Fabricating R-918 attach strips, match drilling rudder trailing edge, match drilling rudder skins to skeleton

The last step before clecoing the skin is to fabricate the two R-918 strips, which will eventually attach the bottom fiberglass fairing onto the rudder. The remaining material on that same long strip of aluminum used to fabricate the shim just so happens to be the perfect length to produce the two 1 1/8"x18" strips called for by the plans (crazy, it's almost as if Van's planned this!). Cutting the strips apart then finishing the corners and edges with the Scotchbrite wheel went well. The strips were then clamped to the bottom rib to be match drilled.

I clecoed on the skins and reamed the appropriate holes to #40. I couldn't resist propping it back up and admiring my new rudder. As a tailwheel instructor, it's hard to overstate the importance of this particular control surface.

There is an eeeeeeever so slight wave in the trailing edge, but it's not huge (only around 1/16" at most). I'd have a problem if there was a lot more waviness here, but this amount is merely cosmetic from what I can tell. It probably won't be noticeable at a distance.

The trailing edge should be drilled square to the rudder since the rivet shanks will be also be square with it. I set the rudder on some 2x4s on my workbench and used a level to check that everything was indeed level.

I managed to improvise by attaching a small level to my drill to make sure the drill bit stayed square to the rudder.

It looks stupid, but it works.

AKZO arrives, testing Harbor Freight sprayer

I decided early on that I'm going to prime my RV-7. I'll probably be flying this airplane for a long time, and I don't know exactly where I'll be taking it. No matter where it goes, I want it to be protected from corrosion for its entire life. Plus, if I ever do decide to sell it, priming will most likely add value in the eyes of a buyer. Priming definitely adds cost and (a LOT of) time to the build, but the benefits are worth it in my opinion.

I ordered some AKZO epoxy primer a while ago from Aircraft Spruce at the recommendations of quite a few builders on the VAF forums. Unfortunately, it was on backorder and wouldn't arrive for around a month. I decided to wait until after priming to dimple the pieces to avoid tearing up my Scotchbrite pads and to make it easier to apply an even coat of primer across each piece. The AKZO is pretty bulletproof once cured, so dimpling after it's applied shouldn't be an issue.

The containers were a little beat up during shipping even though they were thoroughly encased in cardboard and plastic, but the contents are just fine

The AKZO arrived a few days ago, so I went out and bought a bunch of priming supplies. One trip to Harbor Freight later, I now had a Harbor Freight spray gun with regulator (the $20 purple one that a bunch of people have), an inline filter to keep the air clean, a mask, paint cups and filters, and stirring sticks.

The sprayer came with a regulator to control the pressure at the gun – super important for a good finish.

I also needed a rack or two on which to spray the parts, so I got some poultry wire from Home Depot and used some spare 2x4s lying around the garage to build a couple of 2'x5' paint racks that look quite similar to the tops of the EAA workbenches I built. The nice thing about these racks is that the parts can be sprayed and then left on the racks to dry so there's no need to touch the parts until after the primer is cured.

To make sure everything was working properly, I tested the Harbor Freight gun with some water.

I played with the fluid, air, and nozzle settings until I was happy with the amount being sprayed and the spray pattern, then I filled it with some primer and tested it out for real on some scrap aluminum pieces. The AKZO base and curing solution were super easy to measure 1:1 and mix, and the final coat of primer on the parts was strong and looked great. Satisfied, I put away the gun and eagerly waited a couple of days for my first real priming session.

The test parts after scuffing, rinsing, and wiping with acetone.

One finished test skin. I can't imagine a better finish than this!

Match drilling rudder stiffeners, working on lower rib and counterbalance skin

It took me a few days to finish all of these, but seeing them in a row when they're attached to the skins is satisfying.

Since the rudder skins sit flush on the table top, the plans recommend putting the skins on something that you don't mind drilling into while match drilling the stiffeners to the skins. I chose to set the skins on some old (clean) carpet lying out in the garage. I ended up putting the back side of the carpet against the skins before drilling to avoid getting any fibers tangled in the reamer.

Starting with the right skin I reamed the holes to #40, then did the same for the left skin.

