zero-lift line of 6 degrees for a 20-degree elevator deflec- 

 tion, i.e., an elevator effectiveness ,(aou/a5) of 0.3. This 

 condition is theoretically satisfied for a flap-to-stabilizer 

 chord ratio of only 0.05 (Reference 7). Effectiveness factors 

 of this magnitude are rarely obtained in practice, hov?ever, 

 and experimental evidence (Reference 8) indicates that the 

 flap-to-stabilizer chord ratio should be as much as 0.125 

 for installations with sealed gaps. If a sealed gap is not 

 used, a ratio of not less than 0.2 should be selected. 



Lateral Forces? Yaw and Roll Moments 



The balance of forces in the lateral plane must satisfy 

 the relations 



[5] 



[6] 



[7] 



[8] 

 P ^ 



% (2 M^) < [9] 



Here 2 F is the sum of all lateral forces; 2 M is the sum 

 y z 



of all moments about the vertical axis; Z K is the sum of 

 all moments about the longitudinal axis. It is, of course, 

 required that the above conditions be met for zero values of 

 roll angle cp and yaw angle fc 



Conditions [5], [6], and [7] are met if the depressor 



73 



