where A is the the aspect ratio, b/S; b is the span; 5 is a 

 tip correction factor for the isolated monoplane of equiva- 

 lent aspect ratio; ard a is the biplane interference factor 

 for finite aspect ratio (Reference 6) . 



The values M' , and m' ^ depend upon the camber of the 

 oW oH 



airfoils, being zero for symmetrical foils. Reference 6 

 gives m' = - ? p. Also, M' is independent of angle of 

 attack so that M' does not appear the expression for static 

 stability, Equation [3a]. 



For thin airfoils of small circular arc camber ,^p is 

 half the angle subtended by the arc. Thus the camber f 

 (maxiraum height of the mean camber line above the reference 

 chord) is p c/2. 



The lift curve slope, a, for a biplane may be deduced 

 from the expression for the induced angle given by Reference 6; 



a_ 



a = 



1 + a^ 

 o 



p' + ^ -^ -^ + <^ 



tta 



where a is the lift curve slope of the lifting surface for 

 infinite aspect ratio; t is a second tip correction factor for 

 the isolated monoplane airfoil of equivalent aspect ratio; 

 and p' is the biplane interference correction for infinite 

 aspect ratio. The equivalent aspect ratio of a biplane con- 

 sisting of equal areas and spans is identically the aspect 

 ratio of the isolated wings. 



70 



