The unsteady method of Tsakonas et a 
al predicts that the maximum value of 
(Fx)1 in the longitudinal wake will 
occur at approximately 10 degrees after ine 
the experimental value for Propeller 
4661 and approximately 10 degrees before 
the experimental value for Propeller 
4710; see Figure 13. 
A moderately-loaded unsteady 
lifting surface theory developed by 
Kerwin and Lee at MIT. 
A refinement by Kerwin to the 
method of Kerwin and Lee which 
considers the inclination of the 
propeller slipstream for opera- 
tion in inclined flow. 
The variations of kK(px)1_ The results are as follows: 
predicted by the method of Kerwin and iL, In inclined flow, all four of the 
Lee (8) agrees more closely with the calculation methods evaluated 
experimental results than either of the consistently underpredicted the 
other two methods evaluated. However, experimental values of the periodic 
the agreement with experimental results propeller blade loads. The method 
is not as good as that obtained in ~ of Kerwin, which considers the 
inclined flow by the method of Kerwin. inclination of the slipstream 
relative to the propeller axis, 
produced the best correlation with 
experimental values, and the method 
of Tsakonas et al produced the 
worst correlation with experimental 
values. The correlation of each 
method evaluated is as follows: 
The magnitude and the variation of 
the phases with advance coefficient 
predicted by the method of Kerwin and 
Lee agree with the experimental results 
substantially better than do those 
predicted by either of the other two 
predictions evaluated. Except for J> 
1.0 on Propeller 4710, the phases a. 
predicted by Kerwin and Lee are within 5 
degrees of the experimental phases. 
The method of Tsakonas et al 
predicts the first harmonic 
loading to be approximately 35 
percent of the experimental 
value at the lowest advance 
coefficient investigated, 65 
percent of the experimental 
value at the design condition 
In summary, all three of the 
calculation procedures predicted 
K(px)1 to within 20 percent of the 
experimental values at design J. 
However, the agreement at substantially 
off-design J was not as good. In 
general, the method of Kerwin and Lee 
gave the best agreement with experimen- 
tal results in the magnitude and trend 
of k(px)1 Over a range of J. In addi- 
tion, the method of Kerwin and Lee gave 
the best agreement with experimental 
results in phases and in the trends of 
the variation of phases with J. 
SUMMARY AND CONCLUSIONS 
An investigation was undertaken to 
evaluate the periodic single-blade loads 
on propellers and the influence of a 
nearby solid boundary on the periodic 
blade loads in inclined flow and in 
circumferentially non-uniform 
longitudinal velocity fields. 
Systematic model experiments were 
conducted and the results were 
correlated with predictions by the 
following methods: 
and 80 percent of the 
experimental value at the 
highest advance coefficient 
investigated. This method 
predicts a variation of first 
harmonic loading coefficients 
with advance coefficient which 
is substantially different 
from that obtained experiment- 
ally. This method predicts 
that the maximum values of 
loading will occur at 
approximately 15 to 20 degrees 
of blade angular position 
before the experimentally 
determined angle. 
b. The quasi-steady method of 
McCarthy underestimates the 
first harmonic loading by 10 
to 30 percent over a range of 
advance of coefficients with 
closer agreement at higher 
values of J. This method 
predicted a similar trend to 
the experimental data; i.e., 
that the loading coefficient 
decreases with increasing J. 
This method predicts that the 
maximum values of loading will 
occur at approximately 10 to 
20 degrees before the experi- 
mentally determined angle. 
dbo A simple quasi-steady procedure 
developed by McCarthy at DTNSRDC 
which utilizes the open water 
characteristics of the propeller. 
Bc A linearized lightly-loaded 
unsteady lifting surface theory 
developed by Tsakonas and his 
colleagues at Davidson Laboratory. 
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