Rudder skin dimpling
I didn't like how the DRDT2 recommended building the side tables, so I decided to concoct something else. I ended up using the wood from the empennage crate (it was a pain to get all the staples out, but almost all of the wood has been useable for something involved in the build). I drilled a hole where the bottom dimple die goes, and cut slots in the legs for the frame to go through. It's sturdy and seems to do the job.
I had to experiment a bit with whether to have the female dimple die on the top or bottom. If it's on the top, the sheet slides nicely on the table surface as the dimples are facing upwards, but it's easy to get it scratched up if you're not careful with the male die on the bottom. Instead, I chose to have the female die on the bottom so I didn't have to worry about constantly lifting the sheet, but it does chew into the wood a bit and creates some sawdust.
Got the lead counterbalance installed in the rudder. Not sure if I'm just being paranoid but I'm totally not touching that with my bare hands!
I've heard of people using ProSeal to fix the nuts on the interior of the counterbalance since there's no access once everything is riveted together. I actually don't have any ProSeal yet, so used Loctite instead before torquing the bolts down. Fingers crossed they don't back out or that's going to be a mess to fix.
For the trailing edge, I made sure that everything was perfectly straight when getting everything cleco'd together, and indeed it was almost perfect as-is.
My perhaps less-than-brilliant scheme to keep it that way was to use a steel square beam I found at the hardware store as a backrivet plate, which was also perfectly straight when I bought it.
I used a standard flush rivet set on the front face. It turns out the force of backriveting just knocks giant dents into the steel, and leaves the trailing edge with a small indent and a bad rivet that needs to be drilled out. So much for that idea.
Instead, I used some extra aluminum wedge-stock that was used for the trailing edge as a backing plate such that I had 2 parallel faces to use the squeezer. The aluminum stock definitely took some damage and the manufactured heads ended up slightly rounded, but at least the rivets were consistent and cleanly fastened. I alternated sides between rivets, which is what everyone seems to do for aesthetics, but honestly I think it would be more consistent to have all the shop heads on the same side. The resulting trailing edge wasn't quite as perfectly straight as I hoped, but at least there's no warp in it. I'll attempt to use a tool to get out the wavy sections at some point and hopefully straighten it out some more.
One thing that I forgot to do was to rivet the flanges on the outside rib before closing up the trailing edge. This left me with basically zero room to get any kind of bucking bar in there. In fact, it was so narrow that the rivet couldn't even be fully inserted without hitting the shop head of the rivet on the other side. I purchased some steel chisels from the hardware store that were angled enough to slip it behind the rivet to serve as a makeshift bucking bar, and it shouldn't be a surprise that it didn't really work. This ended up with a cracked rivet. I'm currently leaving it as-is, because I don't think I can do any better at bucking that rivet. I may drill it out and use a flush blind rivet instead, however, which is what I should have done in the first place.
In the mean time, I'm a few rivets shy near the corners by the horn where I need to find a specialized bucking bar with a toe, but otherwise I think the rudder is complete. On to finishing the horizontal stabilizer!
While in principle the horizontal stabilizer build should be pretty straight forward, I definitely made several aspects of it way more difficult than it needed to be. First was in countersinking the spar flanges. Supposedly the stops on most countersink cages are .001", and convention is to drill until the rivet sits flush, then stop in .007" further to accept a dimple. Supposedly a 112-degree countersink bit is ideal, but everyone seems to only have the standard 100-degree bit. Nevertheless, it felt like I had to countersink far deeper than that to get an acceptable flush mating between the skin and the spar and I still don't have a great explanation why.
After dimpling the skins, riveting in the rib tips, and attaching the front spar I notice this...
Yep, I riveted in the spar with 36 missing rivets on the spar caps that are now inaccessible from the back side. Bah! I decided I wasn't willing to drill out all the flange rivets, and contacted Van's support to get some options. They said putting Cherry Max rivets would be just as strong, and an easy fix right? I purchase CR3213-4-5 rivets to replace the AN470AD-5 that should have been in there and installed them with a little bit of flexing of the inspar ribs and some chewed up knuckles from scraping against the dimples while operating the rivet puller. Afterwards, while riveting the remaining flange rivets I notice the Cherry Max rivets were starting to back out. I went to the Cherry specifications, and it turns out the grip size on the 4-5 rivets are way too large and they weren't remotely fastened from the backside. Aaargh again. Now the challenge of drilling them out. My first attempt was to drill it out like any other rivet, so I got a 12" long #30 bit and tried to center it as much as possible. It turns out this is extremely difficult, as the Cherry rivets have a steel center section where the mandril goes through, and it's really quite hard. I dulled my bit rather quickly, and just made a mess of the rivet. My next attempt was to use a small high speed cutter bit on a Dremel to grind off the head. This was working okay, but due to the really tight working space it was difficult to navigate in there and get any precision. Needless to say the tool slipped, and I made a nice nick in the spar:
I contacted Van's support again, and this is the first time they didn't have a clear answer for me. It's "probably okay" they said, but it's in a grey area of not being able to guarantee the impact on the spar's strength. I tried my best to measure the depth of the nick, and I think it's under 10% the thickness.. so I decided to scotchbrite the sharp corners off and continue. Furthermore, it's about midway from the center near where they cut out the lightening holes in the spar. Fingers crossed it doesn't become an issue.
