The tapered wings mentioned in the spiroid posts lends itself perfectly to blended winglets. http://www.airportjournals.com/Photos/0212/X/0212004_2.jpg
The lack of sharp corners and thin tapered wings reduces both induced and parasitic drag. This plane stays up.
First flight test: I was able to fly figure-eights and have the plane return to my hand. “Wow! Good job!” from a passerby. Launches into the wind gain about twenty to thirty feet of altitude; the plane holds the wind well, flies steady and straight into the wind and flies very fast downwind. Plane recovers nicely from building hits. Dihedral should be a little more than in the picture above.
I’ve tried two versions of the blended winglet: taper in front and taper in back, and the taper in back, straight-up front flies better.