Cox 



Dr. English and Professor Kruppa both draw attention to the important 

 question of need for "off-design" prediction, such as applies to the "take-off" 

 condition for craft which possess a resistance hump. For such "off-design" 

 conditions, there will be high blade loading with large section angle of attack 

 and cavity thickness. Under such conditions the propeller possesses relatively 

 poor efficiency, but the major concern is to ensure an adequate reserve of 

 power to "take-off" for a propeller designed for a cruise or top-speed condi- 

 tion. No really satisfactory suhcavitating propeller theoretical performance 

 analysis method exists, as yet, for such extreme "off-design" conditions. In 

 the case of a supercavitating propeller, the problem is even more difficult, due 

 to the influence and behavior of thick cavities. As such, the theoretical method 

 proposed in the paper for the design problem is highly unlikely to prove a suit- 

 able basis for the "off-design" prediction purposes, without the incorporation 

 of empirical information based on prior experimental test data. 



960 



