Another aspect of covering, andf covering materials, is that these 'films' and 'cloths' also add stregth and structure to the model. that nbeing the typical iron on covering, and teh typical 'glass sheet' of fiberglass or silk.

The wood parts are really just a shape; a form, a skeleton, and teh covering materials add the require 'stress' to hold it all together.

As in: Can I paint my tail (stab rudder, etc..) in stead of covering it? it's a solid peice of wood.

The answer is usally no., as the paint does not add any structure, were the coveing materials will.