P/L?
I have a Cap 232 that I scaled from an average of several Sarpoulis designs -- 25" span, 125 square inch area, about 7.5 ounces (after many repairs).
It is way too big and way too heavy for the Cox reed valve engines I have, at least if you want to do anything but go in a circle (good trainer, though). I'm currently building something much smaller (~95 squares, maybe 5 ounce max) just so it'll loop!
Consider that when you're building. I don't know, but I suspect my biggest problem is weight -- 7.5 ounces is pretty porky.