时间: 2019年12月12日 07:59

What should be wrong? What do you mean? she demanded with so coldly-haughty an air, that Gibbs was abashed. He felt he had gone too far, and muttered an apology. "I wanted to see to the fire. I'm afraid the coal-box is nearly empty. That old woman is so careless. I beg your pardon, but Mr. Errington is very particular about the room being kept warm." This first glider was tested on the Kill Devil Hill sandhills in North Carolina in the summer of 1900, and proved at any rate the correctness of the principles of the front elevator and warping wings, though its designers were puzzled by the fact that the lift was less than they expected; whilst the 鈥榙rag鈥?(as we call it), or resistance, was also considerably lower than their predictions. The 1901 machine was, in consequence, nearly doubled in area鈥攖he lifting surface being increased from 165 to 308 square feet鈥攖he first trial taking place on July 27th, 1901, again at Kill Devil Hill. It immediately appeared that something was wrong, as the machine dived straight to the ground, and it was only after the operator鈥檚 position had been moved nearly a foot back from what had been calculated as the correct position that the machine would glide鈥攁nd even then the elevator had to be used far more strongly than in the previous year鈥檚 glider. After a good deal of thought the apparent solution of the trouble was finally found.279 This consisted in the fact that with curved surfaces, while at large angles the centre of pressure moves forward as the angle decreases, when a certain limit of angle is reached it travels suddenly backwards and causes the machine to dive. The Wrights had known of this tendency from Lilienthal鈥檚 researches, but had imagined that the phenomenon would disappear if they used a fairly lightly cambered鈥攐r curved鈥攕urface with a very abrupt curve at the front. Having discovered what appeared to be the cause they surmounted the difficulty by 鈥榯russing down鈥?the camber of the wings, with the result that they at once got back to the old conditions of the previous year and could control the machine readily with small movements of the elevator, even being able to follow undulations in the ground. They still found, however, that the lift was not as great as it should have been; while the drag remained, as in the previous glider, surprisingly small. This threw doubt on previous figures as to wind resistance and pressure on curved surfaces; but at the same time confirmed (and this was a most important result) Lilienthal鈥檚 previously questioned theory that at small angles the pressure on a curved surface instead of being normal, or at right angles to, the chord is in fact inclined in front of the perpendicular. The result of this is that the pressure actually tends to draw the machine forward into the wind鈥攈ence the small amount of drag, which had puzzled Wilbur and Orville Wright. � CHAPTER XVI. She considers herself an unexampled victim as it is. I think 'lessons on domestic economy' would about put the finishing stroke to the internal felicity of Ivy Lodge! B. Kenyon. 超碰国产人人做人人爽 Charles. Charles Stu鈥?[Aside.] Ass that I am! Beyond the 1901 experiments in gliding, the record grows more scrappy, less detailed. It appears that once power-driven flight had been achieved, the brothers were not so willing to talk as before; considering the amount of work that they put in, there could have been little time for verbal description of that work鈥攁s already remarked, their tables still stand for the designer and experimenter. The end of the 1901 experiments left both brothers somewhat discouraged, though they had accomplished more than any others. 鈥楬aving set out167 with absolute faith in the existing scientific data, we were driven to doubt one thing after another, till finally, after two years of experiment, we cast it all aside, and decided to rely entirely on our own investigations. Truth and error were everywhere so intimately mixed as to be indistinguishable.... We had taken up aeronautics as a sport. We reluctantly entered upon the scientific side of it.鈥? 鈥楬owever, there is another way of flying which requires no artificial motor, and many workers believe that success will come first by this road. I refer to the soaring flight, by which the machine is permanently sustained in the air by the same means that are employed by soaring birds. They spread their wings to the wind, and sail by the hour, with no perceptible exertion beyond that required to balance and steer themselves.163 What sustains them is not definitely known, though it is almost certain that it is a rising current of air. But whether it be a rising current or something else, it is as well able to support a flying machine as a bird, if man once learns the art of utilising it. In gliding experiments it has long been known that the rate of vertical descent is very much retarded, and the duration of the flight greatly prolonged, if a strong wind blows up the face of the hill parallel to its surface. Our machine, when gliding in still air, has a rate of vertical descent of nearly 6 feet per second, while in a wind blowing 26 miles per hour up a steep hill we made glides in which the rate of descent was less than 2 feet per second. And during the larger part of this time, while the machine remained exactly in the rising current, there was no descent at all, but even a slight rise. If the operator had had sufficient skill to keep himself from passing beyond the rising current he would have been sustained indefinitely at a higher point than that from which he started. The illustration shows one of these very slow glides at a time when the machine was practically at a standstill. The failure to advance more rapidly caused the photographer some trouble in aiming, as you will perceive. In looking at this picture you will readily understand that the excitement of gliding experiments does not entirely cease with the breaking up of camp. In the photographic dark-room at home we pass moments of as thrilling interest as any in the field, when the image begins to appear on the plate and it is yet an open question whether we have a picture of a flying machine or merely a patch of open sky. These slow glides in rising current probably hold out greater hope of extensive practice than any other method164 within man鈥檚 reach, but they have the disadvantage of requiring rather strong winds or very large supporting surfaces. However, when gliding operators have attained greater skill, they can with comparative safety maintain themselves in the air for hours at a time in this way, and thus by constant practice so increase their knowledge and skill that they can rise into the higher air and search out the currents which enable the soaring birds to transport themselves to any desired point by first rising in a circle and then sailing off at a descending angle. This illustration shows the machine, alone, flying in a wind of 35 miles per hour on the face of a steep hill, 100 feet high. It will be seen that the machine not only pulls upward, but also pulls forward in the direction from which the wind blows, thus overcoming both gravity and the speed of the wind. We tried the same experiment with a man on it, but found danger that the forward pull would become so strong, that the men holding the ropes would be dragged from their insecure foothold on the slope of the hill. So this form of experimenting was discontinued after four or five minutes鈥?trial. But, then, after his arrival in Whitford all the painful details of the coroner's inquest were made known to him. He made inquiries in all directions, and learned a great deal about his niece's life in the little town. The prominent feelings in his mind were pity and remorse. Pity for Castalia's unhappy fate, and acute remorse for having been so weak as to let her marriage take place without any attempt to interfere, despite his own secret conviction that it was an ill-assorted and ill-omened one. "You couldn't have helped it, my lord," said the friendly physician, to whom he poured out some of the feelings that oppressed his heart. "Perhaps not; perhaps not. But I ought to have tried. My poor, dear, unhappy girl!" What do you say, Oliver? asked Mr. Bundy. "Shall we remove here?"