Fluids – Lecture 10 Notes
1. Aircraft
Performance Analysis
2. Parasite Drag
Estimation
Reference: Hoerner,S.F., “FluidDynamic Drag”, Ch 3.
Aircraft Performance Analysis
Drag breakdown
The
drag on a
subsonic aircraft
can be broken down as follows.
D
=
D
o
+
D
p
+
D
i
where
D
o
=
“parasite”
drag
of fuselage +
tail +
landing
gear
+
. . .
D
p
=
wing
profile drag
D
i
=
induced drag
We
now
use the wing airfoil drag
polar
c
d
(
c
ℓ
;
Re
) to
give the wing
profile drag, and use lifting
line
to give the induced drag. The nondimensional total drag
coeﬃcient
is then
D
CDA
o
C
2
≡
C
D
=
+
c
d
(
C
L
;
Re
) +
L
(1)
1
ρ V
2
S
S
π eAR
2
where
the
“
∞
”
subscript
on the ﬂight
speed
V
has been dropped. The parasite drag area
CDA
o
will be considered later.
Flight power
The
mechanical power
P
needed for constantvelocity
ﬂight
is given by
η
p
P
=
V
(
D
+
W
sin
γ
)
(2)
where
W
is the weight,
γ
is the
climb
angle
, and
η
p
is the propulsive eﬃciency.
If
P
is
defined as the motor
shaft
power, then
η
p
is the propeller
eﬃciency.
γ
γ
L
D
W
W
W sin
L
D
V
V
γ
In
level
ﬂight,
γ
= 0, and the
power
is
1
η
p
P
=
V
D
=
ρ V
3
S
C
D
(3)
2
1
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The
ﬂight
speed
V
is given by
the Lift
=
Weight
condition, together
with the definition of
the
lift
coeﬃcient
C
L
.
1
L
=
ρ V
2
S C
L
=
W
2
2
W/S
�
1
/
2
V
=
ρ C
L
The
ratio
W/S
is called the
wing loading
, and has the units of force/area, or
pressure.
The
levelﬂight
power
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 Fall '05
 MarkDrela
 Aerodynamics, DI, Aircraft Performance Analysis, Parasite Drag Estimation

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