I’m working on my own design I call the Viper. This version is the A/B model for a K&B 3.25/3.5 motors. I’ve got a Webra 28/32 combo that will go on a slightly larger version.
Basics are a simple geodetic wing and stab for strength, elliptical shape for best glide, rolled balsa or CF tube fuselage (depending on model size) for light weight and killer looks. Polyspan/Dye/Tissue covering, Klass Kote/K&B Epoxy finish on fuse for durability. The stab is ready for decoration at 45g. The fuse has the firewall on, 2 layers of 3/4oz glass and epoxy. The nose is filled with spray foam for stiffness. The fuse is spiral wrapped with carbon tow again for strength and stiffness. It’s light and strong. One thing about using tubes. No tube is perfectly straight…even carbon tubes you buy. It’s not usually very much but there is always a little. I let the tube roll on a counter and see where it stops. Where it stops, the bow in the tube is on top. I mark that with a pen and work from there. The bow can be accounted for as long as it’s on the top or bottom. Don’t set the boom up with the bow on the left or right unless you like continued trimming of the model.
One way to keep weight down but strength is using balsa spars with carbon glued to them. Instead of 1/8×1/4″ spruce, use balsa with .005-.007 carbon glued to it. You’ll need to account for the carbon in the rib slots but I use laser cut ribs from Bob Holman.