NAVWEPS OO-ROT-RO  AtRPLANE PERFORMANCE  TURBOPROP  POWERED  AIRPLANE.  problem will be most .critical if the airplane is  at high altitude, high gross weight, and with  gaps and gear extended. Lower altitude,  jettisoning of weight items, and cleaning up  the airplane will reduce the power required for  flight.  Of course, the propeller on the in-  operative engine must be feathered or the  power required may exceed  that available from  the remaining operating powerplants.  The turbine engine has the preference for  relatively high power settings and high alti-  tudes to provide low specific fuel consumption.  Thus, the off-optimum conditions of range or  endurance can be concerned with  altitudes  less than the optimum.  Altitudes less than  the optimum can reduce the range but the  loss can be minimized on the multiengine  airplane by shutting down some powerplants  and operating the remaining powerplants at a  higher, more efficient output.  In this case  the change of range is confined to the variation  of specific fuel consumption with altitude.  The effect on range is much dependent on  the airplane configuration. When the pro-  peller on the ’ inoperative engine is feathered,  the added drag is at a minimum, but there is  added the trim  drag ,required to balance  the unsymmetrical power. When both these  sources of added drag are accounted for, the  (L/D)-  ,is reduced but not by significant  amounts. Generally, if the specific fuel con-  sumption and propeller efficiency  do not deteri-  orate, the maximum specific  range is not greatly  reduced. On the twin-engine airplane the  power required must .be furnished by the one  remaining engine and this. usually requires  more than the,maximum cruise-rating of the  powerplant.i As a result the powerplant can-  not be operated in the auto-lean or manual  lean, power range and the specific ,fuel con-  sumption increasesgreatly! Thus, noticeable  loss of range must be anticipated when one  engine fails on the twin-engine airplane. The  failure of oneengine on the four (or more)  engine airpla,W may allow the required, power  to be,develo,ped:by.the  three remaining power-  plants operating in an economical power range.  If the airplane is clean, at low altitude, and  low gross weight, ,the failure of one engine is  not likely to cause a, loss of range. However,  then loss. of  ‘ two  engines is likely  ‘ to cause a  considerable loss of range.  Essentially the same situation exists in the  case  of engine failure when cruising at optimum  altitude.  If the propeller on the inoperative  engine is feathered, the loss of range will be  confined to the change in specific fuel con-  sumption from the reduced cruise altitude.  If  a critical power situation exists due to engine  failure, a reduction in altitude provides im-  mediate benefit because of the reduction of  power required and the increase in power  available from the power plants.  In addition,  the jettisoning of expendable weight items  will improve performance and, of course, the  clean configuration provides minimum parasite  drag.  Maximum specific endurance of the turbo-  prop airplane does not vary as greatly with  altitude as the turbojet airplane. While each  configuration has its own particular operating  requirements, low altitude endurance of the  turboprop airplane requires special considera-  tion.  The single-engine turboprop will gen-  eraBy experience an increase in specific endur-  ance with an increase  in altitude from sea level.  However, if the airplane is at low altitude and  must hold or endure for a period of time, the  decision to begin a climb or hold the existing  altitude will depend on the quantity of fuel  available. The decision depends primarily on  the climb fuel,requirements  and the variation of  specific  endurance  with altitude.  A somewhat  similar problem exists with the multiengine  When engine failure produces a critical  power or range situation, improved perform-  ance is possible with- theairplane in ;the clean  configuration at low altitude.  Also, jetti-  soning of expendable weight items will reduce  the power required and improve the specific  range.  173 