Propeller -Induced Appendage Forces 



Frequency Range 



0.03 



0.02 



'^ 



^ 





^ \ / '^- 



o p 



f\r 



--w 



100 125 150 175 



requency (cpa) 



Fig. 10 - Dynamic calibration of the symmetrical appendage 

 system, and flow background levels 



TEST PROCEDURES .■"■':',: 



In undertaking a test run the desired appendage was mounted in the tunnel 

 and the balance- appendage system was calibrated using the technique just de- 

 scribed. The propeller was then moved into the proper position, since it was 

 located approximately 6 propeller diameters downstream during the determina- 

 tion of the calibration and flow background levels. The desired tunnel velocity 

 and propeller rotational speeds were established, and then for each propeller- 

 appendage spacing ratio the induced force, as indicated by the output of the strain 

 gage balance system, was recorded at specific frequencies of interest. The test 

 arrangement was then changed and the entire procedure repeated. As was men- 

 tioned, most of these tests were undertaken at a free stream velocity of 5.23 ft/ 

 sec and a normal rotational speed of 13 rps; thus the advance ratio for most of 

 the tests was 0.603. 



DATA EVALUATION 



The initial test readings consisted of millivolt levels from the wave analyzer 

 and propeller thrust readings from the dynamometer. The thrust value was cor- 

 rected for the tare load determined by operating at test conditions without the 

 propeller on the dynamometer shaft. The net thrust value was determined by ad- 

 justing the measured value by the tare influence. 



179 



