be smoothed out by the boundary layer depending upon its thickness. Therefore, the 

 potential-flow solution will exaggerate the variations in pressure when predicting 

 the flow over the sections. Generally, the section irregularities are within the 

 boundary layer over most of the section, except at the leading edge where the 

 boundary layer is very thin. In this area, surface irregularities would cause 

 serious pressure fluctuations, strongly influencing leading-edge cavitation. 

 Localized flow separation tripped by surface irregularities could also occur. The 

 effect on the pressure distribution could be very complex and unpredictable. 

 Unfortunately, procedures for coupling the influence of the boundary layer to 

 irregular surface pressure predictions are unavailable, so the effect can be con- 

 sidered only qualitatively. 



SUMMARY AND CONCLUSIONS 



The section offsets of Propeller 4718 were measured at 0.5, 0.7, and 0.9 radii. 

 Using a computer interfaced to a coordinate measuring machine, one could automatically 

 measure offsets at 0.5-deg increments across the blade sections. From the measured 

 geometry, pressure distributions were calculated and compared to design values. The 

 following results and conclusions were obtained: 



1. The measured geometry matched the design geometry in general shape. The 

 measured blade sections were generally slightly thicker than design over most of the 

 chord except at the leading edge, where the measured sections were thinner possibly 

 due to hand finishing. 



2. Local irregularities in the blade shape were measured, produced by uneven 

 potting resin, and pressure gage coverplates in the blade surface. 



3. Calculated pressure distributions from the measured offsets matched the 

 pressure distributions for the design geometry in the general shape; therefore, 

 variations in constructed section geometry did not explain the discrepancies in the 

 measured surface pressures. Irregularities in the blade surface produced sharp 

 variations in the pressure distributions, but are not thought to be related to 

 abnormalities in the measured pressure distributions. 



4. The trigonometric series used to describe the blade section for the pressure 

 distribution calculation matched the measured offsets exactly and may have represented 



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