Here's the latest iteration of my Rayzor combat trainer: 1/8" thk. sheet balsa wing for easy/speedy build, 1/8x1/2 hardwood spar for strength (and BC mount), 30" span, 142 sq. in., about 6 oz. RTF.

First pic, finished product except for top-mounted controls.

2nd pic, center section showing tapering MM hardwood.

3rd pic, 1/32" ply. fuselage top piece (extends over stab joint at rear).

4th pic, under side MM area, to be trimmed to ply. outline, 1/8" balsa filler where needed; then fuselage lower piece can be glued on, sandwiching the whole mess to make a very strong MM.

5th pic, LO guide at tip (similar piece at opp. tip without holes), tying wing pieces and spar together.

Convertible to radial mount by sawing off the front end behind engine cutout, and gluing 1/2" balsa pieces top and bottom to attach 1/8" ply. firewall to.  Pin everything with 1/8" dowels.  Pretty much indestructible.

 6th pic, I use a 3" BC with very short pushrod arm to slow the controls down

7th pic, ready for paint.

Thanks...I've been producing variations of this design for a few years.  It flies quite well for a flat wing.