AAE251 HW 6
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Purdue University *
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Course
251
Subject
Aerospace Engineering
Date
Dec 6, 2023
Type
Pages
8
Uploaded by JusticeAtomBear31
1
Name
Team Number
AAE 251: Introduction to Aerospace Design
Homework 6—Drag and Drag Polar
Due Tuesday March 1
st
, 11:59 pm EDT on Gradescope
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2
Question 1 (18 points):
Consider a finite wing with a wing planform area of 220 ft
2
and a wingspan of 36 ft.
At a particular angle of attack
!,
the total drag coefficient
$
!
is 0.0275 and the lift
coefficient
$
"
is 0.15. Assume spanning efficiency factor
%
is
0.873.
(a)
Calculate the zero-lift (parasitic) drag coefficient
$
!,$
.
(5 points)
(b)
Derive the equation for maximum lift-to-drag ratio
+
%
!
%
"
,
&'(
in terms of only
aspect ratio
-.
, drag coefficient
$
!,$
, and spanning efficiency factor
e
.
(5
points)
(c)
Calculate the value for
+
%
!
%
"
,
&'(
(3 points)
(d)
Calculate the new value of the lift to drag ratio
+
"
!
,
)*+
if the angle of attack
remains the same and the aspect ratio AR is decreased by half. Is
+
"
!
,
)*+
better
or worse than the old
+
"
!
,
? Assume lift curve slope
/
$
is 0.15 per degree.
(5
points)
3
Answer 1:
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4
Question 2 [8 points]
Consider a NACA 2415 airfoil that makes up a wing of aspect ratio
-. = 6.5
, average
chord length of 16cm, span of 1.04m and span efficiency factor
% = 0.88
. The wing
sees an incoming flow of
3
,
= 105
m/s when flying at an altitude of
ℎ = 7500
m at an
angle of attack
! = 4°
.
Compute the lift coefficient
8
-
for the
airfoil
.
Hint: Dynamic viscosity coefficient is
9
$
= 17.15 × 10
./
Nsm
.0
at @
$
= 0°$.
Answer 2:
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5
Question 3 [16 points]
For the same scenario and flight conditions in Question 2, compute the following:
(i)
Lift slope
A$
"
/8!
for the finite wing,
(ii)
If you were to plot
$
"
vs
!
and
8
-
vs
!
, the angle
!
∗
where the two plots
intersect,
(iii)
Lift coefficient
$
"
for the finite wing. Is it equal to
8
-
?
(iv)
Drag coefficient
$
!
, and
(v)
The percentage of total drag produced by lift-induced drag.
Answer 3: