Titoff, Russetsky, and Georgiyevskaya 



where . , .~ , . 



a- = local cavitation number, 



S = thickness of the section, 



§2 = pressure -face curvature, 



a^ = nominal angle of attack. 



The form of these equations and hence the absolute values of curvature and pitch 

 will vary according to the initial shape of the sections to be used for the con- 

 struction of the blade. 



Wedge-shaped sections with the pressure-face deflection shifted to the trail- 

 ing edge make it possible to realize large absolute values of curvature and pro- 

 vide for high propeller efficiency in the design conditions. In a number of cases, 

 however, the necessity of providing high efficiency values under transient condi- 

 tions, when cavitation is underdeveloped, makes it necessary to use ordinary 

 segmental or compromise sections. 



It should be noted that, in spite of grave assumptions, the calculation method 

 enables us to obtain fairly reliable data. Figure 5 shows performance curves 

 for a propeller so designed; the small circle in the diagram characterizes the 

 initial design conditions. 



Kr; 



0,8 



0,1 

 0,6 



o,i 



0,2 

 0,i 

 



0,6 0,7 0,8 0,9 1,0 </ 1,1 <3 /,V <5 i,6 J,p 



Fig. 5 - Performance curves of a pro- 

 peller in relation to the initial design 

 condition 



The above procedure for determining the pressure-face curvature and the 

 blade-element pitch suggests that the propeller will operate in the uniform ve- 

 locity field. This is essentially true in the case of a propeller operating behind 

 the strut, where the radial nonuniformity of the velocity field is the determining 

 factor and the circumferential nonuniformity insignificant. When the propeller 



924 



