How two American engineers followed up Lilienthal’s work—Their biplane glider and its ingenious control—First experiments and successes.

For those who might care to study them, Lilienthal had written papers and essays as explanations of his work, and when the news of his death was flashed round the world, inventors were induced to turn to these teachings and read for themselves what he had done. Among those who were interested were two young Americans, unknown then, but now world-famous—Wilbur and Orville Wright. Living in Dayton, Ohio, they were the sons of Milton Wright, a prominent church worker of that city, and they carried on a bicycle store and engineer’s shop. Both were born engineers—keen, clever, patient, and enthusiastic in their work; and they had discussed many times—before they read of Lilienthal’s death—the problem of building an aeroplane. Now this interest was re-awakened; and as Wilbur Wright himself said:

“The brief notice of his (Lilienthal’s) death which appeared in the telegraphic news at that time, aroused a passive interest which had existed from my childhood, and led me to take down from the shelves of our home library a book on “Animal Mechanism” by Professor Marey, which I had already read several times. From this I was led to read more modern works, and as my brother soon became equally interested with myself, we passed from the reading to the thinking, and finally to the working stage.”

What the Wrights first set themselves to do was to investigate previous data. They wanted to prove, if they could, whether this data was sound or badly reasoned: they needed a firm and definite basis of their own before they would build any large machine. So they tested the theories of their predecessors and made experiments, particularly as to the sustaining power of surfaces of various shapes and curves. To this end they built and flew kites, studying the lift they exercised; then they decided to build a light gliding machine, such as Lilienthal had used. But there was a drawback to be faced in all such practical work, and the Wrights saw it clearly; this was to get a sufficient amount of actual flying. It was Wilbur who wrote:

“It seemed to us that the main reason why the problem had remained so long unsolved was that no one had been able to obtain any adequate practice. It would not be considered at all safe for a bicycle rider to attempt to ride through a crowded city street after only five hours’ practice, spread out in bits of 10 seconds each over a period of five years; yet Lilienthal, with this brief practice, was remarkably successful in meeting the fluctuations and eddies of the wind gusts.”

They made up their minds to build a glider with ample wing-surface, so that it would be sustained in light breezes, and to take the machine to where they might be sure of a steady wind, and there fly it as a kite; allow it, that is to say, to ascend into the air at the end of a rope, and hold it steady against the wind while the operator practised his balancing movements.

Their first glider was a biplane, with 165 square feet of lifting surface, as illustrated in Fig. 28; several of its features need explanation. First there is the position of the operator; he can be seen lying prone across the centre of the lower plane. This attitude was adopted by the Wrights to minimise wind-pressure. Should a man be upright in his machine, they calculated that his body would, as the glider passed through the air, offer an appreciable resistance; while, in lying flat, he would offer scarcely any resistance at all.

A small horizontal plane will be noted in front of the main-planes; this was to govern the rising and descending of the machine. The Wrights came to the conclusion that any body-moving method for controlling their craft, such as Lilienthal had adopted, would not be sufficiently powerful in a wind. Lilienthal, it will be remembered, had found his control weaken when he used a machine of large surface. So the Wrights decided that, instead of altering the centre of gravity of their machine when gusts struck it, they would leave the centre of gravity immovable and shift the centre of pressure upon their planes. This was done partly by the elevating plane, as it came to be called. Tilted upward, this had the effect of raising the front of the glider, and causing the centre of pressure to travel backward upon the planes. Tilted down, it made the planes dip forward, and brought the centre of pressure nearer their front edge. When he wanted to rise, the pilot raised the elevator; when he wished to glide earthward, he inclined it down. Here, indeed, was the method such as was described in Fig. 13, when dealing with the machine Sir Hiram Maxim built; and this system of the lifting plane is worthy of special mention. In one way or another, fitted in front of the planes or behind them, it is the recognised method for controlling the rise or descent of an aeroplane.

Apart from governing the ascending or descending movement, there was the question of preventing a machine from slipping sideways; and this the Wrights solved ingeniously. They saw, of course, that when their glider lurched to one side or the other, they would need some power to tilt it back again. So they devised a system by which the plane-ends of their machine—being made flexible—might be warped, or caused to shift up and down. This action the operator controlled, as he lay across the lower plane, by a movement of cords, and its operation is shown in Fig. 29. The effect upon the machine may be described thus: should a wind-gust tilt down one plane-end, the “warp” upon that side of the machine was drawn down also, and the effect of this—seeing that it caused the plane to assume a steeper angle to the air and exercise a greater lift—was to raise the plane-ends that had been driven down by the gust. By a system of connecting the control cords, this balancing influence was made to act with double force; when one wing warped down, the other moved up; and, in this way, while the side of the machine tilted down was made to rise, the other plane-ends, which had been lifted, were made to descend. A dual righting influence was thus obtained. This system, which imitates the flexing movements made by a bird, was an important device; the Wrights patented it—combining the movement with an action of the rudder—and brought cases at law to enforce their rights.

