text: If compressibility effects are negligible, any 
  with altitude is strictly a 
  variation of ~peci)c 
  range 
  function of engine-propeller pcrformanCC. 
  
  The airplane equipped with the reciprocating 
  engine will experience very 
  if any, 
  variation of specific range with altitude at low 
  altitudes, There 
  is negligible variation of 
  brake specific fuel consumption for values of 
  BHP below the maximum cruise power rating 
  is the auto-lean or 
  of the powerplant which 
  manual lean range of engine operation. Thus, 
  an increase in altitude will produce a decrease 
  in specific range only when the increased power 
  requirement exceeds the maximum cruise power 
  rating of the powerplants. One advantage of 
  supercharging is that the cruise power may be 
  maintained at high altitude and the airplane 
  may achieve the range at high altitude with 
  the corresponding increase in TAS. The prin- 
  cipal differences in the high altitude cruise and 
  low altitude cruise are the true airspeeds and 
  climb fuel requirements. 
  
  the turboprop 
  powerplant will exhibit a variation of specific 
  range with altitude 
  for two reasons. First, 
  the specific fuel consumption (c) of the turbine 
  engine improves with 
  tem- 
  peratures common to high altitudes. Also, 
  the low power requirements to achieve opti- 
  mum aerodynamic conditions at low altitude 
  necessitate engine operation at low, inefficient 
  output power. The increased power require- 
  ments at high 
  turbine 
  to operate in an efficient output 
  powerplant 
  the airplane has no 
  range. Thus, while 
  particular preference for altitude, 
  the power- 
  plants prefer the higher altitudes and cause 
  an increase in specific range with altitude. 
  for 
  Generally, 
  efficient cruise operation is defined by airplane 
  gross weight 
  (and power required) or com- 
  presslbility effects. 
  
  The airplane equipped with 