Wereldsma 



2. For the epicyclic gearing a disturbed action of one of the two propellers 

 will be mechanically reflected in the operation of the other propeller, as distinct 

 from conventional gearing, where both propellers are driven independently. 



3. The important advantage of epicyclic gearing, however, is its simple, 

 less-expensive construction, well adapted to the shafting problems of contra- 

 rotating propellers. 



High- Frequency Behavior 



For an analysis of the axial and torsional vibrational behavior of the two 

 propellers, four degrees of freedom have to be taken into consideration, namely, 

 the axial and torsional vibratory motion of both propellers. Also the individual 

 elasticities and inertias of both propeller shafts and gearing systems need to 

 be taken into account (Fig. 12). 



TORSIONAL SYSTEM 



AXIAL SYSTEM 



AFT PROPELLER 



FORWARD 



PROPELLER 



AFT PROPELLER 



Fig. 12 - High-frequency analysis of a contrarotatin^ 

 propeller arrangement 



The individual and mutual coupling effects of both propellers are shown in 

 Fig. 12, and the corresponding equations of motion are given in Fig. 13. Four 

 driving- point impedances can be distinguished, indicated by Zpp, Zp-p, z^^, and 

 z\f^, representing the dynamic behavior of the shafting, gearing, and turbine. 



Four transfer impedances z^f, Zp 



FA> 



7<P 



and 



79 



representing the mechanical 



250 



