MHler 



Fig. 25 - Forces and moments 

 acting on propeller 



instrumentation are shown for blade frequency and are in good agreement. The 

 agreement is equally good for the higher frequencies. Figure 30 shows similar 

 results for blade -frequency torque. 



The effect of the relative angle between the two propellers on the phase 

 angle of the blade -frequency thrust is shown in Figure 31. The curve is drawn 

 through the values obtained from the computer analysis, and again the on-the- 

 spot values are in good agreement. The phase reference is the centerline of the 

 aft propeller blade. It is seen that as the lag of the forward propeller position 

 is increased, the lead of the phase angle is decreased. The phase angles for 

 torque are essentially identical and the agreement of the on-the-spot results is 

 even better. 



Figure 32 shows how the waveform of the thrust changes as the angle be- 

 tween the propeller is changed from 0° to 100° in increments of 20° as recorded 

 from the oscilloscope. 



CONCLUSIONS 



Several dynamometers having high accuracy and good frequency response 

 characteristics are available to obtain reliable measurements of unsteady pro- 

 peller forces both in the towing basins and in the water tunnel. Experimental 

 results can be obtained which are required for evaluating the sophisticated the- 

 ories that are being developed, and parametric studies can be made to explore 

 the details of propeller geometry for their effects upon performance. Evalua- 

 tion tests can also be made to determine the characteristics of specific propel- 

 ler and hull combinations. 



278 



