Category Archives: tanks

A day of dimpling

2017-06-24 08.41.12

When I left off last week, I had dimpled the #8 screw holes and hadn’t yet started in on the 3/32″ skin holes.  There are a lot of them!  Because of the way the tank skin is bent, I needed to do some work getting my DRDT-2 set up.  In New York, I had a nice bench with an overhang set up permanently against the garage wall.  For most work here in Texas, I can get away with bolting my dimpler to one of the EAA work tables.  For the leading edge and tank skins, I need a bit of an overhang.  I thought of a bunch of possible ways to set this up.  In the end, I did something very simple and effective.  I used some 3.5″ x 5/16″ lag screws and a piece of 2×6.  This very solidly tied the extension into the table.  A couple of 1″ lag screws holds the dimpler to the 2×6.  It worked very well.

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So I sat in the comfy chair and twirled a dull drill bit in the holes.  I like this method. It is very fast and easy to control.  It just barely takes off the burr while leaving the hole nice and smooth.

I had high hopes of getting in some practice touch and goes, but all thoughts of that were quickly dashed.  It really poured! Even when the airport was in the clear, there were nasty thunderstorms lurking all around all day long.

The DRDT-2 and the carpet covered boxes worked vey nicely.  The dimpling went quickly, but there were still SOOOO many of them!  I finally got all of them done…

Next, I worked on the fuel caps.  There’s a pretty red anodized base and a cheap looking plastic sealing cap. I can get replacement ones made out of machined aluminum, but at $145, it is pretty pricy.  I don’t like the idea of painting the plastic though.  Will likely defer until it is time to paint the plane.  There are some steps, that I’m really excited to get to.   One of them is this shot of the fuel cap base clecoed in.  Pro-seal time is close at hand!

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One clever hint I saw is to set up a swiveling base for the stands.  The Pro-seal is messy and hard to work with on a good day.  These swivels will let me rotate the tank so that I have a good (better?) angle for both applying the sealant and for riveting.  Not quite done in this picture.  I cut these pieces from the end of the 2×6 I used to support the DRDT-2.  Added a rounded edge and then drilled them out for a 5/16″ hex bolt for the axle. We’ll see how they work soon enough.

Next time, I have a few non-Pro-seal tasks to finish on the tank attach brackets and shims. Standard trim, deburr, prime (just the external parts), and rivet.  If I get really saucy, I’ll do the nut plates on the inboard rib (screws pull in the fuel lever sender.  No gasket, only more tank sealant).  If I’m super productive, I’ll do the first set of sealant tasks (closing the tooling holes and adding the fuel flanges and anti-rotation plate).

Lots of work, but somehow the tanks look the same!

I’m finally back from my month long hiatus.  Some things went as planned, but I didn’t get as much flying in as I hoped.  I had hoped to fly to Fredericksburg for Memorial Day weekend, but the strong area wide thunderstorms put a crimp in those plans.  Somehow in a battle between an 865 pound plane and a Texas thunderstorm, I know who will win!

I did make it up to Denton, TX for my LSA-Inspector course.  I learned a lot.  Much of the course was about how to correctly fill out paperwork to keep the FAA happy, but there was a bit of hands on work.  There was a 60 question test at the end of second day.  I aced it, of course, as it was just a bit of memorization.  This didn’t actually get me my certificate.  I had to go down to the Houston FSDO (Flight Service District Office) to get someone to look at my paperwork in person and get me a temporary certificate.  I’ll get a new Wilbur and Orville FAA card in the mail in a couple of weeks.  I don’t actually need it to work on the plane, but will need it in October when I sign off the condition inspection for N903EN.

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My sister-in-law keeps digging up some of my father-in-law’s old tools (he built a BD-4 and most of a BD-5).  This time, she found a rivet puller and some Avex rivets.

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The last time I took the -12 out, I got a message on the EFIS warning me that the backup battery needed to be tested (It has an internal timer that makes sure the battery is tested once a year).  The test is really simple, actually.  When you shut the EFIS down there’s a button to run a battery test.  The way it tests that the battery will stay up for 45 minutes is to simply keep the display on for 45 minutes and see if there is still battery power remaining.  It passed with flying colors.  I’m good for another year.


2017-06-17 12.33.12 HDRI left off last time after getting some of the countersinks done for the tank baffle on the left tank.  I finished off the other 150 countersinks and then started working down the instructions.  Next up was prepping the #8 screw dimples and putting a slight bend in the trailing edges so they hold down better.  I really like these Avery pliers to do that.

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Then I finished up the J-stiffeners.  Just had to unclamp them, deburr, and dimple.

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The instructions suggest using a C-frame to do these #8 dimples as they will come out “crisper” than if you squeeze them.  I used the C-frame on the trailing edges, but ended up squeezing the side ones.

I still have to dimple the interior 3/32″ holes for the ribs, but I need to build an extension for my DRDT-2 for that.

