Tag Archives: skins

Elevator skin fitting

Hours: 3

First order of business for the Elevator skin was inspecting all edges and holes and there were a few edges that needed some deburring action.
Elevator skin edges needed some filing to remove the burrs

After deburring everything that needed attention, we wrapped the skins around the rib structure. Since the Elevator is a pretty big part, it was very helpful to have a second pair of hands for this.

The last thing I had to do before I can start on closing up the skin is to install the backing plate for the Trim motor inspection plate. The plans call for 1/8 rivets, but the holes were actually 3/32, so I had to first up-drill them. There’s also another small error in the plan, in that it says to rivet all 8 holes, but actually only 7 should be riveted, since the top hole is for the screw that holds the inspection plate in place.
Backing plate goes under the skin Holes are 3/32, so I needed to up-drill them to fit the 1/8 rivets Holes up-drilled and backing plate clecoed in place Quick test fit of the inspection plate

Vertical Stabilizer skin riveting

Hours: 3.5

With the wiring finished and the Antenna fitting done, I am now finally able to close up the Vertical Stabilizer and rivet the skin.

To begin, I closed up the left side of the skin and held it in place with clecos, since this is the side where the Antenna slides through the enlarged rivet hole, while on the right side I had to create the custom notch so that I can pull the skin around the Antenna.
Left side of the Vertical Stabilizer closed up with clecos

Once that was done, I riveted on the support plate for the Antenna onto the top rib of the Vertical Stabilizer.
Riveting the Antenna support plate in place Antenna support plate riveted in place 

Now that the structure is complete, time to mount the Antenna permanently in place. Using two 20mm long M4 screws, washers and Nyloc nuts and some medium strength threadlocker I mounted the Antenna in place. Here’s the Antenna mounted in place and the wire connected to the Antenna using the BNC connector I crimped onto the wire. Antenna ready to be mounted Antenna mounted and wire connected

Riveting the skin

With all the prep work finished, I closed up the right side of the skin, made sure everything fits correctly and clecoed it in place. There are two holes on the bottom on each side that are not riveted, but instead I have to install Rivnuts in them, so I marked out those holes, so I don’t accidentally rivet them.
Vertical Stabilizer skin closed up and ready for riveting Holes where I have to install Rivnuts marked

There were two rivets that I had to shorten in order for them to fit flush near the Antenna. So I made a small template for the dept through a piece of wood and then shortened them accordingly.
Wood piece to hold the rivet in place to shorten Rivets shortened (and normal length on the left for reference)

After that, it was just a matter of pulling the many rivets on both sides of the skin to close the Vertical Stabilizer up for good.
Riveting the right side in progress Riveting the left side in progress Riveting the left side in progress Done riveting the skins of the Vertical Stabilizer

The last part was to install the two rivnuts on the bottom on each side, so after enlarging the holes using my step drill and reaming them out using my hand reamer, I got out my rivnut puller and high strength loctite and put those in place.
Holes enlarged for the rivnuts Rivnuts installed

With the Vertical Stabilizer completed, I then did a quick test fit and mounted it on top of the Fuselage and also attached the Rudder for a moment – almost looks like an airplane.Completed Vertical Stabilizer  Quick test fit of the Vertical Stabilizer and Rudder

Timelapse of building the Vertical Stabilizer

Vertical Stabilizer Navigation Antenna & skin fitting

Hours: 2.5

Before I can close up the Vertical Stabilizer skin, I need to fit the Navigation Antenna, run the wires for the Antenna and the rudder light and fit the skin including up-drilling the countersunk holes in the skin with the rib structure.

So one thing after another, first I gave a quick test fit for the skin and then drilled up all the countersunk holes.
Test fitting the skin and aligning everything to match up-drill the countersunk holes And found one hole that should be dimpled as well

After that was done, I went to work to fit the Rami AV-525 Navigation Antenna I’m going to use. I already fit the Antenna onto the inner rib a while ago before I built the rest of the structure, so now it was a matter of fitting it all with the skin to be able to close the skin around the Antenna.

On the left side, the Antenna comes out one of the pre-drilled rivet holes, so I just had to up-drill that to the correct size.
Enlarged hole for the Antenna on the left side

For the right size, the Antenna comes out offset a bit further behind, so I marked out where I needed to make the hole in the skin, then used a center punch to get a good center to drill the hole:
Marking where the notch for the Antenna has to go Centerpunched the spot for the hole to goHole drilled on the right side for the Antenna

With the hole in place, I cut back a small notch, so that the skin can slot around the Antenna since the arms of the Antenna are fixed to the internal balun.Notch to slot the skin around the Antenna

After all that was done, I put it all together for a final test fit:Left side view of the Antenna in place on the Vertical Stabilizer Right side view of the Antenna in place on the Vertical Stabilizer

Looks all good, so now I need to finish running the wires on the inside and then I can rivet the skin closed.

 

Rudder Tip fitting & riveting the skin

Hours: 2.5

After having primed the inner surface of the Rudder skin the other day, I had all the pieces together to start working on finishing the rudder.

