Propeller -Induced Appendage Forces 



6.0 



4.0 ■ 



2.0 - 



1.0 - 



0.6 . 



0.4 - 



0.2 - 



0.1 



Basic Blade Thickness 

 Double Blade Thickness 



0.25 0.50 



Spacing/Propeller Diameter 



0.75 



Fig. 16 - The effect of propeller blade thickness on the transverse 

 forces for a three -bladed propeller with a symmetrical appendage 



single-bladed propeller, when examined in terms of the ratio of the induced ap- 

 pendage force divided by the single-bladed propeller thrust, resulted in good 

 agreement when compared with the same induced force/thrust ratio associated 

 with a propeller composed of more than one blade. Comparisons must naturally 

 be made at the same frequency. For a three-bladed propeller the first harmonic 

 of blade rate is three times the shaft rate; thus the single-bladed propeller data 

 must also be examined at a frequency corresponding to three times the shaft 

 rate to make a valid comparison. 



Using the single-bladed- propeller technique, the ratio of the induced append- 

 age force and the propeller thrust of a multibladed propeller can be determined 

 quite accurately once reasonable propeller thrusts (or % operating values) are 

 employed. The inaccuracy of this method arises when extremely light propeller 

 loadings are employed, since the induced appendage force is actually composed 

 of two components: one due to propeller loading and one due to propeller blade 

 thickness. The thickness of the propeller should contribute a certain amount to 



187 



