Hi David,

Ahh, vintage Cox engines, my favorites!

Dr. Drela seems to have a handle on glider stuff for sure. Is your wing D-tubed with film covering or fully sheeted? Seems like some of his airfoils take the covering sag characteristics into consideration.

Martin Hepperle's site talks about built up wing airfoils as well.
http://www.mh-aerotools.de/airfoils/index.htm

ps: Martin's site also has the best online Cox museum around too!