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JSBSim is an ongoing attempt at producing an OO Flight Dynamics Model
(FDM) to replace LaRCsim as the default FDM for FlightGear. It can
also be used standalone.

JSBSim uses config files to represent aircraft, engines, propellers,
etc. Also, the flight control system is described in the config
file. Normally, for use with FlightGear, the config files are named
this way [case is significant]:

<FG_ROOT>/Aircraft/<aircraft name>/<aircraft name>.xml

Engines are named like this:

<FG_ROOT>/Engines/<engine name>.xml

Aircraft and engine config files are present in the FGFS Base package
which must be downloaded. See the FlightGear web site for more

How to run FGFS using JSBSim

All the various FDMs are currently compiled into FGFS. You can specify
which FDM you want at run time. You can also specify which aircraft
you want. Currently, for JSBSim only the X-15 and C-172 aircraft are
available. Here is an example command line used to start up FlightGear
using JSBSim as the FDM:

fgfs --fdm=jsb --aircraft=X15 --units-feet --altitude=60000 --uBody=2000 --wBody=120


fgfs --fdm=jsb --aircraft=c172

[Note: uBody is the forward velocity of the aircraft, wBody is the
downward velocity - from the aircraft point of view. This essentially
means that the aircraft is going forward fast and has an angle of
attack of about 4 degrees or so]

The first command line sets up the initial velocity and altitude to
allow the X15 to glide down. Note that if you fire up the engine, it
will burn for only about two minutes and then run out of fuel - but
you will go very, very fast! The second command line example will
start up the C172 on the end of the runway.

Check out the JSBSim home page at Please report
any bugs to, or, or post on the
jsbsim web site using the SourceForge bug tracking system for the

JSBSim is written by Jon S. Berndt and Tony Peden with contributions
by other FlightGear programmers, as well.