Starboard Wing Nearly Ready for Closeout

After nailing on the rear skin support, the wing is ready to accept a fuel tank and upper skins

I am at a good point to pause on building the starboard wing so that I can finish the fuel tank. I completed a quick task before switching gears though – I wanted to add some protection to the wire running through the lower stringer so that it doesn’t have the possibility of being frayed where it passes through the ribs. I bought some fancy edge grommet from Aircraft Spruce called Spring-Fast® Composite Grommet Edging. It’s much more expensive than nylon caterpillar edging, but it’s a better design that can stay in place without glue.

Adding in a small length of edging to the rib to protect the wire running through the channel
This is the other place I wanted the grommet to protect the wires for the landing lights
Front of the Kuntzleman LTR landing light

I did some of the preliminary work a few months ago so I am ready to start the stinky job of sealing the tank. I started with closing the tooling holes on the end ribs and adding the rivnuts to rib 101, which holds the cover for the fuel level sender. The instructions say to put on the AN-style fittings for the fuel pickup and return at this step, but they were a pain to work around when shooting the rivets into the ribs on the other fuel tank so I’ll install and seal the fittings later.

Lightly sanded the areas where sealant will be applied. I also had to enlarge the holes for the fuel pickup and return fittings – 9/16” and 7/16”, respectively. The SEM Solve stuff I use for cleaning the metal before priming is also a great degreaser to use before sealing
Everything I will need is within reach
Mixing up a small batch (33g) of sealant, which is more than enough to fill a 10mL syringe
This stuff is really stinky – respirator needed!
I applied a small bead of sealant to go between the rib and this flange plate. The holes in the plate were not drilled to the proper size for the 4mm rivnuts, so I used a step drill to open them up to 7/32”, and then a 6mm drill to get the final size.
Finished product

Right Nose Skin

I didn’t do a lot last night, partially because I had to make a run to the dump to get rid of the unwanted pieces of the fuselage shipping container. After a late dinner, I folded over the nose skin and clecoed it in place. I used a framing level to evenly apply pressure along the length of the skin.

I will probably have some extra time to work on my plane in the coming days/weeks – the project I have been working on at my day job was very suddenly canceled.

Landing Light Wiring

I continued some of the electrical work for the starboard wing, securing wiring and adding electrical connectors for the lights.

The two lights share a return wire, so I split out the return using a sealing solder sleeve and then cover the whole thing with heat shrink tubing
Deutsch DT connectors completed and labeled
Added a standoff to rib 9 and to the main spar
Sometimes this guy watches me work on the plane… But he doesn’t like all the noise!

I also decided it was time to get rid of the shipping crate for the fuselage kit. The first crates I received last year were assembled using screws, which made for quick disassembly. It seems the factory has switched to using staples, which are much harder to remove. I did try to pull out a few, but at the rate I was going it was going to take a week! So, I resorted to just chopping it up. I was able to salvage a few plywood panels, but the rest will be going to the wood pile at the town dump.

Goodbye, shipping crate!

The last thing I’ll note is that I’ve been looking more into avionics, since I need to start laying some of the wiring as I build the fuselage. I want to go with a nice Garmin G3X panel, but I’m still recovering from the sticker shock! Something I’m considering leaving out is VOR/ILS capability. LPV approaches seem to be all the rage now, and Garmin recently rolled out some well-priced navigators (GNC 355, GNX 375). These might fit the bill for me, and save me from having to buy a more fully-featured unit like the GTN 650 or a dedicated Nav/Comm like the GNC 255.

Second Wing Build Progress

This past weekend I completed several tasks on the starboard wing. The most time-consuming task was aligning the bottom skins onto the spars – the holes didn’t line up very well, and I had trouble getting the inner skin to lay flat on my first 2 attempts. Here’s what I accomplished over 15 hours:

  1. Completed riveting the ribs to the spars
  2. Align the bottom wing skins. I had to pick an alignment such that most of them fit; this took a few tries. That meant the next task was…
  3. File and/or ream holes to get rivets to fit into the holes, deburring and cleaning up metal shavings as I go
  4. Rivet the bottom skins in place
  5. Paint the landing light bracket pieces white
  6. Prime the leading edge skin – and also paint the small section that surrounds the landing lights
  7. Attach leading edge skin
  8. Flip wing over
  9. Run cable assembly for the wingtip lights
  10. Make wiring harness for the landing lights: twist the three conductors together and then put into a braided wire jacket

As I was trying to find the best fit for the skin, I had to trim the skin a little here because it was pushing up against the bracket for the flap, causing the skin to wrinkle
Setting up many, many clecos and rivets after the third alignment attempt
This is the kind of misalignment I had to work with on the main spar cap. I can’t get a rivet into this hole without elongating it.
All nailed down
Priming the leading edge skin
Fitting the leading edge skin
After flipping the wing over, I started working on the electrical
Using a drill to twist the landing light wires together

Right Wing Ribs Riveted

After confirming that the wing skins look ok when clecoed down, I spent a few hours securing the ribs in place. I was able to do a few things better than on the other wing – for example, I figured out that it was much easier to install the step ribs one at a time, rather than cleco them all in and then have to work in tight quarters.

