cc. 



Figure 5 — Leading-Edge Cavity Thickness Distributions 

 at x/c = 0.1 for Model 3770 



Figure 6 — Leading-Edge Cavity Thickness Distributions 

 at x/c = 0.1 for Model 3870 



in the cascade theory are marked by small circles on the curves. The pitch distributions for a finite 

 cavity propeller have a considerable variation along the span of the blade because the short cavity 

 effect on the angle of attack is much larger than the influence of the infinite-cavity cavitation number 

 on the leading-edge cavity thickness and on the angle of attack. The short cavity decreases both the 

 angle of attack and the cavity drag. Thus, when the leading edge is chosen such that each section 

 has an infinite cavity, the pitch distribution is smooth but the efficiency becomes lower as is shown 

 in Figures 2-4 and 7. In any case, the pitch distribution is, in general, larger than those of the 

 models. This may indicate that the effect of flow retardation is significant. 



From the pitch distribution, the angle of attack with respect to the hydrodynamic advance angle 

 (3j, can be figured easily. An example of the angle-of-attack distribution determined from the lifting- 

 line design method is shown in Figure 8 along with that of Model 3770. The camber distributions 

 c /C L for propellers 3770 and 3870 are shown in Figures 9 and 10 respectively. The value ofc /C L 

 is a measure of the camber assuming that c y/C Lo -ax is the actual foil shape without the point 

 drag, having the lift coefficient C Lo of the supercavitating foil in the infinite medium, the additional 

 nose-tail-line angle of attack a, to the shock-free camber y. When the camber shape is given such as 

 by the two-term camber, y is the value of the foil shape which is at the shock-free angle in the blade 

 section. Therefore, c /C L decreases when a is large, but increases when the cascade effect is large 

 with a fixed value of a. 



12 