Now back to the issue of drilling out the Cherry rivets. As usual, and found some inspiration from the VAF forums, which suggested to punch out the mandril first. I went out to Harbor Freight and purchased some cheap punches I didn't care about destroying, and a tiny hammer, and attempted to hammer out the mandrils from the center. Needless to say, they're pretty stuck in there. I'll repeat what many have already said.. but these Cherry rivets are definitely robust. What ended up working pretty well is attaching the punch to a flush rivet set using some heavy tape, and punching out the mandril (plus the steel sheath) using the rivet gun. This actually worked fairly brilliantly. Afterwards, there's just a bare aluminum rivet with a nice hole in the middle that can be drilled out with a #40 bit no problem.
I purchased the correct Cherry Max rivets (always check the grip size before ordering them!) and got them installed. Phew!
Next hiccup was when riveting the skins to the flanges, I noticed I somehow missed dimpling about a dozen of the holes. There are so many rivets already fastened that I can't imagine taking it apart, so now I'm trying to improvise how to get it dimpled with the rivet gun. I've heard of people doing it.. so I improvised an attachment to the gun that would accept the male die, and placed the female end into a piece of wood backed by a bucking bar.
This indeed made a dimple, but it's a little bit too shallow - and there's a noticeable indent in the skin that's distinct from the nice flush appearance from the DRDT2 dimples. Once riveted, the rivet protrudes out ever so slightly due to the shallow dimple. It's just cosmetic.. but it totally bothers me.
Everything else went fairly according to plan. Riveting the interior rivets is definitely a challenge and any slip-up will earn you a nice smiley shaped dent in the skin that will infuriate any detail-oriented person. I purchased one of those rubber cupped swivel rivet sets, but noticed that they can easily leave the manufactured head raised up from the skin due to the stiff rubber cup. Instead, I decided on using the standard rigid mushroom set that makes much more solid contact but seems to have almost no tolerance for error. I think I ended up having the gun bounce on two rivets leaving a small smiley on each one, which resulted in much cursing and swearing.
One of them was rather bad, so I made some attempts at hammering it out. The smiley is largely gone, but the area is noticeably rougher now. Hopefully it will be less noticeable when painted.
Last step was to attach the rear spar, and all the edge rivets could be squeezed which is super easy compared to riveting with the gun. I'll elect to use the squeezer any time it will fit. Now on to the elevator!
The elevator is a surprisingly long section, so I tried to pull out all the components and get them prepped and primed first. What a pain in the butt this is between cleaning, degreasing, scuffing, priming, and all the resulting cleanup of the HVLP gun. It probably took me a half day for one table of parts.
For my last attempt at priming, I took the advice of only putting on enough paint to just notice a change in coloration (I'm using SW-P60G2). In the end, I think it was much too thin. This time I put it on much heavier, and I think they came out much better. At least it's a noticeable green, as opposed to the barely tinged silver from before. I also reduced slightly less than 200% to about 175%.
It was inevitable that I missed a part, however, and it had to be a big one like the trim tab spar. Oh well, I guess I'll collect all the tailcone parts soon and try to prime the whole lot next.
Everything seemed to be going fairly swimmingly until I got to match drilling the closeout tab on the skins near the trim tab. There's about a 1/4" gap from where the shear clip is and where the skin closeout should be. Doh! Not sure how to compensate for this one, so awaiting some feedback from Van's again.
Refolding closeout tab
To deal with my previously botched fold on the closeout tab on the elevator here, I got a response from Van's that suggested to fabricate a new closeout tab from the same type and thickness of material. After putting some thought into this, I couldn't figure out a way to cleanly fabricate one and get it attached flush with the existing tab. Instead, I decided to try and hammer out the existing fold, and refold the tab in the correct position. If it failed miserably, I would just purchase a new skin from the factory.
I used a backriveting plate and a flush rivet set to hammer out the crease of the previous fold, then used the edge of the same backriveting plate to make a new fold. It actually turned out a little better than I was expecting, albeit my expectations were fairly low. There's still a noticeable blemish between the two creases, but I think I'll actually keep it and hope it gets hidden by the paint.