**I. INTRODUCTION**

A Vision in Aeronautics is a project where students use an aeronautical
wind tunnel as tool to explore the world of math, science and
technology. Of particular interest are activities that allow K-12
students to learn how computing and communications technologies are used
within the field of aeronautics. Additionally, this project demonstrates
that the National Information Infrastructure is more useful and readily
available to the under served than one might initially think.

**II. GOALS**

The goals of this wind tunnel project are to:

Provide students basic instruction in the subject of aeronautics.

Use the glamorous subject of aeronautics to inspire students to study
math, science and technology.

Create an environment that fosters teamwork, communication and
leadership skills.

Give students an opportunity to gain an understanding of what real-world
engineering problems entail and the methods professional engineers use
to solve those problems.

Expand the traditional school horizon, through the use of the Internet.

**III. OBJECTIVE**

The objective of this wind tunnel project is to provide a hands-on,
creative, problem-solving experience that incorporates the necessary
elements in which to reach the goals stated above.

**IV. EVALUATION**

Following is an evaluation form that could be given to students who
participate in labs and projects that use the wind tunnel. This
evaluation could be given as a pre-evaluation and as a post-evaluation
in order to assess whether or not any students had a change in attitude
towards math, science and computing technology after participation in a
wind tunnel lab.

  ---------------------------------------- ------------------------------
  **Student Survey to use with the Wind    
  Tunnel Project**                         

  Name (or student identifier)             

  What grade are you in?                   

  What gender are you? (This question is   
  optional)                                

  Which best describes your                American Indian or Alaskan
  race/ethnicity? (This question is        Native
  optional)                                

                                           Asian or Pacific Islander

                                           Black, non-Hispanic

                                           Hispanic

                                           White, non-Hispanic
  ---------------------------------------- ------------------------------

  ---------------------------------------- ------------------------------
  Circle how often do you use a computer?  More than once a day

                                           Once a day

                                           Once a week

                                           Once a month

                                           Once a year

                                           Never
  ---------------------------------------- ------------------------------

  ---------------------------------------- ------------------------------
  If you use a computer, what do you use   Games
  it for? (Circle all that apply)          

                                           Word processing

                                           Solving math problems

                                           Graphics

                                           E-mail

                                           Accessing the Internet

                                           Spread sheets

                                           Classroom projects
  ---------------------------------------- ------------------------------

  -------------------------- -------- -------- -------- -------- --------
  Please circle the number                                       
  that corresponds best to                                       
  your opinion on the                                            
  following statements.                                          

                             Not at                              Great
                             All                                 Extent

  I would like to pursue a   1        2        3        4        5
  career in engineering,                                         
  math or science after high                                     
  school.                                                        

  I feel it is valuable to   1        2        3        4        5
  have technical knowledge                                       
  in math, science and                                           
  computing.                                                     

  Computers are a valuable   1        2        3        4        5
  tool used to help solve                                        
  problems and to visually                                       
  display data.                                                  

  The Internet is a valuable 1        2        3        4        5
  source to find information                                     
  on many topics.                                                

  I feel I have a strong     1        2        3        4        5
  background in math,                                            
  science and computing.                                         
  -------------------------- -------- -------- -------- -------- --------

**V. BUILDING THE TUNNEL**

**A. DESIGN**

A design team of fifteen students was assembled at General B. O. Davis
Jr. Aviation High School in May of 1995. These students went on a field
trip to NASA Lewis on June 5, 1995, for a wind tunnel project kickoff
meeting. The students received a tour of the various wind tunnels at
NASA Lewis in the morning. In the afternoon, the students were briefed
by a NASA engineer, about basic aeronautical theory and about the parts
of a wind tunnel.

The students began the design of their tunnel once back at school. Two
NASA Engineers participated in the project by going to the school to
review the students' design and to give suggestions. Once the design was
completed, the students began building the various parts of the tunnel.
The construction of the tunnel was completed during the summer of 1995.
The students volunteered to work on the construction of the tunnel
during the summer.

The wind tunnel contains three main parts, the contraction cone at the
front of the tunnel, the test section in the middle of the tunnel, and
the diffuser at the back of the tunnel. The project team wanted to
create the largest tunnel that their budget would allow. They,
therefore, iterated between the size of the tunnel and the cost
associated with it, to determine how big they could make the tunnel.

The size of test section and the size of the contraction cone are
related through a contraction ratio. The contraction ratio used, was 12
to 1. This is the ratio between the area of the contraction cone and the
area of the test section. It was determined that a 5' x 5' contraction
cone was the maximum size that could be built. This then dictated that
the test section would be 1.5' x 1.5'. The shape of the contraction cone
was designed by the NASA Lewis aeronautical engineers working on the
project. They developed a bell curve shape that would cause laminar flow
and eliminate flow separation.

