text: flow, nozzle area, etc. to provide engine per- 
  formance scheduled by the throttle or power 
  functions provided 
  lever. These regulatory 
  must account for variations in altitude, tem- 
  perature, and flight velocity. 
  
  When the inlet ram and compressor pressure 
  ratio is fixed, the principal factor affecting the 
  specific fuel consumption is the inlet air temp- 
  erature. When the inlet air 
  temperature is 
  lowered, a given heat addition can provide 
  relatively greater changes in pressure or vol- 
  ume. As a result, a given 
  thrust output 
  requires less fuel flow and the specific fuel con- 
  sumption, c,, is reduced. While the effect of 
  altitude on specific fuel consumption does not 
  compare with 
  the effect on thrust output, the 
  variation is large enough to strongly influence 
  range and endurance conditions. Figure 2.11 
  illustrates a typical variation of specific fuel 
  consumption with altitude. Generally, the 
  specific fuel consumption decreases steadily 
  the tropopause is reached 
  with altitude until 
  and the specific fuel consumption at this point 
  is approximately 80 percent of the sea level 
  value. 
  
  One principal governing factor which must 
  be available is that a selected power setting 
  (RPM) must be maintained throughout a wide 
  range of flight conditions. Figure 2.12 illus- 
  trates the sariation of fuel flow with RPM for 
  a turbojet operating at a particular set of 
  flight conditions. Curve 1 depicts the varia- 
  tion with RPM of the fuel flow required for 
  stabilized, ste,ady state operation of the engine. 
  Each point along this curve 1 defines the fuel 
  flow which 
  is necessary to achieve equilib- 
  rium at a given RPM. The steady state fuel 
  flow produces a turbine, power to equal the 
  compressor power requirement at a particular 
  RPM. The throttle position primarily com- 
  mands .a given, engine speed and, as changes 
  occur in the ambient pressure, temperature, 
  and flight speed, the .steady state fuel flow will 
  vary. The governing’ apparatus must account 
  for these variations in flight conditions and 
  maintain 
  the power setting scheduled by 
  throtrle position. 
  In addition 