about the towpoint, three conditions must be satisfied: 



2 L = L^ - W 

 o 



2 M = 



66 



2 M < 



[1] 

 [2] 



[3] 



when 0=0. 



Here 2 L is the total vertical hydrodynamic force; 2 M 

 is the total force moment about a transverse axis through 

 the towpoint; and W is the weight of the body in water. 



We now define the following: 



density of the fluid; 



velocity of tow; 



dynamic pressure, pU^/2; 



drag of wing and tail, respectively; 



mean chord of wing, and chord of horizontal 

 tail surface; 



lifting surface area of wing and horizontal 

 tail; 



"downwash" angle (inclination of fluid stream- 

 lines relative to the remote flow) at the tail; 



lift coefficients, lw^<3 S , Ivt/q S »• 

 drag coefficients, D /q S^, D /q S ; 

 moment coefficients, M^q S^ C^ , M^/q S^ C^ ; 



^^ ^ 



^W' ^H 



^' ^ 



With the further notation that an appended subscript "0" 

 denotes differentiation with respect to pitch angle, conditions 



67 



