The quasi-steady method and the experiment both indicate that the first harmonic 

 amplitudes of the pressures are larger on the suction side of the blade than on the 

 pressure side of the blade. This trend was consistent for both propellers except 

 for the measurements nearest to the leading edge at the 0.5 and 0.7 radius stations, 

 where the results on the pressure side were larger than the results on the suction 

 side. This variation in fluctuating loading between the suction and pressure sides 

 of the blades did not occur in the theoretical prediction method of Tsakonas et al., 

 further supporting the hypothesis that this method does not adequately predict the 

 distribution of pressures. 



On the suction side of Propeller 4718 at the 0.5 and 0.7 radius positions, the 

 quasi-steady analysis at certain chordwise positions over -predicted the measured 

 first harmonic amplitudes. These over-predicted values were partially due to the 

 strong dependence of the quasi-steady result on the magnitude of the mean pressure 



coefficient, C . Some of the C measurements from the 40 to 70 percent chordwise 



P P * 



locations exhibited a relatively strong speed dependence. The mean pressure coeffi- 

 cients were corrected upward for the speed effect, leaving -C values greater than 

 average over the range of speeds conducted. This would artifically increase the 

 quasi-steady results. A calculation of the quasi-steady results with reduced C 

 values did not reduce the quasi-steady first harmonics enough to match the general 

 trend completely, possibly implying inaccuracies or over-simplifications in the 

 quasi-steady analysis. 



CORRELATION OF FIRST HARMONIC PHASE ANGLE WITH THEORY 



The measured first harmonic phase angles were generally in the range expected. 

 On the suction side of the blade, most phase angles ranged from 60 deg to 120 deg, 

 while on the pressure side of the blade, values ranged from 270 deg to 333 deg. 

 There was no specific variation in phase angle over the chord. Cases of gradual 

 phase angle increase, decrease, and consistency occurred over the chord, with some 

 instances of sudden drops in phase angle near the trailing edge. No overall trend 

 in phase angle occurred, but certain blade sections produced similarities between the 

 two propellers tested. 



36 