In the summer of 1900, with their first machine, the brothers went for experiments to Kitty Hawk, North Carolina. They had chosen this lonely settlement, located on a strip of land that divides Albemarle Sound from the Atlantic Ocean, because they hoped it would provide them with a strong, steady wind; there were also, fairly close to the settlement, suitable sand-hills for gliding.

Upon the first day of their trials the wind was blowing at nearly 30 miles an hour, and they allowed the glider to rise as a kite. Flown in this way, it bore the weight of a man; but they were disappointed at the position it assumed when in the air. Its planes set themselves at an angle which was too steep, and it seemed to give less lifting power than they had expected. They tested their system of control, and found that the wing-warping for sideway balance acted extremely well, proving quicker and more certain than would the shifting from side to side of the operator’s body. The elevating plane was also efficient.

Then they took the glider to the sand-hills. At first the wind was too high, but after waiting a day it dropped to 14 miles an hour, and they were able to make nearly a dozen glides down the side of a slope which had a drop of 1 foot in 6. It had been their idea, in building the machine, that the operator should run before gliding, as Lilienthal had done, and only lie upon the plane when the speed was sufficient to give the surfaces their lift. But in practice they found a better method than this. Two assistants, as illustrated in Fig. 30, took the machine by its plane-ends and ran forward with it, the pilot assuming beforehand his position upon the plane; then, when they had gained a pace sufficient for the machine to soar, they released their hold and it glided forward. Beneath the glider, under the centre of the lower plane, there were two wooden skates or runners, and these took the weight of the machine when it alighted, and allowed it to slide forward across the ground before coming to rest. By the use of these landing skids, and by steering at as fine an angle as possible, the Wrights found they could touch ground, even at 20 miles an hour and lying across the machine, without injury either to themselves or the craft.

The first glides were short, and all close to the ground; but they bore out the tests when the machine had been flown as a kite, and showed that the elevating plane and wing-warp would do their work. The Wrights were, indeed, astonished at the celerity with which the glider responded to the fore-plane.

Writing afterwards of this first visit to Kitty Hawk, Wilbur summarised the experiments thus:

“Although the hours and hours of practice we had hoped to obtain finally dwindled down to about two minutes, we were very much pleased with the general results of the trip, for setting out as we did with almost revolutionary theories on many points and an entirely untried form of machine, we considered it quite a point to be able to return without having our pet theories completely knocked on the head by the hard logic of experience, and our own brains dashed out into the bargain.”

When they came to plan a new craft for the summer of 1901, they agreed they could not better either the theory or the manipulation of their first machine; but they decided to make one nearly double the size. Their reason for doing this was that, having a greater lifting surface, they hoped to fly in quite light breezes and also prolong their glides; and they were encouraged to build a larger machine by the readiness with which the first had responded to its controls. They therefore constructed a biplane which had 308 instead of 165 square feet of surface, and was the largest machine of its kind that had been built.

In July they went into camp on their remote sand-hills, housing the new machine in a wooden shed. The first tests were made in a 13-mile-an-hour wind, but proved disappointing. The machine dived, in spite of a quick movement of the elevator, and landed after gliding only a short distance. The cause was found to be this: the centre of gravity was too far forward. Therefore the pilot took his place some few inches farther back. But in the next glide the craft behaved alarmingly. It reared almost vertically in the air, and would have slipped backwards had not the operator turned down the elevator to its limit, and moved his body forward as well. The machine, when he did this, recovered its balance and settled without injury.

Further tests were made and the curve of the planes reduced—a change which could be effected by altering the trussing of the ribs. Then they obtained striking success. One glide, for instance, measured a distance of 366 feet; and this was bettered by one of 389 feet; while the operator found that he had perfect control over his machine in a wind of 14 miles an hour. A day or so later an attempt was made in a wind of 22 miles an hour, and was successful. Then, in subsequent tests, they glided in a wind as strong as 27 miles an hour.

The success of these trials led them to think of fitting a motor to their machine; and they calculated at first that a petrol engine of about 6 h.p., weighing 100 lbs., would be sufficient to drive a craft through the air; but they hoped to obtain one more powerful than this. Here it should be pointed out that, owing to the experiments of motor-car builders, and the spending of many thousands of pounds, there was now available a petrol motor which might be adapted to aviation. Such engines were heavily built—when considered, that is, from the point of view of fitting to aeroplanes; and the brothers agreed that, as they wanted such a motor for aerial use, and not for placing in a car, they would probably need to build one, specially lightened, in their own workshops.