Rudder Fit

This week I received the missing rod end bearing for the lower rudder hinge.  I screwed it in to the suggested depth and did one of about 20 trial fits to the vertical stabilizer.  

With the forward spar of the vertical stab in front of the mounting bracket, there was about 1/16" of bow to the rear spar.  That doesn't sound like much, but because of the slight variations in holes in the rear spar hinges, this bow ended up making the center hinge hole about 1/8" too far forward.  I didn't want to back out the middle rod end bearing that much (and it would probably cause some binding being that far off of the center line), so I removed the vertical stab and attached it to the aft side of the mounting bracket.  This is a suggestion in the manual, so apparently not all that uncommon.  I had tried this once before and wasn't happy with the result, but with everything bolted down now, this actually lined the hinges up much better.  There was almost no bow to the rear spar, so I was able to play with the screwed in distance of each rod end bearing to get them lined up pretty well.

Even though the hinge line was pretty good, I still had to take the rudder off multiple times to get all of the bearings at the right distance so the rudder could swing freely from stop to stop without binding.  It was fine except for the very bottom where the rudder's control horn connects.  The way they designed that pushes the skins out on both sides, so as-is it rubs the vertical stab at full deflection.  After some fiddling I got it to clear ok.

Next up was putting the elevators back on to measure the total deflection of the rudder in relation to the elevators.  I didn't bother bolting the elevators to each other since this was all temporary.

The instructions indicate what the measurement should be from the rudder's trailing edge to the outside trailing edge of the elevator when the rudder is at full deflection.  Thankfully, it came out perfectly, so no more fiddling.

As much as I'd like to bolt everything together at this point and call it done, there's just not enough room to move around with the tail on.  I dismantled it all and moved the parts back upstairs.

Vertical Stabilizer

It feels like it's been forever since I've spent much time working on the plane.  I got back to working on the vertical stab today.  After measuring over and over, I felt like I had it located correctly, so it was time to drill.  I clamped it in place and drilled the first few holes for bolts in the rear spar.

The bracket that the front spar rivets to (the bracket gets bolted to the front horizontal spar - it's the blue piece in the picture above) can cause some warping of the rear spear, just depending on exact measurements things were built to.  If the front vertical spar sets on the front side of the bracket, it can warp the rear spar in one direction, and if it sets on the back side of the bracket, it can warp it in the other direction.  The instructions say it's supposed to go on the front side of the bracket, but provide a lot of options for shims and other solutions to get the rear spar straight.  To test the rear spar, I put a straight edge across all 3 of the rudder hinge brackets.  They should all line up if the spar is straight.  With the front spar on the front side of the attach bracket, the middle hinge is about 1/16" forward of the top and bottom ones.  I swapped the front spar to the back of the attach bracket, but that reversed the warp significantly.  So I need the spar attached to the front side.  I may end up making a thing shim to go in between the pieces and push the front spar forward just a tiny, tiny amount and see if that makes the hinges line up perfectly.  Before I do that, I'm going to put the rudder on and see if it even matters.  The hinges need to line up so the rudder can swing freely.  Each hinge attaches to the rudder with a bearing, just like the elevators do.  That means I can move the bearings in/out to line up with the hinge holes.  The question is will moving the middle bearing 1/16" forward cause the rudder to bind.  I'll just have to play with it and see.

I went ahead and drilled all of the holes for the front spar and attach bracket rivets.  I won't rivet this together until I take the vertical stab off again.

I can't remember if I showed this before or not, but I had made the elevator control horn stop last time.  I match drilled it to the vertical stab rear spar, aft deck and longerons and temporarily bolted it in place.

The bottom of the rear spar is attached to the aft most bulkhead with 4 bolts.  I drilled those holes and put a couple of bolts in to hold it all together while I work on the rudder fit.  I don't know why the plans don't call it out earlier, but the bottom hinge gets two additional rivets as well. Why it didn't show those during the initial VS build is beyond me.  I can't put them in until I take the VS back off.

