AC3D File Format (.ac)
An AC file is the plain-text scene format written by AC3D, a modeller aimed at flight-simulator and hobbyist work, storing a hierarchy of numbered OBJECT entries that each carry their own surfaces, materials and texture references.
AC3D at a glance#
| Full name | AC3D model |
|---|---|
| File extension | .ac |
| Category | 3D Models |
| Developer | Inivis |
| First released | 1994 |
| Other extensions | .acc.ac3d |
| Compression | Uncompressed |
| FileFlip support | FileFlip reads this format but does not write it |
What a .ac file can hold#
These are the things a AC3D file either supports or does not, and they are what decides whether a conversion keeps everything or quietly drops something.
| Textures and materials | Yes |
|---|
Strengths and limitations of AC3D#
What AC3D does well
- Plain ASCII text, readable and hand-editable without AC3D itself
- The native aircraft and scenery model format of the FlightGear flight simulator
- A simple, well-understood object hierarchy that third-party importers parse without ambiguity
Where AC3D falls short
- No skeletal rig or skinning, only a static per-object hierarchy
- No official standards body, just AC3D's own vendor documentation
- A version digit in the file header means a reader tuned to an older AC3D can miss features a newer file uses
Use AC when the destination is FlightGear or another AC3D-based scenery pipeline, since that's what the format was built to feed.
Convert AC to OBJ or glTF once a model needs to leave the flight-sim world, since few applications outside it open AC3D natively.
How to open a .ac file#
A .ac file opens in the programs below, grouped by the platform you are on. If you would rather not install anything, FileFlip converts AC3D into a format your machine already opens, and it does it in the browser tab rather than on a server.
| Platform | Programs that open it |
|---|---|
| Windows | AC3D, FlightGear |
| macOS | AC3D, FlightGear |
| Linux | AC3D, FlightGear |
| Web | FileFlip |
AC3D questions people ask#
What software creates AC files?
AC files are written by AC3D, a modeller used mainly for flight-simulator aircraft and scenery. FlightGear loads .ac files directly as its native model format, which is why so much of that content exists as AC files.
Is an AC file the same as AC3D or ACC?
An AC file and an AC3D file are the identical format under two spellings of the same extension. ACC is close enough that the same parser reads it, but it adds one extra surface type for triangle strips that TORCS and Speed Dreams use for smoothing and shadow mapping.
Does an AC file support animation?
No. An AC file describes static geometry, materials and an object hierarchy, with nothing for bones, skinning or keyframes. Anything animated has to be handled outside the format, which is one reason AC models get converted to formats like glTF for modern use.
Converting AC3D files#
Convert AC3D to another format
FileFlip does not write .ac files, so nothing on the site converts into this format. It works as a source only.
Every conversion runs inside your browser. The file is read from your disk, the work happens on your own machine, and nothing is uploaded. How FileFlip works names the engine behind each family and how to verify that for yourself.