NAVWEPS oo-80mo 
AIRPLANE PERFORMANCE 
would be to provide the endurance thrust with 
some engine(s) shut down and the remaining 
engine(s) operating at a more efficient power 
output. This technique would cause a mmi- 
mum loss of endurance if at low altitude. The 
feasibility of such a procedure is dependent 
on many operational factors. 
In all cases, the airplane should be in the 
cleanest possible external configuration because 
the specific endurance is directly proportional 
to the (L/D). 
MANEUVERING PERFORMANCE ,...s’ .i :.,cyz’ 
When the airplane is’in turning flight, the 
airplane is not in static equilibrium for there 
must be developed the unbalance of force to 
produce the acceleration of the turn. During 
a steady coordinated turn, the lift is inclined 
to produce a horizontal component of force to 
equal the centrifugal force of the turn. In 
addition, the steady turn is achieved by pro- 
ducing a vertical component of lift which is 
equal to the weight of the airplane. Figure 
2.28 illustrates the forces which act on the 
airplane in a steady, coordinated turn. 
For the case of the steady, coordinatedturn, 
the vertical component oft lift must equal the 
weight of the aircraft so that there will be no 
acceleration in the vertical direction. This 
requirement leads to the following relation- 
ship: 
L *=- W 
where 
1 BE-- cos q5 
n=sec $6 
rz= load factor or “G” 
L=lift, lbs. 
W= weight, Ibs. 
+= bank angle, degrees (phi) 
From this relationship it is apparent that the 
steady, coordinated turn requires specific values 
of load factor, n, at various angles of bank, 6. 
For example, a bank angle of 60’ requires a 
load factor of 2.0 (cos 60’=0.5 or set 60’=2.0) 
to provide the steady, coordinated turn. If 
the airplane were at a 60’ bank and lift were 
not provided to produce the exact load factor 
of 2.0, the aircraft would be accelerating in the 
vertical direction as well as the horizontal di- 
rection and the turn would not be steady. 
Also, any sideforce on the aircraft due to 
sideslip, etc., would place the resultant aero- 
dynamic force out of the plane of symmetry 
perpendicular to the lateral axis and the turn 
would not be coordinated. 
As a consequence of the increase lift re- 
quired to produce the steady turn in a bank, 
’ ihe induced drag is increased above that in- 
curred by steady, wing level, lift-equal-weight 
flight. In a sense, the increased lift required 
in a steady turn will increase the total drag or 
power required in the same manner as increased 
gross weight in level flight. The curves of 
figure 2.28 illustrate the general effect of turn- 
ing flight on the total thrust and power re- 
quired. Of course, the change in thrust re- 
quired at any given speed is due to the change 
in induced drag and the magnitude of change 
depends on the value of induced drag in level 
flight and the angle of bank in .turning flight. 
Since the induced drag generally varies as the 
square of C,, the following data provide an 
illustration of the effect of various degrees of 
bank : 
Load factor, Pcrccnt incrcaw in 
n induced drag from 
lcvcl flight 
Since the, induced drag predominates at low 
speeds, steep turns at low speeds can produce 
significant increases in thrust or power required 
to maintain altitude. Thus, steep turns must 
be avoided after takeoff, during approach, and 
especially during a critical power situation 
from failure or malfunction of a powerplant. 
The greatly increased induced drag is just as 
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