I was going to mount the rudder to the VS, but it looks like I am missing one of the bearings.  I have 3, but they are all the same size.  I need two short ones, plus one long one for the bottom hinge (due to the geometry, each bearing sets at a different distance).  I must not have caught the difference when doing my inventory years ago.  I saw the right number of bearings and figured they were the right sizes.  So yet another order placed to Van's!  Expensive little buggers - $25 for a single bearing.

I fabricated the left rudder stop and drilled it in place.

Empennage Fitting

I received the aluminum bar I needed to make the shims that go underneath the attach angles of the front spar on the horizontal stab.  The plans give measurements to get all of the layout angles for the shims right, but I just put a square piece in place under the attach angle, drilled the bolt holes through to match the existing ones, then traced around the attach angles to get the layout.  A few simple cuts and some sanding and the shims were done and in place (temporarily).

The rear of the horizontal stab has to be elevated a bit to get the incidence set to zero.  An 11/32 bit placed under the rear spar should get everything where it needs to be.  With that in place, I put a 12" long drill bit into the aft tooling holes of the ribs to get a measurement.  Then I put the same long drill bit in the forward tooling holes of the nose ribs and measured there. It was within 1/64", so I'm calling that good!  I drilled the bolt holes in the two vertical attach bars that come out of the fuselage and connect to the rear spar.  I temporarily bolted things together with the top two bolts.

The elevators have to go back on for the 100th time so the pushrod can be put in place, as well as a check for general fitment.  The right elevator looks great in terms of how it lines up with the horizontal stab.

For whatever reason, the left elevator looks less great.  I'm not sure what is causing the difference in gap between the two sides.  There's not really much wiggle room when building them, so it's hard to imagine what I could have done to create such a difference from side to side.

I slid the pushrod into position and bolted it to the bellcrank and the elevator control horns.  This is just temporary for now (I still have to prime the pushrod), but helps to get everything set to the correct length.

When I bolted the pushrod bearing to the control horns, that's when I realized I had a potential problem.  The instructions prior to this point had said to drill the control horns together by clamping the elevator counterbalance arms to the horizontal stab.  In theory, that should put the trailing edges in a neutral position, and drilling the control horns based on that should mean perfect alignment.

Once I got everything hooked up, I saw that with the counterbalance arms level to the horizontal stab, the left elevator trailing edge was 1/2" below the trailing edge of the right side.  I've emailed Van's to find out what the best way forward is.  I've looked online, and there are a suspicious number of people who have had the exact same issue, down to the same 1/2" measurement.  So there is a possibility that I either just built a twisted elevator, or something about the manufacturing of that side continues to spit out some parts that end up being a little off.  Some builders said they noticed it early and instead of lining up the counterbalance arms to drill the control horns together, they lined the trailing edges up instead.  Of course, that means that in neutral they have one counterbalance arm that is up and one that is down.  Ugly.  Others have said they left it all alone and have noticed zero negative flight characteristics (one DAR said that an RV6 he looked at had this issue.  It was already flying, and the builder decided to rebuild the elevator, only to discover it didn't change anything about how the plane flew).  I'll see what Van's has to say.  It's possible I could drill key pieces of the elevator apart and correct it, but I'm not sure.  Worse case scenario, for a few hundred bucks and a weekend of time I could have another elevator built.  Based on what I've seen online though, I wouldn't be surprised if they said that it's unlikely to have any perceivable impact.  The joy of building is that I can always fly it, and if I don't like it, I can always build a new part and replace it.

Moving on from the horizontal stab, it's time to mount the vertical stab.  I drilled and temporarily bolted a mounting plate to the front horizontal stab spar.

The front spar of the vertical stab has to be cut down a bit to fit in place.  I have no idea why they don't just ship the spar the right length or have you cut it before you build the thing.  They do weird things like that all of the time.  I set the vertical stab in place and clamped the rear spar to the aft most bulkhead in the fuselage.  There are a few measurements called out in terms of where the whole thing sets vertically.  After a lot of tapping and back and forth, I finally got it in place.  Next up, ensuring it's actually at a right angle to the horizontal stab.  100 measurements and tapping later, I think I got it.  Every time I'd tap the top portion one way or the other, that meant it slide a little vertically as well, so each tap meant remeasuring both planes.  I haven't drilled or bolted it in place yet.  I wanted to take a step back and come back to it another day to double check things.

