Morgan and Caster 



The most extensive experimental investigation on ducted propellers has 

 been conducted by the Netherlands Ship Model Basin (NSMB). Oosterveld (17) 

 and (45) has made theoretical-experimental comparisons for three ducts de- 

 signed for decelerating the flow at the propeller. These data are shown in 

 Table 5. The theoretical predictions, which did not include the viscous drag, 

 are generally satisfactory for two of the ducts, nozzles 30 and 31, and unsatis- 

 factory for nozzle 32. Including the viscous drag would have improved the pre- 

 diction for nozzle 30 only, and would probably have made the prediction for noz- 

 zle 31 unsatisfactory. 



Table 5 



Measured and Predicted Thrust Coefficients 



According to Oosterveld (45) 



In addition to the theoretical-experimental comparisons for the free-running 

 condition, comparisons have been made at the static condition by Kriebel and 

 Mendenhall (19), Table 3; comparisons were also made by Greenberg and Ord- 

 way (25). Their predictions under-predicted the measured value of the duct 

 thrust by 30%, whereas Kriebel and Mendenhall (19) over -predicted the thrust. 

 Both predictions were unsatisfactory. 



A few theoretical-experimental comparisons of force and moment data have 

 been made for ducted propellers at an angle of incidence by Kriebel and Men- 

 denhall (19). Data for both the Bell X22A and Doak VZ-4DA systems have been 

 compared. The variations of lift, duct thrust, and drag coefficients with propel- 

 ler thrust and angle of incidence are shown in Figs. 21, 22, and 23, respectively, 

 for the Doak system. The theoretical predictions are, in general, greater than 

 the measured results. Prediction of the lift, except for small thrust coefficients, 

 was unsatisfactory while the prediction of duct thrust and pitching moment was 

 marginal. The theoretical predictions of the lift and pitching moment for the 

 Bell X22A system were lower than measured (19) and varied between marginal 

 and satisfactory. 



In summary, the predicted ducted propeller thrust is generally satisfactory, 

 except at the static condition, if separation does not occur on the duct. For the 

 ducted propeller at an angle of attack, the prediction of thrust and pitching mo- 

 ment was marginal, while the prediction of lift was unsatisfactory in one case 

 and marginal to satisfactory in another. In calculating the duct thrust, some of 

 the methods used the measured propeller thrust rather than a theoretical value. 

 Consequently, the predictions may not be as good as the data indicate if all the 



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