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.
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.
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.
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.
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.
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).
Finally got both piles dimpled.
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).
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.
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:
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.
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.
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.