Feb 17, 2024     20-04/05 - Attach Bottom Wing Skins - (80.2 hours)       Category: 20 Bot Skins

Parts Prep (Dimple, Countersink, and Shape)
2/24/23 - 0.4h
This step of the build starts by deburring and dimpling the nut plate holes in the inboard wing ribs. Access is a little off for the hole deburring tool, but it is do-able with the extension. The pneumatic squeezer did a good job with the dimples. I started with the larger #19 holes, and then switched to a reduced diameter #40 dimple die that did not interfere with the larger dimples.
[Hole Deburring Tools, Edge Forming Tool (Vise Grip Style), Hole and Edge Deburring Tools, 22” C-Frame with #40 Reduced Diameter, #30, and #40 Standard Diameter Dimple Dies, Pneumatic Squeezer with #40 Reduced Diameter and #8 Screw Dimple Dies]

Assemble
2/26/23 - 0.3h

10/23/23 - 0.4h
10/26/23 - 0.9h
11/8/23 - 0.9h
11/9/23 - 0.7h
11/10/23 - 3.1h
11/12/23 – 1.4h
11/13/23 – 1.3h
11/15/23 – 1.3h
11/16/23 – 1.6h
11/19/23 – 4.9h
11/20/23 – 1.8h
11/21/23 – 2.3h
11/22/23 – 0.7h
11/24/23 – 1.4h
11/26/23 – 4.2h
12/01/23 – 2.7h
12/02/23 – 1.4h
12/03/23 – 0.9h
12/04/23 – 1.9h
12/08/23 – 1.7h
12/09/23 – 1.2h
12/10/23 – 2.9h

12/13/23 – 1.2h
12/15/23 – 1.2h
12/16/23 – 1.2h
12/22/23 – 0.6h
12/23/23 – 3.1h
12/24/23 – 0.8h
12/27/23 – 1.8h
12/29/23 – 1.1h
12/31/23 – 1.8h
1/6/24 – 2.3h
1/12/24 – 1.5h
1/13/24 – 3.1h
1/14/24 – 1.5h
1/27/24 – 2.5h
1/28/24 – 2.4h
2/2/24 – 2.4h
2/3/24 – 2.1h
2/4/24 – 1.8h
2/09/24 – 0.9h
2/10/24 – 2.1h
2/11/24 – 1.6h
2/15/24 – 0.5h
2/16/24 – 0.9h
2/17/24 – 1.5h

ADAHRS Mounting Bracket (0.3h)
The main assembly on this page is riveting the bottom skins in place, but before that happens the ADAHRS mounting bracket gets riveted to the left inboard J-Channel. A hand squeezer with a longeron yoke had good access to the rivets, and made quick work of setting them with no issues. I'll set the ADAHRS mounting bracket and J-Channel aside until I'm ready to attach the inboard wing skin.

Inboard Bottom Wing Skins (39.6h)
Attaching the inboard bottom wing skins is a time-consuming process. There are a lot of rivets, and access to the majority of them can be difficult. The best advice is to give some thought to setting each individual rivet, find the best bucking bar for that rivet, and be patient. I found one of the most difficult aspects of this task was ensuring the bucking bar was positioned correctly. I used the adjacent cleco in most cases to help align the bucking bar on the rivet to be set. The downside of this method is you need to inspect the rivet shop head before removing the cleco in the next hole in case you need to give the rivet a few more taps or drill it out and try again. Fortunately, I didn't have to re-do many rivets. I bought an inexpensive endoscope camera that works with my phone on Amazon to do a lot of the shop head inspection. The attached pictures of rivet shop heads were taken with that camera. I taped the camera to the end of a large paint stirring stick, and fed it through the lightening holes to take a look. The other inspection method was to push my finger against the shop head, and then measure the indentation with the rivet sizer.

The area around the flap hinge has four rivets that are very close to the hinge on each side. I used the arbor from my C-Frame dimpler with a flat squeezer set to make a small diameter rivet set I could use with the rivet gun. This technique worked great for these rivets, which all set very nicely. Another tricky area is the rivets just forward of the J-Channel. The right wing was easy – I simply set the row of rivets just forward of the J-Channel before I inserted the J-Channel. That technique does not work on the left wing, though, since the ADAHRS mounting bracket is attached to the J-Channel. The small foot on my footed bucking bar was the best option to get under the J-Channel for the rivets on the left wing.

