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14 and bettered under the circumstances? Yet strength factors were introduced, down pressures foreseen, fine lines provided, wing shapes and controls improved, alighting gear developed and instability cured. This is the subject matter of Section II. which is closely allied to Section III.

Aerodynamics (see Section III.). Aerodynamic theory had risen out of the void at the bidding of the applied mathematician before 1909, but it developed at the call of designers who would have been tied to the repetition of old methods had not theory justified de- parture. Once aerodynamic theory was established their inspiration could take wing.

The deductions l from wind tunnel experiments on models 2 ft. long could be but surmises till the principle of dynamic " similarity " emboldened designers to transfer the wind tunnel results to the 4O-ft. machines. " Scale effect," " slipstream effect," pressure distribu- tion, phugoids, and the like, had to be verified on the full-sized aeroplane and measured in the course of flight with the cooperation of a few keen fliers, at a time when pilots at large were almost antag- onistic to " theory." Mathematics had been applied to the motion of aeroplanes through the air in advance of even the earliest flight, and several separate starts were made. England, represented by F. W. Lanchester, was easily first. Lanchester made great strides, at a time when he had no wind channel for his model verifications. Bryan came independently; L. Bairstow had the wind tunnel, of which he has indicated the arrangement in Section VI. and greatly advanced the problems. It was E. T. Busk who in 1913 in his own person as flier verified the theories he had formed and achieved stable flight cm " RE I " (see Plate I., fig. l). America had led in initiating practical flight; France in model experiments, rotary engines and speed records; Germany in length of aeroplane flight and in rigid airships; but in the matter of stability and of scientific analysis on both model and full scale, Britain took the lead before the war and still kept it in 1921. Something of each national temperament is disclosed by these specializations.

Construction and Materials (see Section IV.). Aircraft con- structional methods are to be regarded from two points of view the one where a few craft are to be made as perfect as possible, and the other where bulk production is demanded.

Before 1914 there was no output of aircraft in Britain other than by units; in France there was some manufacturing, in America a little, and in Germany rather more. These countries had factories proper where repetitive processes were employed. An army, small in numbers, was deemed in Britain to need correspondingly few aircraft. A large navy neglected them. When bulk production came it came with a will, but designs that were admirable for unitary construction were found ill adapted to bulk manufacture, and the British story of changes in material and methods which is outlined in Section IV. is typical of the war period everywhere.

The tautening of fabrics with cellulose acetate, the evolution of the fairshaped strut and wire, the steerable tail skid, sewing the fabric to the wing ribs, covering the wheel spoke with fabric, were among the step-by-step advances which all belong to the period before large outputs were contemplated, i.e. the period when, for example, joints were machined from the solid steel bar. The plywood body, the spars of built-up wood, the standard relation of radiator to engine size, the pressed metal turnbuckle and the thorough inter- changeability of detail parts belong to the " bulk output " period, as also incidentally much speeding-up of processes and methods, the evolving of glues and cements, fine castings, new alloys and the wide- spread use of tests not hitherto commercialized but known to be good by the few. It would be truer to say that the World War dis- seminated the science of aeronautics rather than that it fostered it. The war did foster the technics of quantity production.

Aero Engines (see Section V.). Man would have flown long before he did but for the lack of a light engine. One cwt. per horse-power was about the weight of the commercial gas engine, and to fly he wanted one twenty times lighter. The French rotary engine of 1909-10 was the most real promoter of aerial experience of its time, for it weighed 4 Ib. where a motor-car engine weighed ten. How and by what grouping of parts, increases of compression and refinements of design this weight has been cut down to 2 Ib. with fuel economy on a similar scale, appears in Section V. Here it will only be noted that the Germans on the basis of airship experience had inclined rather earlier than others to big powers on aeroplanes, and their aeroplane successes on aerodynamically inferior craft were due to big engines. Their engines were water-cooled, rather heavy but reliable. The radial air-cooled engine of the French has been mentioned above. The British service was late to realize how very big the war aero engine must be, and developed an air-cooled, non-rotary and some good water-cooled motors eventually of adequate sizes. The Americans made good use of the experience poured in upon them from Europe when they began in 1917 to tackle the Liberty engine of 450 H.P. Apart from size, the advances in view to-day are considerable. The means for protecting ourselves from the fire risks on crash due to petrol are also being evolved.

