Tag Archives: rivnut

Canopy Latch and Exhaust System

The canopy latch is inset within an oval area that must be carved out of the top front of the canopy plexiglass and underlying composite frame and held in place with blind M5 rivnuts and screws. Let’s just say that this is a challenging and nerve racking set of tasks. And – that’s a major understatement. But, with patience and a good bit of careful work with my trusty Dremel tool, I was able to achieve what I deem, at this point anyway, a satisfactory result.

The latch mechanism is an over-center affair with a hook engaging a latch pin that mounts to the top underside of windscreen support arch. Four 3,2 x 10mm CSK rivets attach the pin and it’s mounting plate to the arch, along with whatever additional security is afforded by a dollop of JB Weld epoxy. Where exactly to position the pin is an exercise left entirely to the discretion of the builder. Good luck with that.

I think by the time I get the weather seal in place, the latch will pull the canopy closed – firmly and without gaps. We’ll see. All of this latch fitment has happened before having the windscreen and support arch bonded in their forever positions. I’ve got my fingers crossed. Time will tell.

The exhaust system has been languishing in a box and it seemed a good time to see how well (if) it fits with the engine and airframe. It looks… maybe not so bad. Good!

There’s going to be some work needed to get the cabin heat muffler shroud assembled, because I don’t have a part that actually fits. So far, I’ve gotten 2 different parts (and part numbers) from the factory, but neither part matches the mounting rings on muffler. Argh. I’ll have to adapt and/or fabricate something. But, at least it seems the exhaust pipes and muffler do fit. Hooray for that.

Windscreen and Canopy – Initial Fit

Rivets, wires and avionics are friendly territory for me, compared to where I’m headed now. Fitting the windscreen and getting it bonded in position are tasks I’ve been apprehensive about – extremely apprehensive.

Manipulating clear acrylic sheet – Plexiglass and Perspex are brand names – that’s been molded into compound curves of unusual size, is just asking for trouble. I don’t like trouble. Dealing with this stuff is tricky, all by itself. Don’t even get me started about cutting or drilling holes in it. Eventually, I’m going to add sticky gooey pitch black marine adhesive caulk to the mix. That could easily lead to – yes, you guessed it – super trouble!

The time has come. I can’t avoid it any longer.

Because I opted for a factory quick-build kit, it came with the main canopy already trimmed and bonded to its painted composite frame. That’s fortunate because it may well have spared my frazzled nerves just enough to be able to deal with the windscreen.

The initial canopy placement seemed easy enough. Screw holes in the frame aligned with the ones in the slide assemblies. Countersinking of the frame will be needed to correspond with the short M8 stainless steel CSK mounting screws.

The arched windscreen support frame was fitted and match-drilled to align with M5 rivnuts that were installed at the factory. I made cardboard templates for left and right sides because they’re different. (They shouldn’t be – but that’s how the factory built it.)

The trial fit reveals that the rear edge of the windscreen will have to be cut back by at least 4 or 5 cm to align with the arched support frame. The lower rear edges (corners) of the plexiglass will just barely be under the fuselage top skin when it’s riveted in place. Precise positioning of the windscreen is going to be extremely important to avoid any unsightly gaps between the aluminum skin and the plexiglass.

A latch mechanism has to be fitted into the canopy. I inventoried the latch parts when I received them, but I could not have detected that the supplied spring was not correctly formed. I checked with the factory and confirmed the situation. They’re going to send me a replacement spring.

Windscreen cutting, drilling and bonding comes next.

WAAS GPS and COM 1 Antennas

Quite a few Sling 2 aircraft have been built with their GPS antennas mounted on a bracket under the engine cowling. That’s how the factory used to do it. Now guidance has been changed and a location on top of the rear fuselage is preferred. The new location reportedly offers consistently better reliability. I want reliability for IFR flying.

It was no simple task to get RG-400 coax cable for the GPS routed – and satisfactorily secured – on its way from the top-rear of the baggage area, down and then forward along the bottom of the rear fuselage to the center fuselage, and on to finally arrive behind the GTN 650Xi on the instrument panel. It’s done and it worked out very well.

Dealing with the COM 1 antenna coax cable was comparatively easier than for the GPS because the factory-supplied coax was already secured in place, routed from the mounting site on top of the rear fuselage, all the way to the instrument panel area. All I had to do was add the connectors.

The GPS antenna needed holes drilled in the fuselage skin. I used a doubler that came with my panel and harness and the screws provided with the Garmin GA 35 antenna. A TNC 90 degree solder/crimp connector by Amphenol made for a tidy connection at the top rear of the baggage compartment. A section of vinyl hose, covered with black heat shrink, provides good protection and satisfying aesthetics where the coax passes through the bulkhead, into the rear fuselage.