Vertical Stabilizer

Today went a bit slower than I expected it to.  I was all thumbs with riveting, so it felt like for every 1 rivet I put in, I drilled one out.  I'm not sure why it was such a bear.  The locations of the rivets were definitely tight quarters, but nothing much worse than when I skinned the horizontal stab.  Just one of those days I guess.

Things started out easy enough - cleco and rivet the spar doubler and hinge brackets to the rear spar.  The vast majority of these rivets could be done with the squeezer, which is quickly becoming one of my favorite tools.  Not wanting to repeat one of my earlier mistakes that I made on the horizontal stab by putting in rivets earlier than they should, I followed the suggestion in the manual and taped over the handful of holes that would later be used to rivet the ribs to the rear spar.

There are areas of the rear spar that will need to be a flat surface once attached to the fuselage, so the lower portion of the spar and doubler uses countersunk flush rivets as opposed to the universal head rivets used for the rest of the spar.

To get ready for skinning the VS, the ribs were riveted to the front spar to make the skeleton for the skin.

This is where you get a little deja vu.  In order to line everything up and be ready for riveting, the skin has to be clecoed onto the skeleton again, just like it was to get match drilled prior to priming.  This is where good music or a podcast is necessary, since it gets pretty repetitive and mind numbing to cleco, then rivet, then move clecos, continue riveting, move more clecos, rivet, etc.

For whatever reason, the front spar is where I really struggled with riveting.  I just couldn't get the bucking bar held correctly because of the position inside the skin, so a decent number of rivets had to be redone because I didn't get them set to my satisfaction.  The saving grace is that it takes a pretty significantly screwed up rivet to be problematic in reality (based on what the specs in the aircraft maintenance bible say), so while some of my rivet heads won't go in the photo album, they're doing their job.

The tip of the upper rib was a bit of a head scratcher to rivet.  My squeezer wouldn't fit inside the narrow space, and I didn't have a proper bucking bar that would fit either.  I ultimately had to grab a chunk of scrap steel (probably 3/8" or so) I had laying around, clean it up a little bit, then slowly use it to buck the last rivet in the nose.  This was far from ideal because what you need in a bucking bar is mass, but little by little I got the rivets set ok.

And there you have it!  One vertical stabilizer all done.  I did have a couple of minor dings on the skin while riveting tonight.  They're probably unnoticeable to most people, but I know they're there.  A small dab of bondo to fill the slight concavity come paint time will do wonders.

Left Horizontal Stabilizer & Vertical Stabilizer

The right horizontal stabilizer was fitted yesterday, so today we disassembled everything and began deburring all holes and edges, as well as dimpling and countersinking.  Deburring has been a little bit of an experiment. Thicker material seems okay to deburr with the Cleaveland deburring bit in the powered screwdriver, but in thin material the bit either creates too much of a countersink or doesn't actually remove the burr enough to matter.  For thin material we found that using a reamer to match drill created such a smooth surface that deburring was not usually necessary.  When it was necessary, instead of using a bit, running worn out sand paper over the surface was enough to flatten the burr.  I researched deburring until blue in the face, and from what I've found, most commercial specs call for simply running something over the surface to remove the outer burr, but not worrying about creating any kind of a chamfer.  In the future, I will be a little more free with just surface deburring vs using the bit.

The spars are on the thicker side, so those get countersunk as opposed to dimpled.  After some trial and error, we landed on the correct depth for the countersink cage, clamped the spar vertically, and proceeded to countersink.

The nose ribs of the horizontal stabilizer have a front flange tab that has a single hole in them.  The edge distance is not what it should be, but I emailed Van's and they said this is very common for these ribs, and not to worry and build on.

After finishing the right stabilizer, we moved on to the left and repeated the exact same process.  Following that, we started on the vertical stabilizer.  This was actually considerably less involved and may have actually been a better place to start than the horizontal stabs.  We clecoed and drilled the vertical spar and doublers, then the hinge brackets. After finishing the edges and fluting the ribs, those were match drilled to the spar as well. Attaching the skin to the vertical stabilizer skeleton was far easier than the horizontal stabs.  It did not require a jig and wasn't nearly as tight of a fit.