I don't have an Airplanes folder under C:\Users\...\AppData\Roaming\Virtuali
for me and I´m pretty sure that´s default it is under %APPDATA%\Virtuali\Airplanes
Both locations are valid, and GSX will read a GSX.CFG file from both places, with the file in %APPDATA% having the highest priority.
- The location under Simobjects\Airplanes\AIRPLANE_NAME is supposed to be used by 3rd party airplane developers supplying a GSX configuration that gets installed with the airplane. Note that, with P3D V4/V5, this might not necessarily be under the simulator root, because add-ons using the native add-on.xml method of installation might install all the airplane files elsewhere, which is both possible and encouraged by the latest SDK.
Of course, if you downloaded a file made by somebody else, you can as well use this one, but if the airplane has some kind of live update system that might remove "unknown" files from its own folder, there's a risk losing it after an update.
- The location under %APPDATA%\Virtuali\Airplanes\AIRPLANE_NAME doesn't appear UNTIL you edit the airplane yourself with the GSX editor. This will create the folder and the GSX.CFG.
If the you downloaded a file made by somebody else, and you are missing the folder ( because you never edit this plane ), just create one, which must have exactly the same name as the airplane own folder under Simobjects\Airplanes.
There's a priority system so, if a GSX.CFG file is present in the airplane own folder, GSX will read that but, if another GSX.CFG for the same airplane is found in %APPDATA%, GSX will use that INSTEAD.
The advantage of using %APPDATA%, is that nothing will remove a file from there, since it's a place reserved for *your* settings. You can uninstall the airplane, and uninstall the whole simulator, but the file will still be there, unless you remove it yourself or reinstall Windows from scratch with the option to remove all your settings.
And, if you keep TWO copies of a GSX.CFG file, one in Simobjects\Airplanes\AIRPLANE_NAME and another one in %APPDATA%, you have a sort of backup that, if you press "RESET" in the GSX airplane configuration editor, it will remove the file in %APPDATA% but, instead of going back to a default configuration, it will revert to the one in Simobjects\Airplanes, so you won't have to restart from scratch again if you made some edits and realized the didn't work well.