jigs and fixtures, to adaptability for modifications in design. Otherwise the various alterations which are bound to occur would result in an unnecessary expenditure on fresh jigs. It is somewhat unfortunate that in the general design of an aeroplane, in numerous cases, far too little regard is paid to considerations of ease of manufacture, and this is frequently responsible for the many changes in design after a contract has been started. Under an ideal system of standardization, the requirements of manufacture would necessitate consideration in the design of the constructional details.

Metal Construction,
The question of the aircraft materials of the future is not so much a problem as a matter of gradual evolution. In view of the dwindling supplies of suitable timber, it certainly seems more than probable that some form of metal construction will one day constitute the structure of the aeroplane. The manufacture of the various components in wood does not necessitate an extensive plant, the labour necessary is comparatively cheap and easily available, and moreover the transitory nature of the whole business, and the ease with which essential changes in type can be made without the wholesale scrapping of the expensive jigs associated with the use of steel, all strengthen the case in favour of wood. The conclusion of hostilities would introduce another state of affairs, and it is conceivable that the various types will then be standardized for different purposes, which may necessitate the greater use of steel. Certainly the advantage of steel would be better realized under some system of standardized design, but this unfortunately is not possible while present conditions obtain. The advantages of metal as a material considered briefly, are that it permits of design to close limits without the allowance of so-called factors of safety, which are now necessary through the great variation in the strengths of wood, manufacturing procedure would be expedited, while one can reasonably expect a greater degree of precision in the finished machine, due largely to the increased facilities for accurate manufacture of components which metal affords. It is quite possible, of course, given a uniform grade of steel, to design to extremely close limits without fear of collapse ; but the human factor in the shape of fitter, welder, or operator introduces the unknown element, and one for which some allowance must always be made. One cannot assert that any very decided indication exists of a trend in modern design towards metal construction, and it is quite possible that this will not arrive until it is rendered imperative by reason of the scarcity of timber. The precise composition of the metal is rather a controversial matter, some authorities favouring steel, and others some alloy of aluminium, such as, for instance, "duralumin." The production of a suitable alloy constitutes a real problem and one upon which the Advisory Committee for Aeronautics have already made investigations and experiments. A disadvantage with steel is that, although it is quite possible to produce, say, a fuselage entirely of this material to withstand easily the greatest stress encountered in flying, such a structure, owing to the thin nature of the various components, would suffer damage through shocks induced by rolling over rough ground, and also by handling. In addition the effects of crystallization would require some considerable study. These and other reasons indicate that an alloy of aluminium, which for a given weight would be considerably more rigid than steel, offers possibilities as a material. It might prove advantageous to combine both metals, using steel for the more highly stressed parts, such as, for instance, wing spar attachments, inter-plane bracing lugs, and indeed any part where the load to be carried is one induced by tension.
The foregoing is indicative of some of the more important directions in which improvement and development are possible, and certainly ample scope yet exists for the attention of the student, or indeed anyone interested in the future of the aviation industry.