Hope this helps you, it's for the 109 but the same procedure can be used for any aircraft ingame.
http://www.youtube.com/watch?v=riJXEF7kerE
In single player, you really need to use the Full Mission Builder located in the Extras menu in the games main menu. I find it easier to create a dogfight server, password it, load up a default dogfight game and edit the loadouts that way.