They returned to Dayton, and spent the winter in experiment and research. They had taken up aeronautics partly as a sport; they were now drawn deeper and deeper into the scientific study of it. They made a wind-tunnel, sixteen inches square and about six feet long, and tested in it the lift and drag of model wings, made in various sizes and with various aspect ratios. The tables which they compiled from these experiments were continually used by them thereafter, and superseded the tables of Lilienthal and Langley, which took no account of the aspect ratio. When they returned to Kitty Hawk, in the autumn of 1902, they took with them a greatly improved glider. The aspect ratio of the planes was six to one, instead of about three to one, as in their second glider. Further, while preserving the horizontal vane, or elevator, at the front of the machine, they added a vertical vane, or rudder, at the rear. It was their failure to control the lateral balance in the experiments of 1901 that suggested this device to them. From the first they had discarded the method, practised by Lilienthal and Pilcher, of adjusting the lateral balance by shifting the weight of the operator's body. This method seemed to them 'incapable of expansion to meet large conditions, because the weight to be moved and the distance of possible motion were limited, while the disturbing forces steadily increased, both with wing area and with wing velocity'. Accordingly they invented a method of warping the wings, to present them to the wind at different angles on the right and left sides. Thus the force of the wind was used to restore the balance which the wind itself had disturbed. But in their early gliders this warping process acted in an unexpected way. The wing which, in order to raise that side of the machine, was presented to the wind at the greater angle of incidence often proved to be the wing which lagged and sank. The decrease in speed, due to the extra drag, more than counterbalanced the effect of the larger angle. When they attempted to remedy this by introducing a fixed vertical vane in the rear, 'it increased the trouble and made the machine 'absolutely dangerous'. Any side-slip became irrecoverable by causing the vertical fixed vane to strike the wind on the side toward the low wing, instead of on the side toward the high wing, as it should have done to correct the balance. 'It was some time', the brothers remark, 'before a remedy was discovered. This consisted of movable rudders working in conjunction with the twisting of the wings.' So that now three different parts of the machine had to be controlled by wires, worked swiftly and correctly by the operator, to preserve the balance. There were the wing tips which had to be warped. There was the horizontal vane in front which had to be adjusted, to keep the machine in level flight or to bring it to the ground. There was the vertical vane behind which had to be moved this way and that to secure the desired effect from the warping of the wings. 'For the sake of simplicity,' says Wilbur Wright, 'we decided to attach the wires controlling the vertical tail to the wires warping the wings, so that the operator, instead of having to control three things at once, would have to attend to only the forward horizontal rudder and the wing warping mechanism; and only the latter would be needed for controlling lateral balance.'

The thing was done. They had built an aeroplane that could fly; and the later introduction of an engine was as simple a matter as the harnessing of a horse to a carriage. 'With this apparatus', says Wilbur Wright, speaking of the glider of 1902, 'we made nearly seven hundred glides in the two or three weeks following. We flew it in calms and we flew it in winds as high as thirty-five miles an hour. We steered it to right and left, and performed all the evolutions necessary for flight. This was the first time in the history of the world that a movable vertical tail had been used in controlling the direction or the balance of a flying machine. It was also the first time that a movable vertical tail had been used, in combination with wings adjustable to different angles of incidence, in controlling the balance and direction of an aeroplane. We were the first to functionally employ a movable vertical tail in a flying aeroplane. We were the first to employ wings adjustable to respectively different angles of incidence in a flying aeroplane. We were the first to use the two in combination in a flying aeroplane.'

It is a large claim, and every word of it is true. New inventions are commonly the work of many minds, and it would be easy to name at least half a dozen men to whose work the Wrights were indebted. But these were tributaries; the main achievement belongs wholly to the Wrights. Their quiet perseverance, through long years, in the face of every kind of difficulty, is only a part of their distinction; the alertness and humility of mind which refused all traffic with fixed ideas, and made dangers and disappointments the material of education, is what stamps them with greatness. They put themselves to school to the winds. They knew that there is no cheap or easy way to master nature, and that only the human spirit, at its best and highest, can win through in that long struggle. Their patience never failed. 'Skill', says Wilbur Wright, 'comes by the constant repetition of familiar feats rather than by a few overbold attempts at feats for which the performer is yet hardly prepared.' Man must learn to fly as he learns to walk. 'Before trying to rise to any dangerous height a man ought to know that in an emergency his mind and muscles will work by instinct rather than by conscious effort. There is no time to think.'