I attached the skin onto the structure and clecoed it into place.Rudder skin clecoed in place

Fitting the fiberglass tip

Once that was done, I went to work to fit the fiberglass tip onto the skin. I had to trim a little bit away from the bottom of the fiberglass. I made a first rough measurement, trimmed it away using my Dremel and then tried to fit it in.
First trim mark on the fiberglass tip

After aligning it all, I did a second small pass to trim a tiny bit more, placed it into the skin again and then it looked all good.
Tip fit in place and held in place using some clamps

Since the instructions are very explicit to make sure that the alignment of the rudder is perfect, I checked the alignment from all sides and it all looked good.
Rudder checked for alignment using laser level Rear of the rudder checked for alignment using laser level

After all that looked good and triple and quadrupple checking that the fiberglass tip sat flush in the skin I made marks for match drilling the holes and then went to work and carefully drilled the holes into the fiberglass.
First few holed drilled into the fiberglass tip Finished drilling all the holes in the fiberglass tip

Countersinking the front of the fiberglass tip

Once that was done, it was time to countersink the holes in the front. The instructions contradict themselves – only the first 7 holes get countersunk rivets, which mathematically adds up properly to the 32 rivets (2 x 7 on the top and 2 x 9 on the bottom = 32). So after counting all the holes and re-checking the instructions and doing basic math, I decided to only countersink the first 7 holes. I sent an email to the factory yesterday and they confirmed that I was right and they’ll fix the instructions in the next iteration.
Instruction error about countersinking

Before I went to work with the countersinking, I calibrated the micro stop countersinking tool using a scap piece of Aluminum to ensure the depth was set correctly and made sure that I had the correct 120 degree pilot cutter in the tool (I made a whole post about why using the 120 degree pilot was important here).
Calibrating the Microstop Countersinking tool Making a test countersink on a scrap piece of metal

After all that was ready, I went to work, mounted the fiberglass tip gently in my bench vise and started drilling the countersink holes.
First countersunk hole drilled Checking depth using a countersunk rivetAll the countersunk holes drilled in the fiberglass tip

All the countersunk holes came out well and everything sits flush now.
Flush fit of the fiberglass tip in the Rudder

Riveting the skin

So after all that I went to work and started riveting some of the skin.Time to rivet the Rudder skin The close quarter wedge came in handy for riveting in this tight spaceRiveted part of the Rudder skin

Vertical Stabilizer Priming

Hours: 2

In order to finish up the Rudder, I still had to prime the inner mating surfaces of the skin, so in order to get ahead I decided to also prepare the parts for the Vertical Stabilizer and prime those as well.

After removing all the protective plastic from the parts and inspecting them, I unfortunately found that there was some dents in Rib 1, 2 and 3, so I requested replacements from the factory since those are structural parts that shouldn’t be compromised.

I still went ahead and cleaned and degreased all the other parts. Luckily it’s getting a bit warmer, so I could leave the garage door open and do the cleaning outside, to make less of a mess in the garage.

Vertical Stabilizer parts laid out to inspect Cleaning Station with Simple Green cleanerParts cleaned and ready to be primed

Once I was done cleaning all the parts with Simple Green, degreasing them with MEK and rubbing them down with red scotch brite, I set up my small paint booth and primed everything.

Paint booth ready to prime Done priming the parts of the Vertical Stabilizer

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.
120 Degree Pop dimple tool
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.
Nail stuck in the tool
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):
100 degree Dimple tools from ATS on the left and 120 degree tool on the right (after I cut off the thread head)

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.

Pop dimple tool using the hand riveter Dimple using the pop rivet tool came out well and the countersunk rivet sits nice and flush like the others

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

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.

Before closing up the skin, I needed to apply some sealant on this stabilizer plate Metal sealantSealant applied to the stabilizer plate

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

Ready to start riveting Halfway done riveting the right side of the Horizontal Stabilizer Finished riveting the right side of the Horizontal Stabilizer

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

The journey of the Horizontal Stabilizer continues with match up-drilling all the dimpled holes to fit the countersunk rivets. So basically this, multiplied by 200:

After I was done, I took off the skin one last time to clean out all the debris from the drilling and check and fix any burrs. After that it was time to put it back together again and do one last check for alignments before riveting using my self leveling laser level.Cleaning out the debris from reaming out all the holes  Alignment checked using my laser level

And then at last, time to start the riveting. I managed to finish the bottom of the right side, so 3 more sides to go next time.

One small problem I encountered while doing the riveting was, that because I was riveting straight down, it happened twice that some of the mandrels of the 3.2 mm rivets got stuck in the rivet gun, so I had to take it apart and push/pull out the mandrels.

Mandrels stuck in the rivet gun

Horizontal Stabilizer skin fitting

Hours: 1.5

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.

Clecoing the left side of the Horizontal Stabilizer Finished clecoing the left side of the Horizontal Stabilizer Finished clecoing both sides of the Horizontal Stabilizer

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.

Difference in hole size using 100 and 120 degree countersink Flush fit of countersunk rivet

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.