Prerequisites and Tools

Developing custom aircraft for FlightGear requires a solid understanding of 3D modeling, texture mapping, and flight dynamics modeling. The open-source nature of FlightGear gives you complete freedom to create aircraft that range from simple gliders to complex commercial jets. Before diving into model creation, ensure you have the necessary software and a grasp of FlightGear's file structure.

Required Software

The primary 3D modeling tool used by the FlightGear community is Blender (free and open-source). Blender supports the AC3D (.ac) and OpenSceneGraph (.osg) formats that FlightGear natively accepts. Alternative tools include Winged Edge, AC3D (commercial), and SketchUp (via export plugins). For texture creation, GIMP or any standard image editor works well with PNG and DDS formats. For flight dynamics, you will need a text editor to create YASim or JSBSim configuration files; many developers use Notepad++ or VS Code with XML highlighting.

Understanding FlightGear File Structure

Each aircraft in FlightGear resides in a dedicated folder under $FG_ROOT/Aircraft/ (e.g., Aircraft/MyAircraft/). The essential files include:

  • Aircraft model file – typically a .ac or .osg file containing the 3D mesh.
  • Texture files – PNG, DDS, or JPEG images mapped to the model.
  • Flight dynamics configuration – one .yasm (YASim) or .xml (JSBSim) file.
  • Aircraft set file – an aircraft-set.xml that ties everything together and defines properties like name, author, and input bindings.
  • Sound configuration – optional, but recommended for immersion.

Understanding this structure early prevents path errors during import.

Designing the 3D Model

Modeling Guidelines for FlightGear

FlightGear renders models in real time, so polygon count matters. For high-detail aircraft, aim for 100k–300k triangles; for simpler planes, 10k–50k is sufficient. Use efficient topology: avoid n-gons, clean up non-planar faces, and ensure manifold geometry for proper collision detection. Always model with a real-world scale in meters; FlightGear expects one unit = one meter.

Create separate object parts for different animations (e.g., ailerons, elevators, landing gear). Name each object clearly in Blender (e.g., “Left_Aileron”, “Nose_Gear”) to simplify animation setup later. Use origin points at hinge positions for rotations.

UV Mapping and Texturing

After completing the base mesh, unwrap UVs to apply textures. Organize UV islands efficiently to maximize texture space. FlightGear supports up to 4096×4096 pixel textures; use power-of-two dimensions (1024, 2048, 4096). For color maps, use PNG format with lossless compression. For specular and normal maps, DDS with BC3 or BC5 compression is better for performance.

Create your texture in GIMP or Photoshop, ensuring the paint aligns with your UV layout. Many developers use a template paint scheme including rivets, panel lines, and weathering. Save the texture as MyAircraft.png in the aircraft folder.

Exporting from Blender

FlightGear officially supports the AC3D format (.ac) and OpenSceneGraph (.osg/.ive). For Blender, install the FlightGear Tools add-on or use the built-in AC3D exporter (available via the Blender Market). Export with the following settings:

  • Apply all transforms (location, rotation, scale) before export.
  • Choose “Y up” or “Z up” consistently; FlightGear uses Z up.
  • Include texture paths relative to the model file (or embed textures in .osg).
  • Check that all mesh names are ASCII and contain no spaces.

After export, open the .ac file in a text editor to verify paths and fix any export issues. Some developers prefer to export to .obj first, then convert to .ac with external tools like obj2ac.

Creating Flight Dynamics Configuration

FlightGear offers two built-in flight dynamics models: YASim (simpler, easier for beginners) and JSBSim (more accurate, suitable for complex aerodynamics). Both expect a text configuration file that defines mass, geometry, aerodynamics, and engine parameters.

YASim vs JSBSim

YASim uses a force-based approach with a configuration file that lists aerodynamic surfaces (wings, tails, fuselage) and engines. It is easier to tune because it abstracts many complex calculations. A minimal YASim config requires only a few dozen lines. Use YASim for your first aircraft or for planes with simple aerodynamics (e.g., Cessna 172).

