Jan 29, 2023     18-09 - Leak Test and Wing Attach - (20.6 hours)       Category: 18 Fuel Tank

Initial Leak Test
1/6/23 - 1.1h
1/10/23 - 1.6h
1/11/23 - 2.3h
1/12/23 - 1.8h
1/14/23 - 0.6h
1/15/23 - 1.5h
I wanted to leak test the tanks before installing the rear baffle. Discovering and repairing a leak after the rear baffle is installed could result in major tank surgery. The idea behind the preliminary leak test is to temporarily seal the tank as well as possible, so the tank holds enough pressure to test the rivets and fillets that are already finished. I wasn't worried about a perfect seal as long as the tank holds a little positive pressure long enough to spray the rivets with soapy water. Some minor leaks near the areas that are not yet finished are fine, and might be beneficial as a safety measure to not over-pressurize the tank.

I decided to start simple to see what would or would not work to provide a temporary seal. The first step was to install plugs in the finger strainer flanges. I used the two plugs supplied with the kit, wrapped each in Teflon tape, and inserted them finger tight. I turned my attention next to the rear baffle starting with the rivet holes for the aft rib flanges. I simply ran a piece of scotch tape over each line of holes on the inside and outside of the baffle. I set the baffle in position on the tank, and then ran a length of Gorilla duct tape down the top and bottom seams with the skin. I clecod through the duct tape to hold the baffle in place. The fuel caps are also installed, and can be covered with packing tape if the caps leak.

The first test failed because I didn't account for air escaping the tank through the rear baffle rivet holes. I sealed the top of the baffle and the holes on the inner flange of the baffle, but I didn't tape off the holes on the skin. The air worked its way between the skin and the baffle flange, and escaped out the rivet holes through the skin.

Test number two also failed. I taped off all of the baffle holes, but still had leaks in the corners formed by the exterior ribs and the rear baffle. The corners are very difficult to seal off with tape, especially where sealant is nearby preventing a good air-tight seal with the tape to the skin.

Success! I went for try #3 and managed to get the tank to hold enough air pressure to test for leaks with the soapy water. The corners and seams that are taped together still leak, but that is a good safety to ensure the tank isn't over-pressurized. I used a small bike tire compressor to provide the pressure, and I left it running while I did the test. I kept an eye on the balloon, which did not inflate, but had just a little air in it the whole time. The soap test confirmed the air leaks in the corners with lots of bubbles there. The areas with proseal (rivets and fillets) did not have any bubbles, so I feel good that I got a good test and that my sealant job is acceptable. There is always a possibility of finding leaks after the rear baffle is installed, but I think that possibility is minimized as much as I can. I will repeat the initial leak test on the right tank to get a good feel that everything there is OK, too.

Final Leak Test
1/14/23 - 1.0h
1/28/23 - 2.0h
I was anxious about this particular step in the build before I even signed up for the empennage kit. I wasn't sure I could build fuel tanks that didn't leak, and I nearly went with the quick-build wing option to avoid having to build the tanks myself. It turns out that building the tanks goes pretty well as long as you understand the process and the steps, plan, prepare, and take your time. The end result for me was 2 tanks with zero leaks!!! I credit a lot of my fuel tank success to the Van's fuel tank video. I highly recommend watching it all the way through before starting the tank build, watching again with the plans in front of you and stopping to make sure you understand what's going on, and watching it again for the step that you are about to start. There are some excellent tips in the video that are critical to build a leak-proof fuel tank. Two enthusiastic thumbs up for the video!

The leak test was pretty easy to conduct with the supplied test kit. The kit comes with some instructions that supplement the instructions in the plans, and the kit comes with a couple of extra items to test RV-10 fuel tanks. The test set-up diagram in the plans shows a hose clamp at each end of the air hose, but the clamps don't come with the kit. I found that I didn't need the clamps since the air-valve threaded tightly into the hose, and the hose threaded tightly on the fuel vent line union. The only other item to take care of before pressurizing the tank was to put a balloon on the end of the fuel pickup fitting. The balloon likely will leak under pressure, so you'll need something to hold it tightly to the fitting. I threaded some wire lacing tape around the end of the balloon, which worked well for me. The balloon is an important element of the leak test. The idea is the balloon will burst before the tank does if you over-pressurize the tank during the test.

After setting up the leak test, I hooked the air valve up to a small electric bicycle air pump. The balloon inflated almost immediately and stayed inflated after turning off the air pump, which indicated a good positive air pressure inside the tank. I then sprayed every rivet and every seam with soapy water to detect any air leaks. The only leak I detected was on the right tank fuel filler cap. That leak was very obvious, and left me feeling good that I didn't detect any other leaks in the tank. Leaks can always appear in the future, but for now, my tanks are in good shape!
[Leak Test Kit, Balloon, Electric Bicycle Pump, Spray Bottle with Soapy Water]

Assemble
1/28/23 - 4.1h
1/29/23 - 4.6h
The completed fuel tanks attach to the wing spars with AN3 bolts and wing skins with AN509-8R8 screws. The bolts go through the holes in the spar web to the nut plates in the tank attach zee brackets. I reviewed Section 5 of the plans for the appropriate torque (20-25 in-lbs + drag) and any relevant notes for inserting the bolts. This is a case where torque is applied to the bolt rather than the nut, so I accounted for the following note:
“When applying torque to a bolt be sure to have a washer under the bolt head and lubricate the bolt shank. Add to the overall torque value the torque required to overcome the friction associated with turning the shank of the bolt within the assembly.”
The lubricated bolts ended up with 2 - 4 in-lbs of drag, so I torqued all of the bolts to 27 in-lbs. I was very happy to see that all of the holes lined up well with the nut-plates on the zee brackets, and the bolts all went in without too much drama.