Navigation (see Section VI.). Aerial navigation, as distinct from piloting with the ground in view, developed tardily everywhere, though first in Britain. It was a surprise to find that raiding airships

1 See " Flight," 1912, pp. 32, 33.

from Germany disclosed no up-to-date navigating apparatus when they were brought down, nor had their aeroplanes any turn indicator to guide them when immersed in cloud or fog. Even after seeing the Lucas compass (see Plate I., fig. 2) on captured aeroplanes they did not appreciate or copy it, nor its principle of the "space-damped" vertical card, spherical bowl and long period; nor was there any- where an instrument to compare with the British apparatus figured in Section VI. The air speed indicator that uses the principle of Pilot was also a British idea, which displaced the earlier French flat plate pressed back by the wind against a spring, and other such speed-meters.

Control of A ir Traffic and A ir Stations. Air stations and the rules evolved to control traffic have a section (VII.) to themselves. The early stations were fields and each flier a law to himself. When the Air Convention of Oct. 1919 is ratified all aircraft will be taboo that have not a specific factor of strength and an adequate field of view for the flier. As we progress all stations will give wireless warning to those approaching them when they are immersed in fog and will afford facilities for night alighting. The movement is in this direc- tion. The mobility of aircraft makes international agreement on all rules for alighting, racing, and signalling warnings very important. Bodies like the Royal Aero Club in Britain exist in each county and meet annually for these purposes.

Seaplanes (see Section VIII.). The seagoing seaplane is relatively backward. To make a craft light enough to fly and heavy enough to stand the buffets of the open sea up to the speed needed to quit the waves in flight is a problem which was not fully solved even under the war stimulus. It was tackled too late by Britain no less than the others. Even the high-speed " float " seaplane was neglected in England but it eventually advanced in Germany to be a formidable offence against the air enemies of the submarine. Theirs was not, however, a craft that could ride out a sea. The American NC3 made a record by riding on the water for 150 miles in its Atlantic crossing. It was an achievement to withstand the sea so long even though the craft was travelling backwards all the 150 miles. Section VIII. shows that scientific work is being applied to the problem, notably in the matter of stability when changing from waterborne to airborne conditions.

Airships (see Section IX.). Airship knowledge gave to Germany technical advantages which would have been even more valuable to Britain. They did not use on aeroplanes the identical engines of their airships, but the experience of large aero engines of the utmost reliability and economy was there. The dominant advantages of airships are that they fly for long hours, carry large weights, do not descend for an engine failure and can safely fly by night. In con- sequence of night flying they are able on long journeys to outstrip the aeroplane in speed from point to point. High cost of housing and the numbers required to handle them on the ground were their chief hampering factors, but the wonderful development of the mooring mast, a British device, has improved the position. The towing of airship by airship and by submarine, the protection of fabric from deterioration, the use of non-inflammable gas are all landmarks in their evolution. The kite balloon and the parachute also need mention, though opinions differ as to the advisability of giving the latter to the commercial aeroplane as a life-belt is given to the liner. It is of little use unless the jump is made over 200 ft. from the ground; if a high wind is blowing the parachutist meets the ground with the sideways speed of the wind and it absorbs 18% of the useful (passenger) load. This position is, however, the result of great advances which have assuredly not ceased.

Each sectional aspect of aeronautics between 1909 and 1921 divides itself into three periods: before, during and after the war. The dominant emotions and aspirations of those periods governed men's thoughts whether they were flying, designing, calculating; experimenting with engines, model aeroplanes or safety devices; evolving navigational instruments, tests for pilots against gid- diness, or parachutes to save the lookouts on kite balloons. Before the war the aircraft builder starved although it was early accepted that frontiers, rivers, chasms, forests and entrenched positions could be crossed by anyone brave enough to fly, but that acceptance was half-hearted. It now amazes one to realize that in 1911 the speed of flight was regarded as a defect for the military aeroplane, or that vulnerability by gun-fire from the ground was its supposed weakness. The Governments demanded that their aeroplanes should be transported in crates, or towed with folded wings to their jumping-off place (see Plate I., fig. 3). An aeroplane was a mute observer; no means of continuously trans- mitting observations say of artillery fire or enemy movements or for malung photographic records had been tried out, accepted as good or prepared in quantity. Imagination is greater than fact when the imagination is active: all these effects could easily be, and were, imagined once flight was admitted but the state is a herd, and extends its imaginative power like a herd to the distance of the next meal or next year's crop. All nations econo-