NAVWEPS 00-8OT-80  AlR,Pl.ANE PERFORMANCE  heat and causes  the rise of pressure  along line  CD.  The power stroke utilizes the increased  pressure  through the expansion along line DE.  Then the exhaust begins by the initial rejection  along line EB and is completed by the upstroke  along line BA.  The specific fuel consumption of the turbo-  prop powerplant is defined as follows :  engine fuel flow  equivalent shaft horsepower  specific  fuel consumption=  c=lbs. per hr.  ESHP  The net work produced by the cycle of opera-  tion is idealized by the area BCDE on the  pressure-volume  diagram of figure 2.15. Dur-  ing the actual rather than ideal cycle of op-  eration, the intake pressure  is lower than the  exhaust pressure  and the negative work repre-  sents a pumping loss.  The incomplete expan-  sion during the power stroke represents  a basic  loss in the operating cycle because of the re-  jection of combustion products along line EB.  The area EFB represents a basic loss in the  operating cycle because of the rejection of  combustion products along line EB.  The area  EFB represents  a certain amount of energy of  the exhaust gases, a part of which can be ex-  tracted by exhaust turbines as additional shaft  power to be coupled to the crankshaft (turbo-  compound engine) or to be used in operating a  supercharger (turbosupercharger). In  addi-  tion, the exhaust gas energy may be utilized to  augment engine cooling flow (ejector exhaust)  and reduce cowl drag.  Typical values for specific fuel consumption, c,  range from 0.5 to 0.8 lbs. per hr. per ESHP.  The variation of specific  fuel consumption with  operating conditions is similar to that of the  turbojet engine. The minimum specific fuel  consumption is obtained at relatively high  power setting and high altitudes.  The low  inlet air temperature reduces the specific fuel  consumption and the lowest values of c are ob-  tained near altitudes of 25,ooO to 3900  ft.  Thus; the turboprop as well as the turbojet has  a preference  for high altitude operation.  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  is an important type of aircraft powerplant.  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 RECRIPROCATING ENGINE  OPERATING  CHARACTERISTICS. The  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  combustion of the fuel-air mixture liberates  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 