had not been fixed . The complete equations were then used 

 to refine the estimates of wing and tail incidence and camber 

 needed to satisfy design requirements. For this purpose, all 

 quant it ites in [la], [2a], and [3a] are expressed in terms 

 of the effective angles of attack of the wing and horizontal 

 stabilizer. For the condition, 0=0, the latter are 

 respectively, i^^ + p_^ and i„ + 6„ - e. Here (-6) is the angle 



WW xi li 



of zero lift in the free-stream characteristic of the biplane 

 wing or tail. 



If, for brevity, we write cd for i + p ana designate 

 by "a" the slope of the lift curve (i.e., the derivative of 

 the lift coefficient with respect to angle of attack) , the 

 required identities may be written, in the case, 0=0: 



K = °^ -^ ^Wi '• ^H = ^Hp -^ °Hi 



^ =<H t^^ 



' °H0 ~ ^Hi0 



Here d' is the profile drag coefficient, assumed independent 



P 



of angle of attack; and D. is the induced-drag coefficient 



assumed given by 



< = Sr- (1 + 5 4- a) 

 ■X tta 



69 