The next step in the plans was priming and then riveting the stiffeners to the skin, but I wasn't in a position to do that yet so I moved on to the rudder skeleton. One of the first steps here is clecoing the R-904 bottom rib to the R-902 rear spar and enlarging the hole in the rib to 3/8" using the unibit. This is probably basic tool knowledge that I didn't know due to my lack of metalworking experience, but I found the the unibit works best at slower speeds. The final hole ends up being uncomfortably close to the edge of the flange, but this is okay since the spar will handle the load of the bolt that will be secured here.

Next was fabricating a 3"x1 1/8" shim to make sure the rudder horn will sit flush on top of the rib and spar. There's a long piece of aluminum in the kit that just so happens to already be 1 1/8" wide and is the exact same thickness as the rib, and this is the piece from which you cut the shim. This seemed obvious to me, but I've seen multiple people on the forums cut the shim from a larger piece of aluminum that was part of the trim kit (extra sheets of aluminum they include with the kit for use to use however you want/need), and I have no idea if they ever realized it. All you need to do is cut a 3 1/2" section off of this piece and smooth the edges, which is way easier. The long piece of aluminum that remains will be cut in half later to make the two attach strips for the bottom rudder fairing.

The drawing of the piece is 1:1, so that's nice.

The piece then needs 3 holes drilled. Instead of just measuring and drilling (and possibly allowing the drill bit to wander), I decided a better method would be to mark the approximate locations of the holes, clamp the shim into place on the spar, check the fit, then match drill the holes using the spar as a guide. This worked beautifully:

Shim marked with hole locations.

Clamped in place.

Just as I thought – they line up!

One match-drill later, a good-looking piece.

Perfect!

With the shim now clecoed in place, the rudder horn could be installed. Well, almost. The forward end needed to be shaped to fit the inside of the bottom rib, otherwise it wouldn't sit flat against the spar assembly. This was easy enough to do on the Scotchbrite wheel.

Next was assembling the rest of the rudder skeleton and reaming all the holes to #30. As it turns out, the rudder skeleton is fairly well balanced on its own, which is probably a good thing:

Gallon of AKZO for scale.

The skin for the rudder horn needs to be clecoed onto the skeleton and the holes enlarged to #40. Thank goodness for prepunched holes, because this is a suuuuuper tight fit. I had to start at the front, then struggle to cleco pretty much every hole evenly on each side to properly stretch the skin over the ribs.

The rudder horn brace at the bottom needed to be put into place before I could cleco on the rest of the rudder skins. The part is purposefully left too large and must first be trimmed to fit inside the R-904 bottom rib. I took the advice of some other builders on VAF and cut the horn brace to the outside of the punched circles to avoid cutting the piece too short. There will be holes drilled into these flanges to connect the piece to the bottom rib, and those rivets won't have adequate edge distance if too much material gets cut off. Some other builders have made this mistake and ended up ordering one or more additional horn braces to try again, so I proceeded with caution to avoid wasting time and money on replacement pieces. Cutting away from the cut line, grinding little by little, and checking the fit periodically gave me a brace that fit perfectly in place while having enough edge distance on every hole. Cutting north of the machined holes did leave the final piece with some unsightly notches on the edges that had to be rounded off, but at least I don't have to worry about ordering any new parts.

I also rounded off the upper forward corners to allow the piece to sit better in the R-904 rib. The black marks are the minimum allowable edge distance for the rivet holes.

Deburring HS parts, continuing work on rudder stiffeners

Now came the part that everyone complains about – deburring. It's an easy task, but a tedious one considering the sheer number of edges and holes that need to be smoothed out. The edges are handled with a file, the edge finishing tool, and a Scotchbrite pad, and most of the holes can be reached with the electric screwdriver with the hex shank deburring tool attached.

I tried the soldering iron method of removing the blue vinyl for deburring but it was making scratches in the skin, so I ended up just removing it by hand. I might revisit using the soldering iron later...

The insides of the spars and ribs are too narrow to fit the electric screwdriver, so I had to deburr the insides of those holes by hand. This is easily the worst part of the whole deburring process. It's slow, it's tedious, and it makes my hands and fingers cramp up every few holes with the tiny, repetitive motions necessary to turn the bit in the holes with limited clearance. I tried finding a 90-degree drill bit adapter to help me out but nothing was small enough to fit inside the spars. I'll have to do all of these by hand.

