both the measured and predicted amplitudes. These variations could be produced by 

 effects not considered in the quasi-steady procedure, such as unsteady flows of the 

 tip vortex, hub, and fairwater. 



SUMMARY 

 Experiments were described in which blade-surface pressures were measured on two 

 model-side controllable-pitch propellers. Pressures were measured at 40 locations on 

 the blade surface in uniform and inclined flow, over a range of Reynolds number and 

 advance coefficients. The discussion of experimental technique included descriptions 

 of the hardware and data analysis systems. The results are summarized as follows: 



1. Pressure measurement instrumentation 



a. At best, pressures were measured on propeller blades with accuracies 

 comparable to laboratory calibrations of +0.07 psi. 



b. The thin blade gage installation configuration (Figure 5b) displayed 

 negligible loading effects, while the thick blade gage installation configuration 

 (Figure 5a) showed substantial loading effects of varying magnitude. 



2. The mean pressure distributions produced fair correlation with the equiva- 

 lent two-dimensional theory with the following deviations observed. 



a. The C distribution at the 0.5 radius showed a marked deviation from 



P 

 the theoretical prediction on the suction side of the blade, resulting in an un- 

 expected suction peak at the 50 to 70 percent chord position. 



b. Propeller 4679, characterized by wide blades with large swept tips, 



at the 0.7 radius on the suction side, produced a leading-edge suction peak attrib- 

 uted to local blade shape. Also, a reduction occurred in suction pressure through 

 the midchord with increased suction pressures towards the trailing edge. At the 

 0.9 radius on the suction side, suction pressures were greater than predicted, hence 



C . was less than predicted, 

 pmin 



3. At constant J, substantial variations in C occurred at certain gage 



p 6 

 locations over a Reynolds number range of 2 to 5 x 10 . The following results are 



noted: 



a. The variation of C with R appeared independent of J. 



40 



