Sec. 70.29 



SCREW-PROPELLER DESIGN 



617 



I. J £-.1-' . C.^J J-\J .J..J 



5cqI& of -^ where. Ai-x'ton^j 

 Fig. 70.G Plot of Goldstein Factor K(kappa) fob a Scbew Propeller with 4 Blades 



where ^{Ctt^Ss = 1st Approx. (Ctl)s — Desired 

 (Cj.i)s = 0.452 - 0.473 = -0.021. 



„ J . ^ 1st approx. tan /3/ 



2nd approx. tan j3, = ^^ — -, ^ — 



_ 1 / 0.02l \ 



5 \0.473/ 

 = 1.0089 (1st approx. tan fij). 



The calculations for the second approximation 

 are shown in Table 70.f. This repeats the opera- 

 tions in Table 70.e but with a new tan /S/ . 



By the second approximation a {Ctl)s of 

 0.470 is obtained, compared to the desired value 

 of 0.473. This is only 0.63 per cent low, and is well 

 within the required range of accuracy. It is 

 usually found that two approximations of this 

 kind are sufficient. 



The final thrust distribution along the 0-diml 

 radius is shown in Fig. 70.H, plotted from the 

 data in Cols. A and T of Table 70.f. 



70.29 Determination of the Llft-Coeflacient 

 Product and the Hydrodynamic Pitch-Diameter 