The machine of 1902, which might be called the victory machine, deserves a full description. It was a double-decked machine, with two planes fixed by struts one above the other about five feet apart. The planes were thirty-two feet in span, and five feet in chord. The total area of their supporting surfaces was about three hundred and five square feet. The operator lay on his face in the middle of the lower plane. The horizontal rudder in front had a supporting surface of fifteen square feet. The vertical tail, as they called it, which was the true rudder, was reduced after trial to six square feet. The machine was supported on the ground by skids, and was very strongly built. It weighed a hundred and sixteen and a half pounds, to which must be added about a hundred and forty pounds for the weight of the operator. It performed about a thousand glides, with only one injury, though it made many hard landings at full speed on uneven ground. The longest glide was 622-1/2 feet, traversed in twenty-six seconds. The glides were made from the Kill Devil sand-hills, near Kitty Hawk—mounds of sand heaped up by the wind, the biggest having a height of a hundred feet.

The time had now come to invite an engine to bear a part in the proceedings. In the autumn of 1903 the brothers returned to Kitty Hawk for their fourth season of experiment. They had built in the winter a machine weighing six hundred pounds, including the operator and an eight horse-power motor. Finding that the motor gave more power than had been estimated, they added a hundred and fifty pounds of weight in strengthening the wings and other parts. The airscrews, built from their own calculations, gave in useful work two-thirds of the power expended. Before trying this machine, however, they continued their practice with the old glider, and made a number of flights in which they remained in the air for over a minute, often soaring for a considerable time in one spot, without any descent at all.

It was late in the season, the 17th of December 1903, when they first tried the power machine. A general invitation to be present at the trial had been given to the people living within five or six miles, but 'not many were willing to face the rigours of a cold December wind in order to see, as they no doubt thought, another flying machine not fly'. Five persons besides the brothers were present. Mr. Orville Wright's narrative, written for the Aeronautical Society of Great Britain, must be given in his own words:

'On the morning of December 17th, between the hours of 10.30 o'clock and noon, four flights were made, two by Mr. Orville Wright, and two by Mr. Wilbur Wright. The starts were all made from a point on the levels, and about 200 feet west of our camp, which is located about a quarter of a mile north of the Kill Devil Sand Hill, in Dare County, North Carolina. The wind at the time of the flights had a velocity of twenty-seven miles an hour at 10 o'clock, and 24 miles an hour at noon, as recorded by the anemometer at the Kitty Hawk weather bureau station. This anemometer is 30 feet from the ground. Our own measurements, made with a hand-anemometer at a height of four feet from the ground, showed a velocity of about 22 miles when the first flight was made, and 20-1/2 miles at the time of the last one. The flights were directly against the wind. Each time the machine started from the level ground by its own power alone, with no assistance from gravity or any other sources whatever. After a run of about 40 feet along a mono-rail track, which held the machine eight inches from the ground, it rose from the track and, under the direction of the operator, climbed upward on an inclined course till a height of 8 or 10 feet from the ground was reached, after which the course was kept as near horizontal as the wind gusts and the limited skill of the operator would permit. Into the teeth of a December gale the Flyer made its way forward with a speed of 10 miles an hour over the ground, and 30 to 35 miles an hour through the air. It had previously been decided that, for reasons of personal safety, these first trials should be made as close to the ground as possible. The height chosen was scarcely sufficient for manœuvring in so gusty a wind and with no previous acquaintance with the conduct of the machine and its controlling mechanisms. Consequently the first flight was short. The succeeding flights rapidly increased in length and at the fourth trial a flight of 59 seconds was made, in which time the machine flew a little more than a half-mile through the air and a distance of 852 feet over the ground. The landing was due to a slight error of judgement on the part of the operator. After passing over a little hummock of sand, in attempting to bring the machine down to the desired height the operator turned the rudder too far, and the machine turned downward more quickly than had been expected. The reverse movement of the rudder was a fraction of a second too late to prevent the machine from touching the ground and thus ending the flight. The whole occurrence occupied little, if any, more than one second of time.

'Only those who are acquainted with practical aeronautics can appreciate the difficulties of attempting the first trials of a flying machine in a 25-mile gale. As winter was already well set in, we should have postponed our trials to a more favourable season, but for the fact that we were determined, before returning home, to know whether the machine possessed sufficient power to fly, sufficient strength to withstand the shock of landings, and sufficient capacity of control to make flight safe in boisterous winds, as well as in calm air. When these points had been definitely established, we at once packed our goods and returned home, knowing that the age of the flying machine had come at last.'

CHAPTER II

THE AEROPLANE AND THE AIRSHIP