text: certain type of operation. Of course, the 
  effect on service life of any particular 
  load 
  spectrum must be anticipated. 
  
  One exception to the arbitrary time standard 
  for operation at high 
  temperatures or sus- 
  tained high powers is the case of the after- 
  burner operation. When the cooling flow is 
  only that necessary to prevent excessive tem- 
  peratures for adjacent structure and equipment, 
  sustained operation past a time limit may cause 
  damage to these items. 
  
  One necessary feature of the turbojet engine 
  equipped with afterburner is a variable nozzle 
  area. As the afterburner begins functioning, 
  the exit nozzle area must increase to accom- 
  modate the 
  increased combustion products. 
  If the afterburner were to begin functioning 
  without an increase in exit area, the mass flow 
  through the engine would drop and the tem- 
  peratures would increase rapidly. The nozzle 
  area must be controlled to increase as after- 
  burner combustion, begins. As a result, the 
  engine mass flow is given a large increase in 
  jet velocity with the corresponding increase in 
  thrust. 
  
  Many op- 
  erating performance conditions may require 
  thrust be provided for short 
  that additional 
  periods of time. Any means of augmenting 
  the thrust of the turbojet engine must be ac- 
  complished without an increase in engine speed 
  or maximum turbine section temperature. The 
  various forms of afterburning or water injection 
  allow 
  fuel to provide 
  thrust augmentation without increase in engine 
  speed or turbine temperature. 
  
  THRUST AUGMENTATION. 
  
  the use of additional 