cc, 



-2.0 



1 



1 1 1 



""* feaa =SBs =:: __^ 1.5 CHORD LENGTHS 

 ^ 5==:: === =:;:; ^FINITE CAVITY 



INFINITE CAVITY ^^^■^ K - 

 I I I 



0.2 0.4 0.6 



X/C 



Figure 1 1 — Finite Cavity Effects on Foil Shapes 

 r/R = 0.53, Model 3870 



efficiencies of the two different supercavitating propellers are almost the same although the efficiency 

 of the propeller with the optimum pitch is a little better. In other examples the efficiency due to 

 the optimum pitch distribution is also only slightly improved. 



The pressure sides of the blades on Propeller Models 3770 and 3870 have the two-term camber 

 shape. The actual leading-edge cavity thickness of the models were not measured. Figure 1 1 shows 

 that the short cavity effect is considerable in changing the foil shape, especially near the trailing-edge. 

 If the point drag is added at the leading edge the foil shape changes again. There are lifting-surface 

 effects to pitch and camber which must be combined. Therefore, without an actual design and 

 experimental evaluation, there can not be a detailed evaluation of the present theory; only an 

 approximate comparison of the resulting behaviors can be made. Yet the results of the present 

 theory seem to indicate that proper use of supercavitating cascade theory is a correct procedure to 

 use in the preliminary design of a supercavitating propeller. 



In the usage of the supercavitating cascade theory, the following points are reemphasized. 



1 . The angle of shock-free entry for a cascade is considerably different from that of a single 

 foil in an infinite medium. 



2. The leading-edge cavity thickness is one of the important design parameters, and has a linear 

 relationship with the infinite-cavity cavitation number. 



3. Separate treatment of the finite-cavity effect simplifies the application of supercavitating 

 cascade theory to the propeller blade section design. 



4. The results of infinite-cavity cascade theory are acceptable for preliminary design near the 

 blade tip where the actual cavitation number is smaller than the infinite-cavity cavitation number. 



ACKNOWLEDGMENTS 



This work has been supported by the Naval Material Command Direct Laboratory Funding 

 Project on Propellers for High Speed Naval Vehicles. The author also wishes to express his 

 appreciation to Dr. William B. Morgan and Mr. Justin H. McCarthy, Jr. for their many valuable 

 discussions and continuous encouragement. 



L5 



