is a beta 1.4d student version of the FoilSim III program, and you are invited
to participate in the beta testing. If you find errors in the program or
would like to suggest improvements, please send an e-mail to Thomas.J.Benson@nasa.gov.
FoilSim II is still available if you prefer the
FoilSim is a simulation. It is not reality.
FoilSim is an educational computer program. It is not a design program.
FoilSim was built to help students learn how wings work. It produces the correct trends
(for example, doubling velocity will quadruple the lift and drag)
but it does not give the exact value of lift or drag.
FoilSim uses a very simplified
analysis to calculate lift, and it interpolates
experimentally measured drag data to determine the drag.
The drag data was obtained by students using inexpensive models and an inexpensive
Please do not attempt to design, build, or fly a full scale
aircraft using data from FoilSim. It is fine for models, but be careful.
If you see only a grey box at the top of this page, be sure that Java is
enabled in your browser. If Java is enabled, and you are using the Windows XP
operating system, you may need to get a newer version of Java. Go to this link:
try the "Download It Now" button, and then select "Yes" when the download box from Sun pops up.
If you experience difficulties when using the sliders to change variables,
simply click away from the slider and then back to it. If
the arrows on the end of the sliders disappear, click in the areas
where the left and right arrow images should appear, and they
should reappear. These are known Java problems.
With this software
you can investigate how an aircraft wing produces
by changing the values of different factors
that affect lift
that affect drag.
FoilSim III is the latest (July 2010) version of the FoilSim family of
The different versions of FoilSim
require different levels of
knowledge of aerodynamics, experience with the package,
and familiarty with computer technology.
This web page contains the on-line student version of the FoilSim III program.
It includes an on-line user's manual which describes the
various options available in the program and includes hyperlinks to
pages in the
Beginner's Guide to Aerodynamics
describing the math and science of airfoils.
More experienced users can select a
version of the program which does not include
these instructions and loads faster on your computer.
You can download these versions of the program to your computer
by clicking on this yellow button:
With the downloaded version, you can run the program off-line and do not
have to be connected to the Internet.
Elementary Version - FoilSim III
There is a special
version of FoilSim
for elementary students who are just beginning to learn
about wings and airfoils.
This version only lets you change the flight conditions and the geometry of the wing.
Input is performed with buttons, so the student does not have to work the sliders,
input boxes, and choice boxes of the student version.
The only output are lift and drag gages in English units. Again, the student does not
have to select types of output, or interpret graphs.
Student Version - FoilSim II
FoilSim II is still available
for students who are learning about the lift of
airfoils and wings.
This version calculates the lift of an airfoil based on user inputs of flow
conditions and wing geometry. Output is provided by a variety of plots, performance
graphs, and text fields. But FoilSim II
does not make any calculation of the drag of the wing.
Undergraduate versions of FoilSim II are also
available for college students.
Undergraduate Version - FoilSimU III
There is a special
undergraduate version of FoilSim III
for students who are studying computational modeling
of airfoil problems.
This version let you change some of the assumptions in the analysis
and has additional graphics to view the
details of the analysis. There
are on-line and off-line applet versions of this program.
There are several other applets based on FoilSim.
You can investigate the role of aerodynamics in
pitching a baseball by using
the curve of a soccer kick by using
or wind tunnel testing techniques by using
This program is designed to be interactive, so you have to work with the program.
There are a variety of choices which you must make regarding the analysis and the display
of results by using a push button or a drop menu.
To operate a button, move the cursor over the button and
left click with the mouse. The push buttons occur in groups, and the chosen option is
shown as a yellow "lighted" button.
A drop menu has a descriptive word displayed in a box
with an arrow at the right of the
box. To make a choice, click on the arrow, hold down and drag to
make your selection.
The current values of the design variables are presented to you in boxes.
By convention, a white box with
black numbers is an input box and you can change the value of the number.
A black box with
yellow numbers is an output box and the value is computed by the program.
To change the value in an input box, select the box by moving the cursor into the box
and clicking the mouse, then backspace over the old number, enter a new number,
then hit the Enter key on your keyboard. You must hit Enter
to send the new value to the program.
For most input variables you can also use a slider located next to the input box.
Click on the slider bar, hold down and drag the slider bar to change values, or
you can click on the arrows at either end of the slider.
At any time, to return to the original default conditions,
click the red Reset button at the upper right of the program.
program screen is divided into four main parts:
top left side of the screen is the View Window.
The view window includes a graphic of the airfoil that you are
designing and several buttons which control the graphic.
Details of the window
are given in the Graphics section of this page.
upper right side of the screen is the Control Panel.
