Lehman and Kaplan 



0.2 0.4 0.6 0.8 



Spacing/Propeller Diameter 



1.0 



Fig. 31 - Induced force ratio vs spacing ratio for a 

 two-bladed propeller upstream of an appendage, 

 axial measurements, and an appendage angle of 0° 



5. All induced forces on an upstream appendage decrease rapidly with an 

 increase in propeller spacing. This holds whether the appendage is at an attack 

 angle or not. In general, once the spacing has approached a propeller radius, the 

 induced force is less than 1% of the propeller thrust. 



6. Generally, the induced force values associated with the second and third 

 harmonics of blade rate are well below those associated with the blade rate, but 

 there are certain exceptions, such as the axial induced forces with the two- 

 bladed propeller. 



7. The force ratio defined by the unsteady induced appendage force divided 

 by the operating propeller thrust is recognized as not being a proper scaling 

 factor in that both the thickness and loading contributions are lumped together. 

 However, its use for conventional propeller loadings seem valid. 



202 