I clecod the skins in place to check the fit after installing the bolts in the attach zees. The tolerances are very tight, and plans specify a zero to 1/64” gap between the tank skins and the wing skins. I ended up filing a little on the right side to get the tanks to fit properly. I started by installing the screws in the leading edge splice strip from the leading edge back to the spar. The fit between the tanks and the leading edges is excellent. I then worked my way down the spar to the last inboard screw. The “Standard Aircraft Handbook for Mechanics and Technicians” that was provided with the empennage kit has a Standard Torque Table (Figure 6-13), that I used to determine the torque for the screws. The table specifies 12-15 in-lbs for 8-32 and 8-36 screws. Add 7-10 in-lbs for drag, and I came up with a final torque value of 22 in-lbs. The end result was a tight fit between the tanks skins and the spars, and good alignment and fit with the other wing and leading edge skins. Successful building, testing, and installing the tanks is huge milestone in the overall aircraft build!
[Socket Set, Torque Wrenches, Electric Screwdriver, Hobby File, Scotchbrite Pad]

  Jan 20, 2023     18-08 - Rear Baffle - (15.5 hours)       Category: 18 Fuel Tank

Initial Prep (Debur, Trim, Drill, and Cut)
1/13/23 – 1.4h
1/15/23 - 2.0h
The rear baffle is the final major fuel tank part to install, and is also the point of no return for previous build steps. Once the baffle is in place, there is no easy way to get into the tanks to fix leaks short of cutting access holes in the baffle and then fabricating and installing leak-proof access panels. That would be a really big job, which I would like to avoid if at all possible. My approach was to perform an interim low-pressure leak test before permanently installing the rear baffle. I did not detect any leaks following the low-pressure initial test, but leaks may still manifest after the baffle is installed and the higher-pressure test is conducted. More detail on the low-pressure initial test is in section 18-09 of my builder log.

Installation of the rear baffle starts with deburring baffle edges and holes, and also scuffing the contact areas between the baffle, ribs, and zee brackets for good sealant adhesion. I cleaned and degreased the baffle and contact areas. I also blew out debris (loose sealant, dust, dirt, …) from the tanks before starting installation.
[Hole and Edge Deburring Tools]

Final Prep (Dimple, Countersink, and Shape)
1/20/23 - 0.7h
Description
[Edge Forming Tool (Vise Grip Style), Hole and Edge Deburring Tools, 22” C-Frame with #40 Reduced Diameter, #30, and #40 Standard Diameter Dimple Dies, Pneumatic Squeezer with #40 Reduced Diameter Dimple Die]

Assemble
1/13/23 - 3.7h
1/14/23 - 2.5h
1/16/23 - 2.2h
1/18/23 - 2.1h
1/20/23 – 0.9h
The Van's fuel tank build video is organized into chapters, and I reviewed the rear baffle chapter before starting the installation. There are a few differences from the video of an RV-8 tank and the rear baffle on the RV-14, but the basic steps are the same and very helpful to prepare. The sealant has a 2-hour working time, so it's important to get everything set up and ready to go before mixing the sealant. There is a lot to do, and not a lot of time after the sealant is mixed. Parts needed for this step included the rear baffle, the tank zee brackets, AD-41H and AD-42H closed end blind rivets, and AN426-AD4-4 and 4-5 solid rivets. Supplies included a pre-measured 3.5 ounce sealant cartridge, which turned out to be the perfect amount for one tank.

I was fortunate to borrow a SEMCO sealant gun from another builder, and the gun was absolutely fabulous to work with. The sealant cartridge fits neatly in the gun, and the gun at about 60 psi delivered a clean and even bead of sealant. I applied a bead of sealant just forward of the rivet holes for the baffle flange, and on the inside edges of the end rib flanges. The baffle engages the sealant bead when it is put into place. I also added an extra “glob” of sealant in the corners of the end rib flanges to seal off that gap. The video demonstrates a good tip to let gravity help get the sealant where it is needed, which made a lot of sense as I applied the sealant to the tank skins and ribs. The video also showed the application of a thin “smear” of sealant on the rivet holes of the rib flanges. The video only puts sealant on the top and bottom flange holes, but the RV-14 instructions have you put the smear on all of the holes.

The tank baffle was set in place after laying down the sealant. I initially cleco'd the holes that were not countersunk in the skin to ensure good alignment, and I cleco'd the holes in the baffle web for the zee brackets to align the baffle and ribs and to pull the baffle tight to the rib flanges. I then flipped the tank over (baffle side down) to let gravity help the sealant contact the skin and baffle while I cleco'd the rest of the holes in the skin.

The tank went back in the cradle after inserting all of the clecos to start setting the closed-end blind rivets at the top and bottom of the baffle web. Those rivets help pull the baffle tight to the rib flanges. A small amount of sealant is applied to the rivets before they are installed to seal the rivet holes. There are also solid rivets at the end ribs that get set with a squeezer, but don't require sealant since they are outside the sealed fuel area.

I finished this work session by installing the tank attach zee brackets to the baffle web/rib flanges. The zee brackets get a very thin smear of sealant around the rivet holes where they mate to the baffle, and then get riveted into place with AD-42H closed end blind rivets. Like the blind rivets at the top and bottom of the baffle flange, this rivets are also “twirled” in sealant to help seal the rivet holes. The sealant was starting to firm up a bit at this point, but I still got good squeeze-out under the rivet heads.

The end of the tank build process is finally in sight! The build wraps up with riveting the rear baffle to the skin, countersinking the screw holes in the attach brackets, and installing the fuel cap and quick drain. The pneumatic squeezer did a good job with the baffle rivets. There isn't any sealant for these rivets since they are outside the sealed fuel area, so letting the tank sit overnight before setting the rivets is not a problem. After setting the rivets in the countersunk holes, I countersank the remaining holes and riveted them as well. After that, I switched to the #19 (#8 Screw Dimple) countersink bit and finished the 5 holes on each of the attach brackets.

I used some Loctite 565 on the drain fittings to block the spiral leak path around the threaded portion of the fitting. I also skipped ahead a bit to the next step and installed the inboard rib plug at the top of the tank and the fuel filter at the bottom of the tank since I had the Loctite out. All of the fluid fittings are torqued according to Section 5 of the plans to 1.5 – 2 turns after finger tight. I could only get roughly 1 turn on the plugs before they were cleared tight enough, and I didn't want to risk breaking the plug by going for the additional 1/2 turn. I plan to let the tanks sit for another week to ensure the sealant is fully cured before I start leak testing. Fingers crossed that the testing goes well - I really don't want to tear the tanks apart to chase down a leak!
[SEMCO Sealant Gun, Blind Rivet Tool and Wedge, Rivet Hand Squeezer with 1/8” Cupped Set, 3/32” and 1/8” Clecos and Cleco Pliers, 3x Rivet Gun with 1/8” Cupped Rivet Set, Tungsten Bucking Bar, Pneumatic Squeezer with 1/8” Cupped and Flush Rivet Sets, Microstop Countersink Cage with #40 and #19 Countersink Cutters, Socket Wrench]

  Dec 21, 2022     18-07 - Fuel Level Sender - (4.5 hours)       Category: 18 Fuel Tank

Final Prep (Dimple, Countersink, and Shape)
12/19/22 – 1.5h
The fuel level sender unit for each tank comes with a float attached to the end of a long 3/32” wire that has to be bent to fit the tank and provide a full range of motion from empty to full. The plans include a 1:1 scale isometric drawing of the wire geometry, which makes it easy to measure the bend locations. WARNING: The plans were updated with new dimensions for the float wire on 3/26/21. Make sure you are using the latest version of the plans! I used my electronic plans to lay out the bend locations, and fortunately noticed my electronic plans did not match my printed plans in the shop before I made any bends. The printed plans were correct, and the bend locations were updated on the float wires.