The COM 1 antenna needed 4 existing mounting holes to be expanded, in order to accept setting of rivnuts. The KAI called for M4 but the Rami antenna, supplied as part of my custom avionics package, came with 8-32 screws. I decided to set 8-32 rivnuts into the fuselage for this mounting. The way the coax was secured to the internal fuselage structure lent itself more to a 90 degree BNC connector. Again I selected an Amphenol solder/crimp part.

Wingtip Lights

Making a commitment to a specific model of wingtip light turned out to be quite the adventure. I did it. I think I’ll be happy with the choice. Time will tell.

Early on, I considered FAR ยง 91.209 Aircraft Lights and advisory circular AC 20-30B. That led to:

a. Advisory Circular AC 20-74, Aircraft Position Lights and Anti-collision Light Measurements.
b. Advisory Circular AC 43.13-2A, Acceptable Methods, Techniques, and Practices, Aircraft Alterations.
c. Technical Standard Order ('.ISO) C30b, Aircraft Position Lights.

I began to wonder how much time and effort I would have to put in to end up with demonstrably legal and adequate day and night, VFR and IFR lighting on my Sling 2 experimental. Man! This could get involved!

Just like my Warrior, I expect to have a red beacon on top of my VS and 3-in-1 lights on the wingtips. What and how much do I have to do – and prove – to achieve the same thing on my Sling 2? I asked questions on several builder groups and forums. Would 3-in-1 lights on the Sling 2 wingtips be ok? Will they be visible? Will I need a white tail light? Are non-TSO’d lights even legal at night? On and on.

I eventually decided that I was overthinking the whole business. I’d chosen the red LED tail strobe months ago. That’s a done deal. There’s a place on the wingtips for teardrop-shaped lights – and dammit! – they’re going to be cool-looking 3-in-1 LEDs. There!

It simply came down to which light? I’ve got Aveo for the tail. For sync compatibility, I’ve found I have to stick with Aveo on the wings too. They have a TSO’d product. They also have an experimental version of that same light. Even that experimental one is pricey. Aircraft Spruce had a sale on Aveo PowerBurst NG DayLite, w/white base – 300 bucks-a-pair. That’s more palatable than $780/pair for the nearly-almost-TSO’d experimental ones.

So there you have it – the tipping point! Price! Decision made. Hopefully the DAR will be happy when the time comes. I like ’em.

Another thing that gave me pause was how to mount the lights to the wingtips. The KAI no longer matches the composite parts that came with the kit and it hasn’t been updated in a long while. There is a callout for a plate with rivnuts to be mounted by some [unstated] means to the inside of the wingtip, under the site where the light will sit. That area is quite rough and I didn’t see how I was going to make a plate to fit and to get it attached and aligned.

Fortunately, I got some inspiration from a post on the FB Sling Builders group. Epiphany! Rivnuts and epoxy-glue is the way to go. Brilliant! The lights have mounting holes perfectly suited for #6-32 screws. M4 is too big and M3 is too small. Here we go mixing standards again – but what can you do?

I used the rubber base-gaskets provided with the light as a template to mark where holes go in the wingtips. I did some careful drilling and enlarged the hole for the wire bundle with a step-drill.

I needed the screws to be square to the mounting surface. I put each #6-32 x 1.25″ screw into its hole and threaded on a rivnut. I observed some amount of gap under the edges of the rivnut and used a wood-carving bit in the Dremel Tool to machine a small, flat surface for each rivnut to seat against, inside the wingtip. I cleaned up the areas with solvent on a paper towel. I positioned the rivnuts, wide flange to the mounting surface, and secured them gently with their screws. Then I carefully applied [original] JB Weld epoxy to the fiberglass and built up a mound around the rivnut, just below where the screw emerges.

Once the epoxy was cured I had perfectly aligned and ruggedly attached blind anchors for the the lights. This worked so nicely and was so easy to do I can hardly stand it! The rivnuts are not “set” as they normally would be. They’re just glued in place. For this application, the light mounting screws will never be tightened to the point where the rivnuts might compress.

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.

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.

Rivnut Mounting – Step 1 Complete!

I’ve finally gotten to the point of acomplishing the very first step on page VS1 in the Empennage Construction Manual! I’d been worrying about it. Getting the rivnuts securely mounted calls for a rather deliberate process with good technique. It all went very well. What a relief.

Having an effective tool – Astro Pneumatic Tool ADN14 Rivet Nut Drill Adapter Kit – and practice made the day. I’ve seen a couple of other builders recommend this particular tool. Because it relies on a cordless drill motor and identification of an appropriate torque (clutch) setting, I felt there would be a good chance of getting consistently good results. This seems to be the case.

Practice! I got an assortment of metric rivnuts and used the tool to work with them until I knew exactly what to expect. Now I have 14 perfectly mounted rivnuts!

BTW – the KAI mentions using high strength Loctite to insure that the mounted rivnuts don’t slip in their holes. I say – learn how to mount them firmly and they won’t slip. No Loctite is needed. Because IMO – if they’re not tight enough to stay put, then they’re not satisfactorily mounted.