Well, this isn’t the most pleasant post to write, but it’s the way things are. Upon reviewing the work I’ve done so far on this service bulletin, the long and short of things is that I’ve ruined some parts and I’ll be substantially rebuilding the horizontal stab.

I mentioned in the last post that I’d had a few holes that got enlarged in the spar web, due to using a dull bit in the angle drill. At that time, I figured I could just replace those with 5/32” rivets and be fine. But I took a closer look at those holes tonight, and while two of them that are oversize can be safely opened up, the other two are far too large. I thought briefly of asking Van’s support about the possibility of doing another doubler repair here, but some reading on VAF reveals other builders who have gotten some very direct guidance on this topic, and that guidance is that any hole that can’t be fixed by opening up to #20 calls for replacement of the spar. Since I damaged both spars, I’ll be replacing both of them.

There are also some edge distance and hole spacing issues with the doublers I drilled, but that’s kind of beside the point right now, as the doublers will need to be re-drilled with the new spars anyway. While I’m at it, I’m also going to replace both reinforcing angles and all four of the inboard ribs. This is basically all fo the inboard/center structure in the stab. It’s possible that the ribs could be salvaged, but at this point I figure I might as well go all-in on using post-SB parts.

At the moment, my plan is to hold off on ordering anything until after I’ve done all the disassembly required for this replacement work. This is to allow for the possibility of damaging other parts beyond repair; better to make one parts order instead of two. I thought about going ahead with that disassembly work tonight, but I think it’s better that I take the rest of the night off and let this sink in before jumping into more work.

The good news is that the financial damage isn’t horrible. Replacing the parts listed above will cost about $140. Things only start getting significantly more expensive if I have to replace parts of the rear spar or the skins. I don’t think saving the rear spar will be a problem, but the skins might be a different matter – there are a lot of rivets to drill out carefully. Then again, my fancy new rivet removal tool will hopefully make this go better.

At this point, I think my goal will be to complete disassembly by the end of this weekend, and order the parts early next week. A stretch goal might be to get disassembly done tomorrow night and order the parts Friday, that’d save me a few days waiting, but again, rushing disassembly is likely to just make things worse.

Anyway, that’s it for tonight.

Whew…more fun. Tonight I got the doublers fitted and all the drilling done…and there was quite a bit of it.

As of last night I’d clamped the doublers in place, but not really done anything in terms of positioning them or anything. That was what started tonight – lots of tweaking the position while peering inside the stab body with a flashlight and examining the lines I’d drawn. Once I had them aligned the way I wanted, I decided that in the spirit of “measure twice, cut once,” I’d mark each hole location with a Sharpie and remove the doublers just to make sure the locations were good.

Here’s the result of that – good edge distance all around:

Then it was just a matter of clamping them back in place, carefully aligned, and getting started on the drilling…and as mentioned before, there was a lot of it – 30 holes per doubler, many requiring use of the angle drill at awkward angles. Unfortunately, this didn’t go completely well – it turned out that the first #30 bit I was using had gotten dull, and I didn’t notice immediately. The result was that, for a couple holes that were drilled using the spar web as a guide, the bit ended up wandering a bit and widening the hole in the spar web. These spots will need to be opened up to a larger size and I’ll use a 5/32 diameter rivet in them. The real fun here is that all of these holes are common between the ribs, so I’ll have to open the holes with all the parts in assembly, and limited access. The good news is that there’s plenty of extra material around these holes, so edge distance shouldn’t become an issue when enlarging the hole.

Anyway, here’s the scene after I finally got all the holes drilled – just a solid forest of clecos:

That’s enough for tonight. Next, I get to remove these doublers, see if all the holes ended up looking decent, and do a bunch of deburring. Then it’s on to fabbing up the new angle flanges for the main ribs. Before long it’ll be time to so some really fun tight-quarters riveting!

