Comparison of Theory and Experiment on Ducted Propellers 



position, as is sometimes assumed in the theoretical calculations. Also, the 

 finite blade chord and blade thickness may produce considerably different in- 

 duced velocities, even on an average, than given by an actuator-disk model. An 

 example of this difference is the steady axial and radial induced velocities pre- 

 sented in Table 1, which were calculated from actuator -disk theory and propel- 

 ler lifting-surface theory. These data are for a three-bladed marine propeller 



for ; = 0.833 and C 



Tp 



0.578. The lifting- surface calculations, which contain 



both effects of loading and thickness, generally give slightly greater values for 

 the axial induced velocities and considerably different values for the radial in- 

 duced velocities, as compared to the lifting-line calculations. The lifting-surface 

 calculations smooth out the radial velocities in the vicinity of the blade tip. 

 Since these induced velocities are different from those obtained from the 

 actuator-disk model, it is not possible to say whether the linearized theory of 

 the duct is adequate or not in the presence of the propeller. Quite clearly the 

 mathematical model used for the propeller in the pressure distribution data 

 presented must be improved. 



Table 1 



Average Propeller-Induced Velocities from Lifting-Line and 



Lifting-Surface Theory at R^R = 1.05 



Ducted Propeller Forces 



Considerably more force data (measured ducted propeller thrust) than pres- 

 sure distribution data are available on ducted propellers. However, theoretical 

 predictions have not been made for most of available force data. 



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