As seen in Figure 20, the experimental roll moment arm data agree well with the pre- 

 dicted value which indicates that the foil develops an elliptic spanwise load dis- 

 tribution as designed. 



As discussed earlier, TVC inception was identified as the first appearance of 

 cavitation in the vortex core--usually located approximately one chord length down- 

 stream of the foil tip. This procedure offered the best repeatability in identi- 

 fying this type of cavitation inception. The parent foil TVC inception data are 

 given in Figure 21 and show the variation of cavitation index a as a function of lift 

 coefficient for Reynolds numbers R =2.5 and 5 x 10 . As seen in Figure 21, the 

 parent foil TVC inception data agree well with the form of Equation (1) , especially 

 for the C range around design. Also, the inception data show a Reynolds number 

 dependence, given as 



0.36 



(2) 



4 

 This Reynolds number dependence agrees with that of McCorraick. It is further noted 



that the inception data are not symmetric about the vertical O axis. This can be 



attributed to the favorable chordwise pressure distribution of the cambered foil, at 





I I I A--^' 



* -^^ 



^ \ \ \ 





/ 





•^ 





/ 





\ FOIL OUTLINE 



0.9 



/ 



/ 





V - 



0.8 



/ 

 / 





\ 



\ 





/ 





\ 



0.7 



/ 





\ 





1 





\ 



0.6 



_ / 





\ - 





/ 





\ 



0.5 



_ / 





\ - 



0.4 



-/ --H 



^' 



?M1t^ \- 





/ ' 1 



^ 



\ 



0.3 



7 



1 THEORY 





r 



0.2 



f- O PARENT 



A LARGE BULB 





4 

 1 

 1 



0.1 



_ SMALL BULB 





- 





1 1 1 1 





1 1 1 1 



Figure 20 



-8-6-4-2 2 4 6 8 

 ANGLE OF ATTACK O. (deg) 



Roll Moment Arm as a Function of Angle of Attack 



29 



