JSBSim (www.jsbsim.org) was created initially for the open source FlightGear flight simulator (www.flightgear.org), where it replaced LaRCSim (Langley Research Center Simulation) as the default FDM. JSBSim also maintains the ability to run in a standalone, batch mode. This is useful for running tests or sets of tests automatically using the internal scripting capability.
Differently from LaRCSim, JSBSim does not model specific aircraft in program code. The aircraft itself is defined in a file written in an XML-based format where the aircraft mass and geometric properties are specified. Additional statements define:
The configuration file format is set up to be easily comprehensible, for instance featuring textbook-like coefficients, which enables newcomers to become immediately fluent in describing vehicles, and requiring only prior basic theoretical aero knowledge.
One of the more unique features of JSBSim is its method of modeling flight control systems and an autopilot. These are modeled by assembling strings of components that represent filters, switches, summers, gains, sensors, etc.
Another unique feature is displayed in the use of "properties". Properties essentially expose chosen variables as nodes in a tree, in a directory-like hierarchy. This approach facilitates plugging in different FDMs into FlightGear, but it also is a fundamental tool in allowing a wide range of aircraft to be modeled, each having its own unique control system, aerosurfaces, and flight deck instrument panel. The use of properties allows all these items for a craft to be modeled and integrated without the need for specific and unique program source code.
The equations of motion are modeled essentially as they are presented in aerospace textbooks for the benefit of student users, but quaternions are used to track orientation, avoiding "gimbal lock". While JSBSim is designed to model primarily atmospheric flight at lower speeds, coriolis and centripetal accelerations are incorporated into the EOM to permit a wider range of vehicles to be simulated.
Currently under development is an expansion of the atmospheric modeling for JSBSim. The existing model approximates the standard atmosphere of 1976. Recently, source code for the NRLMSISE-00 model was obtained and this is being implemented as a C++ class that can optionally be used. Also, a simple Mars atmosphere is being implemented.
JSBSim can output (log) data in a configurable way. Sets of data that are logically related can be selected to be output at a chosen rate, and individual properties can be selected for output. The output can be streamed to the console, or to a file, and can also be transmitted through a socket.
JSBSim has been used in a variety of ways:
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