in the last section an attempt has been made to show how, during what was from the design standpoint perhaps the most critical period, order gradually became evident out of chaos, ill-considered ideas dropped out through failure to make good, and, though there was still plenty of room for improvement in details, the bulk of the aeroplanes showed a general similarity in form and conception. there was still a great deal to be learnt in finding the best form of wing section, and performances were still low; but it had become definitely possible to say that flying had emerged from the chrysalis stage and had become a science. the period which now began was one of scientific development and improvement—in performance, man?uvrability, and general airworthiness and stability.
the british military aeroplane competition held in the summer of 1912 had done much to show the requirements in design by giving possibly the first opportunity for a definite comparison of the performance of different machines as measured by impartial observers on standard lines—albeit the methods of measuring were crude. these showed that a high speed—for those days—of 75 miles an hour or so was attended by disadvantages in the form of an equally fast low speed, of 50 miles per hour or more, and generally may297 be said to have given designers an idea what to aim for and in what direction improvements were required. in fact, the most noticeable point perhaps of the machines of this time was the marked manner in which a machine that was good in one respect would be found to be wanting in others. it had not yet been possible to combine several desirable attributes in one machine. the nearest approach to this was perhaps to be found in the much discussed government b.e.2 machine, which was produced from the royal aircraft factory at farnborough, in the summer of 1912. though considerably criticised from many points of view it was perhaps the nearest approach to a machine of all-round efficiency that had up to that date appeared. the climbing rate, which subsequently proved so important for military purposes, was still low, seldom, if ever, exceeding 400 feet per minute; while gliding angles (ratio of descent to forward travel over the ground with engine stopped) little exceeded 1 in 8.
the year 1912 and 1913 saw the subsequently all-conquering tractor biplane begin to come into its own. this type, which probably originated in england, and at any rate attained to its greatest excellence prior to the war from the drawing offices of the avro bristol and sopwith firms, dealt a blow at the monoplane from which the latter never recovered.
the two-seater tractor biplane produced by sopwith and piloted by h. g. hawker, showed that it was possible to produce a biplane with at least equal speed to the best monoplanes, whilst having the advantage of greater strength and lower landing speeds. the sopwith machine had a top speed of over 80 miles an hour while landing as slowly as little more than 30 miles298 an hour; and also proved that it was possible to carry 3 passengers with fuel for 4 hours’ flight with a motive power of only 80 horse-power. this increase in efficiency was due to careful attention to detail in every part, improved wing sections, clean fuselage-lines, and simplified undercarriages. at the same time, in the early part of 1913 a tendency manifested itself towards the four-wheeled undercarriage, a pair of smaller wheels being added in front of the main wheels to prevent overturning while running on the ground; and several designs of oleo-pneumatic and steel-spring undercarriages were produced in place of the rubber shock-absorber type which had up till then been almost universal.
these two statements as to undercarriage designs may appear to be contradictory, but in reality they do not conflict as they both showed a greater attention to the importance of good springing, combined with a desire to avoid complication and a mass of struts and wires which increased head resistance.
the olympia aero show of march, 1913, also produced a machine which, although the type was not destined to prove the best for the purpose for which it was designed, was of interest as being the first to be designed specially for war purposes. this was the vickers ‘gun-bus,’ a ‘pusher’ machine, with the propeller revolving behind the main planes between the outriggers carrying the tail, with a seat right in front for a gunner who was provided with a machine gun on a swivelling mount which had a free field of fire in every direction forward. the device which proved the death-blow for this type of aircraft during the war will be dealt with in the appropriate place later, but the machine should not go unrecorded.
299 as a result of a number of accidents to monoplanes the government appointed a committee at the end of 1912 to inquire into the causes of these. the report, which was presented in march, 1913, exonerated the monoplane by coming to the conclusion that the accidents were not caused by conditions peculiar to monoplanes, but pointed out certain desiderata in aeroplane design generally which are worth recording. they recommended that the wings of aeroplanes should be so internally braced as to have sufficient strength in themselves not to collapse if the external bracing wires should give way. the practice, more common in monoplanes than biplanes, of carrying important bracing wires from the wings to the undercarriage was condemned owing to the liability of damage from frequent landings. they also pointed out the desirability of duplicating all main wires and their attachments, and of using stranded cable for control wires. owing to the suspicion that one accident at least had been caused through the tearing of the fabric away from the wing, it was recommended that fabric should be more securely fastened to the ribs of the wings, and that devices for preventing the spreading of tears should be considered. in the last connection it is interesting to note that the french deperdussin firm produced a fabric wing-covering with extra strong threads run at right angles through the fabric at intervals in order to limit the tearing to a defined area.
