the main influence on pitch, thrust, and efficiency. The calculated efficiency is 

 close to that obtained in the model experiments, as shown in Table 2. 



The lifting-surface camber correction factors for the two propellers are shown 



in Figures 23 and 24. The camber correction factor for Model 3870 is much larger 



2 

 than for Model 3770, as in the calculation of Venning and Haberman. The pitch 



distribution and camber correction curves for Model 3870 are quite different from 



those for Model 3770. The former has shorter cavities with four blades and large 



expanded area ratio (EAR), and the latter has longer cavities with three blades and 



smaller EAR. 



EXPERIMENTAL EVALUATION OF THEORY 

 Finally, the Center conducted an experimental program to evaluate the present 



method for designing supercavitating propellers. Two supercavitating propellers 



1 8 

 were designed, using the present method, for a 200-ton (181 metric ton) hydrofoil 



craft. The propeller design criteria are given in Table 3. The propeller design 



characteristics are given in Table 2. 



Two model propellers were manufactured from these designs. The geometry of 

 these propellers is given in Table 4 and drawings of the propellers are shown in 

 Figures 25 and 26. 



The experimental program was divided into two phases. The results of the first 

 phase, the measurements of blade-cavity shapes, are reported in the following 

 section, while the results of model propeller performance are described in the last 

 section. 



EXPERIMENTAL INVESTIGATION OF BLADE-CAVITY 

 THICKNESS DISTRIBUTION 



A series of experiments was performed to determine how well linear theory 



predicted the upper cavity surface location for Propellers 4717C and 4738A. For 



these experiments, brass pins of varying lengths were attached to the backs of the 



propeller blades. During propeller operation in the 36-in. variable-pressure water 



tunnel, one could see when the pins came into contact with the upper cavity surface. 



This experimental procedure has already been used to verify the upper cavity 



19 20 

 surface location for Propeller 4699, ' and the parent design of Propellers 4738A 



29 



