NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 9] 



lbs.). The flying weighl of the aerodrome was L2,120 grammes (26.7 lbs.), the 

 sustaining surface thus amounting to slightly more than 2 square feel 1<> the 

 pound. 



The position of the wings, in accordance with the notation adopted, was 



CP f v>= 1563.2, 

 CP™ = 1374. 

 Since the wings were equal in size, 



cp 3(:P,. + m. =1487.5. 

 o 



The center of gravity was located at 1484, which was 3.5 cm. in the rear of the 

 center of pressure. The flight was approximately horizontal, and the setting 

 seems to have been as accurate as could be desired. The angle of elevation of 

 the wings at the root was 10 : 30', and so well were they guyed that there was no 

 visible yielding at any point during the flight. As the midrod during flight was 

 approximately horizontal the angle of elevation of the wings may be taken as 

 10° 30'; the efficiency of the rear wings was two-thirds that of the front wings, 

 and the effective area was therefore 27 + 27x^=45 square feet. 



The wings being very nearly plane we have therefore the data for deter- 

 mining the soaring speed from the formula of " Aerodynamics " (Chapter VI, 

 p. 60). 



W=P a cos a=kAV 2 F (a) cos a, 



in which TF = 26.7 pounds; A = 45 sq. ft.; &=0.00166; a = 10° 30'; F (a) cos a = 

 0.353. By substituting these values in the formula we obtain 7=32 feet per 

 second. 



The speed actually attained, however, was about 30 miles an hour, or 44 

 feet per second, which seems to indicate that the angle of elevation under pres- 

 sure was reduced to much less than 10° 30'. For a velocity of 44 feet per second, 

 the theoretical value of a would lie but 6 n . In this calculation, however, the hull 

 resistance and that of the system of guy-wires, which must have been compara- 

 tively large, has been omitted. It would appear, therefore, that the actual re- 

 sults obtainable in flight are much more favorable than calculations based on 

 experimental data would presuppose. 



