Paul Kierstead writes:
Ahhh...I am just old enough that I only know of tissue covered balsa
wood planes; didn't know ppl were fabricating their own foam ones, but
of course it makes perfect sense.

It depends on the plane. WHen I was doing it, foam cores and carbon
fiber spars were used for gliders and covered spar-n-rib was used for
powered and/or high performance planes.

Also old enough to have used djgcc a fair bit; many many thanks for
rescuing me from the perils of the crap commercial compliers of the
day (not that things are so much better today).

Well, djgpp is much better today :-)