That 1/4-thick strip may well carry flight loads from the skin to the
spar.

You might also read veeduber's "wood rant":
http://groups.google.com/groups?q=gr...ol.com&rnum=18

(Lou Parker) wrote in message . com...
In many area's on my wood structure it calls for a filler. Usually
spruce, but for no other reason but to fill a gap. These are not
structural in the least, only to fill (i.e. on top of the spar a 1/4"
strip of wood to keep the plywood skin from saging in between the wing
ribs). Has anyone used Balsa wood to accomplish this to save on
weight. There seems to be alot of little areas like this in my plans.
Lou