Model Tests on Contrarotating Propellers 



— 16t 



Fig. 17 - Instantaneous transverse forces 

 of cargo liner propellers 



stiffness against bending is only about a fourth part of that of the conventional 

 propeller shaft, whereas the moments are about half of those of the conventional 

 propeller. 



Figure 16 shows that in many cases the eccentricities for the contrarotating 

 propellers are in opposite direction, so that the bending moment on the forward 

 screw may be reduced by that on the aft screw. The variations in thrust and 

 torque of the forward and aft screw, however, may reinforce each other. 



It can be seen from Fig. 17 that the transverse force variations of the con- 

 ventional screw are large, whereas those of the contrarotating propellers are 

 negligible both in quantity and in direction. 



Additional measurements were conducted to determine the effect of a change 

 of the angular positions of the mutual blade encounter of the contrarotating pro- 

 pellers. From these tests it was concluded that no significant differences occur 

 for different angular positions of the mutual blade encounter. 



Determination of Stopping Abilities 



Investigations have been carried out to compare the contrarotating propel- 

 lers and the conventional screw with respect to their ability to stop the 



155 