We had some nice weather, so I also finished priming the wing skins, since I’ll probably be ready to install this week.

The hard way
The easy way
Yup, much easier this way!
Using up my last can of green primer (I’ve switched to gray for the fuselage)
Ready to attach bottom skins

WG-SKN-005 Fit

After taking some measurements, I found out why the outboard upper skin doesn’t fit will. The pitch of the holes drilled in the skin is just a little bit off compared to the pitch of the holes drilled into the rear spar – over the length of 43 holes, there is a difference of 1/8″. I ran into this on the left wing as well, and after consulting with TAF, the solution was to elongate the holes a little using a file and a reamer.

After I tried elongating a few holes, the skin sits flat and looks good. Next I can take the skins off and start pinning the ribs onto the spars.

Upper Wing Skin Fit Check

After flipping the wing back to normal, I started clecoing down the top skins. The inboard skin seems to fit fine, but the outboard skin doesn’t look right – there are ripples when I cleco it down. I had similar fit issues with the other wing, so I’ll have to go back into the archives to see what I did. I don’t think the problem is caused by the twist jigs being out of alignment; my digital level says they are within 0.1 degrees of each other.

I exhausted my entire supply of 1/8″ and 5/32″ clecos pinning up this wing… Mostly because it does take a lot of clecos to hold all the ribs plus skins in place, but also because I have some other assemblies hanging out in the storage area that are clecoed together, like the right-side fuel tank. Lesson learned: Don’t skimp out on clecos! You’ll definitely use them all.

Looks so pretty, wish I could just glue the skin down without rivets!
Here are the ripples I talked about – this is looking at the aft edge of the outboard skin after I installed just a few 5/32″ clecos
The troublesome outboard skin. I start with clecoing to the main spar since it is the most rigid part of the wing, then the rear spar, then the ribs. In this picture I removed the 5/32″ clecos from the rear spar since that was causing the skin to ripple; it sits nice and flat again after removing those clecos.
This appears to be the issue: holes are not aligned correctly… the green you see is the rear spar underneath the skin. On the left side wing, I reamed these holes a bit to fit. Towards the wing tip, this mis-alignment was severe enough that I had to upsize the holes from 4.0mm to 4.8mm. I’m going to try wiggling things around first.

Skin Fit Check

After working on the ribs so that their flanges were as flush as possible, it’s time to check with skins on and make sure they lie flat. I flipped the wing over and temporarily attached bottom skins, next I’ll flip again to do the top skins.

Only temporarily clecod down – if everything looks good, the skins have to come back off so that I can rivet in the ribs and do wiring for the lights

Right Wing Frame

The right wing is coming along nicely. I prepared most of the parts (cleaning, deburring, priming) for both wings at the same time last year, so this one is coming together faster. It’s amazing though, nearly a year has passed since I was working on the same steps on the opposite wing, can’t believe how the time flies!

Right wing and left wing
Preparing the rear spar assembly
Front and rear spars come together on the wing twist jigs. In this photo I’m starting to populate the ribs
The manual says to bend this portion of the flange as needed so that the bottom flange of the rib sits flush with the bottom edge of the spars. The circled portion overlaps the bottom edge of the rear spar’s channel.
Preparing to tap the flange with a hammer
Just a small jog is all I need
Another important task at this point is making sure the flanges are flush with the spar. You can see the flange is too high so I remove it from the spar so that I can tap it down with a hammer
After tapping – much better alignment!
Looking good so far. A few more corrections to rib flanges are still needed before I’m ready to attach the bottom skins.

Right Wing Build Underway, Big Announcement Today at Oshkosh

I received a replacement right wing rear spar earlier this week so now the wing can get built up. Perry from TAF came up with “quite the contraption” (as he called it) to ensure it made its way to NH undamaged – it’s mostly a long piece of 6″ PVC pipe. But it did the trick, as the spar arrived in perfect condition.

Kinda like the tube used for shipping the fuselage longerons, only bigger!
Peeling off the plastic and deburring the holes
After cleaning and priming, assembly begins! Attaching the step ribs and stiffener plates to the rear spar

Sadly I had to skip Oshkosh this year, as I couldn’t take time off this week to go (I was just on vacation last week!). As much as I wanted to go, I am happy to instead be working on my Sling. When I bought the kit last year, there were only a handful of other people in the US building a Sling 4, maybe a total of 5 people. Now, especially with the release of the TSi, there are quite a few more builders and the Facebook Sling Builders group is very busy. It’s pretty exciting to be part of it; almost every day I think about starting test flights and flying out to Oshkosh to show off this beautiful plane!

One big thing I did miss tonight at Oshkosh was the announcement of a high-wing Sling TSi variant at the “Sling Ding” social event. It looks pretty nice, I’m sure it will be popular! To me, the design looks like it took some cues from the Cessna Cardinal, which I know many pilots loved for its swept back windshield/wing, lack of wing struts compared to 172s/182s, and relatively good performance for a 4-cylinder engine. I was looking at buying a used Cardinal before I decided to get the Sling 4 kit. Maybe this will be my next project!