Propeller 4679 showed behavior similar to Propeller 4718, with some noticeable 

 variations. At the 0.7 radius on the suction side, the suction peak that occurred 

 at the leading edge at design J remained even at the high J condition, implying not 

 a simple angle of attack cause, but perhaps a local effect due to blade geometry at 

 the leading edge. Also, the dip in -C at the 50 percent chord corresponds to a 

 questionable surface mounted gage. The bracket at that position represents the 

 range of pressures recorded in earlier tests, before the surface gage was installed. 

 On the pressure side of the blade, a constant sensitivity of C to J was observed in 

 the aft chord region. This appeared only at the 0.9 radius and could be related to 

 tip-vortex separation and rollup occurring on the opposite side of the blade. 



At the 0.9 radius of Propeller 4679, dramatic tip effects appeared to dominate 

 the variation of pressure coefficient with J. On the suction side, variations with 

 J occurred to a greater degree than for Propeller 4718. Also, from Figure 7c, the 

 measured pressure coefficients at design J were larger than the theoretical predic- 

 tions, contrary to data for Propeller 4718. As J was reduced, large decreases in 

 C occurred near the leading edge. On the pressure side, variation in C was small, 

 and the data were mostly uniform across the chord. This behavior was substantially 

 different from the expected sensitivity of C to J occurring over most of the blade 

 sections, including the 0.9 radius of Propeller 4718. 



It is hypothesized that the formation and position of the tip vortex on 

 Propeller 4679 produced the unconventional pressure distributions at the tip. 

 Figure 20 shows Propeller 4679 operating in uniform flow at advance coefficients of 

 1.077, 0.8, and 0.6. The carriage speed in this preliminary test series was slightly 

 greater than test values reported herein, causing a visible tip vortex even at design 

 J. All three conditions shown were at approximately the same Reynolds number. As J 

 was reduced, a thicker vortex core formed on the back of the blade migrating forward 

 along the broad tip. At J = 0.6, the tip-vortex formation seemed to begin close to 

 the leading edge at the 0.7 radius. Increased tip-vortex separation may have 

 occurred also, but this is unclear from the photographs. If the tip vortex formed 

 well ahead of the 0.9 radius, the tip vortex would have induced higher velocities 

 along the 0.9 radius, causing a decrease in the pressure coefficients on the suction 

 side which are strongly dependent on J. The pressure coefficients on the pressure 



27 