It was determined that an optimal maximum speed for the tunnel would be
around 90 mph. The next step was to find the volumetric flow rate of a
tunnel with a 1.5' x 1.5' test section and a velocity of 90 mph. Ninety
miles an hour was converted to 132 ft/sec. Next, the area of the test
section was found to be 2.25 square feet. The volumetric flow rate
equation is Q = v x A. So, Q = 132 ft/sec x 2.25 ft squared = 297 cubic
ft/sec. This converted into cubic ft/min, is 17,820 CFM. The size of the
motor was based on the desired CFM output of the fan. With a 5 hp motor,
a 36" diameter fan can move 20,650 cubic feet of air per minute, this
was greater than the desired CFM output, so these two pieces of
equipment were selected.

The length of the diffuser section was dictated by the size of the fan,
which was selected to be 36" in diameter. A square to round conversion
piece was designed and the square portion turned out to be 34" x 34".
This became the dimensions of the end of the diffuser section. The
diffusion angle was kept below 6 degrees. The diffusion angle ended up
being 2.9 degrees on each side for a total of a 5.8 degree diffusion
angle. This made the diffuser section 13' long. Figure 1. provides
further explanation about the diffusion angle and the diffuser section.

![](media/image1.emf){width="4.611111111111111in"
height="2.4097222222222223in"}

**Figure 1.**

One of the NASA engineers on the project provided calculations to ensure
that the wind tunnel structure that was designed would be able to
withstand the pressures that would be created by the tunnel. He
calculated the pressure per square foot that would be theoretically
created by a tunnel of this size and specification. This was compared to
the loading standards of the materials used, Plexiglas and plywood and
it was determined that the wind tunnel would be able to withstand the
pressures. The wind tunnel was to be housed next to a roll up door that
led to the outside and the plan was to open the door when running the
wind tunnel, to vent the exhaust. Therefore, the air pressure forces
created when the tunnel was running, was not a concern within the
building.

**B. CONTRACTION CONE**

The contraction cone, also referred to as the inlet, was the only piece
that was not fabricated by the students, due to its the size and
complexity. The fabrication of this piece was contracted to Avon Sheet
Metal Co. The students specified the size and shape of the cone for the
fabricators. Figure 2. shows the specifications developed.

![](media/image2.emf){width="5.947916666666667in"
height="5.7444444444444445in"}

**Figure 2.**

**C. TEST SECTION**

The test section is 1.5' x 1.5'. The test section is made out of plywood
with Plexiglas viewing windows. One of the students became concerned
that the Plexiglas protruding from the plywood frame would create places
for error once the tunnel was used for testing. Therefore the Plexiglas
was inset into the plywood. Figure 3. shows the test section.

![](media/image3.emf){width="5.950694444444444in"
height="3.795138888888889in"}

**Figure 3.**

**D. DIFFUSER SECTION**

Once the dimensions of the diffuser were calculated, how to build it had
to be determined. The main problem was that an eighteen inch square had
to be centered in a thirty-four inch square, thirteen feet apart. The
solution was to build a jig for the diffuser section, that was later
modified and used as the support for the whole tunnel. Figure 4. shows
the dimensions of the diffuser.

![](media/image4.emf){width="5.98125in" height="2.6618055555555555in"}

**Figure 4.**

**E. FAN SECTION**

A 36 inch fan was purchased to create the airflow of the wind tunnel.
This was attached to the back of the diffuser section.

**F. MOTOR**

The 5hp motor and a drive unit were donated by Eurotherm Corporation.
The motor was mounted on top of the fan. The drive unit was used to
convert AC power to DC power and to control the speed of the motor.

**G. FLOW STRAIGHTENER**

A honeycomb material, donated by Hexal Corporation, was mounted to the
front of the contraction cone and used as a flow straightener,

# H. INSTRUMENTATION

Twelve pressure transducers are used to collect pressure readings. Tycon
tubing is used to connect the pressure transducers the test points
inside the test section. Inside the test section, probes are attached to
the tubing. The location of the probes vary within the test section
depending on the test article. The pressure transducers were mounted
into an electrical box to protect them from the environment. Students
from the school's electronics class worked on this part of the project.
From the electrical box, the transducers were then connected to a 16
channel A/D board which was installed inside a 486 IBM compatible
computer. The software package, Control, was used to display the data on
the screen.

