In military airships, and, it may be added, aëroplanes also, the colour should be a neutral tint that is as invisible as possible against the sky. Most of the airships have been made a glaring yellow, so that the india-rubber in the envelopes may be better preserved from the action of light. This protection may have to be sacrificed to the overpowering advantages of invisibility in the case of naval and military airships.
CHAPTER VI
THE ADVENT OF THE AËROPLANE
The year of 1908 will be memorable in aëronautical science for its demonstration of the possibility of mechanical flight. Day after day in France and America was then seen the spectacle of men flying in the air, with a grace equal to that of the soaring bird. This was done with a machine not raised by the buoyancy of a gas, but with one that was heavier than the medium in which it travels, and whose sustentation and direction was accomplished by dexterity and skill. The experiments of the brothers Wright were new triumphs of man, new examples of the old truths that a difficulty is a thing to be overcome, and that the impossibility of to-day may be the achievement of to-morrow. This progress in human flight was not the result of any new discovery; it was the sequence of a long series of experiments; nor was it one nation only that forged the links that connected past researches to the successful issues of the present century.
It is, however, not without honour to the British nation that one of the fundamental principles of the biplane was proposed and elucidated by a Briton in 1866. I refer to the important principle of superposed surfaces advanced in that year by the late F. H. Wenham. He pointed out that the lifting power of such a surface can be most economically obtained by placing a number of small surfaces above each other. Wenham built flying machines on this principle with appliances for the use of his own muscular power. He obtained valuable results as to the driving power of his superposed surfaces, but he did not accomplish flight.
In 1872, H. von Helmholtz emphasised the improbability that man would ever be able to drive a flying machine by his own muscular exertion. After his statements there came a period of stagnation in the attempts to navigate the air by bodies heavier than air.
It is difficult to say how much aëronautical science owes to two illustrious names—Sir Hiram Maxim and the late Professor Langley. The two eminent men took up the subject of flight about the same time in the last decade of the last century, and applied to it all the scientific knowledge of the time. The flying machine had come to be associated in the public mind with foolhardiness and failure. In the discussion following Sir Hiram Maxim’s paper, “Experiments in Aëronautics,” read before the Society of Arts on November 28th, 1894, he said, “At the time I took up this subject it was almost considered a disgrace for anyone to think of it; it was quite out of the question practically.” But these two scientific men stepped into the breach, rescued aëronautics from a fallen position, and fired in its cause the enthusiasm of men of light and leading.
Sir Hiram Maxim built the largest flying machine that had been constructed. It spread 4,000 square feet of supporting surface, and weighed 8,000 lb. The screw propellers were no less than 17 feet 11 inches in diameter, the width of the blade at the tip being 5 feet. The boiler was of 363 h.p. The machine ran on wheels on a railway line, and was restrained from premature flight by two wooden rails placed on each side above the wheels. On one occasion, however, the machine burst through the wooden rails and flew for 300 feet.
In 1896 Langley’s tandem-surfaced model aërodrome had luck with the aërial currents, and flew for more than three-quarters of a mile over the Potomac River. This machine had 70 square feet supporting surface, weighed 72 lb., and had an engine of 1 h.p., weighing 7 lb. It is well known how, in later years, Langley exaggerated his model into a machine which carried a man, and how twice, when it was put to the test over water, at the very moment of being launched, it caught in the launching ways and was pulled into the water. It is interesting to note that the American aviator, Mr. Curtiss, has lately unearthed the Langley flying machine, and flown on it. Thus to Langley has come a posthumous aëronautical honour.
Lilienthal, in Germany, in considering equilibrium, experimented with what are called gliding machines—aëroplanes which are launched from some hillside against the wind, and depend upon gravity for their motive power. In this way the art of balancing could be practised on motorless gliders. With Lilienthal commenced the age of systematic experimental flight; he made the discovery of the driving forward of arched surfaces against the wind; he made some 2,000 glides, and sometimes from a height of 30 metres he glided 300 metres. The underlying principle of maintaining equilibrium in the air has been recognised to be that the centre of pressure should at all times be on the same vertical line as the centre of gravity due to the weight of the apparatus. Lilienthal sought to keep his balance by altering the position of his centre of gravity by movements of his body. One day he was upset by a side gust and was killed. Pilcher, in England, took up his work. With his soaring machines he made some hundred glides, but he also made one too many. One day, in 1899, in attempting to soar from level ground by being towed by horses, his machine broke, and he fell to the ground. He died shortly afterwards, a British martyr of the air.
Mr. Octave Chanute’s experiments in 1896–1902 formed important links in flight development. He first introduced the vital principle of making the surfaces movable instead of the aviator, and he made use of superposed surfaces. Though his work was a stage in the development of the flying machine, it was reserved to two other geniuses, the brothers Wright, to bring flight to a point of progress where prejudiced critics would be for ever silenced.