text: In order to appreciate some of the principal 
  factors controlling 
  the efficiency of a given 
  propeller, figure 2.18 Uustrates the distribu- 
  tion of rotative velocity along the rotating 
  propeller blade. These rotative velocities add 
  to the local inflow velocities to produce a 
  variation of resultant velocity and direction 
  along the blade. The typical distribution of 
  thrust along the propeller blade is shown with 
  the predominating thrust being located on the 
  the 
  outer portions of the blade. Note that 
  tip 
  thrust develops a 
  propeller producing 
  vortex similar 
  lift. 
  the wing producing 
  Evidence of this vortex can be seen by the con- 
  densation phenomenon occurring at this Ioca- 
  tion under certain atmospheric conditions. 
  
  to 
  
  In order to provide high propeller efficiency 
  through a wide range of operation, the pro- 
  peller blade angle must be controllable. The 
  the 
  most convenient means of controlling 
  propeller is the provision of a constant speed 
  governing apparatus. The constant speed gov- 
  erning feature is favorable from the standpoint 
  of engine operation in that engine output and 
  efficiency is positively controlled and governed.  The component velocities at a given propeller 
  blade section are shown by the diagram of 
  figure 2.18. The inflow velocity adds vec- 
  torially 
  to the velocity due to rotation to pro- 
  duce an inclination of the resultant wind with 
  This incli- 
  respect to the planes of rotation. 
  the effective pitch 
  nation is termed + (phi), 