On the suction side of the blade, at the 0.5 radius position, the phase angle 

 of the first harmonic on the two propellers was strikingly similar. Values of 

 120 deg at the leading edge dropped slightly below the quasi-steady phase of 90 deg, 

 remaining constant over most of the chord. In each case, the phase dropped substan- 

 tially at the trailing edge, to approximately 100 deg. This drop in phase angle at 

 the trailing edge was not predicted in the quasi-steady analysis, but justification 



for it existed in the C versus J curve slopes in Figures 21 and 22. The C versus 



P P 



J slopes on the suction side of the blade reversed polarity at the 0.5 and 0.7 radial 



positions on Propeller 4718 and at the 0.5 radial position on Propeller 4679. This 

 polarity reversal could have caused a 180 deg phase angle shift at these gage loca- 

 tions, which was supported by the experimental results. This phase angle shift did 

 not show up in the quasi-steady predictions due to the dominance of the speed 

 correction terms coupled with small C versus J curve slopes and small first-harmonic 

 amplitudes. 



The first-harmonic phase angle on the blade pressure side at the 0.7 radius 

 position (Figures 22d and 23d), was also similar for the two propellers with phase 

 angles of approximately 300 deg, which was 30 deg greater than the quasi-steady 

 prediction of 270 deg. There was an extreme speed dependence of the phase angle for 

 Propeller 4718 at the chordwise positions from the midchord to the trailing edge. 

 This variance in phase angle is attributed to the small measured amplitudes at the 

 corresponding locations causing inaccuracies in the measured phase angles. 



At the 0.9 radius position (Figures 22e, 22f, 23e, and 23f), the four conditions, 

 representing the two propellers and two sides of the blades, each show measured phase 

 angles 30 deg to 60 deg greater than the quasi-steady results of 90 deg and 270 deg 

 on the suction and pressure sides, respectively. Also, in three of the four cases, 

 the phase angles increased from leading edge to trailing edge along the chord. These 

 trends could be related to effects of the tip-vortex rollup process. 



On the pressure side of Propeller 4718 at the 50 percent chord, 0.5 radius 

 position, the first harmonic pressure was 180 deg out of phase from the expected 

 value. Figure 22b demonstrates this unusual variation from the general trends. This 

 behavior implies a phase shift in the first harmonic amplitudes along the chord at 

 the 50 percent position. At this particular gage location, there was no loading 

 effect, as shown in Figure 9b. Therefore, no uncertainty was introduced due to the 



37 



