text: where 
  
  J=propeller advance ratio 
  V=flight velocity, ft. per sec. 
  n=propeller  rotative speed, revolutions 
  
  per sec. 
  
  D = propeller diameter, ft. 
  
  Many di,fferent factors govern the efficiency of 
  a propeller. Generally, a large diameter pro- 
  peller favors a high propeller efficiency from 
  the standpoint of large mass flow. However, 
  a powerful adverse effect on propeller efficiency 
  is produced by high tip speeds and conipressi- 
  bility effects. Of course, small diameter pro- 
  pellers favor low tip speeds. In addition, the 
  propeller and powerplant must be matched for 
  compatibility of output and efficiency. 
  
  Note that the difference between the effec- 
  tive pitch angle, 4, and the blade angle, 8, 
  determines an effective angle of attack for the 
  propeller blade section. Since the angle of 
  factor affecting the 
  attack 
  efficiency of an airfoil section, it is reasonable 
  to make the analogy that the advance ratio, J, 
  and blade angle, 8, are the principal factors 
  affecting .propeller efficiency. The perform- 
  ance of a propelleris 
  typified by the chart of 
  figure 2.19 which- illustrates the variation of 
  propeller efficiency, ~a, with advance ratio, J, 
  for various values of blade angle, 8. The 
  value of vP for each fl 
  J 
  until a peak is reached, then decreases. It is 
  apparent that a fixed pitch propeller may be 
  selected to provide suitable performance in a 
  narrow range of advance ratio but efficiency 
  would suffer considerably outside this range. 