NO. 3 LANGI.EY MEMOIR ON MECHANICAL FLIGHT 85 



on October 27, ;m<l 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, hut 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 dis- 

 tributed 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, 

 ui> to tlie tip, where in spite of the cross-ribs it amounted to 45°. The resist- 

 ance 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. 



1895 



I accordingly had recourse in 1895 to the system of wooden guy-sticks 

 shown in Fig. D, Plate 16, which necessarily added greatly to the weight of the sus- 

 taining surfaces. Each wing was separately strengthened by means of a light 

 rod of spruce, in cross-section about the size of the main front rib, extending 

 across the upper surface of the wing, at a distance of about one-third the 

 width of the wing behind the front rib. It was tied to each of the cross-ribs 

 and to the outer bent portion of the front rib, and at its root was fastened to 

 the frame of the aerodrome. 



This effectually prevented the bending of the front rib and the consequent 

 bagging of the cover, and to that extent marked a decided advance in wing 

 construction. But it was faulty, in that, not being supplemented by wire guy- 

 ing, it offered little resistance to the twisting of the wing about the main front 

 rib, the rear tip of the wing being free to turn up under pressure, as it had 

 done on former occasions. A similar guy-stick was stretched across the tail. To 

 guard against torsion, rods extending diagonally across the wings and tail were 

 used, which, with the aid of the guy-sticks just described, prevented the surfaces 

 from twisting greatly. In addition, a rod joining the front ribs and stretching 

 across from wing to wing tended to maintain a fixed diedral angle. 