I looked at a few options to make the bends, and finally decided to go the simple route of clamping the wire in a bench vise at the bend point, and then hand-bending the wire with a wooden block to help keep the wire straight during the bending process. This method worked really well, and I ended up with nice 90-degree bends right where I wanted them. The bends for both the left and right float wires are the same, and the only difference between the two is the orientation of the float. The left float faces forward in the tank, and the right float faces aft.
[Bench Vise]

Assemble
12/20/22 – 0.9h
12/21/22 – 2.1h
I temporarily installed the fuel senders to ensure the float wire geometry was correct. Each wire needed a little tweak to avoid hitting the top skin, which I think was caused by the factory bend at the shepherd's crook not going quite far enough. The result was a slightly sharper than 90-degree bend at the middle of the wire. I also noticed the end of the float wire extends through the sender unit by about 1/16 to 1/8 of an inch. I'm a little concerned by that since the exposed end rubs against one of the sender wires. I'll either try to move the wire a bit to avoid the contact, or trim the float wire flush with the hole in the sender.

The temporary installation is also a good time to test the electrical function of the senders. I checked for continuity between the sender ground plate and the skin of the tank, and I measured the change in electrical resistance as the float travelled between the full and empty positions. The left sender had a range of 30 ohms full to 240 ohms empty, and the right sender was 30 to 246 ohms.

Final installation starts by applying sealant to the exterior of the aft inboard ribs where the fuel sender will be installed. The instructions call for a 1/16 inch thick layer of sealant, which will later be compressed to a 1/32 inch layer when the sender gets torqued down. I started by putting clecos into each of the nut plate holes to keep the sealant away from the fuel sender installation screws. The screws provide the ground path from the nut plates to the sender ground plate, and I didn't want sealant to interfere with the electrical continuity. I also wrapped the fuel senders in plastic to keep them free from excess sealant while I maneuvered them into place.

I removed the clecos after applying the sealant to the rib, and then visually aligned the fuel sender with the holes. I applied Locktite 565 to each of the screws to provide a fuel seal on the threads, and then tightened the screws evenly until the sender was firmly embedded in the sealant. I formed a fillet around the exterior of the fuel sender and confirmed there was a continuous squeeze-out bead of sealant around the interior hole. I may go back later and encapsulate the screws to add an extra layer of leak protection to the Locktite. The final step was to check for continuity between the ground plate on the fuel level sender and the skin, which checked good on both tanks.
[Allen Wrench, Multi-meter, Locktite 565]

  Dec 17, 2022     18-06 - Tank Vent Line and Inboard End Rib Installation - (11.8 hours)       Category: 18 Fuel Tank

Initial Prep (Debur, Trim, Drill, and Cut)
12/6/22 – 1.9h
The vent lines are made from a coil of AT0-032 x 1/4 soft aluminum tubing. The tubing is coiled for shipping, so it took a little time to hand-straighten it. When the tubing was roughly straight, I measured two lengths of 54 1/16” tubing. I used a tube cutter to cut the pieces to length and deburred both ends before flaring the inboard end. I used a tube flaring tool to flare and burnish the inboard end, which I then fitted with a nut and sleeve to attach to the fitting in the aft inboard rib.

I noticed a problem at this point when I tried to dry-fit the aft inboard rib. The last rivet on the top and bottom of the tank attach bracket is also used in the aft rib. I remember thinking it was odd that the rivet schedule used a slightly longer rivet in these two 9(top and bottom) holes, but I missed the note that says not to rivet those holes in the previous step. The result was I had to drill out four rivets (two in each tank) before I could try to dry fit the aft inboard ribs again in order to align the vent lines properly.

Lesson learned… if something looks strange in the plans, look at all the notes on the page before proceeding!
[Hole Edge Deburring Tools, Scotch-Brite Pad, Tubing Cutter, Tube Flaring Tool]

Final Prep (Dimple, Countersink, and Shape)
12/7/22 – 0.5h
The vent line needs some slight bends in the inboard and outboard tank bays to align the ends with the vent clip on the fuel filler flange and the vent fluid fitting on the aft inboard rib. The vent tubing is soft and easily bent by hand. I tried to maximize the bend radii to avoid creating kinks in the line. The bends also help set the gap between the end of the vent line and the outboard rib by the fuel filler.

Assemble
12/5/22 – 0.7h
12/11/22 – 2.0h
12/12/22 – 2.5h
12/13/22 – 1.0h
12/14/22 – 2.0h
12/17/22 – 1.2h
It was a nice break to get an easy step after 2+ months of riveting and sealant in the previous section. The bulk of the riveting and sealing is complete, so this was a good opportunity to inspect the sealant job and add sealant as needed to problem areas. I asked a fellow RV-14 builder to look at my tanks. In addition to pointing out a few areas for additional sealant, he noted that one of the problem areas on the tank is the fillet on the forward side of the tank attach bracket. That fillet is formed blind since you can't see that joint after the bracket is riveted in place. The fillet was mostly in good shape, but I put additional sealant in the corners to make sure that area was as good as I could make it. We also talked about leak testing the fuel tanks. The final leak test doesn't happen until the tank is complete, which means there's no way to make repairs (if needed) without cutting the tank open. I'd really like to find leaks prior to that point, so I'm brainstorming some ideas to do some limited leak testing before installing the rear baffle.

The first step in this section is to install the fuel vent lines. The vent line snap bushings, tubing, and fitting hardware goes in quickly, and then the tubing is shaped by hand to align with the vent line clip on the fuel filler flange and the vent line fitting in the aft inboard rib. I cleco'd the aft inboard rib in place, and dry fit the fluid fittings to help align the tubing and ensure the tubing had the appropriate gap by the vent line clip.

