text: same thrust required must be obtained with a 
  greater engine RPM. 
  
  At this point it is necessary to consider the 
  effect of the operating condition on powerplant 
  performance. An increase in altitude will 
  im- 
  prove powerplant performance in two respects. 
  First, an increase in altitude when below the 
  tropopause will provide lower inlet Gr tem- 
  peratures which redqce the specific fuel con- 
  sumption (c~). Of course, above the tropo- 
  pause the specific fuel consumption tends to 
  increase. A; 
  the engine RPM 
  necessary to produce the required thrust is low 
  and, generally, well below the normal rated 
  value. Thus, a second benefit of altifude on 
  engine performance is due to the increased 
  RPM required to furnish cruise thrust. An 
  increase in engine speed to the normal rated 
  value will reduce the specific fu,el consumption. 
  The increase in specific range with altitude 
  to 
  
  of the turbojet airplane can be attributed 
  these three factors: 
  
  (1) An increase in altitude will increase the 
  proportion of (V/Tr) and provide a greater 
  TAS for the same TY. 
  
  (2) An increase in altitude  in the tropo- 