After an undetermined number of hours, I finally finished deburring every part of the horizontal stabilizer. The next step is priming. The AKZO I ordered just arrived, so I went out and got a Harbor Freight spray gun along with a regulator, an inline air/oil filter, and some paint mixing cups and filters. I'll be building a couple of painting racks too. The only issue with priming is that it's still pretty humid for most of the day at this time of year, so I'll probably have to wait a couple of weeks before I'll be able to prime with less than 75% relative humidity per the AKZO instructions.

I also worked some more on the rudder stiffeners and got most of them finished. I should be able to get them done by tomorrow, then I can continue working on the rudder.

Assembling HS skeleton and skins, match drilling spars and ribs

I clecoed together the parts of the HS skeleton I have so far. I was right, I need both workbenches to support it.

It's starting to look like something that belongs on an airplane...

I put the HS-00005 and HS-00006 ribs in place with some support to get an idea of what the skeleton will look like with every part in place. This is starting to look great!

Before I could put the skin on, the HS-705 nose ribs needed to be bent to stay in a straight line with the HS-706 ribs. 

Much better.

Every hole attaching the skeleton pieces to one another needed to be either reamed or match-drilled to #30, and then came time to attach the skin. As with the VS skin it takes patience, finesse, and a little muscle to stretch the skin over the ribs correctly, but the end result is worth it. 

I considered trying to put both the left and right skins on at the same time, but I realized I don't have enough clecos for that...

With everything in its place I marked the locations of all the holes I would need to match drill into the spars. Now that I had a point of reference, I removed the HS-702s and went to work trimming the last portion of the spars. The easiest way to do this was to use the hand shears, followed by a quick grind session on the Scotchbrite wheel to smooth the edge and round all corners.

With the HS-702 spars finally, completely done I slipped them back into the assembly and began the drilling process. Reaming the #40 prepunched holes was a non-event, but I admit that actually drilling the holes inboard the HS-707/HS-708 spars had me worried at first. I slipped the HS-00005/HS-00006 ribs back in place to help align the spars with the appropriate holes on the skin, then I match-drilled the holes in the spar. The finished holes lined up perfectly on the spars, a good opportunity for a first-time builder like me to sing the praises of having computer-aided design and prepunched parts.

I turned my attention back to the HS-00005 and HS-00006 ribs. Unfortunately they aren't prepunched, so they have to be clamped into place and then match-drilled with the skin. Clearance is tight here, but the clamps held everything solidly in place for drilling.

The aft flanges of the HS-00006 ribs needed to be pilot drilled on their own, then match-drilled to the front spar assembly once clamped in place. There's no way the drill could fit into this small space with the regular drill bits, so the 12-inch drill bits supplied in the Cleaveland tool kit worked beautifully here. Next was drilling the front of the HS-710 and HS-714 through the entire front spar assembly to the HS-00005 rib behind. This looked like a perfect opportunity for the 12-inch bit to wander, so I rigged up a quick drill guide using some scrap aluminum, a piece of wood, and a clamp to keep the bit where I wanted it. The guide worked well, but it still takes an uncomfortably long time to drill through not one, but four layers of aluminum with a 12-inch drill bit that flexes easily.

It took a lot of careful measuring and positioning to get the guide clamped where I wanted it, but it worked perfectly once it was in place.

The ribs were now clecoed to the front spar, so it was time to match drill the flanges to the aft spar and finally to the upper and lower halves of the skin. I had to make sure the skin sat tight against the ribs before any drilling was to occur, so it was time to once again break out all the clamps.

This rib is going nowhere

I started at the back and match drilled the aft flanges of the HS-00005s using the rear spar as a guide, then worked my way forward to the HS-00006 flanges. Every other new hole that got drilled also received a cleco to allow me to progressively shift the clamps forward.

All clecoed up. Now all that's left to do is deburr...

Working on HS front spars, trimming spar doublers, working on HS ribs

Turning my attention back to the HS-702 spars, I made doubleplussure that I marked the bend line where it was supposed to go before making any cuts. I was determined to take it slow this time around and not make another $70 mistake. When you're building using flight instructor pay, every dollar counts!

