Response of Propulsors to Turbiilence 



DYNAMIC FORCE BALANCE 



CEC CHARGE AMPLIFIER 

 MODEL 2646MI 



SKL VARIABLE ELECTRONIC 



FILTER MODEL 308-A 

 VARIABLE CUTOFF (HIGH PASS) 



SKL VARIABLE ELECTRONIC 



FILTER MODEL 308-A 

 VARIABLE CUTOFF (HIGH PASS) 



SKL VARIABLE ELECTRONIC 

 FILTER MODEL 308-A 

 I KC CUTOFF (LOW PASS) 



[OSCILLOSCOPE I 



- | OSCILLOSCOPE I 



CEC MAGNETIC TAPE RECORDER 

 TYPE GR-2800 



Fig. 10 - Circuitry for data acquisition 



data presented here this frequency was 29 Hz. The third filter was used as a 

 low-pass filter with the cutoff frequency fixed at 1 kHz, 



After the signal was filtered, it was recorded on a CEC Type GR2800 mag- 

 netic tape recorder. The force balance signal was monitored and compared on 

 an oscilloscope at several points in the circuitry as well as from the magnetic 

 tape immediately after being recorded. This was done to detect and prevent any 

 signal distortion in the data acquisition system. 



The data were analyzed by means of the instruments indicated in Fig. 11. 

 The signal was played back from the magnetic tape and passed through a 

 Hewlett-Packard Model 302A wave analyzer. This has a constant bandwidth of 

 7 Hz between the half-power points. The filtered signal was then squared by a 

 Ballantine Model 320 true rms voltmeter and finally integrated for 60 seconds 

 with a Dymec Model 240 IC integrating digital voltmeter. All voltage outputs 

 were then converted to forces by using the measured calibration factors. 



The data are shown in Figs. 12 and 13. As mentioned before, the low- 

 frequency end of the spectrum had to be filtered to eliminate a strong line com- 

 ponent corresponding to the shaft frequency. Consequently it was not possible 

 to determine experimentally the rms thrust coefficients. However, Figs. 12 and 

 13 indicate good agreement between the theoretically predicted and the measured 

 power spectral densities, except where the measurements show a hump. The 

 reason for this discrepancy is at present not clear. 



307 



