Priming elevator stiffeners and skins

Another good day for priming yields another batch of primed parts. This time it's the elevator stiffeners and skins, which I deburred and primed in preparation to get them riveted together.

The days are getting much colder and I'm sick of hauling everything to the backyard every time I want to prime parts, so I decided to prime inside the garage. A few tarps laid down and some strategically placed fans in the cracked garage door set on high made for a passable makeshift paint booth. This means I finally had to buy a proper ventilator rather than skimping by with a cheap dust mask. 

*Insert Bane quote here*

I'm glad the only little stiffeners left in this plane are the ailerons', because getting these scuffed and primed is such a chore. The parts are small, but there are so many that it feels like hours of preparation go by without much progress.

The primer caused my sharpie labels to run, some to the point that they were no longer legible. I was able to use the relative lengths of each stiffener to organize them into the correct order and re-label them so I wouldn't be riveting stiffeners in the wrong places later on.

Sealing and riveting rudder trailing edge, starting leading edge rolling

Now for the most fun/scary part of the whole rudder construction - the trailing edge!

Leading up to this point was stressful. The trailing edge needs to be back riveted to ensure a flush head on each side. You can't backrivet with clecos in, so you can use either tape or tank sealant to keep the trailing edge locked in place between the rudder skins. The tape method is what's recommended by the latest Van's documents since it's a lot cleaner (no mess) and faster (no waiting days for it to cure). The tank sealant method was the method originally recommended, and a lot of builders still prefer it over the tape. I debated back and forth over which method I wanted to use, and I eventually decided to order both the special 3M double-sided tape and some tank sealant and decide later on.

Regardless of which method is used to keep the trailing edge together, it's recommended to use an aluminum angle to ensure the edge stays straight while your adhesive of choice cures. I took care to find the straightest piece of aluminum angle I could find at Lowe's, and I match-drilled holes into the angle along the length of the rudder so it could be clecoed in place after gluing the edge. I did this after I had already dimpled the rudder skins causing a couple of holes to be slightly enlarged, so I recommend match-drilling the angle before dimpling the skins.

When the day came to do the deed, I decided to try the tape method first. I wiped down the wedge and the trailing edges of the skins with acetone to clean the mating surfaces. With the rudder in place on the bench, I took out the tape and began peeling off the protective paper. Immediately the tape itself began pulling apart in shreds. No matter how carefully I peeled, I couldn't get a clean, smooth strip of tape. I couldn't be confident that this tape would work well, so I decided to use the tank sealant instead.

Yeah, this stuff does stink. Time to break out the odor mask!

Tank sealant definitely isn't the nightmare goop a lot of people make it out to be. It actually turned out to be mostly painless, but smelly. The best way I can describe it is "garbage being burned in hot, fresh asphalt."  I ordered the sealant in the caulk-type container on purpose to make mixing and applying easier and cleaner than with your standard tubs.

With the sealant mixed, the container fits nicely into a standard caulk gun. This makes application so much simpler than just using popsicle sticks.

I went to work applying the sealant to one side of the wedge. I worked in sections, shooting a line of sealant down about a third of the wedge at a time then using a wide popsicle stick to spread it evenly over the width of the wedge. This stuff is super thick and takes considerable effort to spread, so patience is needed here. The viscosity also means that any excess won't easily squeeze out when both skins are pressed together, so I had to be careful to make sure the coating was thin and even along the entire length to avoid any major bulges or waviness along the trailing edge.

With one side coated, I flipped the wedge upside down and carefully set it in its place on the bottom skin. I applied sealant to the other side and lowered the top skin in place, then clecoed the aluminum angle in place on the bottom of the assembly to hold everything straight. 

I temporarily put some weight on the trailing edge to help hold it tight, but the clecos provide enough clamping force on their own that this isn't really necessary.

The next step is patience, since the tank sealant needs time to cure. I ended up leaving it for about a week before coming back to it since it was starting to get cooler in the garage and the sealant sures much more slowly in cold temperatures. When I came back, I unclamped the angle and immediately checked how straight the edge turned out.

