Category Archives: Empennage

Finished riveting the Horizontal Stabilizer skin

Hours: 4.5

The pop dimpling tool that I ordered a few days ago arrived on Friday, so I spent some time trying it out to make sure it worked properly so I could finish adding the missing dimple to the skin and finish closing up the Horizontal Stabilizer.

After a bunch of research on them, I actually ordered 2 different tools, one is made by Aircraft Tool Supply and creates a 100 degree dimple, and the other one promises to create a 120 degree dimple, I’m not sure who exactly actually makes it, but it’s sold via Wicks Aircraft tools. The 120 degree tool from Wicks is DT-17014 and it’s supposed to screw into a G28 hand riveter.

Unfortunately the Hand Riveter I own seems to have smaller threads than the G28 hand riveter, so I decided to try it on my Milwaukee rivet gun which had the correct thread size. As I found out when I pulled with it, that ended up with too much force, so the head of the stem (which is a finishing nail) that is supposed to hold the back of the dimple in place actually deformed and got pulled into the top and got stuck.

So after that happened, I had to cut off the nail, but I couldn’t pull it out of the tool, so I got out my Dremel and cut off the top part of the bit where the deformed head got stuck in.

This way I could try to use the tool like the ATS pop dimple tool (5102D-1/8) works, which just sits on top of the rivet puller.
ATS tool on the left and the other one on the right (after I cut off the top):

So now after that modification to the tool, I tried both by holding my test piece onto the existing dimples of the Horizontal Stabilizer and determined (as expected), that the 120 degree dimple has the better fit, so I used that one to make the dimple to the skin. It came out well and the countersunk rivet sits flush like the other dimples. So for one or two dimples, this works out nice and easy and I didn’t have to go and get a dimpling press.

Riveting the skin

Once all that was said and done, I got to work and riveted the complete bottom of the left side skin. Then turned it around, removed all the Clecos from the top side one last time so I could apply the Sealant to the support plate like I did on the other side. And then I finished up riveting the top side.

Timelapse Video of Finishing the Horizontal Stablizer

And lastly as promised, here’s the timelapse video of the whole endeavor of the Horizontal Stablizer.

Riveting the Horizontal Stabilizer skin – part 2

Hours: 1

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Today I spent another hour on riveting the Horizontal Stabilizer to finish closing up the right side.

The top has a support plate as seen below to add some reinforcement to the skin. To prevent the large metal surfaces from rubbing, the instructions call for sealant to be added between the plate and the skin before closing it up. Luckily Matthew had already clarified with TAF what the right sealant to use is, GE5050 Metal Silicone, so I had it ready for a while.

Once that was done, I closed it up one last time, ensuring a proper fit and the finished the riveting work.

So now I’m done with the complete skin on the right side and just need to do the same thing on the left side, but I need to add one more dimple on that side that was missed, so I’m waiting for a dimpling tool to finish that, which should hopefully come in the new few days.

Riveting the Horizontal Stabilizer skin

Hours: 3

Horizontal Stabilizer skin fitting

Hours: 1.5

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Today I was working on fitting the skin onto the Horizontal Stabilizer. It took a lot of clecos to align everything, but eventually it all came together well on both sides. The next step will be to match-drill up the dimpled holes as per the instructions.

The design for the dimples is such that the holes are drilled slightly smaller than the final size. Then they get dimpled and then you assemble everything to fit it together and finally match-drill up the dimpled holes to the final size.

I will post another timelapse video of the whole process once I’m done with the drilling and riveting.

Countersinking experiment

Why it’s important to use a 120 degree countersink pilot for pull rivets

Another thing I recently did was do a small experiment to showcase the reason to use the correct 120 degree countersinking pilot for the countersinking holes that are not dimpled due to the thickness or type of the part (such as the fiberglass tips), after we had a thread about dimpling and countersinking it on the Sling Builders discussion group.
Normal AN style solid aviation rivets are 100 degrees, so most countersinking tools sold by aviation tool supplies by default come with 100 degree countersinking pilots, but blind pull rivets like those used in the Sling are 120 degree, so hence the need to use a 120 degree pilot to get the best fit.

To showcase the why that is so important, I drilled some holes in a 0.04 inch piece of metal (which is the thickness where you start to countersink instead of dimple) and used the 100 degree pilot on one hole and the 120 degree pilot on another. The goal was to insert the same countersunk rivet (which has a 120 degree slant) used for the Sling in both and have it sit flush.
In order to get a flush fit with the metal using the rivet, the 100 degree countersunk had the be deeper. This in turn results in a larger hole and thus wouldn’t have as much material to grip onto. As can be seen below, the 120 degree countersink resulted in about 3.3 mm hole, while the 100 degree resulted in a much larger 3.65 mm hole.

