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Wind Tunnel Averages
| Background: |
When engineers perform wind tunnel tests to measure the forces
of drag and lift on a model, they use a unit of measurement called
a "newton". Newtons are named after the famous English physicist,
Sir Isaac Newton. A newton is the unit of force it takes to change
the velocity of a mass of 1 kilogram, by 1 meter/second over 1 second.
Think of a 1 kilogram section of a wing, flying at 250 meters per
second. A force of 1 newton would change the velocity of the wing
section from 250 meters per second to 251 meters per second, in
one second.
If, for instance, a researcher wishes to test the lift experienced
by a section of a wing, he or she will embed sensors in various
parts of the wing. Each sensor will measure the force of lift on
a specific area of the wing. After those values are fed into a computer,
the computer will display them in newtons. The researcher can then
average all of the values and find the average lift over the entire
wing. This same approach can be used for drag.
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| Directions: |
An average is a way to approximate a value for a large set of numbers.
For example, to find the approximate length of the steps you take
when you walk, we could measure three, four or ten of your usual
walking steps. Then we could average them to find out how long a
stride you usually take.
To find an average, follow these two steps:
Step 1: Add all of the numbers together.
Step 2:Divide the sum by the number of numbers.
The result of this division is the average of the numbers.
For example, let's say an engineer embedded three sensors in
a wind tunnel model to measure the lift force. The computer reported
the following values from each sensor:
250 newtons
300 newtons
350 newtons
Say that the engineer wanted to find the average of the lift forces
over the entire wing. He/She would perform the following steps:
Step 1:
250 newtons + 300 newtons + 350 newtons = 900 newtons
Step 2:
900 newtons = 300 newtons
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The average lift force over the entire wing was 300 newtons.
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Exercise
Directions: A researcher wanted to find out the quantity of the
lift force experienced by different wing types during a wind tunnel test.
She embedded three sensors in each of three types of wings: delta, straight,
and tapered straight. Her results can be found in the table below. Your
task is to find the average lift force for each of the three wing types.
Put your answers in the appropriate squares in the table.
She performed the same experiment again, except that she measured the
drag force from the sensors. Her results can be found in the table below.
Find the average drag force for each of the three wing types. Put your
answers in the appropriate squares in the table.
Drag Tests
Question 1: Which wing shows the greatest amount of average lift?
Question 2: Which wing shows the greatest amount of average lift?
Question 3: Which wing shows the highest individual lift sensor reading?
Question 4: Which wing shows the greatest amount of average drag?
Question 5: Which wing shows the lowest individual drag sensor reading?
Question 6: If you were to build an airplane, which wing would you
use? Why?
Exercise 1 Key
Lift Tests
Drag Tests
Question 1: delta: 607 newtons
Question 2: straight: 316 newtons
Question 3: delta: sensor #2 = 611 newtons
Question 4: straight: 60 newtons
Question 5: delta: sensor #3 = 23 newtons
Question 6: The delta because it has the highest lift and the
lowest drag. Other answers may be appropriate if the reasoning is good.
Graphing Results
| Preparation: |
The lesson Wind Tunnel Averages should be completed prior to starting
this lesson. |
| Background: |
When using the four Tools of Aeronautics, engineers createmany billions
of numbers, which altogether are called data. Wind tunnel tests, flight
simulations, Computational Fluid Dynamics and flight tests all produce
huge amounts of data. It is very difficult for a human to sift through
and analyze millions and millions of numbers. Larger and larger computers
have been built to help engineers perform their analysis tasks. One
of the fastest modern computers can perform a billion mathematical
operations in one second. It would take a human 406 days (without
a break!) to do the same task. However, even though the computer can
process the massive volumes of data generated by the Tools of Aeronautics,
a human engineer is still needed to make decisions based on the data.
Computers can display information in many different ways. One of the
most effective methods of displaying numerical data is on a graph.
Using graphs, engineers can very rapidly analyze and make decisions
based upon very large amounts of data. |
| Directions: |
In this lesson, students will learn how to create a bar graph based
on the averages calculated in the lesson Wind Tunnel Averages.
A bar graph has three basic parts:
Title
All bar graphs need a title that tells what kind of data is being
shown.
Label for Horizontal Axis
The horizontal axis needs to have a label that identifies the type
of data being displayed on that axis (for example, test flights
of the X-99).
Label for Vertical Axis
The vertical axis needs to have a label that identifies the units
of measurement being used (for example, the maximum altitude reached
during a test flight)
Scale for Vertical Axis
The vertical axis needs to have a scale that lists the units of
the measurement used (for example, one mark equals 5,000 feet) The
following information has been used for the graph below.
Title - "X-99 Flight Test Results"
Label for Horizontal Axis - "Test Flight Number"
Label for Vertical Axis - "Maximum Altitude"
Example bar graph
X-99 Flight Test Results
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| Directions |
Create a bar graph from the averages calculated in the lesson Wind
Tunnel Averages. Use the template below to create your bar graph.
The bar graph should display the average lift and drag for each wing
type. Unlike the example bar graph, you will draw two bars for every
wing type - one for lift and one for drag. |
Exercise 1 - Key
Wind Tunnel Test Results
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