Finishing the inboard bottom skins also had some challenges. Before I riveted forward of the J-Channel, I clecod the forward skin in place to check the clearance between the wing skin and the fuel tank skin along the forward wing spar. There were a couple of areas that were just a bit too long, which prevented the skin from sitting flush with the tanks. I removed the clecos, filed the edge of the inboard skin a bit and deburred, and tried again until I got a clean fit between the two skins.

I completed the aileron pushrods prior to installing the bottom skins, and I really wanted to leave the push rods in place rather than trying to install them through the wing access panels after the skin was riveted to the bottom of the wing. Unfortunately, you need that space to set the bottom row of rivets on the forward wing spar flange. I reluctantly removed the pushrod so I could complete the riveting. I was concerned about damaging the rivets that were already set in the wing spar flange just forward of the ones I needed to do here, so I fabricated a “bridge” to help align the bucking bar and protect the rivets that were already set. The bridge worked really well, and I plan to use it for the outboard skins as well. It also protected the wiring that runs along the forward spar flange from the bucking bar.

The final step was to set the rivets on the inboard wing rib, install the wing rib nut plates, and install the nut plates for the wing access panel. I used a hand squeezer for the inboard rib and nut plates, which worked really well. I also went ahead and installed the nut plates around the outboard wing skin access panels.

Outboard Bottom Wing Skins (39.9h)
The outboard bottom wing skin installation starts at the rear spar and moves forward, just like the inboard skins. The rear spar rivets are a long reach, even with the forward part of the skins pulled forward for additional access. There are also a lot of set rivets along the rear spar from previous steps (e.g. gap seals) that complicate accurate placement of the bucking bar. Fortunately, the lessons and techniques learned from the inboard skins apply to the outboard skins, which seemed to speed things up a bit.

Riveting the outboard bottom skins starts with the rivets on the rear spar adjacent to the outboard flap hinge bracket. Rivet gun access is tight in this area, so I went with the small diameter flat set on the end of my C-Frame arbor. I made some rivet gun guides from several layers of duct tape to help hold the very long and narrow rivet set straight, and I drew lines parallel to the rivet set on tape affixed to both sides of the flap hinge to help line things up. That setup provided plenty of clearance for the rivet gun, and the rivets went in nicely. I continued inboard from there, but ran into a problem on the last rivet before the two skin over-lap rivets. I set my rivet gun and bucking bar just a smidgen too far inboard, and ended up with a nice ding where the outboard skin overlaps the inboard skin. After looking at the dent for about two days, I drilled out the rivet next to the dent to attempt to at least minimize the damage. I worked a lot of the dent out, but it is still visible. I decided to stop rather than risking additional damage, set a new rivet, and continued with the two skin overlap rivets on the rear spar. All three rivets went fine this time.

Riveting continued along the rear spar all the way to the outboard end. I learned that I could improve my access and riveting position by standing in front of the hole rather than to the side, and using my shoulder to hold the wing skin out of the way. I also used that technique on the aft half of the wing ribs. Riveting the wing ribs stops just past where the J-Stiffener is riveted into place This makes it easy to set the rivet that will eventually fall just under the J-Stiffener, and there is still plenty of room in the wing rib channels to install the J-Stiffener even though the rivets just forward and aft of the J-Stiffener are already set.

The way the plans are written implies that the overlap joint between the bottom outboard and inboard wing skins should be done last. However, I think the intent is actually to do the overlap joint at the same time as the rest of the ribs since the instruction is in the same step as the other rivets. I did the aft over-lap rivets after I installed the J-Channel on the left wing, but I set the overlap rivets on the right wing without delay and without any issues. Setting the skin overlap rivets at the same time as the rest of the rib rivets is definitely the best approach.

One of the unique aspects of the left wing is the pitot mast. I saved that for the very end to avoid blocking access to other rivets along the main spar. The main spar rivets, toward the middle of the outboard section are some of the most difficult to reach on the entire skin, and any obstruction significantly complicates setting those rivets. I calculated the lengths of the rivets needed to install the pitot mast as shown below, and then riveted it in place according to the manufacturer's directions. One thing I planned to do was to put a small bead of tank sealant around the hole where the pitot mast comes through the skin to prevent water from getting in the wing at that point. I pulled out my remaining tank sealant only to find that it had turned into solid rubber about the consistency of an eraser. The old sealant went into the trash, and I proceeded without it. I'll put some silicon sealant around that area before the wing is exposed to the weather. Overall, the pitot mast installation seems solid.

