Preliminary results from blade loading oaecimenne " conducted in 
idealized flows indicate that: 
1. The unsteady blade loads in either axial or tangential wakes are 
not influenced by the presence of a nearby boundary above the propeller. 
2. In inclined flow without an upstream hull, the experimental un- 
steady loading near the design advance coefficient is nearly two times as 
25,34 
large as that calculated by the method of Tsakonas et al, and approxi- 
mately 80 percent larger than that calculated by the method of MeCaceny oo 
3. In an axial wake with a dominant first harmonic of blade angular 
position which was generated by upstream wire grid screens with zero shaft 
angle, the unsteady loading near the design advance coefficient is within 
approximately 15 percent of the values calculated by the methods of 
25,34 
2 
Tsakonas et al, and McCarthy. ° This is in agreement with previous 
correlations with the method of Tsakonas et al for unsteady shaft (bearing) 
forces and moments for operation in axial calass Le 
These results indicate that the large discrepancy between the experi- 
mental and calculated unsteady bending moments presented in the current 
report appear to be due to the inability of the present theories to 
properly account for all important characteristics of the flow field for 
operation in inclined flow. All available procedures, including the un- 
2252) and the quasi-steady procedure of 
steady theory of Tsakonas et al 
vieGaawy implicitly assumed that the propeller slipstream follows the 
propeller axis rather than the direction of the effective velocity into 
the propeller which is at an angle to the propeller axis in inclined f.iow. 
It is speculated that this failure to consider the true direction of the 
slipstream is the major factor in the analytical underprediction of the 
*The results in Reference 12 were at substantially higher reduced fre- 
quency than the results in the present study; therefore, the quasi-steady 
procedure of McCarthy over-predicted the unsteady loads in Reference 12. 
Boswell, R.J. and S.D. Jessup, "Experimental Determination of Period- 
ic Propeller Blade Loads in a Towing Tank,'' Presented to the 18th American 
Towing Tank Conference, U.S. Naval Academy, Annapolis, Maryland (August 
LOTT) o 
47 
