Monthly Archives: October 2019

Spray Booth – Economy DIY

It’s autumn now, and already too cool to prime parts outside. I need a place in my shop to do it. I tried a cardboard box on a workbench, but quickly decided that a ventilated booth is required.

With about $8 worth of 1×2 wood strips and $20 of plastic sheeting, a $12 dryer duct, and an existing space heater (w/fan) — I was able to quickly build a 4′ x 5′ x 9.5′ tall spray booth.

I only need to work with relatively small parts. The longest pieces in the empennage are only a few feet long and can be suspended with a vertical orientation. Ventilation is minimal. Hopefully it will be enough.

EAA Workshop – Sheet Metal

There was lots of good information and practical hands-on work at the EAA SportAir Workshops this weekend. The Museum of Flight Restoration Center at Paine Field (Everett, WA) makes for a great venue.

Sling builders were well represented, with 3 active projects and at least a couple prospective Sling TSi-leaning workshop attendees. It was nice to see and chat with fellow builder Philip Rueker, taking part in the Electrical course.

I didn’t quite finish my project, but they gave me a certificate anyway. I’m so glad I chose a Sling 2 kit with pulled rivets. I would be absolutely terrified to undertake a project with solid rivets and needing to conjure sufficient skills to wield a pneumatic rivet driver and bucking bar to achieve 14000-plus decent – let alone perfect – results. OMG!

Sling 2 Build – Day 1

My build has officially begun. Even before I can complete the very first step of constructing the empennage, I had to enlarge mounting holes to accommodate M4 rivnut – blind fasteners. The process went well and I’m very glad to be underway.

I’m waiting for a #19 straight chucking reamer to arrive on Tuesday. Then I can enlarge screw clearance holes corresponding to the rivnuts.

Starting Off On the Right Foot

I ordered my quick-build kit in July and I’ve had my empennage sub-kit since August, but have yet to pull my first rivet. I’m finding that it’s taking many hours for research and for me to learn enough background information to make confident choices that will set the direction and metrics I will endeavor to satisfy as I build. I think that’s part of the fun.

Surface priming – materials and techniques – is a significant matter. I’m still wrangling a bit with that, but have determined that I have to be practical, or I’m never going to put pen to paper, so to speak. My priming standards are going to fall somewhere closer to the minimum of bare aluminum rather than the extraordinarily high level demonstrated by the truly awesome work of Pascal Latten for his Sling 2 build. Spray painting can be a messy and tedious business. I’m not a professional and I want to keep things clean and simple as possible, while achieving a worthwhile result. In a nutshell, I’m going to use RustOleum self-etching aerosol primer for most internal mating surfaces. For more exposed areas, such as the hinge areas and outward facing structure of the horizontal and vertical stabilizer assembies, I’ll use Alumiprep 33 and Alodine 1201, coated with more durable PTI 2 part epoxy primer – and ultimately the final color top coat.

Wiring, VOR antenna and external lighting choices figure in early for the empennage build.

Aveo Engineering produces what I think is the best option for the anti-collision light atop the rudder. For reasons that included fit, features and color, I’ve opted for the aviation red Posistrobe MiniMax to complement Aveo 3-in-1 nav/position/strobe lights on the wingtips – exact model number of the wingtip lights TBD. Without a huge amount of work, and or ready access to a completed Sling 2, it’s really mostly an educated guess that the overall lighting results will satisfy FAR 23.1385 – 23.1401. Hopefully it will and the DAR will agree.

Rudder Cap Strobe Mounting Area – small, even for the 1.74in wide MiniMax Light

Working through the electrical current requirements of the LED rudder strobe against AC 43.13B, I’ve tried to determine the necessary gauge and then acquire M27500 shielded cable to replace the TAF-supplied PVC jacketed wire in the kit. Based on actual experience with such wire in my Warrior, I’m not impressed with its suitability for aircraft applications. Based on my calculations, I think readily available 22 gauge conductors would be sufficient to handle peak current less than 3A over a run of 20ft. But, based on some data from the awesome builder I mentioned earlier, it’s possible that 20 gauge wire would be a better choice. I ordered some M27500-20TG4T14 from WireMasters. The minimum order was 100ft. This wire may turn out to be overkill for the small LED light. We’ll see.

You’ll find a chart like this in AC 43.13B

The VOR/GS antenna gets built into the vertical stabilizer, so I have to make a commitment to that, even before I’ve settled on my avionics choices. I’m hopeful that conformance with FAA TSO: C34e, C36e, C40c will make my choice compatible with whatever I finally choose for a VOR/GS receiver. Keeping the antenna price down will also make it easier to go with only a GPS navigator. At least the antenna and wiring will be in place. I’ve opted for the Rami AV-520 which has 2.5in diameter base “puck” with removable whips, built-in balun and coax connection.

I’m aiming for an advanced IFR all-Garmin EFIS panel with autopilot. We’ll see where it ends up.

I’ve ordered a bunch of stuff and it will be here next week. I’m perilously close to the official start my Sling 2 build.

Process for Rivnut Mounting Hole Enlargement

Before I can accomplish Step 1 in my build, I’ll need to enlarge some holes to accommodate larger M4 fasteners. At some point, TAF changed from M3 to M4 size rivnuts for the vertical stabilizer and other empennage sub-assemblies.

The m4 rivnuts have been supplied with the empennage sub-kit, but the formed parts haven’t been revised to accept them. The build instructions have yet to be updated. Correspondence with TAF confirmed that I will need to do hole enlargement. As the builder, it’s up to me to determine how. This involves tracking down proper tools and developing confidence in a process.

The TAF KAI calls for rivnut mounting holes to be as tight as is practicable and I’ve concluded that a size #A straight flute chucking reamer is the right size to achieve that. This results in the final diameter just under a nominal 6,0mm mounting hole size commonly specified for M4 rivnuts.

I found reaming from #12 to #A size was best done in 2 steps. First, #3 and then #A. This allows the beveled tip of the reamer to align and track nicely with the existing hole as I hold the part by hand and feed the reamer using my drill press at about 750 rpm.

There are also holes for the corresponding screws that will have to be enlarged, once I’ve identified each of them and established what fit clearance is best.

I’ve acquired reamers, developed the process and adequately demonstrated the skills to myself. I haven’t actually started on the build yet, but it feels good to see some aluminum chips in the shop. I’m very close to Build Day 1.