The flanges need to be trimmed back and then flattened to match the rest of the spar web, and practicing on my old scrap HS-702s allowed me to find a good method to accomplish this with good results. First, I cut the flange widthwise to halfway along the bend. This gave me a nice large tab, which made it easy to use the hand seamer and some blocks of wood to flatten it and remove any bend from the transition from the spar web to the flange. I then went back to the bandsaw to trim most of that tab off, and finally used the Scotchbrite wheel to grind the remaining material flush with the rest of the web. While it doesn't produce perfect results, I used the plans method of drilling the relief holes with a #30 bit followed by the unibit to form the notch and a round file smooth everything out.

The flanges technically need to have another triangle-shaped section trimmed off before final assembly to make sure the spars don't interfere with the HS-00005 ribs. The only issue with trying to do this right now is that the hole meant to be used as reference for the minimum edge distance to maintain isn't on the spars yet. I'll have to wait until I can cleco on the skin and mark the location of that hole before I can trim this section. In the meantime, I bent the big tabs to 6 degrees and the HS-702s were finally ready to be attached to the rest of the HS assembly for drilling.

Ahh, this looks much more like the picture in the plans.

Joining the front spars using the HS-710 and HS-714 angles started to give me an idea of just how wide this HS was going to be. I'll definitely end up having to move my workbenches closer together to support the part on both work surfaces.

The ends of the angles needed to be trimmed round to fit onto the spar without interfering with the skin when it's attached. I chose to grind each end using a metal grinding disk on the bench grinder, which was honestly a bit scary. It works well, but it's loud, it shoots hot metal shavings everywhere, it quickly heats up the piece, and it takes a long time to grind down this much material. Gloves, safety glasses, earplugs, and a long-sleeve shirt were a must for this operation. In hindsight I may have been able to simply use the bandsaw to trim off the excess material before grinding/polishing with the Scotchbrite wheel, but I still got decent results with the method I used, so eh, whatever.

After forming the ends, the angles needed to be bent to match the 6 degree bends I made in the spars. The plans call for putting the angles in a vise and hitting them with a hammer, but I found that bending them over the edge of my workbench by putting my weight on the tab with a wood block worked far better.

Turning back to the front spar, I wanted to temporarily slip the HS-00005 and HS-00006 ribs in place to check for proper alignment, but first I had to trim part of the aft flanges on the HS-00006 ribs so they would fit in place between the HS-710 and HS-714 angles.

Before (R) and after (L).

Replacement HS parts arrive, drilling and riveting hinge bearing

With all these packages arriving so often, It's like Christmas every week!

The replacement HS-702 spars arrived, so it was time to restart work on the horizontal stabilizer. One of the first things I did was prime the VA-146 hinge bearing with a can of self-etching primer from Lowe's (the AKZO was still on backorder) and rivet it to its VA-411 hinge brackets. This primer tends to be watery and runny and didn't leave a good finish compared to pictures I've seen of AKZO-primed parts, so I probably won't be using the spray can stuff very much after this.

The very first rivet set on my airplane. Historic!

Five more rivets later and I have the first complete, albeit small, part of my airplane!

Deburring VS spars and skins, countersinking VS spar doubler, starting rudder stiffeners

After match drilling everything, I (begrudgingly) took apart the vertical stabilizer assembly and set to work deburring any parts that weren't already done, i.e. the skins and all of the holes. Now that I know what to look for, the burrs left over from punching out the skins were a lot more noticeable than they had been back when I first received the parts. I took care of them the same way as the ribs, with the file, deburring handle, and Scotchbrite pad to smooth everything out.

My deburring kit. Simple, but effective.

For deburring the holes in the skins, ribs, and spars, I used the deburring bit that came with the Cleaveland tool kit. It has a hex shank, making it easy to attach to my electric screwdriver and making for a very easy deburring process. All it took was a one-second button press per hole, and I had very clean, slightly chamfered holes. The only downside is that the constant start-stopping of the screwdriver killed the battery pretty quickly, so I had to recharge it halfway through.

While waiting for the screwdriver to recharge I tackled the task of countersinking the bottom holes of the VS-808PP spar doubler. The bottom of the spar sits flush with the fuselage, so the lower 22ish holes in the assembly need to be dimpled on the VS-803PP rear spar and countersunk on the spar doubler to allow for flush rivets to be installed.

