ok
to get a plane in your skin folder when in game u select a plane you want and click on it when it saves default skin.
this is saved in you skins folder in aces high now to make yor own version of the skin you will ned to make a new folder and remname it .
EG if you are using spit 9 your new folder will be spit9_1 then you copy the bitmaps for the plane in to this folder,add a .txt folder with the name of the plane eg 616 squadronRAF .
now if u done it correct when u open the skin viewer you should be able to select spit 9 and it will show the default skin,in the drop down box you should then be able to find the spit9_1 plane which u have created.
hope this helps