It has just a slight bow along the entire length, but it's well within the .1 inch limit the manual recommends. Which means, it's time to rivet!

Backriveting the trailing edge was one of the most stressful experiences of the empennage thus far. I wanted to avoid having to redo the dozens of hours of work I had sunk into this particular control surface, so I made sure to take my time and follow the instructions to the letter. I set the rivet gun pressure lower than normal so setting the rivets into their recess would be slower and more controlled, then I started at the middle of the trailing edge and set every tenth rivet to lock things into place. From there I partially set the rivets halfway between the last ones, then repeated this process until every hole was filled with a partially-set rivet. I then went back over each rivet in the same order and set the rivets almost fully. Throughout the process I kept check to make sure the small amount of bow wasn't getting any worse.

Since I couldn't get the rivets fully flush using the rivet gun alone, I flipped the rudder over and used the mushroom set to buck the rivets against the backrivet plate. This set each rivet flush into its recess and left me with a finished trailing edge.

The trailing edge isn't bowed quite as much as it looks here - the counterweight on the horn tends to lift the trailing edge when the rudder is laid flat on the workbench.

With the trailing edge out of the way the penultimate task prior to rudder completion was to roll and rivet the leading edge, which proved to be a bit frustrating as things progressed. I used the pipe and tape method to start the bends. The smallest section at the top seemed like it would be the easiest section to bend, but getting it into its desired shape required a lot more force than I had anticipated.

In hindsight I probably should have used duct tape instead of masking tape, but I didn't have any issues with it here.

Riveting rudder skins

Next came the more tedious task of installing the counterbalance skin and the the counterbalance weight. It takes many clecos and a bit of force to get the skin in place, then the rivets need to be bucked since they're too far down to reach with the squeezer yoke I have. It's a little tricky to hold the bucking bar steady in that area, but not too bad.

The counterbalance weight won't yet fit into the rib because of the rivets just installed, so it needs to have a little material filed away. This is just trial and error of filing away a bit, checking the fit, and repeating as necessary. Eventually the weight slides nicely into place.

A warning about this part: the top rib isn't in place to secure the skin and the lower counterbalance rib, so putting the weight in with the skeleton upright and without clecos holding the skin to the spar will cause the lower rib to bend down! Ask me how I know...

The lower four rivets were the only ones that really interfered with anything, so I only needed to shave the counterweight in those four places. 

Installing the bolts and nuts to secure the weight in place took a little improvisation. The nuts need to be torqued correctly and the only socket I had that was long enough to reach the nuts down in the counterbalance horn was slightly loose on the wrench. The screws are Phillips head, and of course they began to strip as soon as there was tension. I had to have force on the screwdriver to prevent it from slipping, so I pressed it tight against my worktable while using the wrench to torque the bolts. It wasn't pretty, but I was able to get both nuts torqued. A dab of torque sealant on each and I could finally start installing the rest of the rudder skin.

The top nine holes at the overlap between the counterbalance skin and main rudder skins was a challenge. The six holes closest to the top could be reached with the squeezer, but the lower three holes on each side had to be bucked. Once again, it was awkward having to blindly balance the bucking bar that far down while making sure the rivet gun is straight. A longer squeezer yoke would have been useful here.

I had forgotten to dimple the hole I'm pointing at here. It overlaps with the counterbalance skin, so there's no good way to dimple it once the skins are riveted on unless you're comfortable trying to dimple both skins at the same time.

The top rib slid into place at this point, and riveting the rest of the skin to the skeleton went well. Pretty much every hole can be reached with the squeezer except for the last three or four near the narrow aft ends of the ribs. I decided to leave these open until after the trailing edge is finished to allow easier access back there.

Looking good!

It looked too good to not stand it up again.

Dimpling and riveting rudder spar

With the parts cured, I dimpled everything then started putting the skeleton together. The spar and the spar doublers went together much like they did on the vertical and horizontal stabilizers, but the rudder now has platenuts that will connect rod end bearings for attaching the rudder to the vertical stabilizer.