**VI. EXPERIMENTS**

**A. VENTURI**

The first test object created was a venturi. A venturi is defined as a
short tube with a constricted throat that is used to determine fluid
pressures and velocities by measurement of the differential pressures
generated at the throat, as fluid traverses the tube. The venturi was
chosen as the first test object because it could be used to verify that
accurate data could be obtained from the tunnel. If the readings
obtained from the tunnel closely matched theoretical calculations,
verification, that the wind tunnel and instrumentation were functioning
properly, would be obtained.

Additionally, the venturi was selected as a test object in which to
demonstrate a basic aeronautic phenomenon, Bernoulli's Principle. When
air flows through a venturi, the physical properties of the venturi
cause the velocity of the air at the beginning of the venturi to be
slower than at the middle of the venturi. The air velocity is also
slower in the back of the venturi than in the middle. Bernoulli's
principle states that there is an inverse relationship between air
velocity and air pressure, which will be explored in more detail later
in this report. But having said that, the air pressure within the
venturi will be greatest in the middle and lower at the front and back.

Two attempts to create a venturi with which meaningful readings could be
gathered failed. These two attempts are explained. The first venturi had
an hourglass shape and was made out of two pieces of Plexiglas. This
venturi was put into the wind tunnel for testing, with probes located
throughout the venturi with which to collect pressure readings. Pressure
readings were obtained from the inlet of the venturi, but the pressure
transducers read zero, for the middle and back sections of the venturi.
These pressure transducers and probes were switched with the probes used
in the front of the venturi, to make sure they were working correctly,
and they were. So, it was decided that inlet area of the venturi was too
restrictive and was not allowing airflow through the rest of the
venturi. It was determined that a venturi with a bigger inlet should be
made.

The second venturi was made from fiberglass into an hour glass shape.
This time pressure readings were obtained from the front and middle
sections of the venturi, but the data from the back portion of the
venturi was the same as in the middle section. One of the NASA engineers
helping with the technical aspects of the project, suggested that the
diffusion angle of the venturi (the angle between the middle section and
the back section of the venturi) rose at too sharp of an incline and was
causing air separation in the back portion of the venturi. The problem
was researched and it was found that the diffusion angle should be no
greater than 6 degrees, in order for the venturi to function correctly.

The third attempt was successful. The entire test section was made into
a venturi. Sheet metal was formed into the shape shown in Figure 5. The
location of the probes, which were used to collect pressure readings at
six different points, are illustrated in Figure 5. The test data that
was obtained is shown in Figure 6. The graphs in Figure 6. can be used
to illustrate Bernoulli's Principle. As the velocity increases, the
pressure decreases and as the velocity decreases, the pressure
increases. The students transferred the data from the data collection
program into a ClarisWorks spread sheet and completed the graphs using
the data. The outcome of the comparison of experimental velocities to
theoretical velocities is shown in Figure 7.

![](media/image5.emf){width="5.9743055555555555in" height="2.68125in"}

**Figure 5.**

## Collection of Experimental Data

![](media/image6.emf){width="5.967361111111111in" height="2.41875in"}

![](media/image7.emf){width="5.7375in" height="5.347916666666666in"}

**Figure 6.**

## Comparison of Experimental and Theoretical Velocities from the Wind Tunnel

  -------------------- ------- -------- -------- -------- -------- ----------
  **Experimental                                                    
  Velocities**                                                     

                                                                   Square
                                                                   inch Area
                                                                   of the
                                                                   Venturi

  Tunnel Velocity      35      45       55       65       75       327.6

  Velocity 0           42.53   50.62    59.2     68.9     79.13    280.6

  Velocity 1           52.85   63.08    73.8     85.4     98.1     224.4

  Velocity 2           65.15   77.9     90.8     105.2    118.8    210

  Velocity 3           49.6    58.07    68.5     78.8     89.8     244.3

  Velocity 4           45.8    54.5     63.8     74.4     84.7     275.1

  Velocity 5           41.5    48.18    56.4     64.1     73.7     296.8

                                                                    

                                                                    

  **Theoretical                                                     
  Velocities**                                                     

                                                                   Square
                                                                   inch Area
                                                                   of the
                                                                   Venturi

  Tunnel Velocity      35      45       55       65       75       327.6

  Velocity 0           40.86   52.54    64.21    75.89    87.56    280.6

  Velocity 1           51.10   65.70    80.29    94.89    109.49   224.4

  Velocity 2           54.60   70.20    85.80    101.40   117.00   210

  Velocity 3           46.99   60.42    73.84    87.27    100.70   244

  Velocity 4           41.68   53.59    65.50    77.40    89.31    275.1

  Velocity 5           38.63   49.67    60.71    71.75    82.78    296.8

                                                                    

                                                                    

  **Experimental                                                    
  Error**                                                          

                                                                   Square
                                                                   inch Area
                                                                   of the
                                                                   Venturi

