NAVWEPS oo-801-80  AIRPLANE PERFORMANCE  provide a comparison of the total range avail-  able from a constant altitude or cruise-climb  where  and  V= velocity, knots  M = Mach number  W= gross weight, lbs.  FF=fuel flow, lbs./hr.  JR= specific  range, nmi./lb.  e=altitude density ratio  Thus, during a cruise-climb flight, a 10 percent  decrease  in gross weight from the consumption  of fuel would create:  For example, if the cruise fuel weight is 50 per-  cent of the gross weight, the climbing cruise  flight path will provide a range 18.2 percent  greater than cruise at constant ,altitude. This  comparison does not include consideration of  any variation of specific  fuel consumption dur-  ing cruise or the effects of compressibility in  defining the optimum aerodynamic conditions  for cruising flight.  However, the comparison  is generally applicable for aircraft which have  subsonic cruise.  0.0  Loo0  .I  1.026  .2  1.057  .3  1.92  .4  1.136  .5  1.182  .6  1.248  .7  1.331  condition  (1) applies to some known condi-  tion of weight, fuel flow, and specific  range at some original basic altitude  during cruise climb.  con&&r (2) applies to some new values of  weight, fuel flow, and specific range at  some different altitude along a partic-  ular cruise path.  no change in Mach number or  ‘ TAS  a 5 percent decrease  in EAS  a 10 percent decrease in C, i.e., higher  altitude  a 10 percent decrease  in fuel flow  an 11 percent increase in specific range  An important comparison can be made between  the constant altitude cruise and the cruise-  climb with respect to the variation of specific  range.  From the previous relationships, a  2 percent reduction in gross weight durmg  When the airplane has a supersonic  cruise for  maximum range, the optimum flight path is  generally one of a constant Mach number.  The optimum flight path is generally-but not  necessarily-a climbing cruise. In this case of  subsonic.  or supersonic cruise, a Machmeter is  of principal importance in cruise control of the  jet airplane.  The @ct of wind on nznge  is of considerable  importance in flying operations. Of course,  a headwind will  always reduce range and a  tailwind  will  always increase range. The  selection of a cruise altitude with the most  favorable (or least unfa:vorable) winds is a rel-  atively simple matter for the case of the  propeller powered airplane. Since the range of  the.propeller powered airplane is relatively un-  affected  by altitude, the altitude with the most  favorable winds is selected  for range. However,  the range of the turbojet airplane is greatly  affected  by altitude so the selection of an op-  timum altitude will  involve considering the  wind profile  ‘ with the variation of range with  altitude.  Since the turbojet range increases  cruise would create a 1 percent increase in  specific range in a constant altitude cruise but  a 2 percent increase  in specific  range in a cruise-  climb at constant .Mach number. Thus, a  higher average specific  range can.be maintained  during the expenditure of a given increment of  fuel.  If an airplane begins a cruise at optimum  conditions at or above the tropopause with a  given weight of fuel, the following  data  168 