Custom Cowl Mounting Strips – Trial Fit

The upgraded cowling strips fit remarkably well. Clecos are in many of the holes at this point and that’s without having to drill anything out. Ultimately, holes will need to be lightly ‘dressed’ with a #30 reamer. This will allow the rivets be positioned and set easily in the 3 and 4 layer stack-up of parts without a fight. The good news is, it’s all a pretty decent situation to begin with.

Earlier I did a little priming of the underside and edges of fastening tabs for the galvanized steel firewall. It’s winter cold outside, and I can’t really do spray painting just now. It was a small hidden area so I brushed on the gray 2-part epoxy primer. It took several days to cure fully. I’ll probably paint the entire firewall, mostly for aesthetics, when the weather warms a bit.

Care will be needed to address some gaps between layers of the parts stack-up. I believe that by removing most (or all) of the clecos across the top edge of the firewall and then riveting around the corner, fitting and pulling one rivet at a time while the pieces are free to move and pull together will allow the gap to close where the rivet is pulled.

I’m planning to install the ballistic parachute and that means I’ll be needing to accomplish some dimpling for most of the holes across the top of CF-RIB-003 and actual countersinking with a 120 deg pilot-cutter, along the top edge reinforcing pieces of the firewall, to accept 3,2 x 8 mm countersunk rivets. More on that in a future installment.

We’ll see how it all goes. Warmer days are ahead.

QB Fuselage Rework – Part 2

Sometimes you have to go backward to go forward. Drilling out rivets is one of those things you have to do sometimes when building and airplane. Fortunately, I’ve had to do very little reverse-assembly. But, there are a couple of parts I needed to add and I’ve opted for an upgrade to the cowling fasteners that calls for replacement of narrow, factory-mounted parts, with wider aftermarket replacements. Drill baby drill!

There’s a reinforcement plate, near where the ballistic parachute rocket canister mounts. The plate rivets to the RIB that forms the back wall of the parachute compartment. Several rivets had to be drilled out and removed so that the plate could be positioned and riveted. Done.

There was also a missing attachment angle for the top right edge of the parachute compartment. It should have been installed at the factory. It’s going on now, but a few rivets had to be removed before the angle was riveted using those same holes.

To go along with the other rework, I’ve opted for an upgrade to the factory-supplied cowl fasteners. I want to use Camloc fasteners rather than the Dzus fasteners that come with the kit. The Camloc parts are more user-friendly when it comes to unfastening and re-fastening of the cowling. For best results, getting the fasteners a little farther away from the edges of the fiberglass cowl is a good thing to do. That involves replacing the factory cowl fastener strips with wider parts that I ordered from Midwest Sky Sports. They make these wider strips and use them for the planes they build and they seem like a good idea to me.

The rivets holding the factory-strips needed to be drilled out. I did it. Now I don’t have that to contemplate anymore. I did a quick fit of the new cowling fastener strips. They look like they fit pretty well. That’s a relief after removing the factory parts.

Rudder Pedals – Trial Fit

The sight of rudder pedals in their proper home makes the whole project seem like it’s on track to be a finished airplane. That’s important for me to realize, now and again, and helps to reinforce the idea that finishing the airplane is possibly doable.

My Sling-branded rudder pedals are an option that I knew about, liked, and deliberately ordered with the quick-build kit. When my QB kit was delivered, the pedal parts I ordered were not there. Most of the related parts I got were for toe-brakes. It took more than 6 months to get things sorted out with the factory and finally get all of the parts for the pedals I ordered — all good now.

The typical braking configuration for Sling airplanes is a simple, single hydraulic master cylinder, lever-operated mechanism that evenly applies the Matco disc brakes for both main wheels. Toe-brakes are a necessity for Sling tail-draggers, but are available as an option for us lowly nose-dragger pilots. Space is pretty tight for 4 independent toe-brake master cylinders with all of the plumbing. From what I’ve been able to determine, Sling pilots find they like the hand-brake, even if they’re used to toe-brakes. I’m going for simplicity. My Piper Warrior has toe-brakes. They’re fine, until they leak all over your pedals and carpet and demand maintenance. I’ve been there, done that and got the T-shirt – thank you very much. Simplicity is a virtue. I’m going through the simple-is-better phase of my life now. You can have toe-brakes in your Sling.

I had hoped that I’d be done with this pedal mounting business – the final assembly. But, it’s turned into a trial attempt. The pedal tubes, bushings and brackets fit nicely, but I did find some clearance issues with the pedal stops that I’ll need to address. That means the whole pedal assembly has to come out again, except for the permanently riveted floor brackets. As I moved the pedals I heard squealing. It’s a little hard to explain, but the edges of the lower hands of the stops can (and do) occasionally touch the edges of the control arms where the nose-wheel pushrods and rudder cables attach. I have to do something. Exactly what, I don’t quite know. Something will come to mind. That’s where procrastination comes in.

