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TBCC Simulator


This is a beta 1.0a version of the TBCC Simulator 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

Turbine Based Combined Cycle (TBCC)

With this software you can design and investigate the performance of a combined turbine and ramjet propulsion system. This combination is often called a turbine-based combined cycle or TBCC propulsion system. A ramjet is particularly well suited for hypersonic cruising flight because the high forward velocity can be used to compress the incoming flow and because there are no components in the high total temperature flow stream. But a ramjet can not develop static thrust. So another propulsion system must be used to bring the ramjet up to speed. A turbine engine works very well as a low speed propulsion system.

There are several different versions of the TBCC Simulator which require different levels of experience with the package, knowledge of compressible flows, and computer technology. This web page contains the on-line version of the 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 NASA's Guide to Hypersonics describing the math and science of the propulsion systems. 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:

Button to Download a Copy of the Program

With the downloaded version, you can run the program off-line and do not have to be connected to the Internet.


This program is designed to be interactive, so you have to work with the program. You can change the value of any of the flow variables and the output display by using the various choice buttons, sliders, and buttons on your computer screen . The current value of flow 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. 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. A black box with yellow numbers is an output box and the value is computed by the program. There are some choices which you must make regarding the display of computed results by using a choice box. A choice box has a descriptive word displayed and an arrow at the right of the box. To make a choice, click on the arrow, hold down and drag to make your selection. At any time, to return to the original default conditions, click the white and red Reset button on the blue bar.

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 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.


The program screen is divided into five main parts:

  1. At the top of the screen is a graphic of the propulsion system that you are studying.
  2. In the middle left side of the screen is the input panel. The contents of the input panel changes depending on your selection.
  3. On the lower left side of the screen are the net results of the calculations and some control buttons.
  4. In the middle right side of the screen are computed results. The contents of this panel can be changed to display plots or output boxes.
  5. On the lower right side of the screen are calculated results for the separate turbine and ramjet propulsion systems.


You can choose from two different types of turbine engines: a simple turbojet, or a jet with afterburner. Sitting under the turbine engine is the or a ramjet. Selection is made on the graphics window by clicking on the engine name. The chosen engine is shown in yellow.

Flight Conditions include the Mach number, airspeed, altitude, pressure, temperature, and throttle and afterburner settings. There are several different combinations of these variables available for input using the choice button on the input panel. The pressure and temperature are computed as functions of the altitude by using a Standard Day atmospheric model. You can invoke the flight input panel at any time by clicking on the word on the blue bar of the graphics window.

Design variables for each engine component can be varied. The components and variables include the Inlet (pressure recovery), Compressor (CPR, compressor efficiency), Burner (fuel,maximum temperature, efficiency, pressure ratio), Turbine (turbine efficiency) and Nozzle (maximum temperature, efficiency, A8/A2) for the turbine and the Inlet, Burner , and Nozzle of the ramjet. As you choose a different component, the part of the engine being affected is highlighted in the graphic by changing from its default color to yellow.

Engine Size can be specified by either the frontal area or the diameter. Engine sizing is doen on the particular type of engine (turbine, afterburner, or ramjet) that you select. The location of the ramjet relative to the turbine engine is also set on the ramjet input panel. As the engine size changes, the grid background changes in proportion to the size. The distance between any two grid lines is 1 foot.

CHOICES: Mode, Units, Output Display

The program works in two modes: Design or Off-Design Mode. In the Design Mode, you can change design variables including the flight conditions, the engine size, the inlet performance, the turbo machinery compressor and turbine performance, the combustors or burner performance, or the nozzle performance. In Design Mode, any change in an input parameter produces a new engine design. You have to be very careful when drawing conclusions about the effects of input variables on performance because you are not comparing the effects on the same engine; you are comparing one engine against another engine.

In Off-Design Mode, you are only working with one combined engine design. You can vary only the flight conditions and you can not change any of the component design parameters except the throttle setting. The values of some of the performance parameters like inlet recovery and nozzle area may change according to choices that you made during design.


The program will calculate an average weight of the engines that you design. The thrust to weight ratio of the engine is displayed in the numerical output and is a measure of the efficiency of the engine. The weight depends on the type and design of the engine, the size of the engine, and the component materials. The program begins with standard materials for the components, but you can change the materials and see the effects on weight of the engine. Just push the blue Materials choice button on any component input panel. You can also select to define your own material by choosing My Material from the menu. Just type in your own values for material density and temperature limit. The program will check the temperature throughout the engine design against the material limits. If you exceed a limit, a flashing warning will occur in the schematic. You can see the temperature limits by choosing "Temp Variation" in the Graphical Output display. You can find which component is exceeding the temperature limits by selecting "Component Performance" on the Output display and looking for the red temperature display. (For the afterburner and the ramjet, the graphical temperature limits are based on the flow temperature, not on the material temperature, and are slightly higher than the material limits. Cooling airflow is often used along the walls of these components to keep the material temperature within limits.)


The white and red Output menu allows you to change the contents of the output window in the middle right side of the screen. You can choose to display output boxes with numerical values of the engine and component performance, as described below. Or you can display graphs of the variation of the value of pressure and temperature at various stations through the engine. You can also display a T-s Plot or a P-v Plot, which are used by engineers to determine engine performance.

To generate your own performance plots, select "Generate" from the graphics window. The input panel will now display some additional buttons and sliders to generate a plot. Choose the variables to be plotted using the pulldown menus and then push the "Begin" data button. Set the value of the independent variable by using the slider or the type-in box. Push the blue "Take Data" button and a data point will appear on the graph. Set a new value for the variable and take another data point (up to 25 points in any order). When you are finished, push the "End" button and two lines will be drawn through your data points; one for the turbine and the other for the ramjet. To start a new graph, push "Begin" and your old graph will vanish. When you are finished, push the red "Exit" button and you will return to free stream conditions.


Numerical Output from the program is displayed on three performance panels. The total engine performance is always displayed at the lower right and includes the engine net thrust, the fuel flow rate, the engine air flow rate, and the specific fuel consumption. An additional Engine Performance output panels shows the fuel-to-air ratio, the engine pressure ratio (EPR) and engine temperature ratio (ETR), gross thrust, and ram drag. Additional component performance parameters, such as the nozzle pressure ratio (NPR), engine thermal efficiency, nozzle exit velocity (V exit), free stream dynamic pressure (q0), and specific impulse (ISP) are displayed. Nozzle exit pressure (Pexit) and fan nozzle exit pressure (P fan exit) and the compressor face Mach number (M2) are also displayed. The Component Performance output panel shows the variation of total pressure and temperature through the engine.


The Education Programs Office will continue to improve and update TBCC Sim based on user input. Changes from previous versions of the program include:

  1. On 1 Sept 06 version 1.0a was released. This is the first version of this program.

Guided Tours


Button to Display Hypersonic Aero Index Button to Display Hi Speed Aero Index Button to Display Aerodynamics Index Button to Display Propulsion Index
NASA's Guide to Hypersonics
Beginner's Guide to Compressible Flow


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Editor: Tom Benson
NASA Official: Tom Benson
Last Updated: Jun 12 2014

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