196 SMITHSONIAN CONTEIBUTIONS TO KNOWLEDGE VOL. '27 



While the main ribs had shown a certain amount of deflection under the sand- 

 ing test, the more serious distortion had been in the cross-rihs, the small guy- 

 wires, which had heen fastened to each cross-rib, becoming loose instead of 

 tight, as had been expected, since the rib tended to increase its curvature in- 

 stead of straightening out. This increase in the curvature of the cross-ribs 

 was partly overcome by tying the guy-wire flat against the cross-rib for a dis- 

 tance of about 2 feet from the rear tip. But while this caused the guy-wire to 

 tighten the general contour of the wing showed very little improvement, as 

 the ribs now assumed a curve more or less like the letter S, the rear tip now 

 being bent downward to form the tail of the elongated S. 



From this sanding test it was seen that the cross-ribs must be materially 

 stiffer, and a new set was accordingly made one-sixteenth of an inch larger in 

 diameter at the various points of measurement. Upon giving the wing, equipped 

 with these larger ribs, a sanding test it was found that, while there had been 

 some improvement, it was entirely too flimsy, even when it had been double- 

 guyed by running a second wire on each cross-rib from the middle of the por- 

 tion in front of the mid-rib to the middle of the portion behind the mid-rib. 

 As the weight of the wing with these larger solid cross-ribs had now increased 

 to more than 33 pounds, and the wing had proved itself altogether too weak 

 for use on the aerodrome, it was evident that some other plan of constructing 

 the ribs which would give greater strength for the same weight must be found. 

 At first sight it might appear that the obvious way of increasing the stiffness 

 of the cross-ribs was to employ a cross-section other than a round one, since 

 material added to the depth of the rib is very much more effective than if 

 added to the width. It must, however, be remembered that these cross-ribs 

 were 11 feet long, and that, as the main mid-rib was (> feet in front of the 

 rear tips of the cross-ribs, with no intermediate bracing, except the light threads 

 by which the cloth cover was attached, it was inevitable that, should the depth 

 be made materially greater than the width, the rib would buckle sideways. 

 Test ribs of 1 beam form, which are later described, were constructed, but, al- 

 though they proved exceedingly stiff, had to be discarded. 



Tn view of these facts the obvious remedy appeared to be to make the rib 

 hollow, and one cross-rib, : ; of an inch in diameter at the point where it crossed 

 the main rib, tapering to g of an inch at the front and | of an inch at the rear 

 tip, was accordingly constructed. Tests showed that this form of rib, which 

 was about 10 grammes lighter than the '.-inch solid ribs, was much stiffer than 

 anything yet constructed. But when a wing, with cross-ribs of this size placed 

 20 inches apart, was sanded it was found that, although a great advance in 

 construction had been made, still further improvement was necessary before a 

 suitable wing for the large aerodrome could be procured. 



