unfotunatelly there is not much progress on the wing pannel skin today. only one half has been completed. I continued procedur using the old wood glue and the result was really good. When using wood glue I'm not worried about the short setting& working time butam always concerned with the time when I use epoxy. the only point which must be considered during using wood glue is not to use it on a big surface specially a big surface of thin balsa. If so ,balsa sheet will be deformated.
Note the the butt joint edges of the skin parts attached to each other with no step shown in the image.

Ehsan