A quick return to riveting and sealing is required to install the aft inboard ribs. I biased the sealant toward the inside half of the rib flanges, and then riveted the ribs in place with a hand-squeezer. There are also 6 AN470 rivets that connect the aft rib, forward rib, and tank attach bracket. I managed to set the 4 center AN 470 rivets with the hand squeezer, but the access to the two end rivets required me to go to a double-offset cupped set in the rivet gun with an angled bucking bar to get into the tight corner. The rivet gun made quick work of the final 2 rivets on each aft inboard rib, which completed the riveting for now.

I like the way Van's gradually introduces new skills as the build progresses. The new skill in this case is working with fluid fittings. The plans have a cryptic instruction to, “Thread the nut onto the bulkhead union and torque the nut.” That brief instruction was the clue to review Section 5 of the plans for additional detail, which in this case is Section 5.27 – Fluid Fittings. There are 3 notes in section 5.27 that are particularly relevant to the installation of the vent line fittings:

1) Torquing the nut on the fluid fitting is different than the torque specs for AN hardware. The procedure is to, “Thread the fitting in with your fingers until you just begin to feel resistance and then an additional 1.5 - 2 turns.”

2) Special sealant is required on the fluid fittings. “Because we cannot always fully tighten tapered thread fittings, and because even after fully tightening the fitting a small spiral leak path remains along the full length of threads, a thread sealant must be used during assembly. Sealants appropriate for use on aircraft NPT fittings are Tite-seal, Permatex #2 and Locktite 565. Do not use RTV, Teflon tape or Fuel Lube on NPT fittings.” I ordered a small tube of Locktite 565 for my vent line fittings. I also plan to use a small amount of tank sealant between the web of the inboard rib and the flange on the fluid fitting. Locktite on the threads, and sealant on the flange.

3) The plans direct the builder to, “apply a small amount of sealant [Locktite] to 2 - 3 threads of the male fitting. Leave the first 2 bare to prevent contamination inside the fluid path.”

I put a little sealant on the flange of the fitting where it contacts the interior side of the rib, and used Locktite 565 on the threads on the exterior side of the fitting to minimize the likelihood of fuel working its way through the threaded portion of the fitting. Torquing the fitting felt a little strange. I threaded the nut on the fitting finger tight, and then marked the nut to keep track of how many rotations I made to tighten the nut. The first quarter turn provided firm resistance, but then the nut became very easy to turn for the next 2 quarters of rotation. It then firmed up again, and became very firm when I had completed about one and half rotations. I decided to stop at that point to not risk damaging the fitting. The same was true of the fitting inside the tank to connect the vent line, and it also took about a turn and a half before the resistance started to dramatically increase. I finished the step by encapsulating the interior fitting with sealant.
[Rivet Squeezer, Flat Squeezer Set, 1/8” Cupped Squeezer Set, 3X Rivet Gun, Double-Offset Rivet Set, Tungsten Bucking Bar, 11/32 Socket and Ratchet, Crecent Wrench, Locktite 565]

  Dec 04, 2022     18-05 - Fuel Tank Primary Assembly - (43.7 hours)       Category: 18 Fuel Tank

Assemble
10/22/22 – 1.2h
10/23/22 – 1.6h
10/25/22 – 1.6h
10/26/22 – 1.4h
10/27/22 – 1.7h
10/30/22 – 1.6h
11/2/22 – 1.4h
11/3/22 – 1.0h
11/6/22 – 3.6h
11/7/22 – 1.9h
11/8/22 – 1.8h
11/9/22 – 1.3h
11/10/22 – 1.5h
11/15/22 – 1.1h
11/16/22 – 2.6h
11/19/22 – 1.9h
11/20/22 – 1.7h
11/24/22 – 1.6h
11/25/22 – 1.8h
11/27/22 – 1.6h
11/28/22 – 1.4h
11/30/22 – 1.6h
12/2/22 – 0.9h
12/3/22 – 2.2h
12/4/22 – 3.7h
Mixing sealant straight out of the cans is messy and time consuming. The sealant sticks to everything, and measuring out just the right amount on the scale takes a lot of dipping and scraping with the mixing sticks. I decided to put the sealant and catalyst into separate syringes to simply squirt the amount of each I needed onto the mixing plate on the scale. This method is much better and cleaner than scooping sealant out of the can with a stick. The syringes are stored in air-tight zip-loc bags, which should be just as good as storing sealant in the can.

I started with back-riveting the fuel tank stiffeners into place. Loading the rivets into the skin before any sealant is applied is nice since the dimples and rivets are totally clean at this point. After getting all of the rivets loaded and taped in place, I mixed 10g of sealant and 1g of catalyst. For reference, this was just enough sealant for me to install 5 stiffeners (1 row) including complete fillets on 2 of the stiffeners. It took roughly an hour from the time I started mixing to starting clean-up at the end. 10g + 1g turns out to be a good amount for me to work. I used the Vans tank assembly video as my technique template for the sealant. I first spread a medium coat of sealant on the bottom of a stiffener and then used a popsicle stick to bevel the sealant over the rivet holes and remove the excess. When I pressed the stiffener into place over the rivets, I noted a small amount of squeeze out around the entire part, which indicated I applied the correct amount of sealant. Back-riveting is standard, but it is easy for the rivet gun to slide a bit due to the sealant. I was happy to see at the end of the process that a very small amount of sealant had worked its way through the rivet hole to the manufactured head of the rivet. Each dark grey circle on the back-rivet tape indicated to me that there shouldn't be any leaks through these rivets! I'll go back later to encapsulate the rivets and finish the fillets to make sure there are no leaks.

The pneumatic squeezer worked well to rivet the quick drain flanges in place. I followed the Vans tank assembly video by applying and troweling sealant on the back of the flange, aligning it to the holes with a couple of clecos, and scooping excess sealant out of the holes with a paper strip. I was surprised to find how difficult it was to insert rivets into holes with sealant in them. The rivets fit fine in the dry holes, but required a lot of effort to insert them for final assembly with the sealant. I used my pick to both align the holes and remove some additional sealant, which allowed me (with a little force) to insert the rivets. The ribs will be exceptionally difficult if I run into the same issue with them.

