coefficient amplitude C .. and the corresponding lagging cosine series phase, ()> 1 : 



C (9) = C cos (e-fj).) 

 p p j. x 



This result at design J is presented for Propellers 4679 and 4718 in Figures 24 

 and 25. Included in the figures are fluctuating and quasi-steady predictions. The 

 small effect of speed or Reynolds number is depicted by the similarity in C 1 and (j> 1 

 at two speeds. There appears to be no correlation between the Reynolds number de- 

 pendency of certain pressure gages measuring mean pressure and the same gages 

 measuring unsteady pressures. 



The corrections to the fluctuating pressure measurements due to loading are 

 shown in Figures 9 and 10 for Propellers 4679 and 4718 at design J. Note that no 

 corrections due to loading occur at r/R = 0.9 on either propeller attributed to the 

 use of the coverplate gage installations. The locations of the largest corrections 

 are the 0.5 and 0.7 radius positions on the suction side of Propeller 4718. These 

 loading corrections were determined from a quasi-steady analysis of the measured 

 mean load corrections in uniform flow. This approximation places some uncertainty 

 on the unsteady measurements associated with gage positions with large corrections, 

 and the difference between the corrected and uncorrected pressure measurement could, 

 conservatively, provide an envelope for the actual measured result. 



Before correlating the measured fluctuating results to the unsteady and quasi- 

 steady predictions, a detailed description of the quasi-steady technique is 

 necessary. 



QUASI-STEADY PROCEDURE FOR PREDICTING FLUCTUATING 

 PRESSURE DISTRIBUTIONS 



The quasi-steady analysis for predicting the fluctuating pressures was an 



32 

 adaptation of a quasi-steady procedure by McCarthy for predicting fluctuating 



thrust and torque on a propeller. The procedure predicts the fluctuating propeller 

 loads from the steady open-water propeller performance characteristics. The proce- 

 dure is applied to predict unsteady pressures using the C versus J curves in 

 Figure 13. The procedure is identical to the technique used earlier to approximate 



32 



