Continuing our assembly of the rear fuselage of a ProCub.
Start by gluing the three horizontal incidence wedgies together. Do not exceed a glue zone of 3″.
In order to install the longerons, a channel must be made in each corner of the fuselage. Using a router and a 1/2″ square end ball bearing bit, route a 1/2″ channel (square channel) down each of the four sides of the fuselage. The router does not (and should not) go all the way to the end of the foam; the channel should just be long enough to accept the carbon fiber 1/2″ round longerons. You will be routing through the 12mm plywood hard points.
Lightly sand all four carbon fiber longerons. 220 grit sandpaper is appropriate. Prepare and mix foam compatible laminating epoxy (for instance, West Systems or AeroMarine) and paint it into the longeron notch.
Do this for all four longerons. We then used two straps, firmly attached around the front and the rear of the fuselage, to ensure that the longerons would not lift away from their placement in the notch. (Not shown.)
A day later, the straps and tape are removed, and 3M 2216 flexible epoxy with stiffening flox is used to fill the gaps. We only put the 2216 for 18″ at each end of the longerons.
Masking tape is excellent for ensuring that the 2216 epoxy does not drip.
The horizontal stabilizer incidence wedgies may now be glued to the top of the rear fuselage. Use pins and wieghts; carefully spread the wedgies so that each side is flush with the fuselage. Use gorilla glue.
Remove the pins and weight; sand each side flush with the fuselage. Use lightweight spackling to fill the gaps.
If you’ve already built your horizontal stabilizer, this would be an excellent time for a test fit.
To be continued.