APPENDIX 

 COMPARISON OF MEASURED AND DESIGN GEOMETRY OF PROPELLER 4718 



In an attempt to explain the discrepancies between the measured and design 

 pressure distributions, the model blade section geometry was investigated. Detailed 

 measurements of Propeller 4718 were made and compared with design section geometry 

 at the 0.5, 0.7, and 0.9 radial positions. Pressure distributions were calculated 

 using the measured geometry and were compared to design predictions. 



Measurements were taken while each blade was supported in a fixture positioning 

 the blade at the design pitch. No measurement of pitch was obtained, because the 

 blades were not attached to the hub. The increased complication of measuring actual 

 pitch was not considered necessary, because of the good agreement between measured 

 and predicted pressures near the blade leading edges at design conditions. The 

 primary concern was the effect of the general variations from design in the geometry 

 of the sections. 



Measurements were obtained using a Validator coordinate measuring machine 

 coupled to a PDP 11 minicomputer. The computer was programmed to automatically 

 measure vertical distances to the blade surface along the 0.5, 0.7, and 0.9 radii 

 positions at 0.5-degree angular increments across the blade surface. Figure 33 shows 

 the measuring arrangement. Upon completion of measurements on the suction side, the 

 blade was rotated 180 deg in the fixture for measurements on the pressure side of the 

 blade. Approximately 120 points were measured at the 0.5 and 0.7 radii, and 90 

 points at the 0.9 radius on each side of the two blades on which the surface pres- 

 sures were measured. The measurements of Cartesian Coordinates (x,y,z) were stored 

 on a 10 megabyte disk pack interfaced to the minicomputer. Later, the data were 

 transferred to magnetic tape, and stored on file on a CDC 6700 computer for further 

 analysis. 



The measured results were transferred from Cartesian Coordinates as measured, 

 to section offsets for comparison to design values. The corrdinate transformation 

 program, REVERSE,* was used to convert the measured blade-surface points to section 

 offsets. To make the transformation, the position of the nose-tail line was needed. 

 To define the nose-tail line the extreme leading and trailing edge points must be 



^Reported informally by M.J. Chambers and T.E. Brockett in NSRDC TN 282, 

 "Computer Programs for Calculating Propeller Geometry," (November 1973). 



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