Van's tank assembly video uses a pneumatic rivet squeezer with a small yoke to rivet the fuel filler flange in place. I planned to do the same on my fuel filler flanges, but my 1” yoke is too big to get adequate access to the rivets due to the funnel shape of the flange. The next option is to buck the rivets, but I was not comfortable with that approach. The tank skins do not have any sub-structure in place at this point of the build, and I was concerned that would lead to damage in the riveting process. I researched some other projects where the flanges were back-riveted with good results, and I decided to try that method. There is some curvature to the skin from the leading edge to the aft edge, which complicates back riveting a bit. I decided to start with the aft-most hole (with the vent clip) and work my way forward. That allowed the skin to follow its natural curve from the aft to forward edge while the rivets being set were held flat on the back-rivet plate. I was happy with the riveting results, and hopefully there won't be any leaks!

Ribs, starting with the inboard forward ribs are up next in the tank assembly. The inboard and outboard ribs are unique since sealant is only needed on the inside edge of the rib and not the entire flange surface. The result is a slightly cleaner installation since there isn't any significant squeeze out on the outside edge of the rib or rivets. The forward inboard rib is a bit difficult to align with the leading edge of the skin, but some “gentle” persuasion with the pick got it into place. I used the pneumatic squeezer for the rivets on this rib, which worked just fine. After riveting the rib in place, I formed a very generous fillet of sealant along the inside edge, and used my remaining sealant from this batch to coat the outside flange where the rib is notched to form the leading edge curve. I stretched the sealant I had as far as I could, but the outside treatment may be a little thin requiring some additional sealant later.

The interior ribs are installed with sealant along the entire flange area. Each rib required 20g +2g of sealant, which was enough to coat the flanges with acceptable squeeze out and create fillets on both sides of the rib flanges. Van's tank assembly video covers the installation of the interior ribs really well. One difference from the video for me was using the squeezer on the aft-most rivets. I have access to a 4” squeezer yoke, but the aft rib flange prevents clean access to the rivet. Bucking all of the rivets, including the aft rivets, worked well. Prior to inserting each rivet, I used a pick to align the hole. That had the additional benefit of removing excess sealant from the hole. I also inserted a cleco adjacent to each rivet I set to help hold things tight as I worked from the leading edge to the aft edge of the tanks. One change I made after the first couple of ribs was to set the tank on end after setting all the rivets for the ribs to work the fillets.

I inspected each of the fillets and encapsulated the rivets that were already set before installing the top J-channel tank stiffener. Most of the fillets looked good, but there were a couple of thin spots that I touched up with some additional sealant. The Van's tank assembly video recommends using an aluminum tube to encapsulate the rivet shop heads, so I bought a .058 x 5/16 x 9" T6 aluminum tube from Van's to make a rivet encapsulation tool. I cut a 3” piece of tubing for the tool, and then finished the tool by deburring both ends of the tube and flaring the end used to encapsulate the rivets. I set the tanks on their sides on the work bench and used a gravity assist to encapsulate the rivets on the bottom side. I let the tanks sit on their sides overnight before flipping them over to encapsulate the rivets on the other side. Fingers (and toes) crossed that there won't be any leaks!

Installation of the J-Channels means the light at the end of the tunnel for this step is a little brighter. The J-Channels for the fuel tanks are just like the J-Channels for the outboard leading edges, with the notable exception of tank sealant. The build instructions specify that the sealant should be applied to the J-Channel rather than the skin, and skin contact with the sealant should be minimized while sliding the J-Channel into position. There will be some contact when the J-Channel is inserted since clearance between the J-Channel and the skin is very tight. The result is a lot of drag on the J-Channel as it gets further down the line of ribs toward its final position. Working and inspecting the sealant fillets on the back side of the J-Channel is also a little tricky, and requires a lighted, flexible mirror to ensure the fillets are done correctly.

The final piece of this step is installation of the tank attach bracket subassembly. Access for the tank attach bracket is really good – both for sealant and riveting. I applied sealant to the bracket flanges similar to the ribs, and I applied sealant to the interior side of the top flange on the forward inboard rib to form a large fillet on the interior junction between the rib and bracket. Actually forming the fillets on the “blind side” of the bracket is similar to working the J-Channel fillets, and requires a small lighted mirror to see how the fillets are formed.
[Large Syringes, Kitchen Scale, Mixing Sticks, Large Back-Rivet Plate, 3x Rivet Gun, Back-Rivet Set, Swivel Flush Set, Tungsten Bucking Bar, Rivet Gauge, Pneumatic Squeezer, 3” Yoke, Flat Squeezer Set, Flexible Mirror with Light]

  Oct 20, 2022     18-04 - Fuel Tank Parts Preparation (2) - (17.1 hours)       Category: 18 Fuel Tank

Initial Prep (Debur, Trim, Drill, and Cut)
10/12/22 – 3.0h
10/13/22 – 1.6h
10/14/22 – 0.8h
The final parts to prepare for the fuel tanks are the Tank Attach Brackets and the top and bottom shims for the tank attach brackets. I also needed to re-do the left and right T-00005B vent line clips from an earlier step. The Vent Line Clips have a pilot hole to final-drill 7/16” holes for the snap bushings that hold the vent line next to the fuel cap flange at the top of the tank. The final hole leaves very little margin on the sides of the clips, and my first attempt got a little off center resulting in a very thin wall on one side of the clip. I also did a poor job trimming and filing the clips, so I decided to try again. The clips came out much better the second time around!

The top and bottom tank attach bracket shims get cleco'd to the brackets and then trimmed flush with the inboard bracket ends. I had to look at the drawing in the plans a couple of times to make sure I was aligning the top shim properly with the bracket. After I had the shim cleco'd in place, I compared it to the completed tank drawing on the first page of the plans for a different perspective, to ensure I had it right. The actual trimming and filing was relatively straight-forward, but I was careful to mark each shim left or right and top/bottom to get them back into the same place later. Dimpling will also take some extra care since the shims are dimpled opposite of each other.
[Band Saw, Dremel with Metal Cutting Disk, Large Flat File, Small Modelling File, Hole and Edge Deburring Tools]

Final Prep (Dimple, Countersink, and Shape)
10/13/22 – 0.8h
Both the top and bottom shims (left and right) need several holes dimpled. I started with the #19 holes on the part of the upper shim that does not contact the tank attach bracket, which is the forward edge of the shim. I dimpled those holes with a #8 Screws dimple die. All of the #40 holes in the top and bottom shim get dimpled as well. I used a reduced diameter 3/32” dimple die to provide some clearance from the larger dimples I just finished, and to dimple the two outboard holes in each of the upper and lower shims. Those holes are very close to each other and the edge of the part, and the reduced diameter die minimizes the chance of damaging the nearby dimples.