So, I’ll need to make a quick stop at Lowe’s aviation department and get a little lumber so that I can run the dimpler off the edge of one of my EAA tables.  Once that’s done, there are a couple of outside pieces to finish up (countersinking the fuel cap, installing some shims, etc…) and then it’s on to the sealant!  Luckily, my hangar neighbor John used the stuff as an Air Force crew chief, so I’ll have some of his expertise to lean on.

I can hardly wait to get the tanks sealed up since things will happen fast after that.  I will finish up the leading edges (just have to put the landing light lens in) and start installing stuff on the wings.  My fuselage is ordered and should be here in early August!


Stiffeners and Tank Brackets

With my wife out of town for ten days, it was time to put some serious time in at the shop!  The tanks have many, many stiffeners that need to be finished off.  I rough shaped the pieces with a file and sander and finished on the ScotchBrite wheel.

Then all the holes have to be dimpled!  Careful to get them the right way!

Next up are the Z brackets that hold the tank to the spar. A lot of the part prep work is done before separating the pieces.  You ream to final size and make all the countersinks right on the whole bar.

Then it was time to cut the pieces apart.  The stock is pretty heavy, so I used the bandsaw.  Then I used a bastard file to trim the roughest part of the edge before finishing the piece on the belt sander (bulk) and ScotchBrite wheel (final).


My buddy Carver showed up to help.  He had been thinking about building an RV-12 or -14 as well (which is how he ended up wandering into my shop in the first place), but now he’s thinking about a Zenith Sport Cruiser.  That’s a nice plane too!  Not super zippy, but it is much easier to build and can haul a lot of stuff into some shorter strips.

I set him up working on the J stiffeners.  You drill one carefully measured hole at the end and then work your way across the tank.  He is not a “tool” guy, so I showed him how to use a marking gauge to measure from the end and a punch to start the hole.  Then we got the stiffener lined up and drilled the other holes.

I worked on prepping the Z-brackets.  The orange tape masked out the connecting surface with the tank (as it will get proseal).

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Carver had a bunch of “honey-do’s” to get to so he headed out while I kept plugging away at the Z-brackets.  All but two of them get 3 nutplates each.  So I started working through the pile until I had them all riveted. up.

Then we get to work on the tank skin.  Most of the skin parts are delivered ready to edge finish.  The tank skins still had some considerable tabs left.  I took them flat with the bastard file and then finished dressing the edge with sandpaper and ScotchBrite.

At this point, the tank baffle is inserted and cleco’d in place.  We need to counter sink all the holes.  Every 10th hole is left in its pristine state.  When we finally proseal this in place, the un-countersunk holes serve as a strong anchor to align the baffle.  We wait for the sealant to set up and then do a quick countersink on those holes.  I checked each hole with a rivet to make sure it was just barely flush.  I’ve got the countersink totally dialed in now (good as I have another 100 holes to go!).

So here’s one tank.  J-stiffener in place.  Baffle countersunk (one side).

2017-05-13 19.24.02 HDR

I’ll be taking a month long break from building at this point.  The next three weekends are full up.  My wife is back from her trip and it’s her birthday.  That means a straight zero chance of getting out to the airport.  Then we’re taking a trip out to Fredericksburg for Memorial Day Weekend (cool 1942 USO Swing Dance).  Then, I’m finally taking the course so I can get my Light Sport Repairman Inspector rating (to sign off on inspections for the RV-12). When I finally have a chance to get back to the shop, I’ll pick back up on the countersinking.  At that point, it will start to get real!  I’ll be mixing proseal and gluing up parts!

Tank part prep

One of the more time consuming building tasks is parts preparation.  The fuel tanks are no exception.  There are 8 ribs, many short stiffeners, a long J-stiffener, and other small parts to prepare.

This last week, my wife was out traveling, so I had more time to play in the shop after work and on the weekend.  My first task was prepping the ribs.  I spent a little time digging out all the parts and sorting out the ribs. The flanges need to be right at 90 degrees and they must also be fluted to lay flat.  I used my carpenters square to check the bends (mostly pretty close!).

Then you need to position and drill a fitting to the inboard rib.  There is an almost identical one on the bottom edge.  I presume that this is to help qualify the kit under the major portion rule.  In any case, it isn’t too hard.  I have a nice marking gauge that makes it easy to scribe sharpie lines.  The next instruction says to use a step drill to make a .75″ hole.  I dug around in my tool chest and the parts boxes, but I could not find my step drill anywhere!   So that was all for the night until I could visit the local Lowe’s aviation department.

Friday evening, I stopped by my son’s shooting range after work.  We ran a couple of boxes of 9mm through his pistol and a nice CZ 75.  The range also had a new fully automatic machine gun that we ran.  After all that fun, we headed down to the shop (with a stop to get the step drill) to get a little work done before a late dinner.   My hangar neighbor, John, was there, so we chatted with him for a bit.  He just got the wings mounted on his RANS S-20 Raven.  Then Ryan drilled pilot holes in the left and right ribs.

