text: Typical minimum values for c range from 0.4 
  to 0.6 lbs. per hr. per BHP and most aircraft 
  powerplaots average 0.5. The turbocompound 
  engine is generally the most efficient because 
  of the power recovery turbines and can ap- 
  It should be 
  proach values of c=O.38 to 0.42. 
  noted that the minimum values of specific fuel 
  consumption will be obtained only within 
  the 
  range of cruise power operation, 30 to 60 per- 
  cent of the maximum power output. Gen- 
  erally, the conditions of minimum specific fuel 
  consumption are achieved with auto-lean or 
  manual lean scheduling of fuel-air ratios and 
  high BMEP and low RPM. The low RPM is 
  the usual requirement to minimize friction 
  horsepower and improve output efficiency. 
  
  The fuel metering requirements for an engine 
  are illustrated by the third graph of figure 2.16 
  which is a plot of fuel-air ratio versus engine 
  airflow. The carburetor must provide specific 
  fuel-air ratios throughout the range of engine 
  airflow to accommodate certain output power. 
  Most modern engines equipped with auto- 
  matic mixture control provide a scheduling of 
  fuel-air ratio for automatic rich or automatic 
  lean operation. The auto-rich scheduling usu- 
  ally provides a fuel-air ratio at or near the 
  maximum heat release value for the middle 
  range of airflows. However, at high airflows 
  a power enrichment must be provided to sup- 
  press detonation. The auto-rich schedule gen- 
  erally will provide an approximate fuel-air 
  ratio of 0.08 which increases to 0.10 or 0.11 at 
  In addition, 
  the airflow for takeoff power. 
  the low airflow and mixture dilution 
  that oc- 
  curs in the idle power range requires enrich- 
  ment for satisfactory operation. 
  
  The effect of &it&c 