~ 31 



d. The prediction of C . from the unsteady theory of Tsakonas et al., 



produced an unrealistic drop in C . near the leading edge. Also, the C distribu- 

 tion was identical for the suction and pressure sides of the blade at a given blade 

 section, contrary to measured results. The validity of the unsteady procedure of 

 Tsakonas et al., appears to be questionable based on consistently poor correlation 

 with measured results in inclined flow. 



CONCLUSIONS 

 The following conclusions were made based on the summarized results: 



1. The pressure measurement system performed satisfactorily, providing 

 sufficient measurement accuracy for the present state of theoretical correlations. 

 Of the pressure distributions that were measured, the most reliable data are consid- 

 ered to be those showing low speed and loading effects. 



2. The measured mean pressure distributions provided fair correlation with 

 equivalent two-dimensional theoretical pressure distributions. Some large discrep- 

 ancies were hypothesized as followed: 



a. At the 0.5 radius on the suction side, unexpected measured suction peaks 

 are thought to be caused by flow interference at the hub and include three- 

 dimensional effects. 



b. The irregularities of the measured pressures on the suction side of 

 Propeller 4679 at the 0.7 and 0.9 radii are felt to be due to the influence of 

 three-dimensional effects and tip-vortex formation from the leading edge. 



3. Variation in the pressure distribution with Reynolds number is believed to 

 be caused by real flow effects, and not instrumentation errors. Reynolds -number 

 effects influenced by three-dimensional separation and tip-vortex formation are 

 possible causes. Relatively thick blade sections, and highly-swept leading edges 

 are the primary factors producing the above effects. 



4. Based on the results of the leading-edge roughness tests, it is concluded 

 that both propellers operated with turbulent boundary layers throughout the Reynolds 

 number range tested. 



5. At the 0.9 radius, the unexpectedly large sensitivity of C to J on the 

 suction side of Propeller 4679 is attributed to tip-vortex separation. 



42 



