text: The reciprocating engine is one of the most 
  efficient powerplants used for aircraft power. 
  The combination of the reciprocating engine 
  and propeller is one of the most efficient means 
  of converting the chemical energy of fuel into 
  flying 
  time or distance. Because of the in- 
  herent high efficiency, the reciprocating engine 
  type of aircraft powerplant. 
  is an important 
  CHARACTERISTICS. The 
  OPERATING 
  function of the typical reciprocating engine in- 
  volves four strokes of the piston to complete 
  one operating cycle. This principal operating 
  cycle is illustrated in figure 2.15 by the varia- 
  tion of pressure and volume within 
  the cylin- 
  der. The first stroke of the operating cycle is 
  the downstroke of the piston with 
  the intake 
  valve open. This stroke draws in a charge of 
  fuel-air mixture along AB of the pressure- 
  volume diagram. The second stroke accom- 
  plishes compression of the fuel-air mixture 
  along line EC. Combustion is initiated by a 
  spark ignition apparatus and combustion takes 
  place in essentially a constant volume. The 
  liberates 
  combustion of the fuel-air mixture 
  
  Since the net work produced during the op- 
  erating cycle is represented by the enclosed area 
  of pressure-volume diagram, the output of the 
  engine is affected by any factor which influences 
  this area. The weight of fuel-air mixture will 
  determine the energy released by combustion 
  and the weight of charge can be altered by 
  altitude,supercharging,etc. Mixturestrength, 
  preignition, spark timing, etc., can affect the 
  energy release of a given airflow and alter the 
  work produced during the operating cycle. 
  
  The mechanical work accomplished during 
  the power stroke is the result of the gas pres- 
  sure sustained on the piston. The linkage of 
  the piston to a crankshaft by the connecting 
  rod applies torque to the output shaft. During 
  this conversion of pressure energy to mechani- 
  cal energy, certain losses are inevitable because 