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I step drilled the full sized hole in both (drill press).  Then I clamped the fitting to the rib, match drilled a couple of holes with clecos before Ryan finished match drilling the other holes.

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Saturday was beautiful.  I got to the shop very early in the day and went flying.  I ended up flying to KGLS Galveston.  It wasn’t a long trip (52 nm), but it was my first trip to a towered airport since last June.  It was also the first time that I landed my RV-12 at any other airport.  So quite a momentous flight!  I used the Dynon navigator (though it is hard to miss Galveston… if you hit the Gulf of Mexico, you’ve gone too far!).  I came in from the NorthWest, but had to cut over to land 18. A nice climbing left turn back to the NorthWest got me headed back to KLVJ. The funny figure-8 at the end happened as I was coming into Pearland.  It looked like there was traffic getting ready to depart Runway 32 (the winds were light, but favored 14).  Since no-one was talking, I decided to circle back and give myself more space.

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I fueled up and watched the local banner tow plane take off, make a low and slow tight turn back and the pick up the banner.

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With the flying out of the way, it was time to settle back into building.  I really wanted to finish getting through the ribs (for both left and right tanks).  I worked production line fashion.  I started by twirling a drill bit in the 3/32″ and 1/8″ holes to knock down the big burrs.  Then I shifted to a fine file to knock down the rather substantial burrs that rimmed the lightening holes and tubing holes (maybe 1/32″ high — it took aggressive filing to get it small).  Then I used a small ScotchBrite wheel and sandpaper wrapped around a bit to get at the holes.  I also hit the flanges with a ScotchBrite pad. A quick file to get the tool marks off the flanges, and on to the next rib.

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Once that was done, I moved over to the grinder with the big ScotchBrite wheel to polish the flanges and to bevel the gaps on the front of the ribs.


The next step is to dimple everything.  I needed to do 100’s of dimples.  I’m using the tank dies to get a slightly larger dimple (the idea is to leave a bit of room for the tank compound).  The dimples have to be very crisp to prevent leakage.   I set up my geezer squeezer on the side of my table so that I could easily strong arm all the dimples.  I felt like Popeye when I was done (right arm only).

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Finally got both piles dimpled.

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Next, I had to dimple for some K1000-08D nutplates.  These are used to mount the fuel level sensor.  The screws will tighten and “smush” the tank compound used as a gasket.  These don’t need any sealant, but they do need to be dimpled so that the gasket lays flat.  I might have considered using the “oops” rivet trick, but the plans call for (and the kit provides) the -08D nutplates, so dimpling seemed fine.  This is not in a critical leak area.  I dimpled these (normal 3/32″ dies) using my DRDT-2 dimpler (now fastened with removable bolts into the work table).

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The final step for that evening was to drill some 7/16″ holes in some tubing clips.  That is a bit of a weird bit size.  But, I had earlier gone through the plans to find as many of these “special” sizes as possible.  Sure enough, I went to my drill bit draw and there was a brand new 7/16″ bit.  The drill press did a fine job of finalizing these holes.  I used the sandpaper wrapped around a drill bit trick to smooth these holes.

2017-05-06 18.22.18

My wife is still out traveling and my son was off work Sunday, so we decided to take a trip down to Gulf Coast Regional Airport.  This was a substantially longer trip than any other I’ve take in the RV-12.  The winds were not too bad at KLVJ (10@160) so the departure on 14 was uneventful.  The trip was very bumpy with a lot of turbulent air. It was clear that the crosswind component was growing, however.  As we got to KLBX, we noted that (1) Runway 17 is right traffic and that the winds were not as forecast.  We had to really crab into the wind.  The airport was also very busy (it has very cheap fuel) with some GA traffic, a Dow Chemical jet, and some folks shooting practice ILS on 17.  My landing was pretty nice, considering the heavy and gusty crosswind.  The restaurant there is very nice.  Reasonable prices, friendly waitstaff, and very good food.  The tie down area does lack for chocks though!  I managed to use the tow bar as an impromptu chock and borrowed another tow bar from a Cessna driver who had just landed (he was fine using his parking brake).   We did eventually scrounge up two pairs of chocks (the RV-12 needs two pairs because it will move on its castering nosewheel with only one pair).

So, the first order of business on getting back to the shop was to make two sets of lightweight chocks to carry along.  I had some scrap 2×3 that I ran through the table saw and the chop saw and made these:

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There was a bit of time to do some work on the 14, so I plunged ahead and got the vent line clips and 00005A stiffeners cut and deburred.

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Then I started marking and cutting the 00004 stiffeners.  There is a lot to cut out (20 all told).  At this point, it was starting to get late, so I left the filing and deburring work until next time.

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Next up:  I’ll finish the tank stiffeners, cut and deburr the tank attach zee’s, rivet on the required nutplates, and match drill the J-stiffener.