Propeller -Induced Appendage Forces 



Spacing = 0.0625 

 Propeller Diameter 



Spacing = 0.3125 

 Propeller Diameter 



Shaft Rate 13 rps 



First Harmonic 



Second Harmonic 



Ay nfarT'^f^», m > f — ^Qr^^rft—. 



Third Harmonic 



80 100 120 140 160 180 



Frequency (cps) 



Fig. 11 - Axial induced appendage force levels as a function of 

 scanned frequency for a double -thickness four-bladed propeller 

 and a symmetrical appendage 



introduction of both axial and transverse forces regardless of whether there was 

 an even or odd number of blades on the propeller. It therefore seems reasonable 

 to conjecture that with extremely close propeller- appendage spacings the action 

 of the propeller on the flow about the appendage is such as to result in an effec- 

 tive angle of attack of the appendage. This contention is further strengthened by 

 the fact that these "inconsistent" induced appendage forces completely disappear 

 with slight increases in the spacing ratio, and it also follows that the effect of the 

 propeller on the flow field about the appendage does decay rapidly. An example 

 of the magnitude of the "contradictory" transverse force associated with four- 

 bladed propeller tests is shown in Fig. 12. 



With those two points clarified the following discussions which involve an 

 appendage at a zero attack angle will be restricted to comments relating only to 

 the appropriate propeller- appendage induced force; i.e., axial induced forces will 

 be discussed with even-bladed propellers and transverse induced forces will be 

 discussed with odd-bladed propellers. 



181 



