Wing half assembly is similar to assembling a chuck glider apart for the necessity of using a dihedral brace. This is needed because the very stiff panels will concentrate landing shocks at the dihedral joints and a simple butt joint is not strong enough to take this. Unlike conventional structures there's no 'give' on impact and so the panel joints need to be as close in strength to the panels - the idea is that the combined D-box/spar assembly doesn't break. Forget using knock-off tips: they are obsolete.
Make 1.5 mm ply dihedral braces that fit inside the spars and extend about 25 mm into each panel. Vacuum 83 gsm carbon cloth onto each side of them. I've already added the tip block during assembly; in fact the carbon TE extends to its outer edge for extra strength. All that is now required is to prepare the panels for assembly and join them.
Mating panel ends are sanded to the correct dihedral angle using jigs. The ends of the spars are hollowed out carefully; a small cylindrical cutter on a Dremel or Minicraft drill running at minimum speed works OK. The dihedral brace should be a snug fit between the upper and lower flanges; sand it until this is true. Assemble the brace into the spars and join the panels in one operation using jigs and 24 hour epoxy.
The joints must now be reinforced on the outside because the two D-boxes and the trailing edges are not yet bonded together. I use a single layer of 83 gsm carbon cloth put on with SP 113 laminating epoxy to join the D-boxes. It is a strip of 45 degree bias cut carbon about 50 mm wide. A 30 mm length of carbon tow is placed on each surface of the TE. I hold all this in place by wrapping the wing in a 100 mm wide strip of release film, starting by taping it to the underside of the dihedral rib and joining the ends with double sided tape. I tape the outside edges of the film to the D-box and TE and then use a heat gun to tighten the film. You get a few epoxy filled wrinkles on the surface but the result sands smooth quite easily.
Alternatively, you can use 100 gsm glass cloth to reinforce the dihedral joint, though the result will not be as strong as carbon reinforcement.
Be very careful when smoothing off the reinforcement. I like to use a Dremel with a 6mm cutting drum for this. Use lots of revs and a very light touch. You'll find that you can quite easily see when you have removed excess epoxy and exposed the surface of the D-box. Be very careful and don't rush this operation; its depressingly easy to cut through the D-box leading edge if you rush at it. This is also a very noisy operation due to the D-box acting like a sounding board, so you may want to wear ear defenders. You'll also generate a lot of carbon dust, so run that extractor fan and wear a mask.
The wing structure is finished by installing a complete 0.8 mm ply rib with a single layer of 83 gsm carbon cloth applied under vacuum as the exterior surface of the root rib.
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