The platenuts only have two holes, and each had a small gap between it and the spar when only one cleco is installed. To keep the platenuts flush for riveting I used a spare bolt and nut to lightly tighten the platenut to the spar. 

Much better!

The rivets called out for use with the platenuts are AN470AD4-5, which are the same length as the rivets used to fasten the spar doublers to the spar. With the addition of the platenuts' thickness, these rivets didn't seem long enough to provide a thick enough shop head. These are critical components and I wanted to be 100% sure that they wouldn't fail, so I just used slightly longer -6 rivets instead. Looking ahead at the elevator diagrams, the platenuts for those are called out to be one length longer than the rivets used for the doublers. I used that as justification for using the longer rivets here.

The longer rivets were a good choice. The shop heads would have been pretty thin with the shorter rivets...

The ribs needed to be dimpled before the can be attached to the spar. The aft end of the R-904 bottom rib is too narrow for the regular dimple dies to fit, so I had to get creative and use the close-quarters dimpling kit I got from Cleveland tools. 

The female die is fixed to a piece of steel and screws into the table. I put the male die in a spare 2x4.

With the 2x4 in place on top, all I have to do is put the rib between the dies and smack the board with a mallet. The clamps keep everything from going flying when the hammer comes down. It's crude, but it works.

Success!

The ribs got riveted onto the spar and I managed to get the horn brace and lower fairing attach strips on without much trouble. There way no way I was going to get the bottom four rivets with the squeezer or the bucking bar, so I used some LP4-3 pop rivets instead. Problem was, I only had three left. Not a big deal since I can order more once I place the order for some tank sealant. Oh yeah! That part's coming up soon!

This part will be hidden by the bottom fairing, so trying to get solid rivets in these holes probably isn't worth the trouble.

Starting the elevators, trimming and drilling elevator stiffeners

Over the past few weeks I worked on and off on trimming the elevator stiffeners between working on other parts. It's more or less the same tedious process as on the rudder stiffeners, but the elevator stiffeners are presented slightly differently.

Instead of having identical long pieces that each have to be cut down to a specific length, the stock elevator trim pieces are notched differently depending on which stiffeners will be made from a certain piece. One long piece was notched to make five small E-720H stiffeners, while others make A, B, C, D, and H stiffeners.

For the right elevator I had to take six stiffeners that I had already cut out and trim them even more to specific lengths called out on the diagram. I had to be careful here - the measurement is from the aftmost hole, which will become the second aftmost hole after the stiffener gets match drilled to the skin, to the end of the stiffener.

Above is an E-720K.

Eventually I was able to get all the stiffeners done, and I clecoed them to the skins for match drilling.

Priming remaining rudder parts

It was another good day to prime so out came the Critter sprayer, AKZO, and paint racks.

For the counterbalance skin I primed the whole inside, but on the outside I only primed the section that would slip under the rest of the rudder skin. I've seen some builders just prime the whole thing inside and out, but I want to preserve the aluminum finish until I can get the whole airplane painted properly.

Backriveting rudder stiffeners

With the stiffeners and skins all cured, I started riveting the stiffeners to the rudder skin. This was my first time backriveting, and it couldn't have gone much better than it did. I'll echo what a lot of other builders say - backriveting is the easiest method of riveting that produces the best-looking results.

Rivets and tape in place.

Or should I say, it produces the best-looking results when done correctly:

This is how the stiffeners should look when they're attached...

...and this is how they look when you're not paying attention. This setup would make it pretty difficult to close the rudder skins together, so I don't recommend it! Thankfully it wasn't too difficult to drill out the rivets on that first stiffener and reattach it the correct way.

We had a Halloween party at our house, so I came back outside and continued riveting anytime I got bored or sick of making small talk with other people. Some curious partygoers ventured out in search of the noise and watched me work for a bit. It made for a good opportunity to show off the build so far and to demonstrate how the rivet gun works.

Priming rudder skins and stiffeners

The rest of the rudder parts had more work ahead before they could be primed, but the stiffeners and skins were ready to go.