The holes on the tank attach bracket flanges are countersunk to accept the skin and shim dimples. I set the countersink cage .007” deeper than flush, which works well for me on countersinks like this. Most of the holes are pretty easy to get to, but the holes at the ends of the brackets don't leave much to square up the countersink cage, so those take a little longer to ensure the countersinks are aligned properly.
[22” C-Frame, #40 Reduced Diameter Dimple Die, #8 Screw Dimple Die, #40 Countersink Cutter, Microstop Countersink Cage]

Prime
10/14/22 – 0.6h
Priming goes very quickly on this step because you only prime parts that are outside the tank. In this case it is the inboard 1/3 of the tank attach brackets and the upper and lower shims. I scuffed the areas to be primed on each part as well as the area on the tank attach brackets that will be inside the tank where the inboard ribs contact the tank attach brackets. I am concerned about the final assembly of the inboard ribs (forward and aft) to the tank attach brackets because of the notches at the top and bottom of each rib. Each notch will need a blob of sealant to prevent fuel from leaking through in addition to the standard sealant treatment on the flanges and rivets. The good news is those areas are accessible from the outside after the tank is assembled, so it will be easy to fix if there is a leak there. Still, I'd rather not chase down and repair leaks when the tanks are finished!
[Grey Scotchbrite Pads, Bon-Ami Cleanser, Dupli-Color Degreaser, Dupli-Color Automotive Self Etching Primer (Green – Rattle Can)]

Assemble
10/16/22 – 3.2h
10/17/22 – 1.1h
10/18/22 – 2.8h
10/19/22 – 1.4h
10/20/22 – 1.8h
This step is completed with some minor assembly including attaching flanges, bearings, shims, and nutplates to the tank attach brackets and inboard ribs. The parts for the tank attach brackets are outside the fuel tank, so no sealant is required to attach the flange bearings, top and bottom shims, and assorted nutplates. Similarly, the K1000-08D nutplates on the aft inboard ribs don't need sealant since they will be covered and sealed later by the fuel sender unit. Access to all of the items on the tank attach brackets and the nutplates on the rib is good for the pneumatic squeezer 3” yoke. The 3” yoke doesn't provide access to all of the rivets for the nutplates on the inboard aft ribs, so I experimented with back-riveting using the 22” C-Frame. This technique will be used to set the very large 3/16” rivets to plug the tooling holes in the inboard and outboard ribs. I was really happy with the ease of back-riveting with the C-Frame and the results. This is definitely a good option for riveting in the future!

The moment I'd been fretting about since before I purchased my first kt finally arrived - assembly with tank sealant. I decided to start with an “easy” step to chalk up an early success with this new-to-me product and process. Each of the inboard and outboard ribs have tooling holes that need to be filled with 3/16” rivets and leak-proofed with sealant. The rivets don't attach parts together, so the process is to apply sealant and drive the rivet in the holes in the ribs.

While I had hoped for an early success, the reality was a dismal failure. The sealant mixing and application went very well. I used a digital kitchen scale to measure out 10g of sealant (white) and 1g of catalyst (black) on an aluminum plate protected with masking tape. I mixed the sealant with a popsicle stick, and used the stick to apply the sealant to the area for the rivet. I found with a little care, some good disposable gloves, and protective paper on the work bench; the sealant was reasonably easy to work with and clean up at the end of the session. The sealant is roughly the consistency of butterscotch ice-cream topping, and is extremely sticky. A plan to contain and control the mess is definitely a good idea before mixing the first batch. I also learned that 70% alcohol wipes are very effective at cleaning sealant off tools and parts before the sealant sets up.

The 3/16” rivets are too large for a standard light-duty pneumatic squeezer to set. The Van's tank assembly video recommends using a C-Frame and rivet gun on the floor to set the large rivets. I set up my C-Frame with a 3/16” cupped set and installed the flat set on the rivet gun to back-rivet. Given the large rivet size, I upped the rivet gun pressure to 60 PSI. I also used small levels to ensure I held the part square in the C-Frame during the riveting process. Unfortunately, my very best effort wasn't good enough to drive the rivet correctly. I tried 3 rivets, and all three ended up tipped and off-center. That may be OK as long as they will stay in place and seal the hole, but they are not pretty. Ultimately, I decided to drill out the rivets. My analysis is the AN470AD6-5 rivets are too long, and it might be worth spending some time with a rivet cutter to shorten them a bit. A shorter rivet also takes less sealant after it is set to encapsulate it. I didn't have access to a rivet cutter, so I needed another option to set the rivets at their original length.

I enlisted the help and advice of a fellow builder friend to try again with the 3/16” rivets. We managed to drill out the bad rivets successfully, and straightened the rib webs where the tilted rivets had twisted them a bit. We used a hand squeezer this time to allow us to set the rivets slowly with as much control as possible. Fortunately, this method worked, and we ended with relatively straight squeezes for each rivet. The rivets are not fully set, since that amount of squeezing would probably tempt fate and end up with badly tilted rivets. Instead, per the plans, we squeezed the rivets enough for them to swell inside the holes and hold firm. After encapsulating the rivet shop heads in sealant, they should be pretty effective fuel tank plugs.

The fuel strainer flanges and anti-rotation plates on the aft inboard ribs use AN470AD4-5 rivets. I am much better equipped to set the 1/8” rivets than the 3/16” rivets used to plug the tooling holes. Getting back to a manageable rivet size and familiar rivet setting process allowed me to clearly see the additional complexity of the tank sealant, and highlighted poor riveting practices that I mostly got away with on dry rivets.

The first thing I did was make plugs for each of the flanges with paper towels to keep sealant from getting inside the threaded area of the flange. The plugs worked great - I simply threaded them into the flange before starting, and threaded them the rest of the way through when I was finished. No mess there at all! I then mixed up another 10g+1g batch for the 4 strainer flanges and 2 anti-rotation plates, and prepared them the same way the Van's tank assembly video does with the fuel filler flange. I put down a medium-thick layer of sealant around the entire contact area, and then used a craft stick to thin and bevel the layer of sealant. A couple of clecos secured the flanges in place, and I could see a reasonable amount of sealant squeeze-out around the edge of the flange and in the rivet holes. I used the rivet squeezer to set each of the rivets with mostly good results. There were a couple of rivets that didn't get set squarely, so I drilled those out and tried again.

