text: The ability of an airplane to convert fuel 
  energy into flying distance is one of the most 
  important items of airplane performance. The 
  problem of eficient range operation of an air- 
  plane appears of two general forms in flying 
  operations: (1) to extract the maximum flying 
  distance from a given fuel load or (2) to fly a 
  specified distance with minimum expenditure 
  of fuel. An obvious common denominator for 
  each of these operating problems is the “spe- 
  cific range, ” nautical miles of flying distance 
  per lb. of fuel. Cruise flight 
  for maximum 
  range cond.itions should be conducted so that 
  the airplane obtains maximum specific range 
  throughout the flight. 
  
  flight hours/hr. 
  lbs. of fuel/hr. 
  specific endurance = 
  
  then, 
  
  1 
  fuel flow, lbs. per hr. 
  
  the specific endurance is 
  By this definition, 
  the reciprocal of the fuel ~flow. Thus, 
  s&ply 
  .ifl.maximum endurance is desired, the flight 
  condition ‘must provide a minimum of fuel 
  flow. This point is readily appreciated as the 
  lowest point of the curve of fuel flow versus 
  velocity. Generally, in subsonic performance, 
  the speed at which maximum endurance is  PERFORMANCE. 
  The principal items of range performance can 
  be visualized by use of the illustrations of figure 
  2.23. From the characteristics of the aero- 
  dynamic configuration and the powerplant, the 
  
  GENERAL  RANGE 