21 



0.2 



0.4 



0.6 



0.8 



1.0 



\ 







o Correct Offsets of Torpedo Model H-60 



\ 



















<; 























k 



















^ 



---. 



^~~°-, 



T n r 









0.2 



0.4 



0.6 



0.8 1.0 



x/b 



1.2 



1.4 



1.6 



1.8 



Figure 12 - Comparison of the Offsets of the Wax Electrolytic-Tank 

 Model of H-60 with the Correct Offsets 



PROCEDURE FOR FINDING PRESSURE FIELDS BY THE DOUBLE-PROBE METHOD 



To demonstrate the usefulness and reliability of the double-probe method in obtaining 

 the field of pressure in the vicinity of a body, the field about the 2.5 in. radius sphere was 

 mapped. The sphere was mounted on the longitudinal wall as described in the single-probe 

 experiment, and the potential gradients in the x and y directions were obtained along longitu- 

 dinal lines at various distances from the centerline. The velocity and direction of flow are 

 obtained from the resultant potential gradient, and the pressure coefficient is obtained from 

 Equation [18] where v^ is now the square of the resultant velocity. 



A reference point was found in the tank far enough from the model that free-stream con- 

 ditions could be assumed to hold. The equivalent free-stream velocity was checked quite 

 frequently to ensure that the line voltage had not changed and altered the sensitivity of the 

 circuit. As the iOO-cycle generator was not available for this investigation, it was necessary 

 to use the 60-cycle line voltage with a voltage regulator. In spite of the voltage regulator, 

 surges in line voltage often changed the potential gradient at the reference point by as much 

 as 1 percent. 



The data were obtained at convenient intervals at constant distances out from the longi- 

 tudinal wall of the tank. In order to fix the relative positions of the curves, potential gradi- 

 ents were obtained along transverse lines at several representative stations. In this way, er- 

 rors arising from drifts in sensitivity of the circuit could be recognized and corrected. 