Since I'll be able to backrivet the stiffeners to the skin well before assembling the rest of the rudder, and since it was a good day to do some priming, I went ahead and primed them. It took a long time to prepare and finally spray the parts so I didn't have much opportunity to take pictures along the way.

Finishing rudder trailing edge countersinking

It's getting close to being time to prime the rest of the rudder parts, so I went back to the trailing edge to finish all the countersinks. I assumed that my earlier method of simply holding the trailing edge with my other hand wouldn't work as well since the holes would be enlarged and wouldn't make for a good guide for the countersink, so I went back to clamping the trailing edge to the smaller edge piece before drilling. It worked alright for a few holes but I started noticing that a couple of the holes were coming out slightly oblong after drilling. I realized that the clamps had started to slip with the vibration of the drill, so I decided to switch back to holding the piece in my hand. As it turns out, the countersink works perfectly even with the enlarged holes as long as you hold the cage tight enough against the piece so the whole thing doesn't move. The rest of the holes came out almost perfect using this method.

The weird lighting in the shop makes the edges of the holes look a little wavy, but they are actually round

Horizontal stabilizer complete! Riveting HS skin

I guess working on both the HS and VS at the same time was beneficial after all - now I can say it only took me 2 more days to finish the horizontal stabilizer!

I started by riveting the HS-707 nose ribs to the HS skins. The skins are pre-bent but still try to force their way open with enough force that clecoing only the ribs in place can be an issue. All of that force is concentrated in just a few holes on that rib, which can both "pop" a crease into the skin and bend the flanges of the rib. Mike Bullock's build log mentions that he used masking tape to help keep the edges of the skin closer together to help prevent this. I used the masking tape, and I also clecoed the HS-708 ribs in place behind the nose ribs (suggested in the next step in the plans to help keep things aligned). I had some trouble getting the bucking bar into place in the tight space near the front-most rivets, and one ended up with a deformed factory head. It had to be replaced, but the rest went into place with some patience.

Before attaching to front spar assembly, I went slightly out of order and riveted on the HS-706 end ribs with the squeezer so I wouldn't have to buck these rivets with the skin on. The VS assembly has you rivet the entire skeleton together before putting on the skin, so I'm not sure why the plans have you putting on the HS skin before the end ribs go into place.

The front spar went into its place rather easily, and I began the process of riveting on the skin using the same technique as with the VS. Starting at the intersection of the HS-706 and 708 ribs, I worked my way to the tip, then back to the root, then straight back to the aft edge of the skin.

The whole thing's a lot lighter and looks a lot better without all the clecos in the middle...

With one side mostly done I could start working on the other side using the same process.

Now we're getting somewhat close to a finished airplane part.

The rear spar assembly went on next. Most of the holes could be reached with the squeezer, but I used the rivet gun and bucking bar on the rivets in spaces too small for the squeezer to reach (i.e. the rivets next to the hinge brackets on top of the spar doublers).

The HS-708 rib is attached to the rear spar using BSPQ-5-4 pop rivets. The ribs had a slight twist in them causing the holes to not completely line up at first, so I took a rivet punch and maneuvered them back into place before inserting the rivets. These went in pretty easily and looked great.

...I went back and fixed that one slanted shop head next to the hinge bracket later on.

This is what the shop heads look like from the inside. Very nice!

The final step: riveting on the end ribs. Thankfully I could reach all of these with the squeezer. Every rivet should be set on the bottom sides of the ribs, but I nearly forgot to leave some of the holes open on the inboard top side for the fiberglass tail fairing that will be installed later. I caught myself just as I was about to make the mistake and saved myself from having to drill out any more rivets than I already had at this point.

Just like that, I have the horizontal stabilizer ready to go!

I couldn't resist propping the VS up along with it just to see how it looked.

There it is – (most of) the tail!

Another sub-assembly down, and many, many more to go. I'll finish up the rudder next, then I'll move on to the elevators. I went ahead and ordered the wing kit since there's an 8-week lead time on every kit except the empennage kit. Planning ahead to avoid any down time is a must. Momentum is the key to success! The wings should be here by early January, giving me just enough time to finish the rudder and the elevators and clean out the shop in preparation for a bigger assembly. Things are starting to get really exciting now!

