the x-y plane to the leading and trailing edges of the blade; inflow velocity ratio 

 V /V ; number of collocation points on the blade, cavity wake, etc. Also, as 

 mentioned previously, the data tape created by the preliminary design program for 

 all the necessary sectional data from the supercavitating cascade theory is fed into 

 the lifting-surface design. 



The output consists of the components of induced velocities resulting from the 

 vortex and source distributions, correction factors for source strength and camber, 

 angle of attack relative to 3> pitch distribution, thrust and torque coefficients, 

 and efficiency. 



NUMERICAL EXPERIMENTS FOR SOLUTION 



The cavity model, the solution for cavity source strength, the number of inter- 

 vals for vortex and source distributions, the number of collocation points, and the 

 like cannot be determined theoretically; instead, they must be determined according 

 to the behavior of numerical output. The output, especially, should show conver- 

 gence, which could be built into the program, if the program is simple and does not 

 require too much time. However, a large program, such as the present one, which 

 requires considerable computer time, cannot be run for all values of parameters so 

 as to check convergence of the solution for each design. Instead, it may be enough 

 to check several aspects of parametric changes for a typical case and to assume that 

 the other cases will reasonably follow the typical case. 



In the present work, designing the Model 4717 supercavitating propeller, various 

 convergence checks have been performed, and the results will be shown in the follow- 

 up. The design conditions for Model 4717C are shown in Table 1. 



The cavity truncation locations were varied from 1.5 to 2.8 chord lengths to 

 check the cavity model. Figures 5 and 6 show that the truncation at 2.2 chord 

 lengths and at 2.5 chord lengths produces almost the same pitch and camber distri- 

 butions (differing less than 1%) ; the pitch distribution is about 3% larger than at 

 1.8 chord lengths. 



The influence of the choice of angular interval on pitch and camber distri- 

 bution is also shown in Figures 5 and 6. By changing 2-deg intervals to 1-deg 



intervals, the camber correction factor c increased about 6% and the pitch diameter 



o 



ratio P/D increased about 1%. Since the magnitude of camber is so small, a change 

 in the correction factor of 10% is within the manufacturing error. If the blade tip 



25 



