text: Note that in the top end of power output, each 
  1 percent RPM change causes a 3.5-percent 
  change in thrust output. This illustrates the 
  power of variation of thrust with 
  rotative 
  iii this example, is N3.“. Also 
  speed which, 
  note that the top 20 percent of RPM controls 
  more than half of the output thrust. 
  
  the fixed geometry engine develops 
  thrust approximately proportional to Na.“, the 
  engine with variable geometrywill demonstrate 
  a much more powerful effect of rotative speed. 
  When the jet engine is equipped with a vari- 
  able nozzle, multispool compressor, variable 
  stator blades, etc., the engine is more likely 
  to develop thrust proportional 
  rotative 
  speed from values of N4.6 to N6.0. For ex- 
  ample, if a variable geometry engine develops 
  thrust proportional to Ns.‘, each one per cent 
  RPM change causes a 5.0-percent thrust change 
  at the top end of power output. Also, the 
  top 13 percent of RPM would control the top 
  50 percent of thrust output. 
  
  While 
  
  Thus, each unit pound of thrust requires 1.12 
  lbs. per hr. fuel flow. Obviously, high engine 
  efficiency would be indicated by a low value of 
  c,. Typical values for turbojet engines with 
  relatively high pressure ratios range from 0.8 
  to 1.2 at design operating conditions in sub- 
  sonic flight. High energy fuels and greater 
  pressure ratios tend to produce the lower values 
  of ct. Supersonic flight with the attendant in- 
  let losses and high compressor inlet air tem- 
  peratures tend to increase the specific fuel con- 
  sumption to values of 1.2 to 2.0. Of course, 
  the use of an afterburner is quite inefficient 