204 SMITHSONIAN" CONTRIBUTIONS TO KNOWLEDGE VOL. 27 



As this test seemed to indicate that the wings constructed in this manner 

 were certainly strong and rigid enough for use on the aerodrome, and that im- 

 mediate further improvement could hardly he made, three similar wings were 

 at once constructed to complete the set. Somewhat later two additional wings 

 were provided, so that when the large aerodrome was taken to Widewater on 

 the Potomac in 1903 one and a half complete sets of wings were on hand, which 

 seemed to be ample to provide for any emergencies that might arise. 



Each of these wings had, as is clearly shown in the drawings, Plates 53 and 

 54, two main ribs, which formed the main strength of the framework and gave 

 the wing longitudinal rigidity. To the main front rib were attached the cross- 

 ribs and the pieces for the curved extension later described. The mid-rib ex- 

 tended across the cross-ribs, parallel to and about 5 feet behind the front rib, 

 this being approximately the line in which lay the center of pressure of the 

 wing. It was upon this rib, therefore, that the greatest strain would fall. 



The mid-rib, Plate 66, Fig. 2, was 731.5 cm. (24 ft.) long, having at the butt 

 an outer diameter of 38 mm. (1.5 in.) and an inner diameter of 25 mm. (lin.), 



1 be walls being, therefore, approximately 6.5 mm. (0.25 in.) thick. From the 

 butt to the middle point the section was uniform, but from this point it had a 

 taper of one-twenty-fourth of an inch to the foot, so that at the tip it had an 

 outer diameter of 25 mm. (1 in.), the thickness of the wall being unchanged. At 

 the butt end a wooden block 8 inches long was glued inside the rib, and at uni- 

 form distances of 75 mm. (30 in.) 10 smaller blocks were glued in where the 

 cross-ribs were attached. The main front rib was of the same form and size, 

 except that it was some 2 inches shorter and had no blocks, except the long one 

 at the butt, glued in it. 



To these main ribs were attached, in the manner later described, the 10 

 cross-ribs, to which the cloth cover was attached. The 8 intermediate cross- 

 ribs have already been described in connection with the tests. The cross-ribs at 

 the end of the wings, upon which greater lateral strains would come from the 

 stretching of the cloth, were made of the larger cross-section shown in Fig. 8 

 of Plate 66. Additional longitudinal stiffness was provided by gluing a strip 



2 mm. thick between the upper and lower halves, as shown in the section. These 

 end ribs, as well as those next to the ends, had small blocks glued into them 

 where they were crossed by the diagonal braces, in addition to the small parti- 

 tions 1 mm. thick, which were glued into the ribs every 3 inches to prevent crush- 

 ing, and the blocks 2.5 and 3 inches lontr respectively, where they were attached 

 to the front rib and to the mid-rib. At the extreme rear edge of the wing the 

 cross ribs were attached to the small "P "-rib, which served to hold the ribs 

 ai equal distances and to keep the cloth cover stretched tight. This " P "-rib, 

 as shown in Plate 66, Fig. 3, had semi-circular walls 4 mm. thick, 21mm. in di- 

 ameter, to the edge of which was glued a flat strip 3 mm. thick. 



