Propeller -Induced Appendage Forces 



Two interesting observations were made during this study. The first con- 

 cerned the introduction of both axial and transverse appendage forces by either 

 an even-bladed or odd-bladed propeller as soon as the appendage was at an attack 

 angle, similar to the case of an upstream appendage discussed previously. The 

 second observation, and one which was perhaps more unusual, concerns the un- 

 dulatory variation of the induced force ratio as a function of propeller- rudder 

 spacing. While this variation of the force ratio would not be expected, particu- 

 larly in view of the test results associated with the case of a propeller down- 

 stream of an appendage, Sugai (12) has hypothesized that such force variations 

 could exist. The present initial experimental data support that hypothesis. 



Figure 31 shows the axial induced rudder force ratio for a two-bladed pro- 

 peller at a 0° rudder angle. Figure 32 shows the induced rudder force ratios 

 with the rudder at an attack angle. The data on these figures show that the un- 

 dulatory variation of the induced force ratio with axial distance exists both with 

 and without rudder angle. Figure 33 illustrates the transverse induced rudder 

 forces associated with a two-bladed propeller. This figure shows that even- 

 bladed propellers induce transverse forces when the rudder is at an attack angle 

 and that the undulatory nature of the force occurs for this case also. 



For the case of transverse induced rudder forces with a three-bladed pro- 

 peller Fig. 34 shows the force ratios associated with a 0° rudder angle and Fig. 

 35 presents data for a 10° rudder angle. These figures again illustrate the un- 

 dulatory nature of the induced rudder force. Figure 36 presents the axial in- 

 duced rudder force associated with a three-bladed propeller. Here once again 

 the existence of an axial force associated with a three-bladed propeller is shown, 

 together with the persistent undulatory variation with distance of the induced 

 force ratio. 



SUMMARY OF EXPERIMENTAL RESULTS 



Since a detailed listing of the many implications which can be derived from 

 the data would be very lengthy, only generalized key observations will be pre- 

 sented here. 



1. Induced appendage forces are associated with only blade harmonic fre- 

 quencies. 



2. Propeller blade thickness is a major factor influencing both the axial and 

 transverse appendage forces. An increase in blade thickness produces significant 

 increases in the induced force ratios. 



3. Appendage asymmetry has a strong influence on the magnitude of the in- 

 duced force ratio for the case of transverse forces (odd-bladed propellers) but 

 only a minor influence on the axial induced force (even-bladed propellers). 



4. Even-bladed propellers induce axial forces and odd-bladed propellers 

 induce transverse forces on an appendage at a zero attack angle. Discrepancies 

 at close propeller spacings can be logically explained as a result of propeller- 

 induced "steady" attack angle changes. 



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