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  TURBOJET OPERATING CHARACTER- 
  ISTICS. The turbojet engine has many oper- 
  ating characteristics which are of great im- 
  portance to the various items of jet airp!ane 
  performance. Certain of these operating char- 
  acteristics will provide a strong influence on 
  the range, endurance, etc., of the jet-powered 
  airplane. Other operating characteristics will 
  require operating 
  techniques which differ 
  greatly from more conventional powerplants. 
  The turbojet engine is essentially a thrust- 
  producing powerplant and 
  the propulsive 
  power produced is a result of the flight speed. 
  The variation of available thrust with speed is 
  relatively small and the engine output is very 
  nearly constant with 
  flight speed. The mo- 
  mentum change given the engine airflow de- 
  relationship: 
  velops thrust by the following 
  
  The factor of 321 evolves from the use of the 
  nautical unit of velocity and implies that 
  each pound of thrust developed at 325 knots 
  is the equivalent of one horsepower of propul- 
  sive power. Since the thrust of the turbojet 
  engine is essentially constant with speed, tht 
  power available increases almost linearly with 
  speed. In this sense, a turbojet with 5000 Ibs. 
  of thrust available could produce a propulsive 
  power of 3,ooO h.p. at 325 knots or 10,000 
  h.p. at 650 knots. The tremendous propulsive 
  power at high velocities is one of the principal 
  features of the turbojet engine. When the 
  engine RPM and operating altitude arc fixed, 
  the variation with speed of turbolet thrust and 
  power available is typified by the first graph 
  of figure 2.10. 