Fortunately, I’ve elected to retain the top bushing brackets with M4 x 12mm SS cap screws, washers and elastic stop-nuts. That makes for straightforward disassembly. (I may eventually be forced to use 4mm pulled rivets, if the retainers show any signs of movement, but for now the M4 screws seem reasonable. Space is very tight and riveting would be a challenge – explanation below.)

Typically, the rudder pedal floor brackets, tubes and stops are fitted and mounted much earlier during fuselage assembly, with just the CF floor sitting ever so conveniently on the workbench. For my factory-assembled QB project, this didn’t happen and I’m doing the fitting and assembly work inside the completed CF structure. It’s certainly more challenging to do this work while kneeling and reaching into the cockpit foot wells.

CF – Rivnut Mounting

Setting rivnuts in the center fuselage (CF) area had been on the TODO list for a long time, but it took until now for me to summon up the nerve to actually do the deed. It turned out to be rather easy. I was in the right frame of mind and it all went very well.

A few of the rivnuts are in locations where I couldn’t use my drill-mounted (Astro ADN14) setting tool – particularly one of the M4’s for the A/P bracket nearest the main spar, and two M5’s that will serve to anchor the rudder return springs to the rear spar carry-through member. Fortunately, I’d acquired a nice hand tool (Astro 1443B) and it worked brilliantly for those. Concern about these rivets were what kept me dragging my feet until I’d worked up my courage to attempt the work.

Each of the holes where a rivnut goes, were enlarged to the proper size. This takes several steps, but it’s the same process I’ve used elsewhere. In places where I can’t see the back side of the mounted rivut, I use a mirror to inspect the crimp. They all looked great.

Various panels and covers in the CF that need to be removable, now have their mountings in place.

Composite Wingtips – Take 1

It didn’t take long before I realized that I’m in for a battle. The fiberglass wingtips, as supplied with the kit, simply don’t come close to fitting the wing. They’re obviously hand-made parts and are nowhere near identical. Frankly, I expected better. But, they are what they are.

I don’t have much hope that if I push the factory for new parts, I’ll get anything [much] better. I’ll count myself fortunate if I can get satisfactory results with less than the 130 hours another Sling 2 builder has put into his wingtips. Jeez – that’s a lot of time!

Right off the bat – the overall length is far too long to fit into the end of the wing panel. The airfoil shape cross-section is decidedly too flat. The up-sweeping trailing edge scallops are oddly different shapes. The lack of alignment at the point where the tapered wing skin is supposed to accept the trailing edge of the wingtip is unfortunately grotesque. Cutting and reforming will be necessary. Ultimately, the wingtips will be permanently mounted with 3,2mm multi-grip blind rivets. I haven’t settled my mind as to how I will mount the wingtip lights.

I decided to make a simple wing-shaped jig from a 2 x 4 foot section plywood. This jig is much less elaborate than others I’ve seen, but it will hopefully result in a useful tool and a reasonably consistent reference I can use to evaluate and correct the various eccentricities of these fiberglass parts.

I’ve been fortunate to be able to see what other builders have encountered and done with their wingtips, and so, I’ll share my adventures too. For the Sling 2 builders, we all seem to be – more or less – in the same boat.

RH Wing – Fuel Tank and Inspection Covers

Practice makes perfect they say. Well, maybe not perfect. But the going seems a little easier when you’ve been there before. So it was for mounting the second fuel tank. It actually fit slightly better than the other one. I knew what to do, and on it went without issue.

I did the same basic steps as I did for the first tank. I felt confident, and the work went quickly. I had to carefully dress a number of the overlapping holes in the tank and spar with the #20 chucking reamer in the lithium drill. I knew what to expect and there were no surprises. I also had to touch the holes in spar web to align with the outermost Z-bracket so I could get the AN3 bolts through and threaded into the anchor nuts. Once again, I used a length of cord to pull on the Z-bracket while the tank was being fitted for the final time. That worked like a charm.

There are several stainless steel rivets, top and bottom of the spar near the root. Those are treated with fuel tank sealant for corrosion protection. The rest of the rivets are aluminum multi-grip. Riveting goes pretty fast when the pieces are fitted in place.

Having both fuel tanks mounted is a big milestone and yielded a rather wonderful sense of satisfaction that was sweetened with a measure of relief. Success! Good result. Yay!