Vertical stabilizer complete! Dimpling and riveting VS parts

Based on previous experience working on the horizontal stabilizer, I decided to finish the vertical stabilizer first. The VS is a lot easier to work on and will be done a bit faster since it's a smaller part. I still needed to dimple the understructure and the skin since I had elected to wait until after priming to dimple everything. The AKZO is pretty much bulletproof now that it's fully cured, so dimpling now wasn't an issue at all. I was able to get most of the holes using the DRDT-2, but the ribs and the very ends of the spars had to be dimpled with the hand squeezer since the DRDT couldn't reach them without deforming the parts.

I ended up having to re-countersink the bottom holes on the spar doubler since the primer had increased the thickness just enough to start showing a gap between the spar and the doubler when they were put together. The countersink cage was still set from the first time I did this, so this task went by quickly. I clecoed the parts together and started squeezing the flush rivets first, then moved on to the round headed ones. Most I was able to reach with the squeezer, but the rivets on the hinge brackets had to be bucked since the squeezer couldn't fit into the limited space. I was a bit nervous at first since this was my first time bucking rivets on the project itself, but I was both relieved and emboldened when they turned out looking nice.

I did end up having to drill a couple rivets out, namely the long -7 rivets that are really easy to fold over instead of squashing straight down. Using a #40 drill as a pilot hole then removing the rest of the rivet with the #30 bit worked well without enlarging any of the holes.

Those two empty holes at the bottom used to contain some pretty poor rivets. Not anymore!

I had one minor slip-up with the rivet gun when I didn't hold enough pressure on the round rivet head and the gun slipped. I have a couple of minor smileys in the spar now, but I doubt this is going to bring the whole airplane down.

A short while later I had a completed rear spar.

Apart, these pieces are flimsy. Together, they're pretty darn strong. ...there's a metaphor in there somewhere. 

With the rear spar done, I began work on the front spar by riveting the ribs to the spar itself. Attaching the 706 and 707 ribs were easy enough, but the only real challenge is keeping the spar still while putting so much force on the rivet gun and bucking bar. The assembly is so light that I ended up having to clamp it AND put weight on it to keep it from moving when I used the rivet gun.

My makeshift VS spar jig. 

When it came to joining the bottom 705 and 704 ribs at the same time, I was forced to use the offset attachment for the rivet gun. Having to indirectly apply pressure to the rivet head while keeping it square and also having to hold the bucking bar steady while the ribs themselves are in the way the whole time is difficult. Still, I powered through and got it done.

I hadn't yet dimpled any skins at this point in the build, so my DRDT-2 wasn't really set up for it. I've seen builders build tabletop shelves to elevate the skins to the level of the DRDT itself, but my impatience made me decide to build a stand that lowers the DRDT to table level instead.

Just a few spare 4x4s joined with some extra 2x4s. Simple, but sturdy. 

I made the stand at a height that brings the lower dimple die on the DRDT level with the table with carpet on top. This should support the skin while still making it easy to maneuver it around to dimple each hole.

Dimpling skins is where the DRDT-2 really comes into its own. Once it's set to the correct pressure, dimpling is way more easy and consistent than with your typical C-frame/hammer setup. There's no listening for that "right sound" to let you know the dimple is deep enough – just push down on the handle and you're good to go.

The DRDT is also supposed to help prevent a known issue with the C-frame – making extra, unwanted holes in the skin should the skin slip off in between hammer strikes. Of course I, being the rebel that I am, decided that no one could tell me what I can and can't do with my DRDT, so I accidentally punched a hole in the VS skin when I pushed the handle down without looking.

My actual reaction: "Wha– NO."

I had just made a mistake, using a tool designed to avoid making that very mistake.

I immediately rushed to the forums for advice. Did I just waste dozens of hours of work, or will I still be able to salvage my poor VS skin?

Thankfully this seems to be a common issue (one that happens more often on the thin rudder skins than anywhere else). I followed the steps others took: flatten the offending hole, drill/ream it to #40, deburr it, and then re-dimple it and put a rivet in it.

