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## AtmosModeler Simulator

#### Glenn Research Center

This is the beta version 1.3d of the AtmosModeler Simulator program, and you are invited to participate in the beta testing. The older version 1.1f 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 nancy.r.hall@nasa.gov.

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 problem.

This is an interactive program in which you can investigate changes in the atmosphere 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 atmosphere. Based on your input velocity, the program also calculates the Mach number, 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: http://www.java.com/en/index.jsp, try the "Download It Now" button, and then select "Yes" when the download box from Sun pops up.

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:

1. 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.
2. 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.
3. 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 altitudes. 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 compressibility effects as the speed of the aircraft increases.

NEW FEATURES

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:

1. 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 for altitude.
2. 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.
3. 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.
4. 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:

Activities:

Guided Tours
• Standard Atmosphere Model:
• CurveBall - Baseball Simulation:
• Mach and Speed of Sound Calculator:
• Speed of Sound:
• Interactive Atmosphere Model: