Davis and English 



It may be noted that in these experiments the lowest cavitation numbers at- 

 tainable were limited to some extent by the tunnel circuit cavitating in addition 

 to the cavitation produced by the propeller itself. It was also necessary to per- 

 form the tests at relatively low values of air content in order to prevent free air 

 from recirculating around the tunnel circuit, and to enable the lowest working 

 section pressures to be obtained. Throughout the tests the air content was kept 

 approximately within the range of 3.5 to 7.0 parts per million by weight. 



REYNOLD'S NUMBER OF TESTS 



To achieve the low cavitation numbers required, the experiments had to be 

 run at high speeds, and this led to high values of Reynold's number. Based on 

 the relative flow and the blade chord lengths at the 70 percent radius, the Reyn- 

 old's number of the tests was about 2 x 10^ compared with 30 x 10^ for the ship. 



DISCUSSION 



W.B. Morgan 



Naval Ship Research and Development Center 

 Washington, D. C. 



This extensive paper shows the amount of work necessary to develop a 

 high-speed propeller for a particular application. An accounting of the details 

 gone through in such a development is most welcomed. 



I have two questions which involve the strength analysis. The first question 

 concerns the use of the simple beam theory for making the stress analysis. The 

 stresses obtained by the authors experimentally indicate that the direction of the 

 principal stresses toward the blade tip deviate considerably from that normally 

 assumed for airfoil-shaped sections, i.e., normal to the nose-tail line. I would 

 like to know, in the use of the simple beam theory, whether or not the principal 

 stresses were considered as normal to the nose-tail line. It should be possible 

 to calculate the location of the principal axis and take into account its true 

 position. 



My second question is whether or not a section with a large annex was con- 

 sidered for strength purposes. 



1016 



