Morgan and Caster 



For NSRDC Model 3650 ducted propeller system, the theoretical and meas- 

 ured ducted forces are presented in Table 2 (20). These results show satisfac- 

 tory agreement between measured and theoretical results. In making these cal- 

 culations, the stator thrust was determined from the measured propeller and 

 duct plus stator thrust and the calculated duct thrust. For this reason, the com- 

 parison may not be truly representative of the accuracy of the calculations. 



Table 2 

 Theoretical and Measured Thrust Coefficients for a 

 Pumpjet and Kort Nozzle Type Ducted Propeller (20) 



*Input. Nomenclature: / = speed coefficient, Cj 



Cj, - duct thrust coefficient, 

 coefficient (c_ 



Tp 



propeller thrust coefficient, 



= stator thrust coefficient, C__ = total thrust 



+ C^ . + c. 



The second set of data shown in Table 2 is for a Kort nozzle type ducted 

 propeller (20), and the agreement is also satisfactory. In this case, the theory 

 over -predicts the duct thrust by about 6% and the total thrust by about 1%. 



Theoretical and measured duct forces for the X22A ducted system are 

 shown in Table 3 (19). On the basis of the total thrust, the theoretical predic- 

 tions are satisfactory for a speed coefficient of 0.22 and higher. The theory 

 over -predicts the duct forces for speed coefficients below 0.22 and slightly 

 under-predicts the duct forces at the higher speed coefficients. The maximum 

 deviation is at a speed coefficient of zero where the predicted duct thrust is 10% 

 high and the total thrust 5.5% high. This unsatisfactory comparison may be due 

 to separation occurring on the inside of the duct. 



Dyne (42) has also made comparisons between theoretical and experimental 

 ducted propeller forces. Results presented in Table 4 show generally satisfac- 

 tory agreement between theory and experiment for three ducted systems but un- 

 satisfactory agreement for one of the four. This unsatisfactory agreement is 

 probable due to separation that occurred on the duct. 



Figure 20 shows the ratio of propeller thrust to total system thrust for a 

 range of thrust coefficients as presented by Weissinger (43). The experimental 

 curve shown in this figure is from the work of Finkeldei (44) and the theoretical 

 curve from the work of Bollheimer (11). The agreement between theory and ex- 

 periment is very satisfactory. 



1334 



