Propeller -Induced Appendage Forces 



6.0 



4.0 ■ 



2.0 - 



1.0 



0.6 - 



0.4 



0.2 - 



0.1 



First Harmonic 



Symmetrical Appendage 



Asymmetry: 1/4 Prop 



Diameter 



Asymmetry: 1/2 Prop 



Diameter 



0.25 0.50 



Spacing/Propeller Diameter 



0.75 



Fig 

 for 



. 18 - Effect of appendage asymmetry on transverse forces 

 a three -bladed propeller with the basic blade thickness 



presented here is valid for engineering purposes when the thrust coefficient of 

 the propeller is representative of actual propeller designs. 



An example of the results of this test technique is shown in the following 

 figures. Figure 19 presents the axial induced appendage force, as determined 

 from single-bladed propeller operation, compared with forces induced by pro- 

 pellers having two and four blades. Of interest on this figure is the fact that the 

 induced force associated with the second harmonic of a two-bladed propeller is 

 about as large as that induced by the first harmonic of a two-bladed propeller. 

 This is somewhat contrary to what might be expected, but it is verified from 

 both the single-bladed and two-bladed measurements for these propellers. Fig- 

 ure 20 presents a comparison of the induced force ratios associated with single- 

 bladed and three -bladed propeller units. These data are shown for both the first 

 and second harmonics of the blade rate. From the preceding figures, as well as 

 other data obtained during different test programs, it appears as if this technique 

 is well suited for experimentally evaluating the induced appendage forces of a 

 particular propeller design. It requires the manufacture of only one blade, and 



189 



