I am developer and a game engine hobbyist. I am impressed with what the BMS dev team has accomplished considering most of it is during their free time. I am writing this more for the people who are willing to contribute and do not know where to start.
First out of courtesy to spare BMS dev time assume it takes a lot of time to manage projects with inexperienced developers. It requires teaching and code reviews. So being prepared when offering your contribution is a good thing.
Good developers are curious and tenacious so I decided to post some links for people to know what they may be getting into.
First get the FreeFalcon code from github: EDIT By I-Hawk - No links to the FF open source repo please
Assume that parts of the BMS code will share some ancestry with that code. Don’t stare at the code but at least be able to tell what part of the game is written where. For example terrain, campaign, flight sim, AI, memory.
If terrain is what you want to do then start here.
http://vterrain.org/
Look at Rendering, LOD, papers and implementations. Most papers are written by PhDs, but at least learn different terrain representations and rendering techniques. Unfortunately most of those papers are outdated because they are not up to the modern GPUs capabilities.
The best paper and implementation I have found so far is this so you can skip all of the above:
http://www.frostbite.com/wp-content/uploads/2013/05/Chapter5-Andersson-Terrain_Rendering_in_Frostbite.pdf
Finally for large worlds floating point arithmetic is not accurate enough. As a rule of thumb with 32bit floating point representation you have 7 decimal digits of accuracy regardless of decimal point. So read about rebasing the origin for large world, even better look here:
https://www.microsoft.com/Products/Games/FSInsider/developers/Pages/GlobalTerrain.aspx
As you can see that is a lot of information and mastering each piece can be a Phd thesis, but just being familiar with the problems and solutions I think is interesting enough.
Best,