For a litany of reasons, I’ve had to take a break from building over the past 6 weeks or so. Now it is time to get back to work!
I have a few empennage jobs to catch up on – including rolling the leading edges. The technique I used was described here. I made up a rolling tool by welding some 3/8″ sockets inside a piece of 1 inch ID galvanized water pipe. This is sold in Australia as “fire pipe”, and has a 3.2 mm wall thickness. The OD is around 33 mm, near enough to the 1 1/4″ that Van’s specify. I drilled three 5mm holes in each end, then welded the sockets in place through the holes, filling the holes up with weld and then grinding the excess down flat with an angle grinder. Finally, I sanded the surface of the pipe to remove any rough points.
I put masking tape on the inside surface of the leading edge skins, to avoid any chance of scratching from the steel pipe. Scrap wood was used to ensure the rolling tool was aligned properly as it was strapped on with Gorilla tape. The wood spacer was then removed, and the section was rolled. After rolling, the Gorilla tape can be carefully torn off, and the masking tape removed.
In the pictures, some flecks of primer can be seen lying around. These come from the blue vinyl, where the primer doesn’t adhere. Primer doesn’t come off any of the Alclad, the adhesion is way too good to be bothered by Gorilla tape.
If the rolling tool is made 670 mm long, a single tool can be used for all sections of the elevators, as well as the rudder.
Riveting the elevator trailing edges was straightforward. The same angled squeezer die I made for the rudder worked fine and both elevator trailing edges are perfectly straight. I’m really sold on the method, no rivet gun required means less chance of unintended stretching/curving of the trailing edge. Like almost everyone else, I had trouble with the aft most outboard rivets on each elevator. There’s very little room there. The usual fallback is to use MS-319-BS pop rivets. I’ve got a few stainless steel cherry max rivets coming in various lengths for these sorts of situations, so I’ll wait for those.
I also fitted the hinge halves to each elevator and trim tab, and fitted the trim tabs. Used a squeezer for all of this riveting as well. There’s not much clearance and it’s important to not squash the hinge. None of the yokes I had worked for the elevator, so I cut the shaft off a 3/8″ x 1/4″ flush die, ground it smooth, and used a bit of gorilla tape to hold it in place on the fixed side of a 4 inch thin nosed flat yoke. This gave the required clearance to get around the back of the hinge bracket, while still being thin enough to get into the narrow gap in the first place (see pictures).
After closing up the first trim tab and riveting the hinge in place, I went to do the last operation – pop rivets on each end of the trim tab – only to find out that these were specified as countersink rivets, and I had not dimpled the holes. It was impossible to get the ends apart to dimple the holes at this point, so I’m going to have to use flush pop rivets on the right hand elevator. No big deal structurally or drag wise, just something to mentally beat myself up for as long as I own the plane. For the other trim tab, I was able to get the outboard side opened up enough to get a squeezer in there and dimple the holes, so that is one out of four sides done per the plans. I may put a layer of glass over the outboard side that has non-flush rivets, it would only be for aesthetics but there’s enough room to do it.
Now the tail-cone is out of the way, it’s time to go back and complete some jobs I shelved at the time. In this case, the elevator trailing edges and foam ribs, which were not done at the time because I didn’t have any pro-seal. For the trailing edges, I am using the same method as I did with the rudder (described here). In fact I used the same 50 x 50 x 5mm section of angle, just a different side and cut in half to separate the two parts that the left and right elevators were previously match drilled to.
This was my first experience with Pro-seal, a gooey substance that absolutely sticks to everything, especially latex gloves and workbenches. Hopefully I got it all done without gluing an elevator to a workbench. I only used the pro-seal for foam ribs (2 each elevator, 3 each trim tab), preferring to use 3M F9460PC double sided tape for the elevator trailing edges (less mess and avoids gluing the elevator to the straight edge).
I included the previously match drilled (half) hinge on the trim tabs when I cleco’d them up after the foam ribs were glued in place. Once the pro-seal cures it is all ready for riveting.
Some of this work took place a few weeks ago, but I didn’t finish both trim tabs until yesterday, so here are the details.
I had to go back and fold the outside edges of the elevator trim tabs – which I held off doing until after they were primed. I cleaned up the saw marks from one of the inner sections removed when I made the supports, and glued on a piece of masonite to build up the thickness of the wedge so that it could be used as a folding jig per the instructions. Since it was from the same cutout, it was a perfect fit. Since I had already dimpled the skins, I also had to drill some indentations in the wedge to avoid damaging any dimples.
I made the folds and match drilled each end, and riveted on the horn and front spar to to the bottom skin.
Finished riveting the elevators, except for the leading and trailing edges.
It turns out to be better if you deviate from Van’s instructions. The manual has you rivet the front spar to the top and bottom skins, and then insert the tip rib assembly. In so doing, you have to buck the four AN470 rivets that join the front spar with the tip rib assembly, by lifting the corner of the elevator skin. I did this with the left elevator.
For the right elevator, I made a change. It’s easier to attach the tip rib assembly to the front spar before inserting the assembly into place. That way, you can use a rivet squeezer to set the AN470 rivets. You need to use a longeron yoke.
One other issue is the two AN426AD3-3 rivets that attach the top and bottom skins with their respective tip rib skin. The instructions have you buck rivets in the top with the bottom skin lifted, and use pulled rivets for the bottom (page 9-14). It’s actually possible to pass a tungsten bucking bar through one of the front lightening holes in the front spar. With a bit of manipulation, it is easy enough to insert the tungsten bar, buck these rivets, then extract the bar back out the front. I drove solid rivets into both the top and bottom skins using this method.
After a perfect storm of distractions over the past few weeks, including a trip to the Avalon Airshow, I’m finally back to work on the elevators. I completed riveting the inspection doubler plate to the bottom skins, rib halves to all skins, and rear spars to the point where the skin assemblies could be cleco’d together. Next step is to use the weird RV-10 specific bucking bar to rivet the remaining skin halves to the rear spar.
I managed to clumsily drop my 12 inch back rivet set on the floor, breaking the delrin ring. Cleaveland tools sell replacements for $7, so now I get to spend more on mail/freight to get a replacement here.
I got to look over not one but two awesome RV-10’s at the air show, and it was worth the trip interstate for that alone.
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.
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.