AA311
Atmospheric Flight Mechanics
Exam #1 Solutions
Problem 1. (10 points)
An aircraft pressure sensor reads 54
.
0 kPA. On this day, the sealevel pressure
is 100
.
0 kPA, the sealevel temperature is 10
◦
C, and the lapse rate is 7
◦
C per kilometer. Compute the
geometric
altitude of the aircraft.
Solution.
Given the pressure
P
(
h
) = 54
.
0 kPA, we must first find
h
in the given nonstandard conditions:
P
(
h
) =
P
SL
T
SL
+
Lh
T
SL

(
g
0
LR
)
We know every value in this expression except for
h
. Solving for
h
, we find:
h
=
T
SL
L
P
(
h
)
P
SL

LR
g
0

1
=

283
.
16 K

0
.
007 K
/
m
1

54
.
0 kPa
100
.
0 kPa

(

0
.
007 K
/
m)(287
.
0368 Nm
/
kgK)
9
.
81 m
/
s
2
=
4796 m
Converting to geometric altitude:
h
= 4796 m
⇒
h
G
=
r
earth
r
earth

h
h
= 4800 m
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Problem 2. (10 points)
An aircraft flies at an altitude of 5000 m. The aircraft’s rectangular wing (8 m
span, 1.5 m chord) is made up of uniform airfoil elements along the span. Suppose that the pressure distri
bution at some distance along the span takes the form as shown in Figure 1. Calculate the lift coefficient
of that airfoil section.
Assume that the flow is uniform along the span, and is not affected by wingtip
vortices. The Pitot tube pressure transducer reads a total pressure of
p
total
= 54640
Pa
. Calculate the
total lift force produced by the wing. How fast is the aircraft flying? Assume the aircraft is flying straight
and level. What is the gross mass of the aircraft (including fuel, and passengers)?
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 Fall '09
 Fluid Dynamics, Aerodynamics, boundary layer thickness, Lh TSL

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