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reduce the airplane drag and increase the rate of climb. The aircraft may continue
to climb untilit reaches the desired cruise altitude or may proceed to perform other
missions as may be assigned to it.
The total takeoff distance is the sum of the ground run si and airborne distance
S2 as shown in Fig. 2.31.ldeally, the takeoff distance should be as small as possible
for quick and efficient operation of the aircraft.
Estimation of ground run. The forces acting on the aircraft during the ground
run are shown in Fig. 2.32.
Let
Fa = T - D - &t,(W - 1) (2.317)
denote the net accelerating force during the ground run. Here, T is the thrust, D is
the aerodynamic drag, L is the aerodynamic lift W is the gross takeoff weight, and
p, is the coefficient of friction between the wheels and the runway. For concrete
runways, p, typically ranges from 0,02 to 0,05. The schematic variation of these
forces during the ground run is shown in Fig. 2.33.
AIRCRAFT PERFORMANCE
l- si T l/
┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┳━━━━┓
┃ Start Lift // \ ┃ T ┃
┃L jf,t : ┃ hobs ┃
┃ -_ -_ c\:~l- ~:8 : ┃ I ┃
┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┻━━━━┛
V=O V=Vstall V.
Fig. 231 Schemahc diagram of an airplane in takeoff.
147
limb
The lift and drag forces are to be estimated for the takeoff configuration with
landing gear. fiaps, and high-lift devices deployed and aircraft operating in the
proximity of the ground.
Then,
ds = Wd(V2)
2g F~ (2.319)
During the ground run, the angle of attck is normally held constant at a selected
value. Assuming that the net accelerating force Fa varies as the square of the
velocit)r, we have
Fa = Fo+(F~F ) V2 (2.320)
--_ p (W- L )
Fig. 2.32 Forces acting on an airplane during takeoff ground run.
V~ (ddV, ) = \~ (V ddsV) = Fa (2.318)
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PERFORMANCE, STABILITY, DYNAMICS, AND CONTROL1(86)
