Comparison of Theory and Experiment on Ducted Propellers 



F I'-'' 



0.02 0.03 



TIP CLEARANCE 

 PROPELLER DIAMETER 



Fig. 24 - Variation of thrust and effi- 

 ciency with tip-clearance by English (31) 



(1) The comparison of the theoretical and experimental pressure dis- 

 tributions on the annular airfoil show that the theoretical predic- 

 tion is satisfactory if no separation occurs on the duct and other 

 viscous effects are small. The linearized theory, of course, does 

 not give as good a prediction as the nonlinear theory. 



(2) The linearized theory predicts annular airfoil forces and moments 

 satisfactorily if no separation occurs on the airfoil. 



(3) The linearized theory gives a satisfactory prediction of the veloci- 

 ties in the annular airfoil if the pressure distribution on the airfoil 

 is satisfactorily predicted. 



(4) The prediction of the duct pressure distribution when a propeller 

 is operating within the duct is satisfactory on the outside of the 

 duct but varies between marginal and unsatisfactory on the inside 

 of the duct. 



(5) The predicted ducted propeller thrust appears to be generally sat- 

 isfactory, except at the static condition, if separation does not oc- 

 cur. However, because of the procedures used, this conclusion is 

 probably optimistic. 



(6) The predicted propeller forces and moments for an angle of attack 

 are marginal. 



1339 



