Figure 17 represents the variation of the speed corrected pressure coefficients 



with J for uniform and inclined flow. Along with the measured pressure coefficients 



for each run, first- and second-order least-squares curves are shown. There are no 



significant differences in the curves for the cases of uniform and inclined flow, as 



expected, except when numerous bad runs shifted the shape of the curve. Generally, 



the slopes of the curves increased in magnitude from trailing edge to leading edge, 



as expected. 



Some gages produced obvious second-order nonlinear C versus J curves. On 



P 

 Propeller 4718, nonlinear ity occurred mainly at the leading edge and at the 0.9 



radius. On Propeller 4679, nonlinearity occurred, with some exceptions, at all 

 blade positions, clouded to some extent by scatter of the data at some gage posi- 

 tions. The nonlinearity which occurred may be associated with effects caused by the 

 tip-vortex separation or crossflow over the blade surface. Comparisons with lifting- 

 surface theories may provide insights into this possibility. 



The variation of the pressure distribution along the chord over a range of J 

 is shown in Figures 18 and 19. As expected, increased sensitivity of the pressure 

 coefficients to J occur towards the leading edge of the blade. From two-dimensional 

 theory, the sensitivity should be zero at the trailing edge and monotonically in- 

 crease towards the leading edge. This generally occurs except on the suction side 

 of both propellers at the 0.5R and 0.7R radius positions, where the point of insensi- 

 tivity to J occurs forward of the trailing edge. In each of these cases, this point 



is shown by the location at which a reversal occurs in the direction of C variation 



P 

 with J at the 90 percent chord position. This could be due to viscous effects or by 



induced velocities from a variable "tip" vortex and the trailing-vortex sheet. 



The results for Propeller 4718 appear consistent with expected trends, with the 



exception of the 50 percent chordwise position at the 0.5 radius on the pressure 



side of the blade. A reversal in the direction of the C variation with J occurs 



P 

 there, completely inconsistent with surrounding gage results. A polarity error in 



the gage output would seem obvious, except for the proper polarity of the measured 



C at design J. Also, this gage has no speed effect or loading correction, and the 



measured unsteady pressures, as explained later, support this result. All this 



supports a real flow effect, but given the expected behavior over the rest of 



propeller, this seems unlikely. 



26 



