Decreasing the value of Lp/D to 1.00 had the effect of increasing C R . The three fore- 

 bodies tested with this L £ /D (Models 2, 5, and 9) had C p values of 0.667, 0.850, and 0.933. 

 Model 9 with the largest C p value has the largest value of C R (0.00026). Model 2 

 (Cp E = 0.667) had a C R value of 0.00024 and Model 4620-5 (C P = 0.850) had a C R value of 

 0.00023. Decreasing the value of Lg/D to 0.50 further increased the values of C R . Two 

 models, 1 and 7, had L £ /D's of 0.50 and C P values of 0.667 and 0.850, respectively. The 

 measured values of C R were 0.00025 for Model 4620-1 and 0.00028 for Model 4620-5. 



The values of C R are given in Figure 1 5 as a function of a forebody slenderness 

 parameter T = (L E /D)/C P . For values of T greater than 2.0 C R assumes a constant minimum 

 value of 0.00020. As T becomes lower than 2.0 the values of C R rise steadily. Values of T 

 for each model are given in Table 6. 



The values of C R based on model volume to the two-thirds power are also given in 

 Table 6. The volume C R 's change the relative merits of the models somewhat but not 

 enough to be significant. 



To further illustrate the significance of C R results, prototype values of C T = (D R 

 + D F (R L ))/(l/2 p U Q " S), and the effective horsepower ehp for nine unappended shapes, 

 which are geometrically similar to the models, have been calculated, 

 where D R is residual drag 



D p is friction drag, at Reynolds number R L 



R L is Reynolds number, U Q L/v 



L is prototype length 



U Q is prototype speed 



S is prototype surface area. 

 Figure 16 gives the values of C T as a function of R L - The ehp values are given in Table 7 

 for six representative speeds. Also given in Table 7 are ehp ratios when ehp of Model 3 has 

 been used as the base. Strictly speaking, this ratio is a function of R L . However, the variation 

 is not discernable in the three significant figures given. These computations were made using 

 the Schoenherr friction line, and no roughness allowance was used. The usual assumption 

 was made of setting C R equal for both the model and prototype scales. A linear ratio of 

 prototype-to-model of 15.79 was used, resulting in a full-scale length of 1 10 m for shape 3. 

 Results indicate a maximum variation in ehp of 4 percent for the nine shapes investigated. 



19 



