It is impossible in the space at disposal to treat of this development even with the meagre amount of detail that has been possible while covering the ‘settling down’ period from 1911 to 1914, and it is proposed, therefore, to indicate the improvements by sketching3 briefly4 the more noticeable difference in various respects between the average machine of 1914 and a similar machine of 1918.
In the first place, it was soon found that it was possible to obtain greater efficiency and, in particular, higher speeds, from tractor machines than from pusher machines with the air-screw behind the main planes. This was for a variety of reasons connected with the308 efficiency of propellers6 and the possibility of reducing resistance to a greater extent in tractor machines by using a ‘stream-line’ fuselage (or body) to connect the main planes with the tail. Full advantage of this could not be taken, however, owing to the difficulty of fixing a machine-gun in a forward direction owing to the presence of the propeller5. This was finally overcome by an ingenious device (known as an ‘Interrupter gear’) which allowed the gun to fire only when none of the propeller blades was passing in front of the muzzle7. The monoplane gradually fell into desuetude8, mainly owing to the difficulty of making that type adequately strong without it becoming prohibitively heavy, and also because of its high landing speed and general lack of man?uvrability. The triplane was also little used except in one or two instances, and, practically speaking, every machine was of the biplane tractor type.
A careful consideration of the salient features leading to maximum efficiency in aeroplanes—particularly in regard to speed and climb, which were the two most important military requirements—showed that a vital feature was the reduction in the amount of weight lifted per horse-power employed; which in 1914 averaged from 20 to 25 lbs. This was effected both by gradual increase in the power and size of the engines used and by great improvement in their detailed9 design (by increasing compression ratio and saving weight whenever possible); with the result that the motive10 power of single-seater aeroplanes rose from 80 and 100 horse-power in 1914 to an average of 200 to 300 horse-power, while the actual weight of the engine fell from 3?-4 lbs. per horse-power to an average of 2? lbs. per horse-power. This meant that while a pre-war309 engine of 100 horse-power would weigh some 400 lbs., the 1918 engine developing three times the power would have less than double the weight. The result of this improvement was that a scout11 aeroplane at the time of the Armistice12 would have 1 horse-power for every 8 lbs. of weight lifted, compared with the 20 or 25 lbs. of its 1914 predecessors13. This produced a considerable increase in the rate of climb, a good postwar machine being able to reach 10,000 feet in about 5 minutes and 20,000 feet in under half an hour. The loading per square foot was also considerably14 increased; this being rendered possible both by improvement in the design of wing sections and by more scientific construction giving increased strength. It will be remembered that in the machine of the very early period each square foot of surface had only to lift a weight of some 1? to 2 lbs., which by 1914 had been increased to about 4 lbs. By 1918 aeroplanes habitually15 had a loading of 8 lbs. or more per square foot of area; which resulted in great increase in speed. Although a speed of 126 miles per hour had been attained16 by a specially17 designed racing18 machine over a short distance in 1914, the average at that period little exceeded, if at all, 100 miles per hour; whereas in 1918 speeds of 130 miles per hour had become a commonplace, and shortly afterwards a speed of over 166 miles an hour was achieved.
In another direction, also, that of size, great developments were made. Before the War a few machines fitted with more than one engine had been built (the first being a triple Gnome-engined biplane built by Messrs Short Bros. at Eastchurch in 1913), but none of large size had been successfully produced, the total weight probably in no case exceeding about 2 tons. In310 1916, however, the twin engine Handley-Page biplane was produced, to be followed by others both in this country and abroad, which represented a very great increase in size and, consequently, load-carrying capacity. By the end of the War period several types were in existence weighing a total of 10 tons when fully19 loaded, of which some 4 tons or more represented ‘useful load’ available for crew, fuel, and bombs or passengers. This was attained through very careful attention to detailed design, which showed that the material could be employed more efficiently20 as size increased, and was also due to the fact that a large machine was not liable to be put through the same evolutions as a small machine, and therefore could safely be built with a lower factor of safety. Owing to the fact that a wing section which is adopted for carrying heavy loads usually has also a somewhat low lift to drag ratio, and is not therefore productive of high speed, these machines are not as fast as light scouts21; but, nevertheless, they proved themselves capable of achieving speeds of 100 miles an hour or more in some cases; which was faster than the average small machine of 1914.
Bristol Fighters in formation.
In one respect the development during the War may perhaps have proved to be somewhat disappointing, as it might have been expected that great improvements would be effected in metal construction, leading almost to the abolition22 of wooden structures. Although, however, a good deal of experimental work was done which resulted in overcoming at any rate the worst of the difficulties, metal-built machines were little used (except to a certain extent in Germany) chiefly on account of the need for rapid production and the danger of delay resulting from switching over from known and311 tried methods to experimental types of construction. The Germans constructed some large machines, such as the giant Siemens-Schukhert machine, entirely23 of metal except for the wing covering, while the Fokker and Jünker firms about the time of the Armistice in 1918 both produced monoplanes with very deep all-metal wings (including the covering) which were entirely unstayed externally, depending for their strength on internal bracing24. In Great Britain cable bracing gave place to a great extent to ‘stream-line wires,’ which are steel rods rolled to a more or less oval section, while tie-rods were also extensively used for the internal bracing of the wings. Great developments in the economical use of material were also made in the direction of using built-up main spars for the wings and inter-plane struts; spars composed of a series of layers (or ‘laminations’) of different pieces of wood also being used.
