Lehman and Kaplan 



For the axial induced force the relative effects of vorticity and thickness of 

 the propeller are shown for a two-bladed propeller in Figs. 42 and 43, where the 

 effect of doubling the propeller thickness is shown to be smaller as compared 

 with the transverse force results. The blade rate results for the case of a four- 

 bladed propeller are shown in Fig. 44, where the influence of the propeller thick- 

 ness increase, relative to the magnitude of the total force, is greater. Thus the 

 influence of propeller thickness for both the transverse and axial appendage 

 forces is significant in determining their total amplitude. 



.035, 



,030- 



,025- 



.020. 



.015 



,010 



,005 



total 



vorticit 



1.0 



1.2 



1.4 



Fig. 42 - Axial force as a function of the advance ratio for a 

 two-bladed propeller: /3 = 0.05, N = 2, to/2c = 0.05 



The present theory includes expressions for forces at higher harmonics of 

 the blade rate. The variation of the second- harmonic axial force for a two- 

 bladed propeller is shown in Fig. 45, and the values for the blade-rate axial 

 force for a four-bladed propeller are shown in Fig. 46. The total force, as well 



218 



