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Aviation History
1910
1910 - 0025.PDF
JANUARY 8, 1910. to each of the 100 wires on which the camber of his surfaces depended. It is no easy matter to adjust wires used for such a purpose, as no sooner is a slack wire tightened up a little too much, than it relieves the strain upon two or three other wires, which become slack in turn. And Pilcher, it must be remembered, worked before the days of those very pretty little wire strainers which com-I monly form a feature in the bracing of modern flyers, and his method of adjustment must have been as tedious as it was effective. Each of his wires he fitted with a curtain-ring—Pilcher was very fond of curtain-rings—and on the rib he fastened a wire eye. The wires were cut to a fixed length in advance, and calculated to allow about an inch between the ring and the eye when in place. This gap was filled up by a piece of string, passed several times through each member to give the required strength, and by pulling on one end of the string a very minute adjustment could be made in the tension. More curtain-rings were employed for fastening the other ends of the wires to the vertical bamboo poles, so that the wings could be folded without twisting the wires. Another little device for which Pilcher's construction is peculiar is his method of plugging his bamboo rods with wood. The wood plugs were glued into the hollow ends of the bamboo, which were then carefully lashed with string. Pilcher was very careful about lashing the ends of his bamboo poles as he evidently fully appreciated their liability to split. His use of wire eyes as lugs is another neat detail well worthy of attention, and these little fittings he would also lash in place. Lilienthars Stiffening Ribs. Lilienthal, who very possibly had a natural objection to the use of a lot of wires, hit upon a very ingenious method of doing away with some of them, for he maintained the camber of his wings by the use of detachable supplementary ribs, of which there were four placed fore and aft above the deck. These ribs were strips of wood having an inverted T section, and they were cut to shape so as to serve as templates. As their permanence would have interfered with the "Flight'' Copyright. Method of attaching the supplementary stiffening ribs on the Lilienthal glider. folding of the wings, they were fitted in such a manner as to be detachable, and the method of doing this was to fasten small steel clamps on to the primary ribs of the wings, through which the flange of the template l/Qggg could slide. As the wings were naturally flexible there was no difficulty in sliding the curved templates in place from one end, and once in position these members were fastened by little clips. Their purpose was primarily to give the wings the desired camber, although they would of course tend to increase the rigidity of the structure ; by their use, the necessity for employing a large number of wires was obviated, in fact, there were only two tie-wires radiating from each of the vertical posts mounted above the hinge plates. Beneath the wings, however, there was a wire to every rib, but even in this respect Lilienthal contrived to do without some 78 wires which Pilcher found necessary. Relative Cambering-. It may be remarked that the number of ribs in each of the two machines is identical, viz., 18, but the camber and arching of the wings themselves is distinctly different in the two cases. Pilcher employed an umbrella-like form, in which the camber may be described as being of a uniform character. Lilienthal, on the other hand, flattened the extremities of his wings to such an extent that the curvature of some of the ribs was virtually reversed. The maximum camber on the Lilienthal glider, as on the Pilcher machines, occurs at the hinge of the wing, which on the former is situated 18 ins., and on the latter 2 ft. 6 ins. behind the leading edge. At this point the camber is deeper on the Lilienthal than on the Pilcher glider, but on the Lilienthal machine the camber is almost confined to this point alone, and is far more concentrated, if the term may be used, than in Pilcher's construction. It is known that Lilienthal experimented with cambers of considerable height in proportion to the chord, and he has stated that the maximum versine (camber) of the wing curvature should be less than -jL of the chord, and preferably only ^ to TV for considerations of stability. Both machines had the surface material attached above the ribs. The Framework. Having compared the wings and supplementary sur faces, it is of interest to consider the main frames of the two machines, by which we imply that central structure to which the whole is braced, and on which the pilot supports his weight. In the Lilienthal glider this member is of somewhat peculiar form, and is best observed by reference to the accompanying plan; it bears in a marked degree that bent-wood furniture appearance to which we have already drawn attention. One of the principal members is an approximately circular hoop of willow, across which pass in a fore and aft direction two willow rods that ultimately converge at a point where the bamboo tail rod emerges from the wing surface. Transversely across the hoop passes the main beam to which reference has already been made, and immediately behind this an orifice is provided in the surface to accommodate the upper part of the pilot's body. Two small bolsters attached to the frame rest under the pilot's shoulders, and the pilot's arms pass through rests provided for them in the corners of the X-shaped main beam. Just in front of this beam is another transverse rod which the pilot can grip with his hands, and in front of the main hoop member is another bent-wood construction lashed in place with wicker, the object of this device being to act as a fender in the event of collision. On Pilcher's glider the main frame consists of two bamboo rods spaced 18 inches apart above the main
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