The offending hole, after clean-up.

Since this rivet won't be structural and only needs to fill this hole, I chose the absolute shortest rivet I have: an AN426AN3-3, normally reserved for attaching stiffeners to the thin rudder skins.

The rivet in place.

It's a good thing I didn't punch that hole any closer to the edge of the skin since the shop head was almost touching the rear spar. Any closer and I probably would have had to replace the entire skin. Luckily there was no interference between the new rivet and the spar and no deformation of the skin itself. It's not too noticeable as is, but I should be able to put some filler over it just before painting the aircraft and no one will ever know it's there.

This is later on after all rivets had been set. The extra rivet looks out of place, but at least it doesn't cause any issues.

With that catastrophe avoided I finished dimpling the skin and clecoed it to the skeleton. It was time for the fun part – riveting on the skin. The plans recommend starting in the center of the skin at the intersection of the front spar and the VS-707 rib, then working your way up toward the tip. I ended up drilling out my first attempt at setting the -4 rivet here since I easily flattened the shop head. A -4 rivet honestly seems too short for the 3 overlapping pieces of dimpled aluminum at this hole and I considered stepping up to a -5 length rivet instead, but I was able to set it better the second time so I didn't bother.

The rest of the rivets set with the rivet gun and bucking bar went by a lot easier and faster than I had predicted. Once you get the correct placement of the gun and bucking bar and have a feel for how much you need to feather the trigger and for how long, it's actually easy to get consistent shop heads down the row.

These are looking nice. In pictures there appears to be a slight gap between the rivets and the skin, but they do actually sit flush in the holes.

At first I was pausing to check the shop head of every rivet with the rivet gauge, but as it's been said (and I was skeptical at first) your eye is actually pretty accurate once you know what the proper shop head thickness and diameter are supposed to look like. I quickly got to the point where I would only have to recheck a shop head after shooting multiple rivets, and this helped the process go by much faster.

The bucking bar was scraping off primer in a few places, so I wrapped it in tape to protect the spar.

With the skin riveted to the front spar and the 707 rib I clecoed on the rear spar. The skin is riveted to the rear spar first, then to the top and bottom ribs to close everything out.

I wanted to make squeezing the rivets as easy as possible, so I set the VS with the spar horizontal to make everything easy to get to. I got the idea from one of Jason Ellis's videos. I couldn't use the squeezer on every rivet – the hinge brackets actually don't allow the squeezer to fully contact the shop head of the rivets in that area. I was forced to use the rivet gun and bucking bar, which really wasn't an issue now that I had a lot of practice with it.

While the part was horizontal I went ahead and set the blind rivets that connect the rear spar to the 707 rib. It's a good thing there isn't an abundance of blind rivets in this build since I only have a manual pop rivet puller. It takes a surprising amount of force to get the mandrel to break free of the rest of the rivet, and it ALWAYS makes a super loud, startling pop when it finally does break. I'd consider getting a pneumatic blind rivet gun if there were a lot more of these, but the hand riveter should suffice for this build. If I decide to build an RV-12 down the line (which uses blind rivets for almost everything) then I'll pick one up.

Some of those scratches are from the rivet puller bouncing when the mandrel suddenly breaks. It just happens too quickly to react.

I set the piece vertical for riveting the top and bottom ribs. The forward-most rivets on either side of the top rib were challenging. That area is too small for my bucking bar, and the squeezer didn't seem to be fitting in the limited space. I pondered how I could solve this without ordering another, smaller bucking bar. I then realized that I could take the flatter, wider flush set and put it inside the rib on the shop head while putting the thicker head outside on the factory head. That juuuust barely allowed the squeezer to fit, and I was able to squeeze all of these rivets without any deformation.

And just like that, I have a finished airplane part sitting on my workbench!

Well, technically it'll be completely finished once I get the fiberglass tip installed, but I'm going to wait and take care of all the fiberglass parts at the same time. For now it feels great to have a chunk of my airplane pretty much complete, the first milestone of this long journey. 

The horizontal stabilizer is next...