The config file format stores and conveys the characteristics of any unique aircraft to the JSBSim executable. The information that is specified in the configuration file includes:

• Administrative
• Geometric and measurement
• Mass and weight/balance
• Buoyant forces
• Ground reactions
• External reactions
• Propulsion
• Systems, Autopilot, and Flight Control
• Aerodynamics
• Input/Output

The basic structure of the configuration file at the highest level is shown beginning with the fdm_config element definition. This is the root element for a JSBSim config file. The name of the aircraft this model represents. A release type of ALPHA or BETA will print out a warning message explaining that this preproduction release may not be of high quality. Often, the version may initially be simply specified as "\$Revision: 1.25 $", so that a configuration management tool such as cvs can automatically generate revision numbers. The fileheader section is where important information about the model is recorded. The authors, their contact information and affiliation, are all documented in this section. Notes about the model, as well as limitations and reference information are also recorded in this section. The name of the model author[s]. The contact email address for an author (optional). The organization that the author[s] belongs to. This is an optional field for a license name and URL. The name of the license, e.g. "GPL". The URL where the license can be found. This field stores the sensitivity classification, such as "classified", "secret", "proprietary", etc. The date that the model was initially created in the form yyyy-mm-dd The version number in the form #.#, or #.#.#, etc. This can also simply be a cvs keyword, such as "\$Revision: 1.25 $". A simple text description of the aircraft model. Notes are general notes about the model, perhaps such as special information helpful in flying it. Limitations for this model should be noted. For instance, if gear is not aerodynamically modeled. All references used in creating this model should be included. A reference consists of an author, a publication date, a reference ID (document ID, etc.), and of course a title. The title is the only item in a reference that is required. The metrics section holds information about the geometric characteristics of the aircraft that are important for the equations of motion and aerodynamics. Wing (or reference) area, wing span (or lateral reference length), and wing chord (or longitudinal reference length) are all recorded in this section. The center of graivty is also recorded in this section. Units may be given as shown in this section. Wing area (reference area) for the vehicle being modeled. The default unit is square feet (FT2). Wingspan (lateral reference length) for the vehicle being modeled. The default unit is feet (FT). The angle the wing makes with the fuselage centerline for the vehicle being modeled. The default unit is degrees (DEG). Chord (longitudinal reference length) for the vehicle being modeled. The default unit is feet (FT). Horizontal tail area. The default unit is square feet (FT2). Horizontal tail arm. This is the distance from the center of gravity to the quarter chord of the horizontal tail. The default unit is feet (FT). Vertical tail area. The default unit is square feet (FT2). Vertical tail arm. The default unit is feet (FT). Mass properties are specified in this section. The moments of inertia are specified first. All of Ixx, Iyy, and Izz are required, in order. The products of inertia are not required but, if present, must appear in order Ixy, Ixz, Iyz. Next, the empty weight of the aircraft, and the CG location are specified, in that order. Finally, any number of point masses can be specified. Moment of Inertia, Ixx Moment of Inertia, Iyy Moment of Inertia, Izz Moment of Inertia, Ixy Moment of Inertia, Ixz Moment of Inertia, Iyz Empty weight of vehicle. A location is a vector, containing an x, Y, and Z, element. The default unit is inches (IN). The unit is specifed in the unit attribute of the location - not in the individual x, y, or z child elements. A direction is a unit vector, containing an x, Y, and Z element which defines a direction in a specified frame. The system definition can be present any number of times in an aircraft definition. This section is used to define an arbitrary system, such as navigation, guidance, or control avionics, electrical systems, etc. The system, autopilot, and flight_control sections of a configuration file are all built the same way, using channel elements that contain strings of component definitions. The autopilot section is not required for many uses, including for use within Flightgear. The autopilot functions can be specified within the autopilot section, or a file name can be given where the autopilot is specified. This element specifies a minimum and/or a maximum limit that the associated component will be allowed to have. The result will be clipped to the specified limits. The domain defines the minimum and maximum input value allowed. The range defines the minimum and maximum output value mapped.. The aerosurface scale component maps an input value (which must fall within the span specified in the domain element) to an output value that falls within the span specified in the range element. For example, if the actual input value is 30% of the distance from the minimum to the maximum domain value, the output would be the value corresponding to 30% of the span of the range, from the minimum range value. The Gain element may contain a fixed numeric value, or it may be a property name. The Gain element may contain a fixed numeric value, or it may be a property name. The Gain element may contain a fixed numeric value, or it may be a property name. An actuator component models a general purpose mechanical effector. The actuator can exhibit a lag, can be rate- and position-limited, can feature a bias, can have a deadband, and it can feature hysteresis. The width value specifies the width of the deadband - i.e. the total span about zero where the input will be mapped to zero output. The noise can be entered as a percentage of the signal, or as an absolute value.