I see.
15 years ago, from 2008 to 2010 I helped à team of enthusiasts who were developing an Open Source flight simulator. The name was Fly!Legacy. I think that it survived 5 years from 2010 to 2015.
Mostly I was involved with matrix computation and correcting or tuning aerodynamic calculations.
If I remember well the most difficult part the team was entangled with was transposition and composition of matrices in the context of referential changes.