Setting rivnuts in the center fuselage (CF) area had been on the TODO list for a long time, but it took until now for me to summon up the nerve to actually do the deed. It turned out to be rather easy. I was in the right frame of mind and it all went very well.
A few of the rivnuts are in locations where I couldn’t use my drill-mounted (Astro ADN14) setting tool – particularly one of the M4’s for the A/P bracket nearest the main spar, and two M5’s that will serve to anchor the rudder return springs to the rear spar carry-through member. Fortunately, I’d acquired a nice hand tool (Astro 1443B) and it worked brilliantly for those. Concern about these rivets were what kept me dragging my feet until I’d worked up my courage to attempt the work.
Each of the holes where a rivnut goes, were enlarged to the proper size. This takes several steps, but it’s the same process I’ve used elsewhere. In places where I can’t see the back side of the mounted rivut, I use a mirror to inspect the crimp. They all looked great.
Various panels and covers in the CF that need to be removable, now have their mountings in place.
Practice makes perfect they say. Well, maybe not perfect. But the going seems a little easier when you’ve been there before. So it was for mounting the second fuel tank. It actually fit slightly better than the other one. I knew what to do, and on it went without issue.
I did the same basic steps as I did for the first tank. I felt confident, and the work went quickly. I had to carefully dress a number of the overlapping holes in the tank and spar with the #20 chucking reamer in the lithium drill. I knew what to expect and there were no surprises. I also had to touch the holes in spar web to align with the outermost Z-bracket so I could get the AN3 bolts through and threaded into the anchor nuts. Once again, I used a length of cord to pull on the Z-bracket while the tank was being fitted for the final time. That worked like a charm.
There are several stainless steel rivets, top and bottom of the spar near the root. Those are treated with fuel tank sealant for corrosion protection. The rest of the rivets are aluminum multi-grip. Riveting goes pretty fast when the pieces are fitted in place.
Having both fuel tanks mounted is a big milestone and yielded a rather wonderful sense of satisfaction that was sweetened with a measure of relief. Success! Good result. Yay!
The M4 rivnuts for the inspection panels went in without a hitch. I had to enlarge the holes in the bottom wing skin to #A – the perfect size (I’ve found) to accept the rivnut prior to setting them with the drill-mounted tool I use. Screw holes in each of the cover panels had to be enlarged for close clearance of M4 stainless steel button-head hex screws.
Compared to mounting a fuel tank, enlarging holes and setting M4 rivnuts seemed easy and definitely less stressful. Still, it was no time to be careless. The wing skin is easy to damage.
It took several steps to get the factory punched holes enlarged to letter number #A diameter, a perfect size to accept M4 rivnuts. I double checked my references and reviewed the process I would use. A series of increasingly larger straight-flute chucking reamers in my trusty lithium-powered drill did the trick.
All of the holes in the wing skin and the inspection covers were in the correct places and the alignments matched perfectly. The drill mounted rivet setting tool worked flawlessly. All rivets are consistent and tight. The screw clearance holes in the covers are ideal. Everything is fits together nicely.
I’ve finally gotten to the point of acomplishing the very first step on page VS1 in the Empennage Construction Manual! I’d been worrying about it. Getting the rivnuts securely mounted calls for a rather deliberate process with good technique. It all went very well. What a relief.
Having an effective tool – Astro Pneumatic Tool ADN14 Rivet Nut Drill Adapter Kit – and practice made the day. I’ve seen a couple of other builders recommend this particular tool. Because it relies on a cordless drill motor and identification of an appropriate torque (clutch) setting, I felt there would be a good chance of getting consistently good results. This seems to be the case.
Practice! I got an assortment of metric rivnuts and used the tool to work with them until I knew exactly what to expect. Now I have 14 perfectly mounted rivnuts!
BTW – the KAI mentions using high strength Loctite to insure that the mounted rivnuts don’t slip in their holes. I say – learn how to mount them firmly and they won’t slip. No Loctite is needed. Because IMO – if they’re not tight enough to stay put, then they’re not satisfactorily mounted.