Aer E 160 Spring 2009 Exam 3 Name: _________________________________
1. For this problem, use a spreadsheet to complete all calculations. The lift coefficient,
CL
, relates the lift generated by an
airfoil to air density, airspeed and the shape of the airfoil. Table 1 shows the result of an experiment repeated 7 times to obtain
an estimate of the lift coefficient under identical conditions.
Table 1. Five wind tunnel measurements of CL at the same angle of
attack, airspeed and air density for an airfoil.
Reading
CL
1 1.005
2 1.060
3 .955
4 .993
5 1.061
6 1.036
7 .900
a) What is the average lift coefficient?
b) What is the standard deviation?
c) Make a histogram with the following ranges:
0.900≤
Cl
≤0.925
,
0.926≤
Cl
≤0.950
,
0.951≤
Cl
≤0.975
,
0.976≤
Cl
≤1.000
,
1.001≤
Cl
≤1.250
2. Equation (1) has been derived for
CL
as a function of angle of attack,
α
, over
−5˚ ≤≤15 ˚
.
CL
=−0.00220.109 0.550
(1)
Place the following data, representing angles of attack, in an input file called alpha.dat. Include the total number of angles
at the top of the file. Then, write a program that reads the values of
α
from the input file, solves Equation (1) at each angle of
attack, and writes, with headings,
α
and
CL
to an output file called cl.dat. Display the input file in one window, the code in a
second window and the output file in a third window for the grader.
,˚
-5.00
-2.50
0.00
2.50
5.00
7.50
10.00
12.50
15.00
