Starting Right Fuel Tank

Since I have all the fuel tank build steps fresh in my mind, I’m building the other one now. It took me about 14 hours to build the first one, not including leak testing and remediation (if needed). Let’s see how long it takes the second time?

Closing up the fuel tank

This weekend I made it my goal to close up the left fuel tank. After one last inspection of the tank’s inside for debris, a final cleaning of all the mating surfaces, and staging all the rivets, screws, brackets, and tools, I mixed up a 66g batch of sealant and got to work. It’s a lot of work to complete within the 2 hour working time of the sealant.

I ran into one problem that I didn’t quite anticpate – the last U-shape bracket that attaches the tank to the main spar is too tight to get a rivet tool into – so I have a mix of rivets facing opposite directions. But one in particular, just above the 90° fitting for the vent, had no clearance on either side to get in a rivet puller. I have no idea how you’re supposed to be able to set a rivet in this location! Some quick thinking led me to a solution to use an M4 screw with nyloc nut in place of the 4.0mm rivet.

A nyloc nut and M4x10mm screw instead of a rivet

After setting all the rivets for the brackets, it’s a race against time to temporarily mount the tank to the wing to set the rivets that secure the back wall of the tank. Of course, I had some trouble getting the tank lined up correctly to the wing, but once I did, the rivets went in pretty easily.

Finally – a complete leading edge!
Looking inside to the fuel level sender cover

Now the tank must sit like this for 3 days for the sealant to cure, then I get to take the tank off again and perform a leak test.

Misc Fiddling with Fuel Tank

I’m back at it with the fuel tank. I was fiddling with the fuel sender cover and decided to add a ground terminal by drilling out one of the closed rivets, and then putting it back in but also adding a little metal tab. My concern is that with all the various gaskets and seals I’m using, there isn’t a good ground path for the fuel level sender, so I could get erroneous readings. It’s temporarily held on with some tape for now until I mix up another batch of sealant.

I also riveted this end rib into place. As you can see in the picture, I had my fluke meter out testing the resistance on the fuel sender as I moved the float arm up and down – seems to be working fine, I measure between 3-185 ohms.

I started pulling off the blue tape I had put over the fuel line fittings so they wouldn’t get gobbed up with sealant. I’m surprised the fuel drain is so close to the fuel pickup – the rivets are just a hair width away from touching the filter mesh!

Elevator complete

I finished buttoning up the elevator last night, it looks good!

With the exception of an anti-collision light on top of rudder, I think I’m complete with all the empennage tasks! Now, back to the wings.. which means returning to my cold, cold garage :-/

Perfectly lined up with the horizontal stabilizer

Swapping an Elevator Skin

After trying to adjust the skins to eliminate the “banana” curve at the end of the right skin, I discovered other builders had also run into this, and it was because the skin was bent incorrectly. Worse, you can’t really fix this either.

The end of the skin (left) should form a straight point, but instead it’s curving up

As it turns out, I had another right skin that came with my original kit that I rejected for missing a line of rivet holes for a stiffening channel (it looks like my kit had a Sling 2 skin instead of a Sling 4 skin, since the Sling 2 doesn’t have this stiffening channel). I decided to test fit this skin to see how the end lined up. As luck would have it, this one lines up much better than the replacement skin.

So, I decided to measure where the missing holes needed to be, and simply drilled the original right skin.

The red line is where 8 holes should be for the stiffening channel at the top of the photo

With that problem out of the way, I was able to finish clecoing and riveting up the skin. I finished one side and will complete the other side next.

At the moment, I have the elevator temporarily attached to the horizontal stabilizer with some 1/4″ bolts, and I’m using clamps on the ends to keep the elevator horns lined up perfectly while I rivet the skin.

Elevator skin alignment

One of my fellow builders (Thanks Pascal!) recommended temporarily attaching the elevator to the HS to make sure the “horns” (end part of the elevator) line up perfectly with the HS skins before nailing the elevator skins down. The correct hardware to attach these two parts is AN4 bolts, which I don’t have yet, but I used some common 1/4″ bolts I had on hand. I then used some clamps to line up the horns to the horizontal stab.

I found that I need to adjust the skin to make things fit right. One of the folded ends of the skin doesn’t look quite straight, it looks like the bottom-left diagram in the picture below. The manual says to remove the clecos, adjust skin and try again. I’m not quite sure how this will help though – the holes are drilled pretty tight, and don’t leave much room for adjustment. I’m thinking that I will use a reamer to open the holes up to #31 size and then try again.

Here’s an in-process photo. This thing starts to look much bigger when you put the parts together!

