AC D = AD T /(Ipu k 2 27ry k k) (7) 



where k is the wire diameter 



u k is the velocity in the laminar boundary layer at height k 

 y k is the radius of the model at the wire location 



The relationship between AC D and AC T is 



u k \ 2 27ry k k 



AC T = AC D l-j — ^-cosa k (8) 



where a k is the tangent angle of the model profile at the wire location. Values of u k were 

 determined from the Pohlhausen one-parameter family of velocity profiles, using laminar 

 boundary-layer parameters, calculated by the method given in Reference 8. 



To calculate C p , a virtual origin x Q < xg is defined so that the frictional drag of a 

 turbulent flow over the wetted-surface area of the model between x = x Q and x = L is equal 

 to the total frictional drag on the model (laminar and turbulent) plus the drag of a stimulator, 

 if present. This situation is illustrated in Figure 8 and can be expressed by 



D„ +AD T = D F (S, ') (9) 



r 1 t O 



Equation (6) can now be written as 



C R = C T -C Ft (S L _ Xo )^p (10) 



where 



C F t = V(W S L-*o) 



By analogy with Equation (9) and by converting to coefficient form, we can also write 



S S 



C Ft <S x2 _ Xo ) J ^ = C Fg (S x£ )-^ + AC T (11) 



This expression provides a means to evaluate x Q . 



The frictional drag arising from the turbulent flow region S L _ x on the model is now 

 considered to be the drag due to the flow over an equivalent flat plate of constant width - 

 27ry = S L _ x /(L- x ). With this assumption, frictional drag becomes a function of Reynolds 

 number alone, and Equations (10) and (11) reduce to 



13 