in spite, however, of the whitewashing of the monoplane by the government committee just mentioned, considerable stir was occasioned later in the year by the decision of the war office not to order any more monoplanes; and from this time forward until the war300 period the british army was provided exclusively with biplanes. even prior to this the popularity of the monoplane had begun to wane. at the olympia aero show in march, 1913, biplanes for the first time outnumbered the ‘single-deckers’ (as the germans call monoplanes); which had the effect of reducing the wing-loading. in the case of the biplanes exhibited this averaged about 4? lbs. per square foot, while in the case of the monoplanes in the same exhibition the lowest was 5? lbs., and the highest over 8? lbs. per square foot of area. it may here be mentioned that it was not until the war period that the importance of loading per horse-power was recognised as the true criterion of aeroplane efficiency, far greater interest being displayed in the amount of weight borne per unit area of wing.
an idea of the state of development arrived at about this time may be gained from the fact that the commandant of the military wing of the royal flying corps in a lecture before the royal aeronautical society read in february, 1913, asked for single-seater scout aeroplanes with a speed of 90 miles an hour and a landing speed of 45 miles an hour—a performance which even two years later would have been considered modest in the extreme. it serves to show that, although higher performances were put up by individual machines on occasion, the general development had not yet reached the stage when such performances could be obtained in machines suitable for military purposes. so far as seaplanes were concerned, up to the beginning of 1913 little attempt had been made to study the novel problems involved, and the bulk of the machines at the monaco meeting in april, 1913, for instance, consisted of land301 machines fitted with floats, in many cases of a most primitive nature, without other alterations. most of those which succeeded in leaving the water did so through sheer pull of engine power; while practically all were incapable of getting off except in a fair sea, which enabled the pilot to jump the machine into the air across the trough between two waves. stability problems had not yet been considered, and in only one or two cases was fin area added at the rear high up, to counterbalance the effect of the floats low down in front. both twin and single-float machines were used, while the flying boat was only just beginning to come into being from the workshops of sopwith in great britain, borel-denhaut in france, and curtiss in america. in view of the approaching importance of amphibious seaplanes, mention should be made of the flying boat (or ‘bat boat’ as it was called, following rudyard kipling) which was built by sopwith in 1913 with a wheeled landing-carriage which could be wound up above the bottom surface of the boat so as to be out of the way when alighting on water.
during 1913 the (at one time almost universal) practice originated by the wright brothers, of warping the wings for lateral stability, began to die out and the bulk of aeroplanes began to be fitted with flaps (or ‘ailerons’) instead. this was a distinct change for the better, as continually warping the wings by bending down the extremities of the rear spars was bound in time to produce ‘fatigue’ in that member and lead to breakage; and the practice became completely obsolete during the next two or three years.
the gordon-bennett race of september, 1913, was again won by a deperdussin machine, somewhat302 similar to that of the previous year, but with exceedingly small wings, only 107 square feet in area. the shape of these wings was instructive as showing how what, from the general utility point of view, may be disadvantageous can, for a special purpose, be turned to account. with a span of 21 feet, the chord was 5 feet, giving the inefficient ‘aspect ratio’ of slightly over 4 to 1 only. the object of this was to reduce the lift, and therefore the resistance, to as low a point as possible. the total weight was 1,500 lbs., giving a wing-loading of 14 lbs. per square foot—a hitherto undreamt-of figure. the result was that the machine took an enormously long run before starting; and after touching the ground on landing ran for nearly a mile before stopping; but she beat all records by attaining a speed of 126 miles per hour. where this performance is mainly interesting is in contrast to the machines of 1920, which with an even higher speed capacity would yet be able to land at not more than 40 or 50 miles per hour, and would be thoroughly efficient flying machines.
r.a.f. aeroplane.
