Morgan and Caster 



I would like to make the following two comments on this paper: 



(1) Shroud static pressure distribution measurements made under the 

 shrouded propeller research wind-tunnel program conducted by 

 Hamilton Standard and reported in HSER 4048 indicate a definite 

 pressure jump at the propeller plane particularly at low forward 

 speeds. The tip clearance was 0.25 percent of the diameter. This 

 appears to be inconsistent with the views expressed in this paper. 



(2) The generally favorable comparison of the theoretical and experi- 

 mental pressure distribution reported in this paper is in agree- 

 ment with similar comparisons made with shrouded propeller per- 

 formance method developed from the Therm -Ordway theory by 

 Hamilton Standard reported in HSER 4776 and the test data of HSER 

 4348. However, in these latter comparisons the pressure distribu- 

 tions inside as well as outside of the duct were quite accurately 

 predicted by the calculation method. 



REPLY TO DISCUSSION 



Wm. B. Morgan and E. B. Caster 



We wish to thank the discussers for contributing to the paper by their taking 

 time to make pertinent comments. The problem posed by Dr. Silo vie is a diffi- 

 cult one, both from the standpoint of the interaction and from the fact that the 

 duct operates partially in the boundary layer of the ship. One way of approach- 

 ing this problem is to design the unit as if the duct is whole, then multiply the 

 duct force (thrust or drag) by the ratio of circumference of the partial duct to 

 the complete duct. This method should give the approximate effect of the duct 

 on the propeller and vice versa. The partial duct on a ship also gives a lift 

 force; whether its direction is up or down depends on the duct shape, and the ef- 

 fect of this force should be considered, since the ship trim could be changed 

 enough to affect the ship's resistance. 



Dr. Dyne discussed what we found to be one of the most distrubing aspects 

 of the comparisons, i.e., there were little data available where the duct and pro- 

 peller were designed and compared by the same method. In fact, only for the 

 duct by itself were we able to find such data which included experimental pres- 

 sure distributions. Some of the data presented were for a more or less exact 

 solution in inviscid flow (18, 22) of the duct, but the propeller was treated as a 

 pressure jump. References (18, 22) give no method for doing the direct propel- 

 ler problem. The linearized procedure given in Ref. (20) can start with either 

 the propeller thrust or total thrust. The calculations for the theoretical data 

 given in Ref. (20) for the pumpjet-type ducted propeller when operated at two 

 propeller loading conditions started with the measured propeller thrust, and, for 



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