exclusively. On the opposite side of the blades, roughness was measured due to the 

 resin filled gage wire channels. In most cases, the resin potting material was not 

 satisfactorily faired into the blade surface. This was not viewed as a serious 

 problem because pressures were not measured in these areas. Pressure distribution 

 calculations were performed replacing the rough side of the blade with smooth design 

 offsets. Results showed that the irregularities on one side of the blade did not 

 influence the pressure distribution on the other side of the blade. 



CALCULATION OF PRESSURE DISTRIBUTIONS FROM MEASURED SECTIONS 



Pressure distributions were calculated from measured offsets using the procedure 



30 

 of Brockett. The measured sections were assumed to be at the two-dimensional 



ideal angle of attack (see Table 2), representing the design J condition. To perform 



the pressure distribution computations, the measured offsets were modified and 



supplemented as described below. 



1. A cosine function distribution of offsets was required for the calculation, 

 therefore, 120 offsets were interpolated across the chord of each section. The 

 cosine distribution produces a progressively finer increment of points towards the 

 ends of the section. 



2. The leading edge point was not measured, so a reasonable leading edge shape 

 was extrapolated by fitting a second order curve of the form: 



y = A Jx. + A n 

 o 1 



where A and A, = constants, 

 o 1 



The curve passed through the leading edge with an infinite slope, and through the 

 first reasonable measured offset, with the same slope as the interpolated offsets. 

 In some cases the first measured offset was too close to the section centerline, 

 possibly indicating that the section chordlength was shorter than the assumed design 

 value. Figure 35 shows these results. 



47 



