Miller 



The variation of blade frequency thrust, torque, side forces, and bending 

 moments with mean propeller loading for the single propellers is shown in Figs. 

 21, 22, 23, and 24, respectively. The directions of these forces and moments 

 are defined in Fig. 25. The unsteady thrust and torque were obtained in the 

 three-cycle wake, where they were dominant, while the side forces and bending 

 moments were obtained in the four-cycle wake. The thrust and side forces are 

 nondimensionalized on design thrust, and the torque and bending moments on the 

 torque measured at design thrust. As the loading decreased with increasing ad- 

 vance coefficient, all six blade frequency components increased for the unskewed 

 propellers. This is apparently due to the increased amplitude of the velocity 

 variations as the mean velocity was increased. The decrease in these compo- 

 nents at the higher velocities for the skewed propeller is not understood. The 

 largest unsteady forces were obtained with the expanded area ratio of 0.60, al- 

 though with only three blade widths the value for the maximum cannot be deter- 

 mined accurately. The skewed propeller showed a considerable reduction of the 

 unsteady forces over those of the unskewed propeller. The blade frequency 

 thrust and torque were only about 10% and the side forces and moments about 

 50% of those for the unskewed propeller of the same blade width. 



0.5 0.6 0.7 0.8 0.9 1.0 



.2 1.3 



Advance Coefficient, J = — ;r 

 ' nD 



Fig. 21 - Blade -frequency thrust 



Phase angles are shown in Figs. 26-28. The angles given are those by which 

 the sinusoidal components of propeller loading lead the same frequency compo- 

 nents of the longitudinal velocity at the radial line through the midchord of the 

 root section of a propeller blade. The thrust is assumed to be in the direction 

 for normal propulsion of a ship, i.e., in phase with the torque and opposite to the 

 direction shown in Fig. 25. With this assumption, and from steady theory, the 



274 



