So you've got your generic joystick from a computer shop that thinks it's pretty incredible, and you've found that it's being detected. You run the test, and establish which button is which. Great. So now it's just a matter of lazily copying the nearest comparable XML to the right numbers in a file bearing the name the stick reports itself to be, save and go fight the Red Baron ...
Only the first thing is you might wonder what its name is. It's not a Logitech Nagasaki Pro, it's not a Microsoft Rattlesnake ... what it is is what it says it is. Something like "5-Axis, 12-Button Joystick ".
If you get stuck in the same places I do, then that would be the first little obstacle. Yes, that really is its name.
The other "tip" (when you find saving all your cut and pastes under this unspecific name doesn't work) is just to look carefully at it. See? There's a space at the end. You've been caught out several thousand times by spaces that form part of a name, and this is yet another of those times. Save another file with a name that ends with a space, and you'll see: it just works.
(I could give you the details that come before the acceptance of the anonymous name and the spotting of the space, and tell you exactly how to do this, but really if you just follow the instructions it'll work just fine, so there's no point in that. There's no problem with the existing HOWTOs; the only problem is with your joystick's name).
OK and in Flight Gear you can't fight the Red Baron. All you can do is crash a Cessna 172 without any fire or bloodshed.