JSBSim is a more physics-complete model that requires defining aerodynamic coefficients, stability derivatives, and propulsion tables. It produces more realistic behavior, especially for high-speed aircraft, but demands significantly more data and tuning. Use JSBSim if you have access to real aerodynamic data or want precise stall/spin characteristics.

Key Parameters to Configure

Regardless of the system, you must define:

  • Mass and balance – empty weight, center of gravity (CG), moment of inertia.
  • Wing geometry – span, chord, sweep, dihedral, incidence.
  • Control surfaces – elevator, ailerons, rudder (hinge points, deflection limits).
  • Engine and propeller – power, RPM range, propeller diameter, P-factor.
  • Landing gear – position, spring/damper constants, friction.

Study existing aircraft configurations from FlightGear's default aircraft to understand the syntax. For YASim, the .yasm file is well-documented in the FlightGear YASim Wiki. For JSBSim, refer to the JSBSim Reference Manual.

Importing Your Aircraft into FlightGear

Directory Structure and Naming

Create a new folder under $FG_ROOT/Aircraft/ named after your aircraft (e.g., MyAircraft). Inside, place these files:

  • Models/MyAircraft.ac (your 3D model)
  • Textures/MyAircraft.png (your texture)
  • myaircraft-set.xml (aircraft configuration)
  • myaircraft.yasm or myaircraft.xml (flight dynamics)
  • myaircraft-sound.xml (optional)

Maintain consistent lowercase naming with no spaces to avoid case-sensitivity issues on Linux. The folder name and the set file must match the aircraft name that appears in FlightGear's UI.

The aircraft-set.xml File

This file is FlightGear's manifest. A basic structure looks like this:

<PropertyList>
  <name>My Custom Aircraft</name>
  <author>Your Name</author>
  <release>1.0</release>
  <aircraft>myaircraft.yasm</aircraft>
  <model>Models/MyAircraft.ac</model>
  <sound>myaircraft-sound.xml</sound>
</PropertyList>

Ensure the paths are relative to the aircraft folder. The <aircraft> tag points to your flight dynamics file. You can also add <first-run> dialogs and property overrides. For a complete reference, see the FlightGear Aircraft Sets documentation.

Testing and Debugging

Launch FlightGear with --aircraft=myaircraft (or select it from the list). If the model does not appear, check the terminal output for missing file errors. Common issues include:

  • Texture not found – verify the path in the .ac file and that the texture file exists.
  • Model invisible or broken – check polygon orientation (normals should point outward).
  • Flight dynamics not loading – validate the .yasm/.xml syntax; compare with a known working config.
  • Wrong CG or stability – adjust mass distribution and aerodynamic parameters incrementally.

Use FlightGear's built-in Property Browser (Ctrl+P) to inspect and modify live parameters. The --generic=file,osc,out,output.csv option can log data for analysis.

Advanced Tips and Community Resources

Optimizing Performance

For smooth performance, especially with complex cockpits and systems, follow these tips:

  • Reduce polygon count where not visible (e.g., interior of wheel wells).
  • Use LOD (level of detail) variants: create a low-poly model for distant views.
  • Combine multiple small objects into one mesh with a shared material to minimize draw calls.
  • Employ texture atlasing to bundle many small textures into one large file.

Adding Systems and Animations

Beyond basic flight, you can add interactive systems like landing gear retraction, flaps, yoke controls, and glass cockpits. FlightGear uses XML animation files (in the Animations/ folder) and Nasal scripts for logic. Start with the official Animation How-To. For advanced functionality, explore the Systems and Panel XML files found in default aircraft.

Community Help and Templates

The FlightGear community is active and helpful. Use the following resources:

Consider contributing your aircraft to the official FGAddon repository once it reaches a stable state. This allows others to test and improve your work.

Conclusion

Developing your own aircraft models for FlightGear is a deeply rewarding process that combines artistic modeling with engineering principles. By following the structured workflow outlined above—designing a clean 3D model, mapping textures accurately, crafting a flight dynamics configuration, and correctly importing everything into FlightGear—you can bring a unique aircraft to life in the virtual skies. Start small, iterate often, and leverage the supportive community. With patience and persistence, your custom aircraft will become a proud part of your flight simulation experience. Happy modeling and smooth flying!