AIT Physics lab using NASA Foilsim simulator
What Factors Affect the LIFT of a wing….and why does
a curveball CURVE? (Bernoulli’s Principle…..)
Open the program titled FoilSim on the lower left corner of the screen
We are now going to explore some of the factors which effect the lift of a wing. We will be using the input
sliders and boxes located at the lower left and will be watching the
output scale marked "Lift" at the bottom on the left. In this lesson we will be most interested in answering
the question, "What changes the lift of a wing ?" In the next
lesson we will explore "How does the lift change ?" If you have been playing with the
package, it will now be necessary to set the input to some initial conditions.
Let's set the following conditions:
Airspeed
Altitude
Angle
Thickness
Camber
Area
= 100 mph
= 0 feet
= 0 degrees
= 0.5
= 0
= 1.0 sq ft
WHAT IS THE VALUE OF THE LIFT ?
Increase the speed to 150
WHAT HAPPENS TO THE LIFT ?
Increase the Thickness to 0.7 and the Area to 10.
WHAT HAPPENS TO THE LIFT ?
OK - let's change the Angle of attack to 10 degrees.
WHAT HAPPENS TO THE LIFT?
-->
A symmetric airfoil inclined to the incoming flow will generate lift.
You don't need a curved airfoil to generate lift !!
<--
Increase the Angle to 15 degrees.
WHAT HAPPENS TO THE LIFT ?
-->
Increasing the angle of attack will increase the amount of lift.
<--
Let's decrease the Thickness to 0.05. This will approximate a flat plate.
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WHAT HAPPENS TO THE LIFT ?
-->
-->
Decreasing the thickness will decrease the amount of lift. <-But a flat plate at angle of attack will generate a lot of lift. <--
Let's do a little experiment with this flat plate !
Suppose we had the door to our house which is about 7 feet by 4 feet = 28 square feet. (Set the Area =
28) And suppose we were in a tornado which generates a wind of
150 mph. (Set Airspeed = 150) And suppose the door was inclined to the wind at only 10 degrees. (Set
Angle = 10)
HOW MUCH FORCE IS GENERATED ON THE DOOR?
Suppose, instead of a 28 square foot door we had a 4 X 8 sheet of plywood. (Area = 32)
HOW MUCH FORCE IS GENERATED ON THE SHEET?
--> Increasing the area will increase the amount of lift. <--Well, back to airfoils.
Let's look
at an airplane problem. Let's set the Thickness to 0.5, and the wing Area to 180 square feet (6 ft chord
and 30 ft wing span). At 150 miles per hour, and 10 degrees Angle of attack this will generate 12,600
pounds of Lift. This will easily lift a 10,000 airplane off the ground.
Let's see what happens at 25,000 feet Altitude.
IS THERE ENOUGH LIFT GENERATED TO KEEP OUR
PLANE FLYING ?
-->
Increasing the altitude will decrease the lift
<--
What can we do ?
Let's increase our Airspeed to 200 mph.
IS THERE ENOUGH LIFT GENERATED TO KEEP OUR
PLANE FLYING ?
-->
Increasing the airspeed will increase the lift
<--
Well, we've changed all the input conditions except the camber
(or curvature) of the airfoil so let's set the Camber = 0.2
WHAT HAPPENS TO THE LIFT ?
-->
Increasing the camber will increase the lift
<--
Let's check these results at a different set of conditions. Set
Airspeed = 100, Altitude = 0, Camber = 0, then change to
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Camber = 0.2
WHAT HAPPENS ?
--> Lift appears to be a very strong function of the airfoil
camber <-(As an engineer, when you see a result which you weren't
expecting, it's a good idea to repeat the experiment !)
In this lesson we have seen the effects of various shape and
flow factors on the lift of a wing. So far, we've just taken a
qualitative look. In the next lesson we're going to be carefully
comparing results to find quantitative (numerical) result.
Let's summarize what we've learned:
·
Increasing the angle of attack will increase the lift
·
Increasing the thickness will increase the lift
·
Increasing the area will increase the lift
·
Increasing the altitude will decrease the lift
·
Increasing the airspeed will increase the lift
·
Increasing the camber will increase the lift
·
A symmetric airfoil, or even a flat plate at angle of attack will
generate lift.
·
Lift appears to be a very strong function of the airfoil camber.
Part 2: Pressure and The Curveball
(Click the Play Ball buton in the lower left corner if the baseball isn't already on the screen.)
We want to examine how the spin with which a baseball is thrown relates to the pressure of the air flowing
around the surface of the ball. Be sure you have chosen Speed at Surface on the Plotter Control Panel,
Dodger Stadium (sea level) on the Baseball Input Panel, and Left Hander on the Airfoil View Panel.
Now we are ready to throw our second pitch. We want to throw a Curveball, so slowly slide the Spin slider
all the way to the left or click the word Curveball.
· WHAT ARE THE CHANGES YOU SEE TAKING PLACE ?