The control panel holds several push buttons which
control the input and output to be displayed. You can choose either
Imperial Units or Metric Units by using the pull down menu at the top.
Input choices have
blue letters and the selected input panel appears at the lower left.
Output choices have red letters and the output panel appears at the lower
You will always see the computed lift, drag, Reynold's number
and lift to drag ratio. You can display lift and drag as numerical
values or as dimensionless coefficients.
Details of the input
and output variables are given below.
lower right side of the screen is the Output Window.
The output can be presented as
graphs of airfoil performance,
a probe which you can move through the flowfield,
lift and drag gages, or printed
numerical values of certain parameters.
You select the type of output displayed by using the push
buttons labeled "Output:" on the upper right panel.
lower left side of the screen is the Input Window.
Various input panels are displayed in this window.
You select the input panel by using the push
buttons labeled "Input:" on the upper right panel.
The View Window contains a schematic drawing of the wing that
you are designing and some buttons to control the schematic drawing.
Possible choices are colored blue
while the selected option is colored yellow.
the wing as viewed looking along the leading edge. The cross section
appears as an airfoil or circle with the flow going from left to right.
You can move the picture within the window by moving the cursor into
the window, holding down the left mouse button, and dragging the airfoil
to a new location. You can also "Zoom" in close to the airfoil by using
the green slider at the left of the window. If you get lost, pushing
the red Find button will return the airfoil to the initial position.
the wing as viewed from above looking down onto the planform. The flow
is from bottom to top. Since FoilSim only solves for the two-dimensional
flow past objects, you won't see any flow in this view. It is provided
only to display the geometry of the wing area.
Side - 3D
shows an orthographic projection of the three dimensional wing.
particles flowing past the airfoil. The particles are drawn as line
"traces". The inclination of the trace is at the local flow angle, and
the left most part of the trace is the particle location. Particles
are being periodically released from a constant streamwise location
upstream of the airfoil.The streamwise distance between any two particles
is proportional to the local velocity.
a snapshot of the moving particles. In this view, you can change the
streamwise release point of the particles by moving the cursor into
the view window, holding down the left mouse, and dragging the particles
to the left or right. In this view, the particles are color coded by
the time at which they are released. (All of the yellow particles were
released at the same streamwise location at the same time.)
are collections of the particle traces to form a solid flow line.
shows only the geometry of the wing or airfoil with some descriptive
labels but with no flow field.
There are several different output options available for the
Output Window at the lower right.
You select the type of output by using the push buttons
on the control panel. The default setting is Plot and
a graph will appear in the window. The type of graph is described
below and you can vary the plot by using the Plot Selection input panel.
If you display a plot and begin to change the
input variables, it may become necessary to rescale the plot axes by
pushing the white Rescale button at the lower left of the window.
The types of available plots are
The default plot
is the Surface Pressure. The yellow line will be a plot of the
lower surface pressure, and the purple line a plot of the upper surface
pressure. For reference, the green line shows the value of free stream
You may also display
the Surface Velocity. As with the pressure, the yellow line will
be a plot of the lower surface, and the purple line a plot of the upper
You may also display
the Drag Polar. A drag polar is a plot of lift coefficient versus
drag coefficient for a selected geometry at various angles of attack.
The remaining plot
choices show Lift, Drag, Lift Coefficient -Cl, or
Drag Coefficient - Cd versus each of the input variables.
For these plots, the current value of the flow conditions is shown as
a red dot on the plot.
shows the current value of lift (or lift coefficient) and drag
(or drag coefficient) displayed
in scientific notation. The gages are displayed in the output window
and move as the lift and drag are varied. This display shows the relative
sensitivity of lift and drag to the input variables.
lets you explore the flow around the wing. A probe control panel appears
in the output window when you select "Probe" from the control panel.
By default, the probe is
turned off. You turn the probe on by pushing one of the white buttons
on the probe panel. The probe itself will then appear in the view window. You
change the location of the probe using the sliders to the left and below
the gage on the probe panel. The value of the pressure or the velocity at the location
of the probe tip (magenta ball on the view window) is displayed on the
gage. Or a green trail of "smoke" is swept downstream from the probe
location. You turn the probe off by using the red button located above
options provides a written list of important input and computed variables
in the Output Window. You have two options for performance output;
the Data option gives the computed lift, drag and flow conditions, the
Geometry option shows the coordinates of the airfoil geometry and the
local value of velocity and pressure. These numbers correspond to the
plots of velocity and pressure described above.
Some additional output
from the program is displayed on the Control Panel and some input panels.
