Honestly, just integrate everything in the firespitter .dll. Prop engines, adjustable landing gear, air brakes, texture/fuel switching, tweakable control deflection, landing effects... It's like a plane designer's Christmas list. Really, quite a few people, I think, don't realize quite how much of all the sweet new B9 functionality is from Firespitter. More or less everything in the HX series, to start with, and most of the rest. It's sort of like Firespitter with a load of structural parts and a futuristic theme. (I know, I know, there's the RPM stuff, the HotRockets stuff, and stuff from every single API I've ever heard of, and quite a few that I haven't, but still, point is, Firespitter is useful.)