LOL! Nice ones guys!

Seriously BigCrate, it depends on what you mean.
If you just want to "make" a P38 to go into one of the open source sims like MSFS200 or any of the others, then its probably doable for you. Not to mention that theres probably already P38 FM's available for those sims, and you can look at the inputs already there for guidance. So get into the numbers play with them, understand what it takes, and see what you come up with. Its a fun and quite educational process.
However if your talking essentially about making your own sim dedicated to the P38, then your into a WHOLE nuther world. You have to know a whole lot about programming, designing physics engines, developing your own system to mimic flight (ie the "flight model" as a whole), and then figure out how to get the critical information about an aircrafts attributes into the system. Simple isn't it? Oh and then you have to do the whole thing with network systems, or you can just settle for simple AI enemies, if you want, and little things like terrain and art and ......
Well you get the point.
I suggest you play with some of the open source sims and try to understand what goes into modeling an aircraft first.