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· WHAT HAPPENED THE SIDE FORCE AT THE BOTTOM OF THE INPUT PANEL ?
One very important but slight change you may have noted happened on the Plotter View Panel. The yellow
and green curves are no longer on top of each other. You can now see that the green curve is going higher
than the yellow curve.
· DO YOU THINK THIS MIGHT SOMEHOW BE RELATED TO THE FACT THAT WE NOW HAVE A
SIDE FORCE?
Our graph is showing that the air stream on the right of the ball (green) is moving faster than the air
stream on the left of the ball (yellow).
· CAN YOU THINK OF A REASON WHY THIS HAPPENS?
The reason has to do with the little bit of friction between the surface of the spinning ball and the air
right next to it. As the ball rotates in the same direction as the air going by it (the right side), this
friction drags the air along a little faster. On the other side (the left) the ball is rotating against the air.
The friction causes this air on the yellow side to slow down a little.
That's fine, but it still doesn't explain the side force. To do that, you need to select the Surface Pressure
button on the Plotter Input Panel.
· WHAT HAPPENS TO THE GREEN AND YELLOW LINES?
Do you see that the color of the MAXIMUM on the Surface SPEED plot becomes the MINIMUM on the
Surface PRESSURE plot? Click back and forth between the Speed at Surface and Surface Pressure
buttons and watch what happens.
· TRY TO STATE THE RELATIONSHIP BETWEEN THE SPEED OF THE AIR AT THE SURFACE OF
THE BASEBALL AND THE PRESSURE IT EXERTS.
At this point you should have derived the relationship that actually causes the ball to curve.
---> AS THE AIR MOVES FASTER IT EXERTS LESS PRESSURE <--In the non-rotating Fastball, the air speeds up equally on both sides of the ball (remember the curves were
on top of each other?) so the reduced pressure on both sides was the same and no net side force. The
Fastball goes straight.
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When the ball spins, the slower moving air on one side has more pressure than the faster moving air on the
other side. The difference in pressure "PUSHES" the ball into a curved path. This difference in pressure
creates the Side Force.
FoilSim: Software for Teaching
About Airfoils
Interactive graphical displays help students
perform simulated flow experiments.
Discuss this and other technologies
with colleagues at the
Reader Forum
John H. Glenn Research Center, Cleveland, Ohio
FoilSim is a computer program that calculates and graphically depicts information on
flows of air around airfoils of various shapes. Although it is useful primarily as a teaching
tool to enhance mathematical and scientific curricula, it was derived from "real-life"
flow-computing software of engineering quality. To make the underlying flow-computing
software useful in education, it was augmented with a graphical user interface that
enables students to manipulate the features of the program easily and that guides the
students through the learning process. The team that designed FoilSim combined the
highly technical knowledge of scientists with the understanding of experienced educators
to generate a product that is not too complex to be understood by students, yet it provides
an entertaining and interactive way for students to explore substantial mathematical and
scientific concepts.
FoilSim generates an interactive display, called the Airfoil View Panel (see figure),
which contains a simulated view of a wing being tested in a wind tunnel with air moving
past it from left to right. Students can change the position, orientation and shape of the
wing by moving slider controls in the display to vary the parameters of altitude, angle of
attack, thickness, and curvature. Other parameters that can be varied are the wing area
and the airspeed. The software displays plots of pressure or airspeed above and below the
airfoil surface. A simulated probe monitors airspeed and pressure at a particular point on
or close to the surface of the airfoil. The software calculates the lift of the airfoil,
enabling students to learn factors that influence lift.
Interactive lessons that accompany the program prompt students to engage in problem
solving and discovery. These lessons include:




Factors That Affect Lift
How Lift Changes
Flow Field Details
The Lift Coefficient
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
Baseball Lessons
In Baseball Lessons, students learn more about aerodynamics by controlling conditions of
a baseball pitch, including altitude (location), speed, and spin.
The overall reaction from FoilSim users has been overwhelmingly positive. A highschool teacher reported that all of his students were using FoilSim and were beginning to
"appreciate the process of experimenting." A student obtained a superior rating for a
science-fair project that incorporated FoilSim. Parents, flight instructors, and engineers,
each having a different reason to use FoilSim, have all expressed their delight with the
program.
FoilSim Generates an Interactive Display that shows aspects of the flow around an airfoil. Through the
controls in the display, the user can explore the effects of design parameters like thickness, curvature, and
angle of attack.
This work was done by Tom Benson, Bruce Bream, and Beth Lewandowski of Glenn
Research Center; John Eigenauer and Ruth Petersen of RMS Information Systems;
Roger Storm of Fairview Park City Schools; Darryl Palmer, Jr., of Cleveland State
University; and Carol Galica of Thigpen and Associates. For further information, visit
the FoilSim web site at http://www.grc.nasa.gov/Other_Groups/K-12/aerosim/. LEW16711
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