The M4 rivnuts for the inspection panels went in without a hitch. I had to enlarge the holes in the bottom wing skin to #A – the perfect size (I’ve found) to accept the rivnut prior to setting them with the drill-mounted tool I use. Screw holes in each of the cover panels had to be enlarged for close clearance of M4 stainless steel button-head hex screws.

LH Wing – Inspection Covers

Compared to mounting a fuel tank, enlarging holes and setting M4 rivnuts seemed easy and definitely less stressful. Still, it was no time to be careless. The wing skin is easy to damage.

It took several steps to get the factory punched holes enlarged to letter number #A diameter, a perfect size to accept M4 rivnuts. I double checked my references and reviewed the process I would use. A series of increasingly larger straight-flute chucking reamers in my trusty lithium-powered drill did the trick.

All of the holes in the wing skin and the inspection covers were in the correct places and the alignments matched perfectly. The drill mounted rivet setting tool worked flawlessly. All rivets are consistent and tight. The screw clearance holes in the covers are ideal. Everything is fits together nicely.

LH Fuel Tank Fitment – Success!

I took a bunch of photos and texted them to Jean d’Assonville. After several days of phone tag – one or the other of us were busy – we connected for a brief chat. That’s all it took.

It turns out that I was in pretty good shape after all. My hell was all in my head. Having quite a few rivets that were hand-fitted at various places around the fuel tank flanges is a good sign. The thing that really set me free was to hear that it is acceptable to dress stubborn rivet holes with a chucking reamer or drill. The same thing is true for Z-bracket holes on the spar. You have to do what you have to do. I just needed to hear the guidance. I’ve learned from experience – it doesn’t usually pay to be impetuous.

A shim is necessary under the top of the Z-bracket at the root of the tank. The other Z-brackets fit well enough. Other builders have needed to shim several brackets. Mine were flat on the spar. Another good thing.

Over a period of several days I evaluated fitment and planned my procedure. Then, I carefully fit the tank in place, one last time, as I’ve done twenty times or more by now.

I made a little shim from material I had on hand. A washer would have worked too, but I thought aluminum against aluminum might be better than against steel. Slightly more surface area is probably not such a bad thing either.

I fitted as many rivets as I could – by hand. The remaining 4,0 mm holes around the flanges were match-reamed with a #20, straight-flute chucking-reamer and deburred. Clecos and additional rivets were hand-fitted.

A mix of AN3-4A and 3A bolts, with washers, were threaded through the spar web and into the anchor nuts on the Z-brackets. (I began with the 4A length for 2 outer brackets, but then worried that the length might turn out to be slightly long.) At the root Z-bracket, two AN3-13A bolts, with washers and nuts and with the shim in place – were finger-tightened.

Finally – today, I mixed up a tiny bit of Flamemaster CS-3204 B-2, as recommended by Sling Aircraft to deter galvanic corrosion between the aluminum and the stainless steel rivets that are called out for use at the wing root – top and bottom.

Dipping the SS rivets in the sealant – one-by-one, I placed them and then pulled them with my trusty Milwaukee M12 lithium battery-powered tool. Rivet pulling continued with for the balance of 4,0mm aluminum rivets. Lastly, the 3,2 x 8mm rivets around the leading edge at RIB-105 were pulled. The Z-bracket bolts were all torqued. The 4A and 3A lengths are both fine. It’s all good. The fuel tank is mounted!

LH Fuel Tank Fitment, Plan B – Vertical Stands

With a seat-of-the-pants concept, a circular saw and a box of screws, I’ve managed to fashion a pair of Sling 2 custom vertical wing panel stands. Poof! It all came together.

With the LH wing panel on the stands, I’ve got much better access. Hopefully this will be the day I get the tank mounted.

Unfortunately, most of the same fit and alignment issues persist. This is starting to feel like Fuel Tank Fitment Hell.

Before I do something that’s un-recoverable, I’ll reach out to Jean d’Assonville at Sling Aircraft (TAF) USA before it gets any later in the day. It’s Friday and hopefully I can get out of this hell before the weekend. Stay tuned.

LH Fuel Tank – Final Fit (or Not)

The LH wing panel assembly has been back up on the workbench for several days. I can’t see any reason not to tackle permanent mounting of the fuel tank.

Well – I found a few reasons to not mount the tank today. I’m struggling to fully fit the tank and to align the rivet holes. I don’t have convenient access to the bottom surface of the wing panel. Gravity doesn’t seem to be helping either.

There’s a curious mix of places where rivets fit easily and squarely and other places where they won’t fit squarely, or at all. I’ll have to shift to Plan B. I think that means building some sort of stand(s) to hold the wing panel in a vertical leading-edge-up orientation.