Ro 



I, 



des 



A similar loading correction was made to the fluctuating pressure coefficients. 



Because the runs conducted with the taped-over gage holes were performed in uniform 



flow only, the loading corrections to the fluctuating pressure coefficients had to 



be approximated. The approximation is based on an assumed quasi-steady variation in 



the local loading pressure coefficient C T (9), with local advance coefficient J(9), 



P^ _ 



calculated from the variation of the mean loading pressure coefficient C , with 



advance coefficient J from Figure 7. The procedure was identical to that used 



(see page 32) to calculate predicted unsteady pressure coefficients. In the present 



case, the C . versus J curves were used instead of C versus J curves, as described 

 pL p 



in the later section. For each pressure gage, a first-harmonic loading pressure 

 coefficient amplitude C . and phase <|) - were calculated for each run conducted and 

 were vectorially subtracted from the measured fluctuating first harmonic pressure 

 coefficient. The propeller shaft inclination produced a constant tangential wake, 

 producing a first-harmonic phase angle due to load effects, called the loading phase, 

 <J) .. of 270 deg. To more accurately approximate the unsteady correction, the phase 

 of C .. , (J) 1 , was shifted from the quasi-steady prediction of (f> T , = 270 deg to <j> T .. = 

 300 deg. This adjustment was based on a similar phase lag in previously measured 

 unsteady propeller blade loads in inclined flow by Jessup and Boswell. 



Figures 9 and 10 show the uncorrected and corrected first harmonic pressure 

 coefficients and phases. Loading effects did not occur at the 0.9 radial positions, 

 so comparisons there were deleted. Note that on some gages the correction is con- 

 siderable and is only an approximation. When analyzing results from these gages, 

 consideration must, be made for the uncertainty of the correction. (Some discussion 

 of this point will be given subsequently.) Fortunately, most gages show little or 

 no loading correction. 



MEASURED MEAN PRESSURE DISTRIBUTIONS 



Figure 11 depicts the measured and predicted mean pressure distributions for 

 Propellers 4718 and 4679 at design advance coefficient at the 0.5, 0.7, and 0.9 

 radial positions. The measured mean pressure coefficients represent average values 

 over the range of speeds tested for each propeller to allow general comparisons with 

 theory. 



15 



