ce The unsteady theory of Kerwin 
and Lee showed, in general, 
somewhat better agreement with 
experimental data over a range 
of advance coefficient than 
either the quasi-steady method 
of McCarthy or the unsteady 
method of Tsakonas et al. 
This applies to both ampli- 
tudes and phases. This method 
underpredicted the periodic 
loads by approximately 5 to 20 
percent of the experimental 
values, with closer agreement 
being obtained for the Fy 
and My components at the 
higher values of J. This 
method predicts the phases to 
within 5 to 15 degrees of the 
experimental values for most, 
but not all, conditions 
evaluated. In general, the 
agreement is better for the 
higher values of advance 
coefficient J; i.e., J near or 
higher than the design value. 
ais The method of Kerwin, which is 
the only method evaluated that 
considers the inclination of 
the slipstream relative to the 
propeller axis, produced 
consistently the best agree- 
ment with experimental data, 
including both amplitudes and 
phases over the range of 
parameters evaluated. In 
particular, for low values of 
J this method yielded substan- 
tially better correlation with 
experimental results than any 
of the other methods evaluated. 
At high values of advance 
coefficient this method yields 
substantially the same results 
as the method of Kerwin and 
Lee. Thus, the inclination of 
the propeller slipstream rela- 
tive to the propeller axis can 
significantly influence the 
periodic propeller blade 
loads, and the importance of 
this inclination increases 
with increasing time-average 
loading. 
In longitudinal flow, all of the 
calculation procedures evaluated 
predict the amplitude of the 
periodic single-blade axial force 
to within 20 percent of the experi- 
mental values at design J. However, 
the agreement at substantially 
off-design J is not as good. In 
general, the method of Kerwin and 
Lee agrees best with experimental 
results in the magnitude and the 
trend of periodic single-blade 
axial force coefficient over a 
range of J. In addition, the 
method of Kerwin and Lee agrees the 
best with experimental phases and 
in the trends of the variation of 
phases with J. 
36 The periodic blade loads in 
inclined flow are not significantly 
influenced by the presence of a 
nearby boundary. 
ACKNOWLEDGEMENTS 
The work reported herein was funded 
by the Naval Sea Systems Command (NAVSEA 
O5R), Task ARea S)379-SLO01, Task 19977. 
The authors are indebted to many 
members of the staff of the David W. 
Taylor Naval Ship Research and Develop- 
ment Center. Special appreciation is 
extended to Mr. Michael Jeffers for 
development of the on-line data analysis 
system, to Mr. Benjamin Wisler for 
assistance in conducting experiment, to 
Dr. William B. Morgan and Mr. Richard A. 
Cumming for overall guidance. 
The authors also wish to acknowledge 
Mr. Claude Williams of ORI, Inc., for 
assistance in handling propeller 
performance computer programs. 
REFERENCES 
1. Boswell, R.J., et al, "Experimental 
Determination of Mean and Unsteady 
Loads on a Model CP Propeller 
Blade for Various Simulated Modes 
of Ship Operation," The Eleventh 
Symposium on Naval Hydrodynamics, 
Sponsored Jointly by the Office of 
Naval Research and University 
College London, Mechanical 
Engineering Publications Limited, 
London and New York, pp 789-834 
(Apr 1976). 
2. Boswell, R.J., J.J. Nelka, and S.B. 
Denny, "Experimental Unsteady and 
Mean Loads on a CP Propeller Blade 
on the FF-1088 for Simulated Modes 
of Operation," DTNSRDC Report 
76-0125, Defense Documentation 
Center ADA-34804 (Oct 1976). 
3. Jessup, S.D., R.J. Boswell, and 
J.J. Nelka, "Experimental 
Unsteady and Time-Average Loads on 
the Blades of the CP Propeller on 
a Model of the DD-963 Class 
Destroyer for Simulated Modes of 
Operation," DTNSRDC Report 
77-0110, Defense Documentation 
Center ADA-048385 (Dec 1977). 
