text: NAVWEPS OO-ROT-RO 
  AIRPLANE PERFORMANCE 
  
  The governing of the engine-propeller combi- 
  nation will allow operation throughout a wide 
  range of power and speed while maintaining 
  efficient operation. 
  
  If the envelope of maximum propeller dfi- 
  ciency is available, the propulsive horsepower 
  available will appear as shown in the second 
  chart of figure 2.19. The propulsive power 
  available, Pa, is the product of the propeller 
  efficiency and applied shaft horsepower. 