OK, so I didn’t get the SB done this weekend like I thought I might. Temperatures here have finally been crossing into the 100s this weekend, which definitely is keeping the work sessions short. And today, I spent some time helping a neighbor unload an aircraft he bought, and also went to a flying club safety meeting that ended up running about three hours. So not a lot got done today, but hey, we’ll talk about it anyway.

First up was demurring the doublers. I ended up reinstalling the vise on the workbench for this, it made it a whole lot easier. It’s also necessary to radius one side of the doubler forks, to ensure it can nest properly inside the spar channel.

Next up are adding some markings to help with fitting and drilling the doublers. They already have some prepunched holes, but these are in addition to the holes that already exist in the spars. Those existing holes will be used as guides to add the additional holes in the doublers, and it’s necessary to ensure they have proper edge distance. We start by drawing a horizontal line using the prepunched holes as a guide.

Next, I added my own touch. I watched a Youtube video demonstrating the SB, and the guys doing that handled the edge distance issues by clamping the doublers, marking the holes in the spars, removing the doublers, evaluating edge distance, and then retrying a couple times. It seemed a lot easier to me to simply draw lines around the perimeter of the doubler, which would represent the closest that any hole could be to the edge. This way, when fitting the doublers, I can just ensure that none of the edge distance lines are visible through the rivet holes.

One of the marked doublers:

Next, it was time to fit the doublers. However, there’s another fitment concern here – it’s possible for the doublers to interfere with the vertical stab attachment, which goes right in the middle of that forward spar joint. I was starting to consider how I could mark the area to prevent this, and I realized that there was a much easier approach.

The vertical stab attaches at its forward spar using a spice plate, which is drilled and riveted to the vertical stab spar, and then bolts to the horizontal stab forward spar. The bolt holes already exist in both parts, though they’re currently undersize. But since they’re prepunched, all I had to do was dig up the splice plate and cleco it in place. This also has the benefit of tying the two spar halves together, making the h-stab a bit more stable in its partially-disassembled state:

That was about as far as I got today. I did start fitting the doublers, getting them clamped in place and seeing how much fun it would be to position them properly, but I didn’t get any photos of that. I’ll pick back up on that task probably tomorrow night. For what are probably fairly obvious reasons, it’s really important to get the installation of these doublers right. Badly-placed or subpar holes here definitely have the potential to compromise what is an extremely important structure. So there’s going to be a lot of “measure twice, drill one” going on here.

Whew…it’s a hot weekend in Houston. The rest of the summer has been relatively balmy, with his peaking in the 90s, but this weekend (and for the next several days), we’re sitting up over 100°. I got an early start this morning, but by mid-morning I was already in a state where I’d work for about half an hour, then retire inside to cool off for a while. Still, I made good progress.First up was getting that last reinforcing angle out. That just took some strategic application of force, and eventually it popped right out. An inspection of the rivet holes in the spar web looks good, none of them appear to have gotten oversize or had any damage done around them. Success! Then I just had to drive all those rivet remains out of both angles. No big deal there, just a bit tedious.

Tonight, I’ll start this post a bit differently from usual, with a story of sorts. A couple years ago, I decided to get myself a new tool: a cordless impact driver. My reasoning for this was to facilitate swapping out wheels on my car at track events. Not too long after that driver came in, I had occasion to remove a couple wheels on the car. Right after finishing that job, I think I actually said out loud, “why in the world did I wait so long to get one of these?”

Yeah, I had another one of those moments tonight. Recall that the last time I worked on this SB, last weekend, I spent 3.5 hours painstakingly drilling out 24 rivets, and then worried heavily that those were relatively easy compared to the 16 inside the stab. Well, tonight, over the course of a little over half an hour, I drilled out all 16 of those rivets, using the new tool I got from Cleaveland. I think it’s safe to say, at this point, that this thing was well worth the money.

