NAVWEPS OO-EOT-80  AIRPLANE PERFORMANCE  number, cruise-climb, or whatever the appro-  priate technique) will result in a loss of range  capability.  turboprop airplane but additional factors are  available to influence the specific endurance at  low altitude.  In other words, low altitude  endurance can be improved by shutting down  some powerplants and operating the remaining  powerplants at higher, more efbcient power  setting.  Many operational factors could decide  whether such procedure would be a suitable  technique.  The failure of an engine during the optimum  cruise of a multiengine turbojet airplane will  cause a noticeable loss of range. Since the  optimum cruise of the turbojet is generally a  thrust-limited cruise, the loss of part of the  total thrust means that the airplane must  descend  to a lower altitude.  For example, if a  twin-engine jet begins an optimum cruise at  35,000 ft. (e=O.31) and one powerplant fails,  the airplane must descend to a lower altitude  so that the operative engine can provide the  cruise thrust.  The resulting altitude would be  approximately 16,030 ft. (~=0.61).  Thus, the  airplane will experience a loss of the range  remaining at the point of engine failure and  loss could be accounted for by the reduced  velocity (TM)  and the increase in specific fuel  consumption (c~) from the higher ambient air  temperature.  In the case of the example air-  plane, engine failure would cause a 30 to 40  percent loss of range from the point of engine  failure.  Of course, the jettisoning of expend-  able weight items would allow higher altitude  and would increase the specific range.  TURBOJET POWERED AIRPLANE.  In-  creasing altitude has a powerful effect on both  the range and endurance of the turbojet air-  plane.  As a result of this powerful effect, the  typical turbojet airplane will  achieve maxi-  mum specific endurance at or near the tropo-  pause.  Also, the maximum specific range will  be obtained at even higher altitudes since the  peak specific range generally occurs at the  highest altitude at which the normal rating of  the engine can sustain the optimum aero-  dynamic conditions.  At low altitude cruise  conditions, the engine speed necessary  to sus-  tain optimum aerodynamic conditions is very  low and the specific fuel consumption is rela-  tively poor.  Thus, at low altitude, the air-  plane prefers the  low  speeds to  obtain  (&/CD)-  but the powerplant prefers the  higher speeds common to higher engine effi-  ciency.  The compromise results in maximum  specific range at flight speeds well above the  optimum aerodynamic conditions.  In a sense,  low  altitude cruise conditions are engine  dictated.  Maximum endurance in the turbojet air-  plane varies with altitude but the variation is  due to the changes in  ‘ fuel flow necessary  to  provide the thrust required at (I./D),...  The  low inlet air temperature of the tropopause  and the greater engine speed reduce the specific  fuel consumption to a minimum.  If the single-  engine turbojet airplane is at low altitude  and must hold or endure for a period of time,  a climb should begin to take advantage of the  higher specific endurance at higher altitude.  The altitude to which to climb will be deter-  mined by the quantity of fuel remaining.  In  the case of the multiengine turbojet at low  altitude,  some slightly  different procedure  may be utilized.  If all powerplants are oper-  ating, it is desirable to climb to a higher  altitude which is a function of the remaining  fuel quantity.  An alternative at low altitude  Altitude is the one most important factor  affecting the specific range of the turbojet  airplane. Any operation below the optimum  altitude will have a noticeable effect on the  range capability  and proper consideration  must be given to the loss of range.  In addi-  tion, turbojet airplanes designed specifically for  long range will have a large percent of the  gross weight as fuel.  The large changes in  gross weight during cruise will require partic-  ular methods of cruise control to extract the  maximum flight range.  A variation from the  optimum flight path of cruise (constant Mach  17s 