This is the beta version 1.3d of the AtmosModeler
Simulator program, and you are invited to participate in the
beta testing. The older
of the program is still available if you prefer a simpler version.
If you find errors in the program or would like to
suggest improvements, please send an e-mail to
Due to IT
security concerns, many users are currently experiencing problems running NASA Glenn
educational applets. There are
security settings that you can adjust that may correct
This is an interactive program in which you can investigate
changes in the
and its effects on aerodynamic variables.
It uses mathematical models of the
standard atmosphere of the Earth and Mars.
You can find the equations
for the standard Earth atmosphere at this web site in both
Imperial (English) units and metric
units. Similar information is available on the Martian
Based on your input velocity, the program also calculates the
dynamic pressure, and
stagnation, or total,
temperature and pressure
on your aircraft. The stagnation temperature is the temperature of the
airflow at a stagnation point, such as the leading edge of the wing or nose of the aircraft.
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 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
The pressure, temperature,
and density of the atmosphere constantly
change. At any one time there are great variations in the properties
of the atmosphere, depending on location around the planet and height
above the surface of the planet. The mathematical models used in this
simulator show an average variation of properties of the
atmosphere at various heights, but not at various locations. The
simulator will not predict the temperature or pressure at any single
location at any time. But it will help us understand the relations
among the values of a given variable at different heights. The
simulator can also demonstrate the relative magnitude of the
variables on the Earth and Mars.
The simulator is divided into three main sections:
On the left is the graphic showing the altitude of interest and
the velocity or Mach number of your aircraft. You can set the
altitude by clicking on the aircraft image, holding the mouse
button down, and moving the aircraft to a new location. The altitude roughly
corresponds to the nose of the aircraft image. The velocity is set by the
slider at the right. Click on the yellow bar and slide it to your
desired velocity. If you select "Mach number" using the radio buttons on the right,
then the velocity slider will change into Mach number input.
At the upper right are the input selection buttons and text fields. You can choose
to look at aircraft on Earth or Mars, and you can display the
input and output in either Imperial (English) or metric units using the menu buttons.
You input desired values of altitude using the white input box or the slider
in the left graphics window. To use the input box, simply backspace
over the current value, enter a new value, then hit Enter to send the
value to the program. You can also input either the velocity or the mach number by
using the radio buttons next to the label. The active input will have a black dot on
the radio button, and the input box will be black print on a white background.
The lower right portion of the simulator provides output
information. You can display
either the temperature, pressure, density,
speed of sound, dynamic pressure, force ratio,
total pressure, or total temperature on your aircraft in the
output boxes, labeled "Data". Or, you can display "Output Gauges"
which display the atmospheric static temperature and pressure.
The speed of sound depends on
the type of gas in the atmosphere (nitrogen and oxygen for the
Earth and carbon dioxide for Mars) and on the square root of the
temperature of the gas.
The dynamic pressure
depends on the gas density and the square of the velocity and is an
important design constraint on aircraft structures.
You can make a comparison of the
aerodynamic force generated on an aircraft at two
The force ratio displayed here compares the aerodynamic force
generated by a given aircraft design, at the specified velocity, at the
selected altitude (and planet) to the force generated by the same
aircraft, at the same velocity, at sea level on the Earth.
You can compare the Mach number
of a vehicle at two altitudes or on different planets.
The Mach number is computed at the specified altitude and velocity.
Since the speed of sound depends on the temperature and
the gas, you will note some important differences in Mach number.
The gas is characterized by the ratio of
specific heats, denoted by the Greek letter gamma.
The default value for air is 1.4, but you can change this value using the input box.
As the Mach number gets closer to (or exceeds) one,
compressibility effects, like shock waves and wave drag, become
more important to the aircraft. Finally, the program determines the
stagnation, or total,
temperature and pressure which occurs on the
wing leading or nose of your aircraft. The total temperature and pressure
depend on the local, atmospheric,
static temperature and pressure and on the velocity of the aircraft. The
total temperature and pressure computed here includes
as the speed of the aircraft increases.
The NASA Glenn Educational
Programs Office will continue to improve and update AtmosModeler based on user input.
Changes from previous versions of the program include:
On 7 Nov 13,
version 1.3d was released. This version corrects an error in the calculation
of the Mach number during initiation. There is also a small change to the graphics
that was required for new security restrictions on Java programs for some
browsers. You may no longer see a graphic of an airplane when using the slider
On 29 May 13,
version 1.3c was released. This version corrects an error in the calculation
of the total pressure. The correction was suggested by Mark Bushman and involves
inclusion of the compressibility effects that occur at high speed. The user can now also
input the ratio of specific heats(gamma) which characterize the gas in the atmosphere.
On 16 May 12,
version 1.3b was released. This version calculates the total pressure and allows
for either velocity inputs or Mach number inputs in addition to the altitude
input, as suggested by a user. Version 1.3a was a development
version and not released.
On 7 Dec 05,
version 1.2a was released. This version included the ability to
vary the velocity, to calculate the Mach number, and to have
multiple output displays: graphs and data tables.
You can download your own copy of this program to run off-line by
clicking on the yellow button: