Almost as soon as they began their trials of the glider, the brothers got another surprise. According to the Lilienthal tables of air pressures, their machine of 165 square feet needed a wind of only from seventeen to twenty-one miles an hour to support it as a kite with a pilot aboard. But they found that much stronger winds were needed to lift it. Since suitable winds would not be plentiful, their plan of practicing by the hour aboard the glider while flying it as a kite would have to be postponed. Instead, they flew it as a kite, loaded with about fifty pounds of chain, but with no man aboard. They held it with two ropes, and operated the balancing system by cords from the ground. Though the results were promising, inspiring confidence in the system of maintaining equilibrium, the brothers knew that only by actual gliding experience could they confirm what the kite experiments had indicated as being true. One thing that puzzled them was that the machine appeared to be greatly deficient in lifting power as compared with calculated lift of curved surfaces of its size. In wondering what might be the cause of this wide discrepancy between expected and actual lifts, the Wrights considered the possibility that it might be because the curvature of the wings was less than that used by Lilienthal. Or could it be that the cloth covering was too porous and permitted some of the lifting power of the wind to be lost? They wondered, too, if the Lilienthal tables they had followed, relating to air pressure on wing surfaces, could be in error. They next determined to try gliding on the side of a hill. That meant toting their machine four miles south of their camp to a great sand dune about one hundred feet high, called Kill Devil Hill. On their first day at the hill, the wind was about twenty-five miles an hour. As they lacked previous experience at gliding they decided to wait for less of a blow for their first attempt. The next day the wind had subsided to fourteen miles an hour, and they made about a dozen glides. “Bill” Tate was there and assisted them. In making these glides, the machine was usually only two or three feet from the soft, sandy ground, and though the brothers repeatedly made landings while moving at a speed of twenty miles an hour, neither operator nor machine was harmed. The slope of the hill toward the northeast was about 9½ degrees, or a drop of approximately one foot in six. After moving at a rate of about twenty-five to thirty miles an hour with reference to the wind, or ten to fifteen miles over the ground, the machine, while keeping its course parallel to the slope, increased its speed, thus indicating that it could glide on a slope less steep.