Tail Kit

Tonight I primed the top and top side skins. I started in the afternoon cleaning and etching, then came back into the garage in the evening to paint. I used a new paint nozzle on my gun, and it made a big difference in quality. I’ve been using the original nozzle since I started about a year ago, and it was past due for a replacement. The combination of high air flow and new nozzle made a huge improvement over my initial attempts at priming. I finally feel like I am getting the hang of painting with the spray gun.

I heard back from Vans this week about the cracked dimples. I was anticipating installing a doubler plate, but their advice was to upsize the holes and install oops-rivets (rivets with a -4 shank and a -3 machine head). I didn’t think upsizing the hole would remove the cracks, but I did it anyway. On one hole the crack was removed, and on the other it was better but still not completely eliminated. I carefully inspected and filed down the dimple slightly to remove the remains of the crack, and plan to install oops rivets tomorrow. I took pictures and emailed to Vans and Jason for a second and third opinion.

I also heard back from Vans on the spar deburring question. Here is their response

Just a quick follow up, Engineering has just given me a written response to your initial question about deburring (or lack thereof) on your wing spar.

Van’s Engineering Response;regarding an RV-14 W-00006C Spar doubler (waffle) plate’s un-deburred edges.

There are considerably higher stress concentrations elsewhere in the spar than along the edges of the spar doubler (waffle plate), e.g. the spar to center section attach holes and the notch in the spar web where the flange terminates. Early version waffle plates were not deburred and were deemed acceptable. Spars were static-tested to 150% of Limit Load (aka Ultimate). Experience has shown that static tests exceeding ultimate loads tend to produce shape failures at locations removed from the main spar. As part of the annual condition inspection, it is required to examine the connection between the wing spar and center section. This would reveal any evidence of fatigue cracking at these higher stress concentrations. Therefore, the un-deburred waffle plate edges are not critical.

Last night, and again tonight I spent time deburring the top side skins. I finished deburring these skins, and these are now ready to be primed. My goal is to prime them this weekend, so they are ready to go when I need them in the near future.

At this point I have a number of tasks to complete. I need to fix my cracked dimples, finish up my wiring runs (install a couple of zip ties), install the aft deck, then install the top skins, finishing the aft fuse. Then I need to start working through the QB sections, checking that all steps were completed.

Jason came over for a visit today and reviewed my work on the aft fuse. We talked about some of the wiring runs and some of the more challenging rivets. His comment in the write up of “very high quality” was really encouraging. We also looked over the QB wings and fuse and he gave me some great advice while also pointing out some issues. There is a lack of deburring on the wing spar “waffles”, which I emailed Vans about. Also a couple of scratches and notches that I’ll need to debur.

Later in the day, I went to work riveting a few rivets that I had found to be difficult on the aft fuse, and had left until after I had talked to Jason. These rivets were instructed by the j-channel, and when I set them using the foot of my I long bar, the rivets had a tendency to cleave over. Jason offered a couple of simple suggestions, including taping my other bucking bar to increase mass and center the rivet along the center of mass. This worked great!

Unfortunately I ended up cracking dimples on two rivets, when I stupidly set the rivet while it was not completely square with the holes. For some reason, a alignment issue caused the rivets to not sit squarely in the hole, and instead of investigating and perhaps reeming the hole, I set the rivet. This caused the rivet to transfer stress to the bulkhead flange and crack the edge of the dimple. Really stupidly, I did it twice, on different bulkheads. I didn’t detect the first one until after setting the second rivet. I emailed Vans asking for advice, and went to bed feeling frustrated.

There are a few holes on the aft deck components that need to be match drilled, as they are fabricated by the builder. Today I clecoed and clamped together these parts and drilled the 5 holes.

Today I primed the aft deck components and some of the top skin reinforcing parts. I used 50 grams of part A, and it was just enough to get a coating I was happy with.

Tonight I spent an hour deburring some of the remaining parts for the aft fuselage. Not much to go now, just some aft deck components, and top skin parts with associated stiffeners.

