After returning to Washington, one of the wings was inverted, and a quantity of sand, equal in weight to the pressure upon the wing in flight, was added, under which the yielding at the tip amounted to 65°, or from +20° to −45°, showing that the wings were entirely too weak to sustain the aerodrome.
In speaking of the efforts to strengthen the wings, it must be constantly remembered that this could hardly be done in any way which did not involve increased weight; that is, it could hardly be done at all, since increased weight was forbidden.
The first attempt at systematic guying was made on October 27. As shown in Fig. B, Plate [16], two guy-posts extending beneath the midrod were connected by guy-wires with the outer extremities of the wing, by means of which it was sought to hold the wing in place and prevent its extremity from twisting upward, while a third wire connecting with the bowsprit prevented its moving backward. In addition, two aluminum wires, stretched across above from wing to wing, kept the lower guys tight.
On October 27, Aerodrome No. 5, equipped with large new wings and tail, having a combined area of 3.7 square metres (40 sq. ft.), the wings being each 64 cm. × 192 cm. (25.25 in. × 75.75 in.), turned sharply and completely round, apparently through some internal current of the main wind against which it was advancing. Owing to this almost instantaneous turn, it lost headway and came down. This led to the subsequent construction and use of a much larger vertical rudder, intended to prevent in future any such sudden pivoting and consequent loss of momentum. The wings showed a tendency to “pocket”[28] and bag, which indicated some serious fault in their construction.
As a result of these experiments, it was decided on October 29 to attempt to make the wings stiffer (though their weight was almost prohibitory), by inserting more cross-pieces, cross-pinning and guying them so as to make them more rigid as a whole, and less liable to pocket.
At this time an automatic device in the form of a sliding tail was designed, which it was thought would cause the center of pressure to move backward when the aerodrome reared, and forward when it plunged downward, but the device, though afterward constructed, was never brought to trial in the field.
Aerodrome No. 5, equipped with a new set of wings similar to those used [p085] on October 27, and guyed as in the previous experiment, was again launched on November 21, with the results recorded in Chapter IX [◊]. The failure was attributed to the twisting of the wings under pressure to such an extent that not only was their effective area greatly reduced, but the outer portions were upturned so as to catch the air upon the upper surfaces, the result being in part a downward pressure.
On the following day a pair of the wings was inverted and a weight of sand equal to the air pressure to which they were subjected in flight, was distributed over their surfaces. Under the action of this, the twisting of the wing was seen to increase from the root, which was held with comparative rigidity, up to the tip, where in spite of the cross-ribs it amounted to 45°. The resistance to torsion lay chiefly in the front rib, which, in addition, could be bent easily, allowing the surface to become distorted with great loss of lifting power.
The experiments of 1894 had demonstrated the urgent necessity for greater rigidity in the sustaining surfaces, which might, as it seemed, be obtained either by increasing the strength of the framing (which meant additional weight) or by resorting to some new and untried construction, or by a proper system of guying. Guying seemingly offered the most feasible solution of the problem; but although the system of wire guying was thoroughly tried, the result was very unsatisfactory, as the wings continued to twist and bag in a way that was extremely discouraging.