flow is determined mainly by the shaft poluet  put into the propeller rather than thrust. Thus,  the powerplant fuel flow could be related di-  rectly to power required to maintain the air-  plane in steady, level flight.  This fact allows  study of the range of the propeller powered  airplane by analysis of the curves of power  required versus velocity.  Figure 2.24 illustrates a typical curve of  power required versus velocity which, for the  propeller powered airplane, would be analo-  gous to the variation of fuel flow versus veloc-  ity. Maximum endurance  condition would be  obtained at the point of minimum power re-  quired since this would require the lowest fuel  flow to keep the airplane in steady, level flight.  Maximum range condition would occur where  the proportion between velocity and power re-  quired is greatest and this point is located by  a straight line from the origin tangent to the  curve.  The maximum range condition is obtained  at maximum lift-drag ratio and it is important  to note that (L/D),,  for a given airplane  configuration occurs at a particular angle of  attack and li5t coefficient and is unaffected by  weight or altitude (within  compressibility  limits).  Since approximately 50 percent of  the total dra.g a ’ t (L/D)*  is induced drag, the  propeller powered airplane which is designed  specifically i3r IJong range will have a strong  preference  for rbe thigh aspect rario planform.  The effect ,df tihe variation of airplane gross  weight is illustrated by the second graph of  figure 2.24.  ‘ The flight condition of (L/D),.,  is achieved a ’ t,one-particular value of lift coefIi-  cient for a given airplane configuration.  Hence, a variation of gross weight will alter  the values of airspeed, power required, and spe-  cific range obtained at (L/D)m.r.  If a given  configuration  ‘ of airplane is operated at con-  stant altitude and the lift  coefficient for  WDL  the following  relationships will  awb :  The effect of altitude on the range of the  propeller powered airplane may be appreciated  by inspection of the final graph of figure 2.24.  If a given configuration of airplane is operated  at constant gross weight and the lift coefficient  when flight is maintained at the optimum con-  ditions of (L/D),.,.  The variations of veloc-  ity and power required must be monitored by  the pilot as part of the cruise control to main-  tain .(L/D),.+  When the airplane fuel weight  is a small part of the gross-weight and the range  is small, then cruise control procedure can be  simplified to essentially a constant speed and  power setting throughout cruise. However,  the long range airplane has a fuel weight which  is a conside ’ rable part of the gross weight and  cruise control procedure must employ sched-  uled airspeed and power changes to maintain  optimum range conditions.  Thus a 10 percent increase in gross weight  would create:  a 5 percent increase in velocity  a 15 percent increase in power required  a 9 percent decrease  in specific range  and,  where  condition  (1) applies to some known condi-  tion of velocity, power required, and  specific range for (L/D),., at some basic  weight, WI  condition  (2) applies to some new values of  velocity, power required, and specific  range for (L/D),.,  at some different  weight, WI  V= velocity, knots  W= gross weight, Jbs.  Pr=power required, h.p.  SK= specific  range, nmi/lb.  161  -4  v*-  E  VI  K  pr*  w* s ’ *  -=H  PC WI  SRs WI  -=-  SRI  W,  NAVWEPS OS80140  AIRPLANE PERFORMANCE 