Comparison of Theory and Experiment on Ducted Propellers 



0.2 n.4 



Fig. 13 - Radial variation of the axial in- 

 duced velocity distributions in midplane of 

 ARL ducts Al, A2, and A3 (35) 



Ducts Bl, B2, and B3. ARL ducts Al, A2, and A3 all have chord-diameter ratios 

 of 1.0, a section angle of attack of zero, and a NACA 0006 thickness distribution. 

 The maximum camber ratios for these ducts are 0.0659, 0.0385, and 0.0118, re- 

 spectively. Ducts Bl, B2, and B3 were described in a previous section. 



In Fig. 13 the theoretical predictions for A2 and A3 are within experimental 

 error and therefore, satisfactory; whereas for Duct Al, which has the largest 

 camber ratio, the prediction is unsatisfactory. In Fig. 14, satisfactory predic- 

 tions are obtained for Duct B2; Duct Bl is marginal, whereas for Duct B3 

 (accelerating-type duct) the prediction is unsatisfactory. 



It should be noted that the velocities were predicted by Ryall et al. (35) on 

 the basis of using only 74% of the contribution from the vortex distribution. As 

 discussed previously, the stated reason for this reduction (35) was to correct 

 for viscous flow effects. Even though the comparison between theory and exper- 

 iment for the majority of ducts was satisfactory, it is difficult to draw general 

 conclusions as to the applicability of the linearized theory from these data. Ad- 

 ditional experimental results are needed for duct shapes for which the viscous 

 effects would be expected to be small. 



Ducted -Propeller Pressure Distribution 



In this section, experimental and theoretical pressure distributions on ducts 

 when a propeller is operating on the inside will be presented for a number of 



1327 



