Here’s my latest, a 24″ flying wing which I built with a new (to me) method. 
I picked an airfoil and then cut 1/4″ off the outside – the approximate thickness of Dollar Tree foam sans paper. I cut out 10 of these airfoil shapes in different sizes, then glued them to a sheet of foam which would become the bottom of the wing. I glued another sheet of foam over the top of them to complete the shape of the airfoil. 
If that description is none too clear, here’s a photo where you can see the airfoil ‘ribs’ inside of the hollow wing.
The airfoil shape extends all the way to the trailing edge of the elevons. (Usually, I use flat elevons made from a sheet of balsa.) It was very tail heavy in testing, and I wound up moving the motor forward several inches to balance things.
Here’s the finished product:
AUW: 193 grams / 6.8 ounces
- KEDA 0.9oz 3000kV outrunner from StrongRC
- 12A Turnigy Plush ESC
- 5030 propeller
- 850mAh 2-cell LiPos
- (2x) HXT500 6 gram servos
- OrangeRX R615 receiver