The predictions were calculated by a combination of the propeller design 



28 29 30 



procedure ' and equivalent two-dimensional blade section methods. Initially, 



28 

 from the lifting-line prediction, the radial loading distribution was obtained, 



providing the required lift coefficient for a given section of chord length. 

 Assuming a NACA 66 thickness airfoil section, with an a = 0.8 meanline, a two- 

 dimensional camber ratio and ideal angle of attack were calculated to produce the 



desired loading.* The two-dimensional theoretical pressure distribution was calcu- 



30 

 lated by the method of Brockett using the assumed thickness shape, meanline, and 



ideal angle of attack. 



Before comparing results of the two propellers, one should note the qualitative 

 geometric differences. Propeller 4718 was designed to resemble a conventional CP 

 propeller with moderate skew and planform. Propeller 4679 was designed with 

 increased skew, increased pitch, and increased expanded area ratio, producing much 

 larger chord lengths for an equivalent overall diameter. In planar-wing terminology, 

 Propeller 4679 resembles a delta wing, especially at the outer radial positions. 

 Therefore, the pressure distribution at the outer radii of Propeller 4679 could be 

 dominated by the real fluid effects of cross-flow and tip-vortex roll-up observed on 

 low-aspect ratio wings, and would be less likely to match predicted two-dimensional 

 pressure distributions. At the inner radii, the measured flow characteristics of the 

 two propellers would be expected to be similar due to the effect of the hub and the 

 close similarity of the local planforms. 



On the suction side, at the 0.5 radius, both propellers display similar measured 

 results. The measured negative pressure coefficient, -C , is less than the theoreti- 

 cal value near the leading edge region, and greater than the theoretical value near 

 the trailing edge. 



On the pressure side, at the 0.5 radius, the measured results on Propeller 4718 

 more closely resemble the theory with irregular peaks in the measured result at the 

 10 percent and 50 percent chord positions. Measured magnitudes of C on Propeller 

 4679 are generally less than theoretical predictions over the forward portion of the 



29 

 *The final propeller geometry is determined using lifting surface techniques 



to arrive at the corrected camber, and ideal angle of attack to produce a chordwise 



load distribution equivalent to that calculated in two dimensions. 



16 



