Fully Cavitating Propeller for a Hydrofoil Ship 



7 



0-6 



SHARP LEADING EDGES 



THICKENED LEADING 



EDGES + + 



Fig. 30 - Efficiency comparison — effect of thickened 

 leading edges — screw T95 



thrust and torque, as might be expected, since thrust increases with decreasing 

 advance coefficient in the flying conditions, Fig. 32, and reduces with decreasing 

 advance coefficient in the takeoff conditions. Fig. 33. Although the structural 

 design of screw T95 differs appreciably from the screw blade tested at De Havil- 

 land it seems worthwhile attempting to correlate the results at the 20 percent 

 chord position as far as possible. For example, if in Fig. 32 an advance coeffi- 

 cient of 0.95 is taken as the flying condition, then the thrust developed by a 44- 

 inch diameter propeller is 29,200 Ibf and the peak maximum principal stress is 

 19,800 lbf/in2. If we now assume that the thrust of screw T95 can be increased 

 to 40,000 Ibf by increasing the camber, say, without appreciably affecting the 

 structural properties, then we can scale the stress directly as thrust. This then 

 produces a stress of 27,100 Ibf/in^ for a 40,000 Ibf thrust as compared with 

 about 22,000 Ibf/in^ from De Havilland's tests. Further, if we assume the 



999 



