Tag Archives: fitting

VS – Trial Fit

One things leads to another. A question about the factory-installed rudder cables got me started down the road of test-fitting the vertical stabilizer. I was very pleased to find that it was easy to do and the fit appears to be excellent.

I hadn’t really expected to do this step just now. But, in order to evaluate much about the rudder cables, the entire control mechanism for the rudder and steerable nose-wheel needs to in place and adjusted. I learned this during a customer support exchange with Sling Aircraft’s Jean d’Assonville. I’d called him because I was concerned that the rudder cables may have been installed improperly during factory the quick-build of my fuselage. Jean assured me that it was very unlikely that the cables were wrong.

I was wondering because the KAI talks about one cable being slightly longer than the other. Somehow they seemed to be the other way around. Jean said that the only way to properly evaluate the setup would be to assemble everything. It only takes 15 minutes, he tells me! LOL. But, he really meant it!

It’s going to take me hours and hours, over days and days, to get the entire rudder control mechanism in place. That’s not only because I’m slow and plodding, but also because I’m not ready to install the nose-wheel yet. It’ll all just have to wait until I get the avionics rack, LRU’s and harness in place while the wheels are off and the fuselage is low and as easily accessible as it can be.

So then. I still don’t know for certain that the rudder cables are installed properly. But, I did get inspired to get the VS out from storage in the house and get it fitted on the fuselage. Technically, that’s progress! The nice fit between the fuselage and vertical stabilizer is satisfying too.

Rudder Pedals – Final Fit

Trial fitting revealed that clearance between the arms on the pedal tubes and the hands of the travel-stops, bolted to each opposite arm, was nil. I could actually hear a squeak sound where there was contact, as I worked the pedals back and forth with my hands.

I pondered what to do about it, using my tried and true procrastination skills. As I have no proper equipment for clamping and bending anything heavier than light sheet metal – removing a bit of material from the the lower hand of each travel-stop came to my mind as the answer.

The pedal tubes were removed from the center-fuselage and the travel-stops unbolted from their respective arms. The Scotch-Brite wheel on my bench grinder did a fine job and I was easily able to remove about 1.5mm of material from the lower hands of the travel-stops to open up a satisfactory clearance.

The parts were reassembled and the pedal tubes reinstalled on the floor of the center fuselage. This time around, I installed the upper retainer brackets differently than I had for the trial fit. By now, I’ve noticed what several other builders and the factory are doing. For each bearing, there are a pair of top retainers. Rather than both retainers being together on the same side of the lower bracket, I’ve put one on either side, with space between. That seems to be the way it’s supposed to be. I like it.

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.

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.

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 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.

Rudder Pedals – Tubes, Brackets and Bearings

Work in the center fuselage continued with trial fitting of the rudder pedal tubes. It’s looking good. Initially, the pilot-side (LH) mounting brackets were easily positioned and the 4,0 x 10mm rivets dropped easily into most of the holes. And, after clearing a bit of paint in the holes, the rest of the rivets fit as well.

The flight control linkages rely heavily on composite Vesconite bushings, or bearings, depending on how you want to think about their purposes at different places around the airframe. I’ve known for some time, after reading accounts and watching videos posted by other Sling builders, that getting smooth, friction-free action of the controls takes some care. Some folks use the expression – black magic.

These bushings are supposedly designed to be self-lubricating. That’s all well and good, but I know some builders have resorted to supplemental lubrication. I’m trying to avoid greasy, oily, dirt-collecting areas inside the cabin if I possibly can. I’m having some luck – so far.

Two key factors need careful attention – clearance and alignment. Having enough, but not too much clearance, makes alignment slightly less critical. Buttery smooth operation, without additional lubrication, seems to be achievable.

Opening up the U-shaped retainer areas in the floor brackets and the top caps, so that no squeezing of the captured bearings occurs, makes all the difference. I used a small sanding drum on my Dremel tool at a low RPM setting. Eventually, I was able to capture the bearings in the brackets without causing any pinching of the bearing around the pedal tubes.

Next, I used some fine sandpaper around a piece of dowel to relieve a small amount of material from the bearing’s inner surface, particularly at the edges of where a saw had cut them in half. They were once circular and then cut into halves. Some cuts were better than others, but it’s not unusual to find a slight overhang from one or both halves that narrows the bearing bore at the seams where the halves meet when they’re captured in the brackets. Just a slight amount of narrowing can cause binding.

After repeated cycles of fitting and filing, the result is smooth, friction-free operation.

The rudder pedal tubes came nicely coated with gray primer. Areas on the tubes were masked from paint where the bearings ride. Except – one of the masking areas is misplaced by 1cm. I’d read about this, and sure enough, when I measured I found the off-by-1cm error too. The Vesconite bearings are designed to ride directly on the steel. Relatively soft paint would likely gum up the bearing and defeat the self-lubricating properties. I put some protective masking tape around the tube and used a strip of fine sandpaper to precisely remove additional paint.

Last, but not least – I can see how the Sling-branded rudder pedals are going to look. I think it’s much cooler than the plain T-bars. It took almost 6 months after my quick-build kit was delivered to finally get all of the pedal parts. That was a full year after I’d placed my quick-build order, which included the option. All’s well that ends well.

The Sling-branded pedals are essentially the same as the ones for toe-brakes, except that they are mounted on the standard pedal tubes and the hand-brake configuration is used. The toe-brake option has different pedal tubes, different brackets on the floor and no hand-brake. I know because I got a bunch of those parts. I worked with the factory and eventually got all of the parts I actually needed for my pedals.