Skinned the Elevator

I’m continuing with closing out empennage tasks; like the rudder skin issue I described last week, I also had a problem with one of the elevator skins from the original kit I bought. The skin was missing a row of pre-drilled holes for a stiffening channel, and I couldn’t see an easy way to match-drill in the right place, so TAF sent me a replacement skin a few months ago. After prepping and priming the skin Tuesday night, I clecoed it together Wed night. So far, so good, but I have to pay attention to the alignment of the left and right ends to make sure they align perfectly – I’ve seen other builders use a laser level and/or a digital inclinometer to achieve this, and I’ll do the same.

These empennage parts go together so much faster than the fuel tank! With that being said, I’m anxious to get back to the wing. I’m ready to complete the close out of my left tank, after which it must be attached to the wing so that the sealant sets in place correctly. We’ve had a long stretch of cold weather in NH lately so it’s too cold to work in the garage right now. The data sheet for the Flamemaster CS3204 sealant doesn’t list an acceptable temperature range for curing, it just says that it cures at room temperature and will take longer at colder temperatures.

Skinned the Rudder

After a long period of working on the fuel tank, I’m at a step where it needs to be attached to the wing. Unfortunately it’s ridiculously cold in NH right now, which makes working in the garage unpleasant. So, I decided to take a break from the wing and finish up some empennage tasks.

I had to request a new rudder skin from TAF a while ago, as the original one that came with my kit was damaged. The replacement skin arrived after I had already started working on the wing, so I didn’t get back to finishing the rudder until now.

It felt nice to quickly finish something in a day! The only thing that slowed me down was having to modify some rivets to shorten them to fit on the aft edge of the skin. Below is the (almost) complete rudder – the only thing left to do is attach the fiberglass cap, which I’m purposely waiting to do until I decide on which recognition strobe I’m going to use. I guess I also have the task of filling the rivet heads at some point.

Next up is the elevator, which also had a skin problem, but I have the replacements in-hand.

Newest piece in my kit, manufactured in 2018. Most of the other parts I have were made in 2016.
Clecoed Up
Done! I may try attaching it to the vertical stab to see how it looks

Misc Fuel tank tasks

I spent Sunday and Monday prepping a few miscellaneous parts: fuel tank cap, fuel drain, and brackets that attach the tank the the main wing spar. My kit was missing one of the brackets, but Jean D sent me replacements a few weeks ago. Here’s the replacement part with my name on it, how’s that for personalized service?!

The various brackets need to have anchor plates attached, held in with tiny 2.4mm (3/32″) flush rivets. Strangely my kit did not include enough of these rivets – I have 24 anchor plates, and each needs 2 rivets = 48 rivets, but the kit only included 34. This size in countersunk-style is a little hard to find, I had to go to a speciality rivet supplier (Jay-Cee) to find some to buy.

After mixing up some more of the smelly sealant, I attached the fuel cap and drain. One of the rivet mandrels broke on the drain, doh! Normally I’d just drill it out and replace, bit I’m afraid to drill this one out because of course it’s the one closest to the fuel pick-up screen and I don’t want to damage that! Luckily it looks like the rivet body formed ok so I’ll just file down what’s left of the mandrel.

The fuel cap is pretty nice, it sits flush with the skin and opens with a key. I was a little surprised though that it’s only held in place with the sealant.

Fuel tank ribs sealed

The five ribs that make up the fuel tank are now installed and sealed for the left tank. Very messy, stinky work! By far, my least-favorite part of this build so far. And there’s still more to do on this tank. And I still have a whole other tank to build!

I’m glad I masked off the areas on the skin first, it made things look much cleaner once the tape was removed. I think all my fillet and fay seals look good, but it looks like a few rivets didn’t seat properly as I was rushing to shoot them in – I’ll have to drill those out and try again.

I used 80g of part A + 8g of part B fuel tank sealant, and that seemed to be enough to complete this part of the job. It was also as much sealant as I could apply within the 2 hour working window. Luckily you can safely plan to clean up excess oozing sealant after the 2 hours, it was still easy enough (though not easy) to remove with acetone and a rag.

The instructions say to install the fuel line fittings on rib 101 and 105 prior to installing the rib in the skin – I don’t agree with this, as it made it much more difficult to accomplish the fillet seal, especially on rib 101 with the fittings that are very close to the edge of the rib. I’ll change up the order a bit when I work on the right fuel tank. I did make sure to protect the fittings with tape so that they don’t get plugged up with sealant – I’ve read several accident reports involving loss of engine power due to fuel starvation, caused by blockage. Here’s one. And here’s another infamous one involving an RV-10. So I’m trying to be very careful.

Not too many in-process photos to share since my gloves had sealant all over, but here’s some decent before-and-after pics. In the interest of time, I just used my finger to shape the fillet seals this time – I’ve done that before with silicone caulk and it seems to work just fine.

I taped off the fittings so that they don’t get plugged up