Hey Brett....are you saying fill the belly pan with balsa or to add balsa to the wing on the inside? Having a bit of trouble picturing this.
Thankee a bunch.
Shug
Neither, or at least that's not what we did. When you put the belly pan in place, there is a joint between it and the former (F2) right in front of the wing. That joint is a severe weak point, and in some cases there is a gap. Face off the front of the belly pan until you get to clean bare wood all the way across. Same with F2. Reassemble, and there will be a gap from where the material is missing. Put everything in place, make the gap even with a perma-grit file or something. Then cut a slice of end-grain balsa to perfectly fit the gap. Then when ready to assemble, glue it in with lots of epoxy (since your 3/32 or 1/8 end grain spacer will have pores that go all the way through, and you need to fill them up).
Same at the *rear* end of the belly pan, of course. Try not to twist the rear of the fuselage as you assemble the belly pan, but for sure don't install the tail until the rest of it is assembled completely and the glue is cured everywhere else. That way you can shave the stab platform to make sure it is parallel to the wing in all three dimensions. Nothing is more important. Even 1/32 of skew in the tail, for instance, might make it completely untrimmable. That's the same with any airplane.
Of course, clean off all the monokote from the joining surfaces wing and fuselage, both on the belly pan and the rest of the fuselage, until you get clean bare wood all the way across the joints. If you have to shim it to fix any gaps, do so, with hard balsa - I would put the grain running spanwise and glue the shims to the wing (which you should also clean of any covering or stray glue to get to *bare wood*).
If you are a real stickler, it wouldn't be a bad idea to, once it is assembled, inlay a series of 3/16" square x 2" spruce pieces right across the joint, or strip the covering and fiberglass it.
I saw from some other thread that you plan on a Magnum 52, which should not be a bad shaker, so this is possibly overkill. On the other hand, a very critical part of the original "Big Jim" approach to getting engines to run was building the fuselage, particularly the nose, very rigid. When it was made an ARF, putting a butt joint right at the front of the wing, a fair fraction of which had monokote as the mating surface, did not continue that plan. There was probably no other way to do it with the wing in one piece and having to fit in the box for shipping, but right where the nose meets the very rigid wing LE is where all the stress concentrates.
Brett
p.s. I note that yours seems to have monokote completely covering the wing/fuselage joint on both sides. Removing it from the fuse should be pretty easy, just peel it up. Be VERY CAREFUL, however, removing it from the wing. The temptation will be to take a ruler and a sharp #11 blade and slice off a 1/4" strip. But don't do that because it will be nearly impossible to manage that without cutting into the center section sheeting - again, the very worse place to leave a weak spot. To remove it hold a razor blade flat against the surface with the edge where you want the cut to be, then lift the covering up with the corner of an exacto knife and pull it against the razor blade edge. It won't be all that even because you will have to go in 1" segments, but at least you won't cut into the wood. An alternative is to use a soldering iron or woodburning tool to melt a line in the covering, but again, that risks scoring the balsa sheeting underneath.
You must remove the covering from the joining surfaces because the covering and the covering adhesive makes for a very poor joint.
Also, before you mix any glue check that the "key" that keys the wing to the fuse is straight. Many people have had Vectors with that key misaligned, and if you don't do something, the wing will be skewed with respect to the fuselage. Trim as necessary, again, being very careful to again not cut into the center section sheeting.
It wouldn't hurt anything to glob on some Epoxolite on the ends of the motor mounts when assembling, to make sure the motor mounts are firmly glued to the top of the "key".
p.p.s. I don't recall there being a hole at the rear end of the tank compartment on the one I worked on. I would fuel proof the tank compartment, and then close that hole off so fuel cannot get into the rest of the fuselage.