I was surprised at how much stray sealant ended up on the part and tools. Even a minor touch of wet sealant on your gloves will end up absolutely covering everything else you touch. There isn't much you can do about it other than clean as much as you can when you're done – the alcohol wipes are great!
[Pneumatic squeezer, 3” Squeezer Yoke, 1/8” Cupped Squeezer Set, 3/16” Flat squeezer Set, 22” C-Frame, Flat Rivet Set, 3x Rivet Gun, Hand Squeezer, Digital Scale, Mixing Sticks, Dupli-Color Degreaser, 70% Alcohol Wipes, Acetone, Shop Rags]

  Oct 10, 2022     18-03 - Fuel Tank Skins Preparation - (31.5 hours)       Category: 18 Fuel Tank

Initial Prep (Debur, Trim, Drill, and Cut)
9/12/22 – 1.9h
9/16/22 – 0.3h
9/17/22 – 2.1h
9/18/22 – 1.9h
9/26/22 – 1.1h
9/27/22 – 1.3h
9/28/22 – 4.4h
9/29/22 – 1.1h
10/2/22 – 5.7h
Like the outboard leading edges, the fuel tanks have a J-Channel along the top of the skin that gets match drilled to the skin. I cut the fuel tank J-Stiffeners from the 72” J-Channel stock for the outboard leading edges and tanks using a Dremel with a metal cutting disk, and completed the cut with a Dremel sanding barrel and disk. After trimming the J-Channels to the proper length, the inboard #40 “starter” hole is drilled according to the dimensions in the plans, and the rest of the holes are match-drilled to the skin from there.
[Dremel with Metal Cutting Disk, #40 Drill, Scotch Brite Flap Wheel, Hole and Edge Deburring Tools]

Final Prep (Dimple, Countersink, and Shape)
9/17/22 – 0.6h
9/18/22 – 1.1h
9/26/2 – 0.4h
9/30/22 - 3.4h
10/4/22 – 1.6h
10/5/22 – 0.6h
10/10/22 – 1.6h
The rivet holes where the fuel tank skins attach to the rear baffle are countersunk rather than dimpled due to the combined thickness of the skin and baffle. However, the skin is still only .032” thick, so extra care is in order to ensure the countersinks stay true to the center of the hole and don't go too deep. The plans specify that countersinks up to .005” too shallow are acceptable, and preferable to countersinks that are too deep. I set the countersink cage to .002” shallow, which worked for me to get close to flush, with a little margin for deburring. The nearly flush rivets can be shaved flush later.

The rear baffle gets cleco'd into place to provide a stable pilot hole for the countersinks. There is a note to leave every 10th hole uncountersunk to help with alignment of the baffle during the final assembly. I'm not totally convinced that will make a huge difference, but I deferred to the hundreds of tanks built before mine and followed the plans. The alignment holes will be countersunk and riveted after the tank is completely assembled and the sealant has cured.

Dimpling the skins takes a little extra care because there are a few different things going on. First, the holes for the rear-baffle were countersunk, so obviously none of those holes are dimpled. Similarly, the fuel tank drain flanges, which are attached to the outside of the skin, are provided with countersinks. The holes in the skin where the flanges attach are not countersunk. The trickiest “no-dimple” zone are the #8 screw holes on the inboard edge of the skin that align with the fuel tank attach brackets. Those holes, as well as the holes in the attach bracket shims, will be countersunk later in the tank assembly process. The plans include a note to “Dimple the screw holes in the fuel tank skins using the C-frame tool and a hammer rather than forming them with a rivet squeezer. This will result in "crisper", better looking skin dimples.”

The final step in this section is to countersink the fuel tank cap flanges for the dimples in the tank skins. I countersunk the flanges .007” deeper than flush, which worked well to get a good fit with the dimpled holes. The trickiest part of this step was clamping the fuel cap flange to the bench, which isn't particularly difficult.
[#40 Countersink Cutter, Microstop Countersink Cage, 22” C-Frame, Edge Forming Tool (Vise Grip Style), 22” C-Frame, #40 Standard Diameter Dimple Die, #40 Reduced Diameter Dimple Die, #8 Screw Dimple Die]

Assemble
9/15/22 – 2.4h
This section of the plans starts with a warm-up task to attach nut-plates to the Tank Attach Zees. Each bracket, with the exception of the most inboard one on each tank, gets three nut-plates that will align with the holes in the spar to help hold the fuel tanks in place.
[Pneumatic Squeezer, Flat Squeezer Set]

  Sep 12, 2022     18-02 - Fuel Tank Parts Preparation (1) - (25.5 hours)       Category: 18 Fuel Tank

Initial Prep (Debur, Trim, Drill, and Cut)
8/31/22 – 1.8h
9/1/22 – 2.2h
9/2/22 – 4.0h
9/3/22 – 3.5h
9/5/22 – 2.6h
9/6/22 – 0.8h
9/7/22 – 1.7h
9/8/22 – 0.7h
9/9/22 – 0.3h
9/10/22 – 3.3h
The outboard leading edges were a good dress rehearsal for the fuel tanks. The structure is virtually the same, with the addition of some plumbing and the rear baffle. Part preparation is also nearly identical starting with straightening and deburring the fuel tank ribs. One thing I learned from the leading edges is to spread out the flutes in the ribs if possible. If there are flutes between holes that are next to each other, it is harder to buck those rivets later since you have to use a narrow bucking bar to get between the flutes. This time around I avoided putting flutes between consecutive holes as much as possible. The other thing I noticed is each rib takes me approximately an hour to prepare.

The inboard rib for each fuel tank comes in two pieces (forward and aft) to allow for a tank attach bracket to be inserted between the rib pieces. The aft inboard ribs have a large hole surrounded by #30 rivet holes to attach a finger strainer flange, which holds a strainer to remove large particles from fuel exiting the tank prior to entering the rest of the fuel system. The plans detail steps to add an additional finger strainer flange hole at the top of the rib. The plans specify the center location of the 3/4" upper finger strainer flange hole, which is enlarged to final size with a step drill followed by match-drilling the flange for the rivet holes. According to another builder's log, the upper finger strainer is for future growth for a powerplant that requires a fuel return line to the tanks. The hole will ultimately be sealed for now, but is available if needed in the future. A confusing aspect of the plans for this step is the language change from only addressing the left tank and expecting the builder to mirror those instructions for the right, to discussing both left and right inboard ribs together in the plans. For example, there is a step to final drill “the two remaining finger strainer flanges that will attach to the lower region of the rib.” When I first read the plans, I mistakenly thought the reference was to the upper and lower flanges (two) on each rib. The plans actually refer to the single pre-cut flange hole at the bottom of both inboard ribs (two).

