@NicolasGomes:
Note that
each and everyone here who make aircraft for FlightGear have started from scratch, not knowing how to do it. In other words,
exactly from where you are now, so...
If you look at the whole aircraft with all 3D modeling, FDM, systems etc. at once it will seem like an insurmountable task, like now.
Take in in in smaller chunks:
- First learn enough to see where the aircraft are (I guess you are already here),
- then enough to understand the more common file structures and what the more important files do,
- then get more familiar with what happens in each file (some are more difficult to understand than other),
- then expand from there.
When you start to get a hang of what goes where you can tinker on an existing aircraft and borrow things to a simplified (and ugly) prototype. Remember:
Perfection is the enemy of productivity.
It will take a bit of time to get there (several day to a couple of weeks, depending on how much time you have available). Also, people work on the aircraft they are most interested in, on what is left of their spare time. They are not willing to spend their time on doing the work for you, but would very likely be willing to help you out if they see that you are doing the larger part and are making an effort to learn along the way.