ss SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. Ik 



the above is expressed in the following formulae, which it will be remembered 

 take account only of wings following each other in the same or nearly the same 

 plane, and are not applicable where one wing is either above or below the plane 

 of the olher. In the formulas, CP is the resultant center of pressure upon both 

 wings expressed in the notation described in Chapter If, CP,„ is the center of 

 pressure of the front wings, and CP™ the center of pressure of the rear wings. 

 If the value of n lie between one-half and unity, 



M + l 



while if the value of n lie between unity and H, 



(i Y\n 

 m = 



Iu either case 



m= 15 



CP fw +mnCPr 



1 + inn 

 where the leading and following wings are equal 



« = 1, m = § and CP= - • 



The steady flight of one of the gliding models referred to led to the con 

 struction of a new set of wings for No. 5, patterned after those used on the glid- 

 ing model. These wings, shown in Plate 17, were rectangular in outline, 200 

 cm.xSO cm. (6.56 ft. x 2.62 ft.), qaeh wing having an area of 1.6 square metres 

 (17.1 sq. ft.) They were constructed with spruce framing covered with China 

 silk, and were strongly guyed with piano wire in much the same manner as the 

 light, skin covered wings already described, which bad preceded them. The com- 

 bined weight of the two pair was 1950 grammes (4.3 pounds). 



The long central rib was now much the larger of the two which, as in (lie 

 preceding wing, formed the foundation of the structure. It occupied a position 

 two fifths the distance from front to rcai'. and presumably coincided at all points 

 with Hie center of pressure of fore and aft sections of the wings, so that the pres- 

 sure in front of Hie rib was at all points balanced by the pressure in the rear, 

 and there was consequently little tendency in the win- to twist under pressure 

 of the wind. The two main ribs were rigidly connected by cross-ribs of spruce, 

 20 cm. (8 inches) apart, steamed and bent to the desired form. The curvature 

 of these ribs was the same for all, and in depth was one-twelfth the width of the 

 win- while the highest point of curvature was one-sixth of the distance from 

 front to rear, these ratios bavin- been chosen as approximating those found in 

 the win- of the soaring bird. These wings were subsequently used in the first 

 successful flights of the following year. 



