above the propeller. The pressures were recorded 60 times per revolution, at every 

 six-degrees of blade angular position, as triggered by the shaft encoder. The other 

 quantities were recorded once per revolution. 



Zeros were recorded before each experimental run. The zero before each run was 

 subtracted from the data recorded during the run as part of the data analysis. 

 Zeros recorded on consecutive runs were compared to observe zero drift. 



Zeros were collected by recording the gage pressures with the propeller at rest. 

 Each static pressure value was corrected to its shaft centerline value in the 

 computer analysis by accounting for the static head difference between an individual 

 gage location at zero collection and the shaft centerline. This computation was 

 based on the propeller angular position which was recorded during the zero collection, 

 and the individual gage angle relative to the propeller shaft reference angle which 



was stored in the analysis program. 



25 

 This procedure was an improvement over a preliminary experiment, where zeros 



were collected by averaging pressure values during slow propeller rotation. 



After the carriage had reached the desired speed and the propeller rotational 

 speed had been set, pressure data were recorded at each of the 60 blade angular 

 positions over 75 records. Each record involved collecting data from 20 pressure 

 side gages on Blade 2 in the first revolution, 20 suction side gages on Blade 3 in 

 the second revolution, and 3 once per revolution signals on the third revolution (V , 

 n, and wave height WH) . Therefore, each of the 75 records included data from three 

 revolutions. It was not feasible to obtain all of the data simultaneously due to 

 computer limitations. 



After completion of a run, the computer analysis was performed. As part of the 

 analysis, the cyclic variation in hydrostatic head, p , produced during each propel- 

 ler revolution, was subtracted from the measured pressure at each of the 60 blade 

 angular positions. This procedure produced essentially constant measured pressure 

 with angular position in uniform flow. The analysis provided the following output 

 after each run: 



1. Quantities averaged over one record: 



V (I), n(I), J(I), p(9,N,I), WH(I), I = 1 to 75 records, N = 1 to 40 gages 



11 