the rheims aviation meeting, at which the gordon-bennett race was flown, also saw the first appearance of the morane ‘parasol’ monoplane. the morane monoplane had been for some time an interesting machine as being the only type which had no fixed surface in rear to give automatic stability, the movable elevator being balanced through being hinged about one-third of the way back from the front edge. this made the machine difficult to fly except in the hands of experts, but it was very quick and handy on the controls and therefore useful for racing purposes. in the ‘parasol’ the modification was introduced of raising the wing above the body, the pilot looking out303 beneath it, in order to give as good a view as possible.
before passing to the year 1914 mention should be made of the feat performed by nesteroff, a russian, and pégoud, a french pilot, who were the first to demonstrate the possibilities of flying upside-down and looping the loop. though perhaps not coming strictly within the purview of a chapter on design (though certain alterations were made to the top wing-bracing of the machine for this purpose) this performance was of extreme importance to the development of aviation by showing the possibility of recovering, given reasonable height, from any position in the air; which led designers to consider the extra stresses to which an aeroplane might be subjected and to take steps to provide for them by increasing strength where necessary.
when the year 1914 opened a speed of 126 miles per hour had been attained and a height of 19,600 feet had been reached. the sopwith and avro (the forerunner of the famous training machine of the war period) were probably the two leading tractor biplanes of the world, both two-seaters with a speed variation from 40 miles per hour up to some 90 miles per hour with 80 horse-power engines. the french were still pinning their faith mainly to monoplanes, while the germans were beginning to come into prominence with both monoplanes and biplanes of the ‘taube’ type. these had wings swept backward and also upturned at the wing-tips which, though it gave a certain measure of automatic stability, rendered the machine somewhat clumsy in the air, and their performances were not on the whole as high as those of either france or great britain.
304 early in 1914 it became known that the experimental work of edward busk—who was so lamentably killed during an experimental flight later in the year—following upon the researches of bairstow and others had resulted in the production at the royal aircraft factory at farnborough of a truly automatically stable aeroplane. this was the ‘r.e.’ (reconnaissance experimental), a development of the b.e. which has already been referred to. the remarkable feature of this design was that there was no particular device to which one could point out as the cause of the stability. the stable result was attained simply by detailed design of each part of the aeroplane, with due regard to its relation to, and effect on, other parts in the air. weights and areas were so nicely arranged that under practically any conditions the machine tended to right itself. it did not, therefore, claim to be a machine which it was impossible to upset, but one which if left to itself would tend to right itself from whatever direction a gust might come. when the principles were extended to the ‘b.e. 2c’ type (largely used at the outbreak of the war) the latter machine, if the engine were switched off at a height of not less than 1,000 feet above the ground, would after a few moments assume its correct gliding angle and glide down to the ground.
the paris aero salon of december, 1913, had been remarkable chiefly for the large number of machines of which the chassis and bodywork had been constructed of steel-tubing; for the excess of monoplanes over biplanes; and (in the latter) predominance of ‘pusher’ machines (with propeller in rear of the main planes) compared with the growing british preference for ‘tractors’ (with air-screw in front). incidentally, the305 maurice farman, the last relic of the old type box-kite with elevator in front appeared shorn of this prefix, and became known as the ‘short-horn’ in contradistinction to its front-elevatored predecessor which, owing to its general reliability and easy flying capabilities, had long been affectionately called the ‘mechanical cow.’ the 1913 salon also saw some lingering attempts at attaining automatic stability by pendulum and other freak devices.
apart from the appearance of ‘r.e.1,’ perhaps the most notable development towards the end of 1913 was the appearance of the sopwith ‘tabloid’ tractor biplane. this single-seater machine, evolved from the two-seater previously referred to, fitted with a gnome engine of 80 horse-power, had the, for those days, remarkable speed of 92 miles an hour; while a still more notable feature was that it could remain in level flight at not more than 37 miles per hour. this machine is of particular importance because it was the prototype and forerunner of the successive designs of single-seater scout fighting machines which were used so extensively from 1914 to 1918. it was also probably the first machine to be capable of reaching a height of 1,000 feet within one minute. it was closely followed by the ‘bristol bullet,’ which was exhibited at the olympia aero show of march, 1914. this last pre-war show was mainly remarkable for the good workmanship displayed—rather than for any distinct advance in design. in fact, there was a notable diversity in the types displayed, but in detailed design considerable improvements were to be seen, such as the general adoption of stranded steel cable in place of piano wire for the main bracing.
