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. CHAPTER VIII THE WRIGHT MOTOR-DRIVEN PLANE Final gliding tests--Building of the motor--How a petrol engine works--Driving, control, and launching of the Wright machine.