Historical or non-historical, these skins that "work" on "any aircraf" aren't really skins. They're a pattern applied to the object.
Thing is, IL-2 aircraft are low detail meshes. Most of the finer detail on the surfaces, such as panel lines, engines, other machinery, etc. etc. becomes from textures. That's why there are texture templates for creating new skins for particular aircraft.
Removing all that detail with random logos copypasted on blank background and calling it an universal skin is a bit of a cop-out.
The MiG-13, Bf-110 and Bf-109Z skins are more like it, but I think you should pay more attention to things like cockpit not being painted on the inside, or the exhaust manifolds, or propeller spinners not being fuzzy at all (this is more important than you might think because of the way IL-2 spinners are rendered...).
On the other hand it's great that you're doing something to begin with, that's where everyone starts to experiment and see where their skills go. But, at the same time, I would suggest trying to make one or two skins for individual aircraft, using the templates to help you get the detail, and to know which parts of the texture are the fuselage, top of wings, underside of wings, etc.
What image editor do you use? I'm sure people will be glad to help or guide towards tutorials on several different graphics programs.