I have flown and designed several wings and unless you are trying for something special, there's not too much to wing design. Basically, you balance at 10%-15% and kick the ailerons up to give you some reflex unless you have a special reflex airfoil like the Evans wings. Do this and it'll fly.

I notice the SPAD reference in your post. I was flying .46 powered Coroplast planes a few years ago and decided to make a flying wing. I took a plane I was flying and cut the fuselage off just in front of the stab. I made twin fins from scrap Coroplast and screwed them on. I yanked out the rudder and elevator servos and plugged the dual aileron servos into aileron and elevator. I set my JR 8103 to elevons, cranked in about 3/16 up elevon, cranked the engine and hand launched. It flew right off the board.

It was slightly nose heavy so I ended up moving the battery back between the fins. I never could get it to snap or spin. Basically, it was a dull, stable plastic airplane design. Not nearly as much fun as the original Coroplane.

I have attached some photos. The notch in the fin was in the scrap. (People ask) I did later paint it, but that didn't make the flying any better.

The bottom line is just about anything will fly tailless. Balance it nose heavy and kick up the ailerons.