Experimental Determination of Unsteady Propeller Forces 



The water-tunnel dynamometer was designed theoretically, using a computer 

 analysis to obtain the dynamic characteristics. The dynamic calibrations of the 

 completed system agreed quite well with the predicted frequency response 

 curves, except for a small resonance in bending moment and side force. Analog 

 instrumentation for obtaining on-the-spot measurements of amplitudes and phase 

 angle of the harmonic frequency components was developed for the water-tunnel 

 tests. Both amplitude and phase values obtained from this instrumentation agree 

 very well with those computed from the digitized tape recordings. 



Water-tunnel tests of propellers with three blade widths showed the unsteady 

 forces to be maximum for an expanded area ratio of 0.60. A propeller having 

 extreme skew and the same blade width had only 10% of the thrust and torque and 

 50% of the side forces and moments on the unskewed propeller. Tests of a set 

 of tandem propellers showed that the phase angle between the two sets of blades 

 has a considerable effect on the unsteady forces. For any given application, the 

 vibratory forces can be reduced by proper adjustment of the angle between the 

 two sets of blades. 



Future work will include determinations of the effect of pitch ratio and skew 

 and studies of contrarotating and tandem propellers. Propellers for specific 

 applications will be designed and their performance will be evaluated experi- 

 mentally. 



ACKNOWLEDGMENTS 



The author gratefully acknowledges the assistance of Robert Boswell and 

 Mrs. Mary Dickerson in conducting the tests and analyzing the experimental 

 data, Garnell Belt and Dusan Lysey in preparing the figures, and Shirley Child- 

 ers in preparing the manuscript. 



REFERENCES 



1. Tachmindji, A.J. and Dickerson, M.C., "The Measurement of Thrust Fluc- 

 tuations and Free Space Oscillating Pressures for a Propeller," David 

 Taylor Model Basin Report 1107 (Jan. 1957) 



2. van Manen, J.D. and Wereldsma, R., "Dynamic Measurements on Propeller 

 Models," International Shipbuilding Progress, Vol. 6, No. 63 (Nov. 1959) 



3. Krohn, J.K., "Numerical and Experimental Investigations of the Dependence 

 of the Fluctuations of Thrust and Torque on the Blade Area Ratios of Four- 

 Bladed Ship Propellers," HSVA Report 1236 (May 1961), prepared under 

 ONR Contract No. N62558-2223 



4. Norrie, D.H., "Research in Propulsion Vibration at the University of Ade- 

 laide," Transactions of Royal Institute of Naval Architects, Vol. 106 (1964), 

 p. 81 



287 