Tonight I riveted on the two aft angle stiffeners, one on each side, below the inspection cover. This was easy, except for the bottom most rivet on each side. No matter what I tried, I struggled to get a bucking bar on the rivet. It worked out ok on one side, and was a mess on the other. Unfortunately, access to the bottom most rivet is almost impossible, so I have not attempted to replace it, for fear of making the situation worse. I’ll review it with my tech counselor when he comes (hopefully soon).

Inside view of right hand stiffener

Today I completed a couple of steps on the aft fuse by attaching the rudder stops and about 30 nut plates.

The rudder stops turned out to be easier than I thought. I was able to start by squeezing the aft two rivets easily, and then bucking the forward two without much trouble. I did the right aft side, then the left aft side, then right forward side, then left. Both came out fine.

Then I dimpled a set of nutplates and started riveting them on. I dimpled 4 nut plates that I shouldn’t have, as I found an error in the drawings. The diagram called out for 9 dimpled nutplates and 5 un-dimpled on each side. But it should have been 7 dimpled and 7 in-dimpled, as there are 7 that sit flush with the longerons. I have a ton of these things, so it didn’t matter at this stage.

I started with all the un-dimpled nutplates, which was quick and easy. Unfortunately I had to drill out a rivet when I inserted it without checking that it was passing through the nutplate. It wasn’t, so I drilled and redid that one.

When I moved onto the dimpled nutplates, I realized I hadn’t held the nutplates steady enough when dimpling. As a result, many of them were slightly bow shaped. This was problematic, as they wouldn’t sit flush against the holes, and had a tendency to break when the second rivet was set. It took me a few nutplates to realize what was going on, and then I drilled out several, dimpled new nutplates (this time holding them level when dimpling), and then re-riveted them on.

The end result was ok. Some of my rivets didn’t set as well as I wanted, but these are not structural, and plenty strong enough to support the screws they will be holding. my main concern was making sure they were straight, aligned with the hole, and not likely to snap off.

This is a compilation of several sessions over the last week. I worked each of the last 5 evenings back riveting the rows of rivets connecting the side and bottom skins, and the bottom most rivets between the side skins and forward two bulkheads.

I decided to back-rivet in part because it gives a better finish, but also because these rivets are impossible to do solo any other way. In theory, back-riveting is easy; lay the part flat on a slab of steel with a rivet inserted in the hole, then put the rivet gun on the shop head and set it. These rivets were tricky because of the curvature of the skin. By using cushions and pillows, and small lengths of timber, I was able to roll the fuselage on it’s side to get the correct angle.

I started with the forward right side and worked aft. I was fairly successful just guessing the angle by closely inspecting where the rivet head appeared to be contacting the plate. Once I had it set up, I could quickly set around 10 rivets before needing to move the plate and re-calibrate.

Everything went well, until I got to the aft most section. I was most concerned about the aft-most rivet, which passes through three parts; the side skin, the aft bottom skin, and a bulkhead flange. By putting a little weight on the fuse, and keeping the angle shallow, I ended up with a great result. But as I worked forward, I didn’t roll the fuse enough and ended up setting 8 rivets with too shallow of an angle. Part of the rivet head on these rivets protruded from the skin, and needed to be replaced.

I spent an evening removing these 8 rivets, most came out easy but two of them gave me trouble.

I didn’t enlarge any holes, so I redid these eight the next night with the same size 3-3.5 rivets. This time, I went slowly and used my iPhone’s digital level to record the angles. 10 degrees of roll for the bottom/side skins worked great, and about 26 degrees for the next holes up on the bulkheads seemed about right.

Eventually the right hand side came out looking great. Then it was on to the left hand side.

After some experimenting, I found that the angle at which the gun contacts the rivet head is critical for getting a good looking head. Any slight angle, and the heads don’t set straight. A had a few rivets that weren’t quite level on the shop head, but I left them in and moved on. For the most part though, the heads looked great.

I had no trouble with the left hand side, I just used the digital level to ensure I was getting as close to 10 degrees as possible, and 26 on the couple of bulkhead rivets. I worked from the aft end forward, and was done in about 45 minutes. Most of the time was spent adjusting the angle of the fuselage, and checking that the hull was flat against the back riveting plate.