I had been a little nervous about countersinking since I had never really been taught the proper way to set up the cage. My past attempts on practice pieces had yielded poor results, so I watched a few videos on the subject before attempting to do it on my airplane. I set the countersink cage using some scrap left over from my earlier mistake on the horizontal stabilizer. All I did was start with the cage set to barely make a countersink, then slowly increase the amount of material cut away until I could get the appropriate rivet to sit flush in the hole.

There will be a spar sitting on top of this countersink, however, so the rivet actually needs to sit around .007" lower in the hole. I have no way of measuring this (that's a little more than 1/128"; I mean, really?) but a few of the videos I watched mentioned that the proper depth would yield a very slight ring of polished aluminum showing around the head of the rivet. An eighth of a turn further on the countersink cage gave me the ring I was looking for.

I cautiously took my now set countersink cage and went to countersink the first hole in the spar doubler. By not applying too much pressure and just allowing the weight of the drill to rest on the piece, the hole makes a slight chatter while being cut and the chattering stops when the cut is complete. Testing with a rivet showed the ring I wanted. To test the depth I dimpled the corresponding hole on the rear spar (using my new DRDT-2, this thing is soooo nice) and fit the pieces together, then put a rivet in the hole to check the overall fit. It works!

I went to work countersinking the rest of the necessary holes and felt a feeling of accomplishment and newfound confidence once I had finished. Now that the cage is set for the #30 countersink, I'm considering just buying another countersink for the other size holes just so I don't have to reset this one every time I need to change the bit.

The screwdriver had finished charging by this point so I used it to deburr the remaining holes. And just like that, work on the VS is done (for now). With the relative speed and ease of assembling the vertical stabilizer compared to all of the odd little tasks done on the horizontal stabilizer, I'm surprised the plans don't have builders begin with the VS. Interestingly, RV-10 builders actually do work on the VS first (that's Jason Ellis's YouTube channel, by the way; his build videos are super informative and entertaining and were a huge influence on me when I first decided to build an airplane).

At this point the only things left to do on the VS are to prime, dimple, and rivet in that order. I'm taking the suggestion to prime the parts before dimpling to make it easier to scuff the surfaces and shoot the primer without the dimples messing up either my Scotchbrite pads or the primer application itself. The AKZO epoxy primer I'll be using is supposed to be pretty damn hard to scratch or remove after it's cured, so I should have no problem dimpling the holes after the primer is applied.



Work on the vertical stabilizer took a lot less time to complete than I expected, so I started work on the rudder while my replacement HS spars were still in transit.

The first step in building the rudder is the most tedious – fabricating the stiffeners. Here's the process I used:

1) The preformed R-915 stiffener, one of eight.

2) Cut in half at the prepunched marks using the hand shears (the piece is too long for the bandsaw).

3) Remove blue vinyl.

4) Use the bandsaw to cut to the desired length (R-915A leaves all 18 holes, and each subsequent stiffener removes one more hole until R-915H which only has 11 holes) while leaving at least 1/4" of material on each end for minimum edge distance for the rivets. This one is an R-915D, so 3 holes are removed from the forward end of the stiffener.

5) With the shears, trim the forward end per the plans by cutting from the center of one notch to the center of the other notch. This is easy to do on the R-915As since the notches are already there, but this is the end that gets removed when shortening the piece for each new stiffener. I used a cut-off piece of scrap R-915 as a template and traced the notches onto the shorter pieces.

6) Grind the edge to its final length (remember to leave 1/4" for rivet minimum edge distance) and remove the burrs using the Scotchbrite wheel. It should be a smooth transition from one edge to another, without any sharp corners.

7) Draw the cut line from each notch on the aft end of the piece. This will be the part that fits into the aft end of the rudder.

8) Trim the excess material using the band saw. The hand shears work too but may deform the piece, so I prefer the band saw.

9) Smooth the edges and grind to the cut line using the Scotchbrite wheel. This is easily the most tedious part since grinding the material is slow and you've got to keep the edge straight the whole time. Then, round the corners and remove any burrs.

10) Repeat for each stiffener. Oh, did I mention that you have to make 16 of these things? This will take a while...