The fuel tanks have several skin stiffeners that attach to the bottom skin of the tanks. The stiffeners are roughly 9” long L-channel pieces that fit between the ribs. Each tank gets 10 outboard stiffeners and 1 slightly shorter inboard stiffener, which are cut from long L-channels. The inboard stiffener L-channel also includes 2 fuel tank vent clips. The vent clips get riveted to the fuel filler flange and hold the vent line in place at the top of the tank. The plans specify step-drilling the hole in the vent clip to 7/16” for the snap bushing around the vent line. The vent clips are maybe 5/8” wide, so the vent line hole gets very close to the edges of the clips. In my case, the drilling process got a little off center on one of the clips and the final hole is right on the edge. That vent clip is too fragile to reliably hold the vent line in place, so I ordered a new L-channel from Van's to try again.

The Tank Attach Zees are also attached together in two long strips, and have to be separated. Before separating, all the holes are final drilled, and the #40 holes are countersunk for flush rivets that hold nut plates in place. I learned from the skin stiffeners, that it is easier to do some of the deburring work before cutting the pieces apart. I deburred all of the holes as well as the lightening holes in each attach zee first. I also took an initial pass at deburring the long edges to remove the larger tooling marks. I used a band saw to separate the parts, and then the 6” cut and polish wheel on the bench grinder to remove the tabs that were left over.
[Fluting Pliers, #12 Drill, #30 Drill, #40 Drill, Step Drill, Band Saw, 6” Scotch Brite Cut and Polish Wheel, Hole and Edge Deburring Tools]

Final Prep (Dimple, Countersink, and Shape)
9/4/22 – 2.0h
9/8/22 – 0.5h
9/10/22 – 0.4h
Dimpling and countersinking wrapped up the part preparation for this step. The #40 holes in the rib flanges were dimpled first. The plans include a note that “the top flange aft hole in each Tank Inboard Rib – Fwd” has limited access, so a pop rivet dimple tool is required for that hole on both inboard forward ribs. I could dimple the rest of the holes in the rib flanges with a pneumatic squeezer and reduced diameter dimple die. The aft inboard rib also has some holes in the web for nut-plates that need to be dimpled. The nut-plates are used to attach the fuel sender unit, and are dimpled flush on the outside surface of the rib. The best approach for these dimples was a reduced diameter dimple die in a 22” C-Frame. I also used the C-Frame to dimple the skin stiffeners with a standard-size dimple die. The bend for the stiffener flanges is far enough from the holes that the standard die works well here.

The Tank Attach Zees are made from relatively thick aluminum, so they are countersunk rather than dimpled. The only holes that need to be countersunk are the #40 holes for the nut-plates in the top flanges of most brackets. The inboard attach zee does not have any nut-plates, so there is no countersinking required on that one. The nut-plates for the inboard attach zee were actually riveted to the main spar several steps ago. Now I know what those 3 nut-plates in the spar are for!
[Scotch Brite Flap Wheel, Pneumatic Squeezer with Reduced Diameter 3/32” Dimple Die, PoP Rivet 3/32” Dimple Die, Blind Rivet Puller, 22” C-Frame with 3/32” Dimple Die and Reduced Diameter 3/32” Dimple Die, 3/32” Countersink Cutter, Microstop Countersink Cage]

Prime
9/11/22 – 1.4h
9/12/22 – 0.3h
The plans for the tank include the note, “Do not prime any areas that will be in the inside of the tank.” The mating surfaces get scuffed (aggressively), cleaned, and then sealant is applied to those areas. There are, however, a few exterior tank parts that can be primed if desired. The tank attach zees are outside the tank, with the exception of the bottom flange which is attached to the outside of the rear tank baffle with blind rivets. The bottom flange on the tank attach zees gets a small amount of sealant around the rivet holes. I decided to mask off the bottom flange, and prime the rest of the tank attach zees before installing the nutplates on the top flange.
[Grey Scotchbrite Pads, Bon-Ami Cleanser, Dupli-Color Degreaser, Rust-Oleum Automotive Self Etching Primer (Green – Rattle Can)]

  Aug 31, 2022     18-01 - Fuel Tank (Plans) - (7.0 hours) Category: 18 Fuel Tank

The time to build the fuel tanks is finally here. This is the step in the entire airplane build process that I am most hesitant about, and it nearly tipped the scales to going with quick build wings vs. my final decision for the standard build option. There are also builder assist programs that will help with the tanks, but that route was simply too expensive. We'll see if this phase of the build is much ado about nothing, or something I needed professional help with!

As usual, I scanned the safety directives and alerts, service bulletins, notifications and letters, and revisions and changes on the Van's support page to ensure my plans and parts are up to date. I was surprised to find only one revision to the plans, which tells me the design and construction steps are really solid. The change had to do with the geometry of the float wire for the fuel sender unit, which was already corrected on the plans I received with the kit. Another useful section of the Van's website is their video on fuel tank construction. I watched the video start to finish twice, and plan to keep it cued up as I go through my build process to review specific techniques at each stage of the build. The video uses an RV-8 tank as the example, which has several differences from the RV-14 tank; but most of the video is still relevant and I highly recommend it.
https://www.vansaircraft.com/faq/fuel-tank-construction-tips-and-techniques-video-series/

The fuel tank is a unique part of the build due to the internal plumbing and the need for sealant to prevent leaks through the various joints and rivets. Structurally, the tanks are similar to the outboard leading edges with notable differences with the inboard rib and the addition of skin stiffeners on the bottom skin. The inboard rib is split into two pieces to allow a tank attach bracket to extend through it. Another difference for me is priming is limited to specific parts on the exterior of the tank. Van's fuel tank tips video stresses the need to clean the parts well before applying the sealant, and warns against the problems of using too much sealant. The plans have very detailed written steps compared to other sections of the build, and they should be good at keeping everything on track.

Time for fun with tank sealant!