On the Control Panel,
you can choose to display the lift or the lift
coefficient by using the drop menu.
Similarly, you can either display the
is displayed in the output box to the right of the drop menu. Lift and drag
may be expressed in either Imperial (English) or metric units (pounds or Newtons).
The Reynolds number
ratio of inertial forces to viscous forces and affects the
calculated value of the lift and drag.
Reynold's number and
lift to drag ratio
are always displayed on the Control Panel.
On the Flight Test input panel is a group of output boxes that give the
atmospheric conditions of the air. The pressure,
temperature, density, and viscosity will change depending on the altitude and planetary
inputs. On the Size input panel the geometric aspect ratio of the
wing is displayed. The aspect ratio is defined to be the square of the
span divided by the wing area
and is included in the calculation of
The input variables
are located on input panels that are displayed at the lower left.
You can select the input to display by using the push buttons on
the control panel. You can choose to vary the Shape,
the Size, or perform a Flight Test of a wing design. You can also display
the Plot Selection Panel and a panel to control the Analysis used in FoilSim III.
If you choose to
Flight Test, you can change the value of
lift and drag by varying the speed, or the altitude.
You can flight test your wing on the earth (default), on Mars, or in
the water by using the drop menu at the upper right. You can also
choose to specify your own values of temperature and pressure for air,
or to specify your own fluid by providing a value of the fluid density.
If you choose Shape,
you can select a classic airfoil shape, an ellipse, or a thin plate
cross section by using the drop menu. You can change the camber,
thickness, or the angle of attack of
the cross section. The definitions of these geometric variables are given
on the wing geometry web page.
There are some push buttons on the airfoil Shape
input panel to let you chose some "basic" airfoil shapes: symmetric airfoil, flat bottom foil,
negative camber, flat plate, high camber, curved plate, or ellipse. Clicking on these
buttons will set a representative value of camber, thickness, and angle of attack.
You can also
choose to investigate the lift and drag created by a rotating
cylinder, or a spinning ball. For these
problems you must specify the spin rate and radius and the span of the cylinder.
If you choose Size,
you can vary the layout of the wing. You can change the chord, span,
or the wing area. The ratio of the span to the chord
is called the Aspect Ratio and this parameter also has an effect on the
of the wing. If you have selected
a cylinder or ball shape, this input panel is not used.
There are a variety
of Analysis options in FoilSim III. The option being used is shown
by a yellow lighted button on the Analysis panel. You can change the analysis
by clicking on a white button. The default
Stall Model that decreases the lift for angles of attack greater than
10 degrees. The optional analysis uses Ideal Flow that neglects
viscous and compressibility effects. The actual calculations are done with ideal
flow and the stall model corrects for flow separation at high angles of attack.
The actual calculation is done for a two-dimensional (2D) foil. The Aspect Ratio
correction includes the 3D wing tip effects on lift. The Induced Drag correction
includes the 3D wing tips effects on drag. The drag of an airfoil
is determined by a table look-up for
values of drag coefficient.
The values were obtained at
a specific Reynold's number. The Reynolds number correction includes
the effects of changing Reynolds number to the test conditions.
The drag of a cylinder or ball is based on
as a function of Reynolds number.
The NASA Glenn Educational
Programs Office will continue to improve and update FoilSim III based on user input.
Changes from previous versions of the program include:
On 21 Mar 11,
version 1.4d was released. This version modifies the geometry output
to include the volume of the wing. This addition was prompted by user email.
On 17 Feb 11,
version 1.4c was released. This version modifies the plotting package
to include more significant figures for small amounts of lift and drag. This fix
was prompted by user email.
On 29 Nov 10,
version 1.4b was released. This version corrects
a graphics problem with the drag coefficient as a function of angle of attack, camber,
and thickness. And we have corrected a drag determination error for negative camber
On 23 Nov 10,
version 1.4a was released. In response to a user email, we have some basic
airfoil shapes available on the airfoil "Shape" input panel.
On 23 Sep 10,
version 1.3b was released. In response to user emails, we have moved the
choice button for Imperial or Metric Units back to the control panel.
On 27 Jul 10,
version 1.3a was released. This is the first release version for FoilSim III and
includes a drag calculation which was not available in FoilSim II. Earlier versions of FoilSim III
were developmental versions and not released to the public. With the release of FoilSim III,
upgrades and revisions will cease for FoilSim II.
The wind tunnel data used in the FoilSim III computer program was
obtained by Anthony Vila, a student at Vanderbilt University, during a
summer intern session at NASA Glenn in 2010.