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## AtmosModeler Simulator

#### Glenn Research Center

This is the beta version 1.2a 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 benson@grc.nasa.gov.

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. You can find the equations for the standard Earth atmosphere at this web site in both English units and metric units. Based on your input velocity, the program also calculates the Mach number, dynamic pressure, and stagnation, or total, temperature 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 is divided into three main sections:

1. On the left is the graphic showing the altitude of interest and the velocity 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 left. Click on the yellow bar and slide it to your desired velocity.
2. At the upper right are the input selection buttons and text fields. You can display the input and output in either English or metric units. You can also input desired values of altitude and velocity using the white input boxes. Simply backspace over the current value, enter a new value, then hit Enter to send the value to the program.
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, Mach number, or total temperature on your aircraft in the output box. Output gauges also display the atmospheric temperature and pressure. The speed of sound depends on the type of gas in the atmosphere 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. 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, which occurs on the wing leading or nose of your aircraft. The total temperature depends on the local, atmospheric, static temperature and on the velocity of the aircraft.

You can download your own copy of this program to run off-line by clicking on the yellow button:

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