26 



Vi«f/2 Lin 



t^^o ■ '''' 



The change in minimum pressure coefficient for a small change in eccentricity is 



A / ^ \ _ 27?^(27? + e^ -3) Ae 

 2 



where A e, obtained from differentiating Equation [27], is given approximately by 



/Sa 8b\ 

 U ~ J j 



1 - e^ (Sa db , 

 Ae = --- [30] 



Although the shape of the body may depart appreciably from the shape of an ellipsoid, 

 the required value of the eccentricity for the above equations may be found for that ellipsoid 

 which has the same minimum pressure coefficient as the body investigated. Then the errors 

 in the semimajor and semiminor axes of the body may be used to estimate the change in ec- 

 centricity. 



To find the effect of a slight misalignment of the body, Equation [24] may be differ- 

 entiated with respect to a . The change in pressure coefficient for small angles of attack 

 (a = 0) is" 



The greatest change of pressure occurs not at the pressure minimum, ft = 0, but at 



f£^=i[2-e2]-^/2 J32J 



At this point 



i>l)"''' 



and 



= - (Q77 Aa 



''kp^o')a 



[33] 



[31] 



