Control Stick Mounts

What should have been 5 minutes of work turned into 2 hours! While attaching the control stick brackets (CF-BKT-009-X-C-) per sheet E6 of the manual, a mandrel broke off a rivet in a hard-to-reach location. It took me over an hour to remove it. First I tried drilling it out from the rear, and found that was nearly impossible. I switched to using a Dremel with a small grinding wheel to grind away the rivet face, until enough of the rivet was gone so that I could push it through as if I had drilled it out; that wound up working. All that grinding damaged the foam, so I had to replace the pieces and replace them.

This is the bracket for the control stick – one on each side, seemed simple enough
Though hard to reach (especially in the corners), these rivets went in OK…
… but then this rivet mandrel decided to snap off! I might have been tempted to just cut off the mandrel, but the rivet didn’t form fully on the opposite side, so it needed to come out. Normally it’s really easy to drill out a rivet… except here, there’s no way to get a drill into this space!
Finally after grinding out the old rivet, I put in a new rivet and then replaced the foam

Cabin Heater

Since I live in New England, having effective heat in the airplane will be important to me. As I was reviewing the updated fuselage manual for the Sling TSi, I noticed that TAF updated the cabin heater design, from a system that uses ram air flowing through a cuff over the muffler, to a system that uses a heat exchanger coupled into the Rotax cylinder head water coolant loop – which is the same approach used in cars. I think this is a much better design, and greatly reduces the possibility of carbon monoxide and other exhaust gases coming into the cabin. I also think it’s important to be able to send warm air onto the windshield to clear fog.

After a bit of sleuthing, I believe I’ve found the unit that TAF sources, a Siroco Tenere Performa 4D heater. I have an email into TAF to see if they’ll sell the parts to me to put this into my Sling 4. I’m also considering coming up with something on my own. This box weighs about 4 pounds, uses 80W for the blower motor, and will supply up to 20,000 BTUs of heat per hour, which should be more than enough. But it doesn’t really have any way to direct airflow, so the TSi kit also supplies (I think) a bunch of hoses and ducts with butterfly valves to control the airflow.

I’m surprised to see there aren’t many off-the-shelf options for cabin heaters that take advantage of the Rotax engine’s water cooling system. Kitfox offers a very simple device for their planes — it’s really just a case fan bolted onto a heat exchanger. I’ve also read that Vans may have something for their RV-12. But I’d like to see something closer to what’s in cars, with dampers and doors in a blower assembly that directs airflow to your feet, face, or defroster vents.

Forward Floor Insulating Foam

There’s an interior skin that goes over the forward floor bottom skin, so I needed to install the insulating foam first.

A reinforcement skin CF-SKN-007-L/R fits between the bottom skin and the stringers/main spar; I just wanted to make sure I have a pic capturing that I installed it correctly
Checking fit of all the foam pieces before I remove the adhesive backing
All of the foam pieces now taped to the skin
CF-SKN-011-C-C- sits above the foam. For some reason I thought I would be attaching the foam to this skin, so I had masked off the areas with painters tape
Oh well, I guess it still looks neat!
Starting to place rivets, using the manual to help identify which holes do NOT get riveted at this step

Forward Floor Stringers

Having completed page E3 (Main Spar and Undercarriage Channel), the next step is to attach the forward floor stringers. The rivets go up through the bottom skin, so I had to rotate the fuselage assembly onto its side. It winds up resting on the forward upright for the main spar carry thru, which I clamped onto my work table. Once I put it back down, I’ll add the insulation foam to the floor.

Hopefully the plane won’t ever bank this hard in flight!
View from the belly side
Not an exciting task, but I filled all the rivet heads now since I’m not sure when I’ll have easy access to the belly again

Main and Rear Spar Carry-Thrus

I’ve been quite busy the last week with family and friends so I only had an hour here or there to make progress on the plane. Most of the work has been on attachment of the spar carry-thrus to the center fuselage. Those are attached now, so I think the next step is to rotate the assembly onto its side to attach the forward floor channels to the bottom skin.

These brackets (CF-BKT-023-L/R) that sit on the main gear channel are quite thick and weren’t perfectly formed. I had to spend some effort with a hammer fixing the flanges to make them flat (see next pic)
The red arrows indicate where these brackets were bulging a bit and needed some hammering to flatten them
After adjustment, the brackets fit better. Still, I had holes that didn’t line up, especially the three holes that go into the upper surface of the main gear channel.
This elevator control stop (CT-STO-001-X-A-) needed some notches cut into it for an adjacent rivet to have room to form properly
CT-STO-001-X-A-: not sure what happened here, but the holes in the bracket don’t match the holes in the skin. One of the parts is a newer revision? I wound up drilling new holes in the skin to line up with the outer holes in the bracket
Aileron control stop CT-STO-003-X-A-. The holes for the bracket were 4.0mm but the holes in the skin were drilled to 3.2mm so I had to open them up with a reamer
Only after I had already riveted these brackets did I realize I needed to leave the red circled holes open – there’s a close out bracket that comes in a later step. The manual really should have a note about this! It was not easy to drill out these rivets, I had to use a right-angle adapter. Also in this pic, the purple circle shows why the notches were needed in the elevator control stop
Main gear uprights riveted in.. lots of rivets. I put these in before attaching the main spar carry-thru, which is not the order the manual states; my thinking was that these rivets would be harder to access once the main spar carrythru is attached (…I was right!)
Installing the rivets for the main spar carry-thru from underneath, not the easiest angle to work from.
Floor ribs riveted into the main spar carry-thru webbing. Pretty tight quarters here to get my rivet tools into!
I attached these support tooling brackets after riveting in the carry-thru. Notice the holes drilled 1-2-3-4-5 into these brackets? Nice thoughtful detail!

Resuming Fuselage Work

I had planned to spend Sunday doing the majority of the sealing work on the right fuel tank, but I discovered a crease in the leading edge of the skin. I spent a bunch of time trying to smooth it out, but I was not satisfied with the result. I have to ask TAF to send me a new skin, so unfortunately that means the wing is on hold for now.

Now I’m back to working on the fuselage. We had good weather today so with the remainder of the day I primed a few more parts that I will probably need this week. Afterward I decided to spend some time putting in the 1/4” “super” insulation foam I recently got from Aircraft Spruce. Like other builders, I opted to get denser & thicker foam than what is supplied with the kit.

At first I cut the material using a standard box cutter, which works ok but tears the material a little, even with a brand new blade. I remembered that I had a nifty rotary cutter made by Fiskars, which cuts this material without tearing and leaves a clean, square edge. I cut pieces to fit underneath the baggage floor and for the center fuselage floor between the seat ribs.

This Fiskars rotary cutter is perfect for cutting the foam
Perfect cut using the cutting wheel
Foam squares attached to the baggage floor, after I attached the channels
Foam pieces cut for the rear seat floor, but not yet set in place with the adhesive backing

Next up will be attaching the main spar carry-through to the mid and front lower floor sections, so this assembly is about to start becoming quite big.


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