90 SMITHSONIAN CONTEIBUTIONS TO KNOWLEDGE VOL. L I 



.Ironic was 11,775 granules (26 pounds), and the sustaining surfaces therefore 

 amounted to 2.6 square feel to the pound, which, as the evenl proved, was amply 



sufficient. 



The " tail-rudder," shown in Plate 17, comprised a vertical and horizontal 

 surface of silk intersecting in a central rod or axis, having a length of 115 cm. 

 (3.8 feet). The framing was of spruce and consisted of two sets of four arms, 

 each radiating from the central rod, the hexagonal outline of the surfaces be- 

 ing formed of piano wire, over which the silk was drawn and sewed. The area 

 of each surface was aboul 0.6 square metres (6.45 square feet), and the total 

 weight was 371 grammes (0.8 pounds). 



A flat steel spring inserted in the forward end between the rudder and the 

 midrod gave it a certain desirable degree of elasticity in a vertical direction. 

 The rudder was held in place by a pin passing through the midrod, and was so 

 set as to coincide with the line of direct flight, its purpose, as already explained, 

 being to guide the aerodrome, but to take no part in its sustention. 



In balancing Aerodrome No. 5 on May (i, the wings were so adjusted that in 

 accordance with the notation given above, p. 15: 



CP f «,= 1575 



('!>,„ =1415.5; 



and as the wings were of equal size, from what has preceded in the present 



CP>= 3CP '«+ 2CP "° =1501.2. 



The center of gravity was located at 14!>7, so that there should have been a very 

 slight tendency on the part of the aerodrome to rise, as was actually the case. 

 The formula was perhaps not quite so accurate as the prolonged flight of the 

 aerodrome would seem to indicate, as it takes no account of the thrust of the 

 propellers, which in action tended to elevate the aerodrome in front while their 

 resistance would tend to depress it when they had ceased to revolve, which con- 

 sideration accounts for the action of the aerodrome on May (i, as described in 

 Chaptei EX. The formula may, however, be regarded as approximately correct. 

 In the final successful trial with No. 6 on November 28, 1896, the wings used 

 were similar in general construction and manner of guying to those of No. 5 on 

 May 6, hut. as shown in the photograph (Plate 29 A, Chaptei' X). the front rib at 

 its outer extremity was bent to a quadrant to connect with the midrib, this con- 

 struction being somewhal stronger than that adopted in the wings of No. 5. The 

 curvature was hut one eighteenth of the width of the vring instead of one-twelfth 

 as in Xo. .">. The front and rear pairs were similar and equal and had a com- 

 bined area of 7. square luetics (.".4 sq. ft.), and a weigh! of :!17>4 grammes (4.74 



