I started riveting the elevators together today. Counterbalance arms first, then the front spars. It’s always good, after all the preparation work, to place together finished and primed parts and have them fit together nicely and without a hitch.
It was a sizzling hot day in Tassie – a good day to put on the bunny suit and prime the elevator parts. It was quite a big job to degrease, etch, spray on EAP-12 and then prime the zillion parts that make up the elevators. Just as I was shooting the primer mid afternoon, half of the motors on the compressor tripped out, so the remaining two were on 100% of the time trying to pump enough really hot air to feed the spray gun and breathing gear. I noticed the change, so after finishing I checked the compressor head temperatures with my finger tip – and promptly got burnt! I switched off the compressor for a few hours and waited until things cooled down before doing the skins.
I had to put off priming the elevators for a few days – didn’t have enough uninterrupted time available – so over the past few days I made up the trim tabs. There was a bit more to them than I initially thought, even though they only have a couple of parts. Quite a few fiddly things to do, and wooden parts/jigs to make up.
I looked through the wing manual, and note that the trim tabs are the only place in the -10 where a folded trailing edge is done. As such I only made up a folding brake wide enough to hold these parts. I found a few old scraps of 6×2 hardwood from a house extension that was done a few years ago. The wood looks shocking but it’s dead straight. I took a couple of middle hinges off some doors temporarily, and used them to make up the folding brake. It worked really well!
I put off folding the sides of the tabs, I’ll do that after priming. The dimpled holes for the horn will get in the way of the wedge for the inboard side, I’ll just drill some shallow holes in the wedge to accommodate them. Once again, I match drilled the hinge before dimpling/countersinking the skin/spar. I did set up one elevator skin with spars, hinge and trim tab and verified that everything matched up well and the trailing edges lined up.
I already had the place set up for priming, now I’ve got even more parts to do. Weather’s nice and warm right now, so just need to choose a day and start early.
There always seemed to be more to do, but I finally finished match drilling and de-burring the elevators, and disassembled them ready for dimpling.
I made up a doubler plate for the static wick anchors, just so as to not require any additional skin rivets than the standard arrangement on the outer rib – same as I did with the rudder. The wick is a little forward of where I’d like it but not too bad. I had a look at wick mounting points on various aircraft types at the aerodrome, and there’s a fair bit of variation. Interestingly enough, almost every wick I saw was cracked/broken/falling-apart. I’m planning to not butcher the skin to place one 12 inches inboard of the outer edge. I’m only doing wick mounts because they’re easy to do now, and hard to do after assembly. I have a paper on the maths for wick design, and there’s a lot of assumptions that go into the front end of the models, so it’s all a bit academic I think.
Building tip: Match drill the trim tab hinge to the elevator skin / rear spar while you have the elevator assembled for match drilling, before the skin is dimpled and the spar is countersunk. The spar is quite thin, and when countersunk, some holes could be slightly enlarged. Similarly, the #40 skin holes expand when dimpled. As such, match drilling the hinge before these operations occur will be more accurate than doing so if you follow the order of the plans and do them afterwards.
Over the past few days I’ve finished assembling both elevators, have match drilled the RH elevator, and have started to disassemble and de-burr the RH elevator.
I had my first disaster. In a moment of sheer laziness, after marking the VA-140 trailing edge wedge for the RH elevator, I used the drop saw to trim it to size, without supporting it properly. The inevitable result is shown in one of the pictures. Fortunately, I have the wing kit here, which contains a total of 6 VA-140 wedges, so I pulled one of those and trimmed it to size, properly this time. I’m now short of a VA-140 trailing edge in the wing kit, which will have to be replaced sometime in the future.
The construction manual said to “cleco every hole” in both of the spars while match drilling. I thought this was over the top and not necessary, but I did it anyway. I also match drilled the trailing edge into the large angle section I have here, for later assembly. The elevator skins all have large burrs on every punched hole (see picture). Even after match drilling, the burrs remained. I don’t know whether this is a characteristic of the factory process for thin 0.016 inch skins, or whether the CNC punches were a bit worn out, but it meant I had to work fairly hard on each hole to get it de-burred properly. I find it better to de-burr as I go during disassembly, rather than pull everything apart and then de-burr. It’s easier to do the outside holes on the ribs while the ribs are all cleco’d together and supported, for example.
Another hour or two and the RH elevator parts will all be ready for dimpling, then I’ll go back and wind through the same process with the LH elevator.
Made a start on the elevators. There’s a lot of small parts to prepare for the elevators, all fairly straightforward but tedious. I’ve never been very eager to use aviation snips – always seem to have to bend parts back into shape. Since there are 16 ribs to cut, it’s easy to set up a jig for saw cuts, and do them as a batch. One cut is wider and could be done with the drop saw (have to drop very slowly though since the material is so thin). The other cut is thinner and has to be done on the band saw. It took four hours to cut and de-bur the 16 pairs of ribs, and a similar amount of time to prepare the rest of the elevator parts and skins.