After popping the heads off all those rivets, I managed to get one of the reinforcement angles out without too much drama, just by hitting the rivet shafts with a center punch. The other angle didn’t want to come out so easily, so I left that for tonight. Probably I just need to work in the rivet shafts there with a punch and hammer, but this was about 10:00 at night, and my neighbor has a newborn…I figure it’s good to try and keep the noise down.

But hey, this is great news – with the exception of getting that other angle knocked loose, I’m now finished with disassembly tasks. After this there’s some trimming of the spar flanges, fitting of the reinforcement doublers, and some modification to the ribs…then it all gets riveted together again. I think there may be a good chance I’m able to get this SB work wrapped up this weekend.

Whew. While I’m making decent progress on getting this SB done, it’s proving to be a real drag, and I can say with conviction that I’ll be happy when it’s done.

First up today was drilling out the rivets common between the inboard stab ribs and the spars. These took…some time. Universal head rivets are already a little tricker to drill out than flush ones, since it’s harder to keep the bit centered on the round head, but adding in the limited access made these a lot more fun. Long story short, pretty much each rivet presented its own unique challenge. But I did get them done, and without any apparent damage.

Next up were the rivets between the spar webs and the reinforcement angles. For these, I had better access…sort of. It was easy to get to the forward side of the spar, but that side had the shop heads, not the manufactured heads which is where you normally do the drilling out.

In the end, I decided to drill these rivets out from the shop head side. My reasoning here is that that’s the side where the angles are, and if I’m going to damage a part and need to replace it, I want it to be the reinforcement angles – which I’m removing anyway – and not the actual spars – which would be a royal pain to replace.

I’m not sure if that was a good idea or not, but so far, I’ve managed to not do any real damage. I did slightly enlarge one hole, and I put some semi-deep scratches on one of the angles, but those should be easily removable. But boy, did it ever take a long time to get all these out. Drilling the shop head means there’s no real way to be sure the drill is centered not he rivet shank, so some serious care is in order.

So, at the end of the day, I had all the rivets in the center of the spar removed, which is good news:

The bad news is that, as much trouble as I had getting these rivets out, they’re still comparatively a cakewalk compared to what’s coming. Now I have the sixteen inboard rivets to deal with, which are inside the stab structure:

I’m really torn about whether to drill these out from the angle side (with the shop heads) or the spar side. Access is far tighter on the angle side, which would kind of multiply the difficulty of drilling out from the shop head side. It’d also make it a lot harder to drive out the rivet shanks after drilling them out. But there’s still that whole point of preferring to damage the angles. I’m seriously considering pausing work on this SB and ordering a rivet removal tool from Cleveland. Using that tool makes it easier to be certain of being centered on the shop head, and also prevents drilling too deep. I’ve looked at this tool in the past, but never felt it was necessary…but adding in the limited access and high stakes here is making me think it might be worth it.

Actually, I might ask around a the neighborhood coffee thing tomorrow morning, maybe someone has one of those already and I can borrow it. I know there are a few people out here with some serious tool collections.

Back at it again! Before I got to actual plane work tonight, I had a goodie box from Aircraft Spruce waiting for me at home. There was only one thing (well, four things) in there I really needed – four longer AN3 bolts to properly assemble the throttle. I also bought a bunch of AN3 nylock nuts and washers, just cause it seemed my supply was a little lower than it ought to be. I’ve been trying to keep separate the nuts I use for temporary assemblies, and only use new ones for final assembly, but I think I’ve been going through more than I need to. Technically nylock nuts shouldn’t really be reused at all, since the nylon locking stuff degrades after a while. And lest anyone think this isn’t serious business – the deadly crash at the Reno Air Races a few years back was traced to a nut that had been reused too many times and lost its ability to stay tight.

Anyway, I’ll put that soapbox away…the last thing in the box was the expensive item I added so I could get free shipping. It’s my heated AoA pitot tube from Dynon, and hoo boy is it shiny and fun to look at:

Not going to need that any time soon really, so it’s now sitting on a shelf. Before getting going on the real work for the night, I took those bolts and reassembled the throttle quadrant to its now-painted mount, then added the cover plate just to see what it looked like. I think this turned out pretty well:

I even laid it in the fuselage to see what it would look like in place. Seems decent to me:

That went on a shelf too – I decided not to actually install it in the fuselage, as specified in the manual. I figure I might as well leave it out until I really need it there.

And then it was on to the real work of the night, getting going on the h-stab service bulletin work. At a high level, the work involves removing the inboard ribs, partially disassembling the forward spar, doing the work to add the reinforcements, and then putting everything back together. Tonight I just worked on drilling out all the rivets between the skin and those four ribs.

There’s been no shortage of rivets I’ve drilled out over the course of this project, but they were always in small numbers, just a few at a time. Here, I was removing them en masse, which opened the door to getting careless. Drilling out rivets is precise work, and it’s a lot harder to keep the precision up when you’re doing it 40 or so times. Nevertheless, I got all the rivets out, and there’s only one hole where I think I may have enlarged it slightly.

The ribs are still in place for now – I also have to drill out the rivets attaching them to the spars. That part is going to be tougher; I won’t have great access to the manufactured heads, so I’ll probably have to use an angle drill for them. And there will still be even harder ones once I get to removing the reinforcement angles from the spar – those project into the stab a bit. That’ll be where I’ll have to be really careful not to damage anything.

But anyway, that was all I got done tonight. Hopefully I can get all this SB work knocked out this weekend, and move on to mounting this thing to the fuselage…

OK, again not a lot got done tonight. What was supposed to be a quick adjustment to the riding mower ended in a stripped bolt and general annoyance, but even though I wanted to go inside and mope, I decided to still do something on the plane. (also, this would not be the end of frustration tonight…more on that later)

While I didn’t log anything as useful work last night, I did spend some time tidying up a workbench, dismounting the vise, and moving away the tool cabinets I usually have beside it – this was all in preparation for bringing the horizontal stab down off the wall. The time to fit it to the fuselage is upon me, but before I do that, there’s a service bulletin to be dealt with. This involves adding some reinforcement to the forward spar of the stab, where cracking has been observed in some aircraft. It’s not required that the repair be done unless cracks are observed, but it seems prudent to me to do it now as preventative maintenance.

Anyway, last night wrapped with me bringing the stab down to the bench, ready for work to start. Tonight I began by removing the elevators – which I’d just been storing installed on the stab. First, I removed the AN4 bolt through the center bearing. This bolt runs through that bearing and each elevate control horn. It’s important to be careful removing this bolt; in the space between each control horn and the center bearing is a handmade spacer, sized carefully to exactly fill the gap and prevent binding of the surfaces. So I carefully removed the bolt, placed the spacers back on it in the correct portion and orientation, and made sure to mark which side of the airplane the bolt head should go to.

Next up are the two outboard pivot bolts for each elevator. Nothing too horrible here, though access to these things is a bit obnoxious. But I got all four off, removed the elevators, and set them aside. OK, now to just put these four AN3 pivot bolt/nut/washer combos with that AN4 assembly I removed earlier…hmmm…uhh, where did that go?

And this is the other frustration of the night. I looked for that stupid bolt/but/washer/spacer assemblly for half an hour, to no avail. I don’t even understand how I could have possibly lost it. At no point between the time I marked it and the time I finished removing the elevators was I outside of about a ten-for circle. There just aren’t that many places I could have physically put it.

But…I never found it. Even after going inside, sitting for a bit, and then going back with a hopefully-clearer mind.

So I guess either it’ll magically turn up, or I’ll get to repeat the exercise of fabricating those spacers. Probably have to order another AN4 bolt, pretty sure it was a unique length that I only had one of. Which is also annoying since I just placed an order with Spruce for some assorted stuff.

Oh well. I guess tomorrow I’ll see if I can get going on actual SB work.