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 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. 
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. 
NAVWEPS OO-ROT-RO 
AtRPLANE PERFORMANCE 
TURBOPROP POWERED AIRPLANE. 
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. 
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