The delta uses KF-m 3 airfoil and it is optimized to fly slow while carrying a payload. It flights for 40 minutes with 2 2200mAh LiPo batteries. A video of the delta flying.
I got a lot of help in the RCGroups forum and now I need to create a thread for this plane. Pictures for the most recent version:
This is an earlier prototype, the one I made before the most recent.
And here I am, holding the previous prototype: