Lehman and Kaplan 



10. Op 

 8.0- 



6.0- 

 4.0 



;^ 3.0 



i-i 



« 



o 



S 2.0 



S i.O 



3 



-a 



c 0.8 



X 



c^ 0.6 

 o 



0.4 



0.3 



0.2 



Open Symbols = 1st Harmonic 

 Solid Symbols = 2nd Harmonic 



0.2 0.4 0.6 0.8 



Spacing/Propeller Diameter 



Fig. 24 - Induced force ratio vs spacing ratio for a 

 two-bladed propeller downstream of an appendage, 

 axial measurements, and an appendage angle of 0° 



approaching that associated with the first harmonic value for the condition of 

 zero appendage attack angle. It must be remembered in this discussion that the 

 direction of the axial and transverse forces remains referred to the free stream 

 velocity vector and not the appendage chord. 



The transverse induced appendage forces associated with a two-bladed pro- 

 peller are zero for the case of zero appendage attack angle (except for very 

 close spacing ratios, as noted earlier), but with the introduction of an attack 

 angle of 10° the transverse induced forces exceed the axial induced values, as 

 shown in Fig. 27. 



For the case of the three-bladed propeller. Fig. 28 presents the transverse 

 induced appendage forces for a 0° appendage attack angle and Fig. 29 presents 

 the forces for a 10° appendage attack angle. A comparison of these figures again 

 shows the strong influence that appendage attack angle has on the induced forces; 

 the force ratios are decreased by about a factor of 2 when the appendage is at an 



194 



