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.

Sheet Metal Training – Closing my Knowledge and Skills Gap

Before I start pulling rivets for real, I’m taking some time to train and practice related skills. There are many useful videos on the Internet. I also found a nice, inexpensive training kit from a homebuilt airplane company in Oregon. I’m signed up for an EAA SportAir sheetmetal workshop – October 26 – 27, at The Museum of Flight Restoration Facility, Paine Field in Washington.

The emphasis of the training resources are centered more on solid rivets and the expectation of somewhat less complete fabrication than what the Sling kits exhibit, but it still seems useful to be introduced to working directly with the metal.

Practice Parts

Before I tackle the training kit – using its materials, I’ve been experimenting with scrap pieces of aluminum sheet and angle, I found at my local Home Depot. It’s a good thing too. I surprised myself as I realized laying out and drilling holes for some short lines of rivets, posed more challenges than I expected. I made real scrap out of my scrap material. I’m learning.

Empennage Kit – Inventory and Inspection

I checked that correct quantity of every part number listed on the kit packing packing list was present and undamaged. I went so far as to measure the thickness of all RIB parts and compared to the value listed on the packing list. Overall the sub-kit is excellent, however, I noticed a couple of small but unexpected deviations and contacted TAF to discuss them.

Empennage Kit Inventory

Empennage Kit Delivery

While waiting for my quickbuild kit to arrive, sometime in March 2020, I’d arranged with Barry Jay (TAF) to take delivery of a sub-kit to get my end of the build going. The kit is here before my workshop is complete!

Sling 2 Demo Flight

My demo flight in a Sling 2 at The Airplane Factory in Torrance, California

  • Sling 2 with Rotax 912iS Engine
  • In the Cockpit
  • Post Flight with Barry Jay

I loved it and put Plan A in motion – ordered my Sling 2 quickbuild kit!

PNW Summer Sets In

Not much happened with regard to experimental amateur aircraft building in June. I did get my Warrior through owner-assisted annual inspection and flew it around the Olympic Peninsula.

Wanting to get my Sling 2 show on the road, I’ve booked a last minute trip to TAF USA in Torrance, CA. The goal is to test fly a Sling 2 with the Rotax 912iS engine. If it I love it, Plan A is to get my order in queue before the rush at Oshkosh. There is no plan B.

Workshop – A Brief Recess

The side and roof panels and the doors are in place. Plastic sheet will hopefully keep any weather out until I can get back to working on it. My brother and his wife are coming to visit for a week. Then there are some other chores that need doing around the house.