Comparison of Theory and Experiment on Ducted Propellers 



Fig. 15 - Pressure distribution on NSRDC duct model 3650 

 for ] = 1.Z7. C^p = 1.330 



appears in the predictions by Meyerhoff (22), and the more realistic treatment 

 of the propeller in the linearized theory is apparent. Theoretical predictions of 

 the duct pressure distributions have been made at off-design conditions using 

 both the nonlinear and the linearized theory. The comparisons, especially on 

 the inside of the duct, are not as good as the data presented in Fig. 15 for higher 

 propeller loadings. Part of the problem at these conditions may be due to the 

 inaccuracy involved in estimating the effect of the stator vanes. This may also 

 be the reason the predicted pressure distribution on the inside of the duct was 

 not as good as on the outside for the design speed coefficient (22). 



The most extensive duct pressure distributions have been measured on the 

 Bell X22A ducted propeller system. This system consists of a duct with a 

 chord-diameter ratio of 0.525 and a maximum thickness ratio of 0.172, of a 

 three-bladed, controllable -pitch propeller, and of six streamlined support struts 

 aft of the propeller. A one-third scale model of this system was tested in the 

 8 X 10-foot subsonic wind tunnel at NSRDC (40). Data were recorded for zero as 

 well as a number of other angles of incidence at several forward flight speeds. 

 Tests of a full-scale system were conducted at the NASA Ames Research Center 

 in their 40 x 80-foot wind tunnel (41). Experimental pressure distributions are 

 presented in Figs. 16 and 17 at two operating conditions for the full-scale model 

 only, since the one -third scale test results were similar. 



The theoretical predictions shown on Fig. 16 were calculated by Kriebel and 

 Mendenhall (19) and those shown on Fig. 17 by Hough and Kaskel (21). The meth- 

 ods used by both were similar, except that Kriebel and Mendenhall used a non- 

 linear approximation to correct the duct velocity distribution and they used a 



1329 