Apart from the metallic25 construction of aeroplanes an enormous amount of work was done in the testing of different steels and light alloys26 for use in engines, and by the end of the War period a number of aircraft engines were in use of which the pistons27 and other parts were of such alloys; the chief difficulty having been not so much in the design as in the successful heat-treatment and casting of the metal.
An important development in connection with the inspection28 and testing of aircraft parts, particularly in the case of metal, was the experimental application of X-ray photography, which showed up latent defects, both in the material and in manufacture, which would otherwise have passed unnoticed. This method was also used to test the penetration29 of glue into the wood on each side of joints30, so giving a measure of the strength;312 and for the effect of ‘doping’ the wings, dope being a film (of cellulose acetate dissolved in acetone with other chemicals) applied31 to the covering of wings and bodies to render the linen32 taut33 and weatherproof, besides giving it a smooth surface for the lessening34 of ‘skin friction’ when passing rapidly through the air.
An important result of this experimental work was that it in many cases enabled designers to produce aeroplane parts from less costly35 material than had previously36 been considered necessary, without impairing37 the strength. It may be mentioned that it was found undesirable38 to use welded joints on aircraft in any part where the material is subject to a tensile or bending load, owing to the danger resulting from bad workmanship causing the material to become brittle—an effect which cannot be discovered except by cutting through the weld, which, of course, involves a test to destruction. Written, as it has been, in August, 1920, it is impossible in this chapter to give any conception of how the developments of War will be applied to commercial aeroplanes, as few truly commercial machines have yet been designed, and even those still show distinct traces of the survival of war mentality39. When, however, the inevitable40 recasting of ideas arrives, it will become evident, whatever the apparent modification41 in the relative importance of different aspects of design, that enormous advances were made under the impetus42 of War which have left an indelible mark on progress.
We have, during the seventeen years since aeroplanes first took the air, seen them grow from tentative experimental structures of unknown and unknowable performance to highly scientific products, of which not only the performances (in speed, load-carrying capacity,313 and climb) are known, but of which the precise strength and degree of stability can be forecast with some accuracy on the drawing board. For the rest, with the future lies—apart from some revolutionary change in fundamental design—the steady development of a now well-tried and well-found engineering structure.
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1
struts
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| （框架的）支杆( strut的名词复数 )； 支柱； 趾高气扬的步态； （尤指跳舞或表演时）卖弄 | |
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2
aeronautical
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| adj.航空（学）的 | |
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3
sketching
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| n.草图 | |
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4
briefly
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| adv.简单地，简短地 | |
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propeller
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| n.螺旋桨，推进器 | |
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propellers
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| n.螺旋桨，推进器( propeller的名词复数 ) | |
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7
muzzle
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| n.鼻口部；口套；枪(炮)口；vt.使缄默 | |
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8
desuetude
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| n.废止，不用 | |
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9
detailed
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| adj.详细的，详尽的，极注意细节的，完全的 | |
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10
motive
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| n.动机，目的；adv.发动的，运动的 | |
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scout
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| n.童子军，侦察员；v.侦察，搜索 | |
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12
armistice
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| n.休战，停战协定 | |
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13
predecessors
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| n.前任( predecessor的名词复数 )；前辈；（被取代的）原有事物；前身 | |
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14
considerably
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| adv.极大地；相当大地；在很大程度上 | |
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15
habitually
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| ad.习惯地，通常地 | |
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16
attained
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| （通常经过努力）实现( attain的过去式和过去分词 )； 达到； 获得； 达到（某年龄、水平、状况） | |
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17
specially
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| adv.特定地；特殊地；明确地 | |
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18
racing
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| n.竞赛，赛马；adj.竞赛用的，赛马用的 | |
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19
fully
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| adv.完全地，全部地，彻底地；充分地 | |
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efficiently
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| adv.高效率地，有能力地 | |
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21
scouts
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| 侦察员[机，舰]( scout的名词复数 )； 童子军； 搜索； 童子军成员 | |
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22
abolition
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| n.废除，取消 | |
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23
entirely
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| ad.全部地，完整地；完全地，彻底地 | |
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24
bracing
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| adj.令人振奋的 | |
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25
metallic
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| adj.金属的；金属制的；含金属的；产金属的；像金属的 | |
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26
alloys
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| n.合金( alloy的名词复数 ) | |
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27
pistons
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| 活塞( piston的名词复数 ) | |
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28
inspection
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| n.检查，审查，检阅 | |
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29
penetration
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| n.穿透，穿人，渗透 | |
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30
joints
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| 接头( joint的名词复数 )； 关节； 公共场所（尤指价格低廉的饮食和娱乐场所） （非正式）； 一块烤肉 （英式英语） | |
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31
applied
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| adj.应用的；v.应用，适用 | |
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32
linen
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| n.亚麻布，亚麻线，亚麻制品；adj.亚麻布制的，亚麻的 | |
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33
taut
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| adj.拉紧的，绷紧的，紧张的 | |
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34
lessening
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| 减轻，减少，变小 | |
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35
costly
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| adj.昂贵的，价值高的，豪华的 | |
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36
previously
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| adv.以前，先前（地） | |
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37
impairing
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| v.损害，削弱( impair的现在分词 ) | |
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38
undesirable
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| adj.不受欢迎的，不良的，不合意的，讨厌的；n.不受欢迎的人，不良分子 | |
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39
mentality
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| n.心理，思想，脑力 | |
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40
inevitable
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| adj.不可避免的，必然发生的 | |
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41
modification
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| n.修改，改进，缓和，减轻 | |
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42
impetus
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| n.推动，促进，刺激；推动力 | |
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