  Tunnel Velocity      0       0        0        0        0        327.6

  Velocity 0           4.08    3.65     7.81     9.21     9.63     280.6

  Velocity 1           3.43    3.98     8.09     10.00    10.40    224.4

  Velocity 2           19.32   10.97    5.83     3.75     1.54     210

  Velocity 3           5.55    3.89     7.24     9.71     10.82    244

  Velocity 4           9.89    1.70     2.59     3.88     5.16     275.1

  Velocity 5           7.42    3.00     7.10     10.66    10.97    296.8
  -------------------- ------- -------- -------- -------- -------- ----------

**Figure 7.**

B. 2415 NACA AIRFOIL

The second test object created was a 2415 NACA airfoil. The correct
shape for an 2415 NACA airfoil with an eight inch chord was obtained
from references. The airfoil itself was made out of wood and sheet
metal. Five ribs where made from 3/4 inch pine wood. Dowel rods were
used to connect the ribs together, this completed the form. Sheet metal
was then bent over and glued to the top of the form. Next,
instrumentation tubes were installed. The airfoil was then mounted on a
steel plate and secured to the wall of the test section with three
bolts, see Figure 8. In the wall of the test section three slots were
cut which allowed the airfoil to rotate from -8 degrees to +25 degrees.
A protractor was used to determine the angle. The 0 degrees mark was
lined up with where the wing was horizontal. Lastly, the sheet metal was
glued to the bottom of the form.

The airfoil was used to demonstrate how lift is created. Additionally,
the airfoil was used to explain angle of attack and stall. Tufts of yarn
were added to the model to visualize the airflow. The students were able
to see when the airfoil first began to stall; the pressure readings on
the computer dropped and the tufts began to swirl.

Students collected the pressure readings, shown in Figure 9., from the
airfoil as it was rotated in two degree increments. They started at a
negative angle of attack and took readings until the airfoil stalled.
Students created a graph from the data they collected. Refer to Figure
10. to see how the graphs illustrate that at a negative angle the lower
surface creates a lower pressure, at -2 degrees there is no lift and at
11 degrees the airfoil begins to stall. (Had the angle marking system
been more accurate, 0 lift would have occurred at 0 degrees.)

The data collected, by the students, on the 2415 NACA airfoil was used
to calculate the pressure coefficient and the lift coefficient of the
airfoil. It was then compared to a computer simulation of the same type
of airfoil. The readings where satisfactorily accurate. See Figure 9.
for the spread sheet created to calculate the coefficients and Figure 11
though Figure 16 for a graph of the results. Refer to the Lesson Plans
to see how to calculate the coefficients.

![](media/image8.emf){width="4.736111111111111in"
height="3.736111111111111in"}

**Figure 8.**

![](media/image9.emf){width="6.0256944444444445in"
height="4.320138888888889in"}

**Figure 9.**

![](media/image10.emf){width="6.010416666666667in"
height="2.042361111111111in"}

**Figure 10.**

**C. WHEEL PANT PROJECT**

The wind tunnel team was contacted by researchers in the NASA Lewis
Structural Systems Branch. These researchers were interested in using
the Aviation High School wind tunnel to perform initial tests on a NASA
Lewis research project. The purpose of project was to design a wheel
pant for small private aircraft. A wheel pant is an aerodynamic cover
for the wheel of aircraft that do not have retracting landing gear.

The students built a strut and attached a 3/8" diameter rod and the 4.5"
diameter wheel and the 1/3 scale fiberglass wheel pant to it that were
supplied by the NASA engineers. This structure was mounted in the wind
tunnel and testing occurred to determine if drag could be reduced by
using the wheel pant. Drag is a force and this force was measured with
gram weights on a balance/pulley system, see Figure 17. The middle of
the strut was mounted to the test section floor, but it was able to
pivot back and forth. When the tunnel was turned on, the top of the
strut started to move backwards due to drag and the bottom of the strut
moved forward, since it was pivoting in the middle. A string was
attached to the bottom of the strut and run through a pulley. The other
end of the string was attached to pan which held gram weights. Gram
weights were placed on the pan until the strut was straight again. The
weight, in grams, corresponded to the drag of the strut system.

Three tests were performed. The first test was on the strut and wheel
alone. The second test was on the wheel and the wheel pant, with the
tire protruding from the bottom of the wheel pant. The third test was on
the closed wheel pant; no tire was protruding. Measured forces were 200g
for the strut and wheel, 150g for the strut, wheel and pant, and 120g
for the strut and closed wheel pant. These initial readings showed that
the wheel pant does appear to reduce drag.

![](media/image11.emf){width="5.923611111111111in"
height="7.496527777777778in"}

**Figure 17.**