Propeller -Induced Appendage Forces 



6.0 



4.0 



2.0 



1.0 



0.6- 



0.4 



0.2- 



0.1 



-First Harmonic 



3-Bladed Propeller 



— 1-Bladed Propeller 



0.25 0.50 



Spacing/Propeller Diameter 



0.75 



Fig. 20 - Comparison of three -bladed and single -bladed operation 

 with transverse induced forces and a symmetrical appendage 



For the smaller span appendages, fairings having the same cross section as 

 the appendage itself were attached to the tunnel walls. All appendages had a 

 ogival cross section and a chord length of 8 in. One foil had a maximum thick- 

 ness of 1.0 in., and the other had a maximum thickness of 0.5 in. Figure 23 

 illustrates the effect of foil thickness and span on the axial induced forces asso- 

 ciated with the two-bladed propeller. 



Appendage Attack Angle 



The effect of appendage attack angle on induced appendage forces is of con- 

 siderable interest, since the appendage attack angle significantly changes the in- 

 duced appendage forces compared to the case with a zero appendage attack angle. 

 Figures 24 and 25 present the axial induced forces with a two-bladed propeller 

 at appendage attack angles of 0° and 10°. A comparison of the data contained on 

 these two figures is shown in Fig. 26. This figure shows that the induced ap- 

 pendage forces associated with both the first and second harmonics of the blade 

 rate increase with appendage attack angle, with the second harmonic value 



191 



