cwatters,
The RC models I referred to above are called "fun fly models" here in the U.S. They usually have an AR of 2.5 to 3 with rectangular wings. The deltas you mentioned would be extreme low aspect ratio (below 2) with quite different performance and possibly more inclined to tip stall than a rectangular wing.
This aspect ratio 3 seems to provide for extreme slow flight, lift off in one fuselage length and extreme maneuvering as you mentioned when fitted with large control surfaces. For a full size, the large controls would not be desired as it will not be designed for aerobatics.
But the rigid light structure is desired. Of course, with less power the climb would not be spectacular, but the stable slow flight is my primary interest. The models have thick cantilever wings and I would do the same. Most full size ultralights look something like your drawing with struts and wires everywhere. A thick cantilever wing is simpler to build and less drag. Thats why RC models are built with cantilever almost always.
Genghis,
I think the main consideration with scale is reynolds number. In that respect a low aspect ratio with wide chord wings has a favorable higher reynolds number. So what works for RC models should work well in full scale also, I think. If anyone has comments about why we don't see more aircraft of AR 2.2 to 3, please advise.
slowrotor