So the moral of the story, make sure you use the correct countersinking pilot when working with pull rivets. I’ve created a separate page on drilling, rivet sizing and countersinking as a quick reference for myself and figured it might be useful for others.

Rudder structure riveting

Hours: 1.5

Rudder & Horizontal Stabilizer Skin Priming

Hours: 2

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I did a quick test fit of the skin on the Horizontal Stabilizer yesterday and everything looks good. I’m waiting for the sealant that goes between the Support Plate and the skin, which should arrive tomorrow. So I decided to prepare the next part of the Empennage and and prime the Rudder parts and the mating surfaces of the Horizontal Stabilizer skin.

After I did some more reading about priming preparation and I’ve slightly changed the process for the Rudder pieces. I’ll see how it turns out tomorrow once it’s dried. After removing the protective plastic, I cleaned off the parts with MEK, then scruffed them up with a red (fine) Scotch brite pad and then went on to priming.

After the preparation, I unfolded my small paint booth I made out of some hardboard. I got the design from a video on the Family Handyman. If anyone wants to make their own and wants to skip the video, I’ve created some quick plans in Solidworks and took some pictures of the folding. What you need:

2 sheets of 24 by 24 inches
2 sheets of 24 by 48 inches
Duct tape to create the “hinges”

Lastly, I did some more organizing of the Rivets and Clecos and making use of my label maker.

Horizontal Stabilizer wiring

Hours: 1

Horizontal Stabilizer

Now back to the building part. When I riveted the ribs and spars of the Horizontal Stabilizer a few days ago, I was short a couple of the 4.0mm rivets. In order to finish the part, I took some from the Elevator hardware bag.

Today I reviewed the rest of the steps for the Horizontal Stabilizer and realized I need a whole lot more of them to actually finish riveting the Skin onto the Horizontal Stabilizer. I also need some sealant to put between the Stabilizer Plate and the skin, which I know Matthew posted on his blog when he did the part, so I re-read his post and noticed that he was actually also missing a bunch of the 4.0mm rivets, so it looks like the factory may be short when they put together that bag, I’ll let them know tomorrow.

I did finish up the wiring that will connect to the elevator trim. This gave me the chance to make use of the step drill bits I bought. I used my digital caliper to translate the metric instructions (9.5mm) to the closest fractional inches (3/8th) to enlarge some holes for the rubber grommets.
After that I installing some flexible grommet edging I bought as spare as the kit was missing that since it was shipped based on Revision 0, which didn’t include that part. I’ll have to see if there were any other parts that were added in Revision 1 after my kit was put together.

The beginning of a riveting story – Horizontal Stabilizer

Hours: 6

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When we took inventory of the Empennage kit, we thought we were missing some parts of the Elevator and so I decided to start with the Horizontal Stabilizer instead, but as it turned out after double checking again, the parts were just hiding inside a channel.

Parts Prep

So after some researching I had done ahead of time, here’s the process I decided to follow for preparing the parts for priming:

Removing the protective plastic
Cleaning and Scrubbing the parts with Simple Green Extreme Aircraft cleaner (diluted 1 part cleaner to 2 parts water) and Scotch Brite Pads.
Washing off the cleaning solution with water and drying the parts
Final de-greasing using MEK

Priming

After all that was done, it was time for priming, which in on itself is a whole big topic with different opinions the more people you ask. I’ve decided to prime the mating surfaces and while at first I was thinking of using NAPA 7220, ended up using Rustoleum Self Etching Primer after I saw that Matthew seems to have good results with it and it’s easier to find in the local hardware store.

Riveting

Since my kit was shipped out before the newer revision for the Empennage kit was finished, the printed copy only had the basic CAD drawings, but no instructions, so it’s a matter of combining the larger print outs with the instructions using my small laptop.

Also seen above is the Rivet Gun I’m using – it’s the Milwaukee M12 Rivet gun, which fits in nicely with all my other tools and allows me to build the airplane without the need for a noisy compressor.

After I put together everything with Clecos it was time to pull rivets.

And here’s the riveted structure (minus the skin) of the Horizontal Stabilizer:

I’m also trying to record my progress with some timelapses, so here it goes:

Sarah's Sling TSi Build Log

Documenting the journey of building a Sling TSi aircraft in my garage.