Rivet Length Calculation:
Rivet Length (RL) = Total Material Thickness + (1.5*Rivet Diameter)
Thicknesses
- Spar Flange = 0.0625” = 1/16”
- Pitot Mount = 0.0625” = 1/16”
- Bottom Outboard Skin = 0.025” = 1/40”
- Rivet Diameter (AN426AD3-?) = 0.09375” = 3/32”

Pitot Mount and Skin:
- RL = 0.0625” + 0.025” + (1.5 * 0.09375”) = 0.228125” = 3.65/16”
- Result: AN426AD3-4 Rivet

Spar, Pitot Mount, and Skin:
- RL = 0.0625” + 0.0625” + 0.025” + (1.5 * 0.09375”) = 0.290625” = 4.65/16”
- Result: AN426AD3-5 Rivet

This page of the plans took nearly 2 years to complete start to finish. There were some significant breaks in there when I worked on other things, but this step is significant and takes time and patience. I got a lot of practice with both left-handed and right-handed riveting, and lots of callouses on my finger tips from measuring the diameter of set rivets to ensure they were set adequately. A lot of people put this step off for later in the build, which is understandable. Just don't underestimate the time and effort it will take to complete!

[Hand Rivet Squeezer, 3" Squeezer Yoke, 4" Squeezer Yoke, 3x Rivet Gun, Flat Swivel Rivet Set, Small Diameter Flat Rivet Set, Rivet Set Arbors (Short and Long), Assorted Bucking Bars, Endoscope, Inspection Mirror]

  Oct 20, 2023     20-04 - Miscellaneous Projects - Attach Bottom Wing Skins - (20 hours)       Category: 20 Bot Skins

There are several projects that may be easier to complete before the bottom wing skins are installed. The idea is to complete all of the wing internal systems like pitot plumbing, wiring, and subsystem brackets/mounts while access to the inside of the wing is wide-open; and avoid doing a lot of work through the small wing access panels later. The projects include:
- Garmin GAP 26 Pitot/AoA Probe Installation
- Construct the ADAHRS/Magnetometer bracket (Section 62)
- Assemble, temporarily Install, and adjust the aileron control system (Section 23)
- Assemble, temporarily Install, and adjust the aileron trim system (Section OP-38)
- Assemble and install the autopilot roll servo bracket and wiring (Section 56)
- Assemble and temporarily Install landing and taxi lights and wiring (Section OP-52A)

NOTE: I highly recommend building the ADAHRS/Magnetometer bracket before installing the lower wing skins. It is much easier to test fit and adjust the bracket and mount when it is completely accessible. The fit on my bracket was incredibly tight, and required several adjustments to both the bracket and mount.

GAP-26 Pitot/AoA Probe Installation – Completed 10/20/2023
I decided to install a Garmin GAP 26 heated (unregulated) pitot/AoA probe instead of the plans pitot tube. The probe is installed with a mast, which requires modifications to the bottom wing skin as described previously in 20-03. The three tasks remaining for the pitot/AoA probe installation are interfacing the probe with the mast, electrical wiring, and pneumatic plumbing in the wing.

The Garmin pitot/AoA probe comes with tapped mounting holes, which have to be matched to screw holes in the pitot mast. The trick is to figure out how to very accurately and precisely transfer the location of the mounting screw holes from the pitot/AoA probe to the mast that overlays the pre-drilled holes – essentially blind match-drilling. I believe the installation of the Dynon probe is opposite of the Garmin probe since the holes in the Dynon probe are not pre-drilled, which requires the builder to match drill through the mast into the probe, and then tap the holes in the probe. Both probes have their challenges that the builder has to analyze and work through.

The fore and aft edges of each mounting hole was the easiest measurement to find and mark on the pitot mast. I inserted long screws in the probe holes to account for the angle of the holes and how that angle translates to the hole locations on the mast. I marked the fore and aft edges of the holes on the main body of the probe, and then transferred those locations to the mast with the probe inserted in the mast.

The top/bottom location of the hole centers was more difficult to figure out. I ultimately required 3 tries to get this measurement right. The first two attempts resulted in misaligned holes, which required me to cut off the end of the mast with the bad holes and try again. That was not a very effective approach, and I had to pay attention to how many times I could trim the mast and still maintain the minimum 4” distance between the probe and wing as specified in the Garmin G3X Touch Installation Manual. Fortunately, my second attempt was really close on at least one hole on each side of the mast, and I could make accurate measurements of those holes before trimming the mast for the final attempt. Eventually, I had good markings for the fore, aft, top, and bottom edges of each hole on the pitot mast.

I started each hole in the mast with a very small #53 pilot hole. I used a center punch and drill guide to get the pilot hole as close to the center point as possible along the angle created by the curved mast. I also used the pre-drilled holes in the probe as targets to see what adjustments needed to be made as the mast holes were upsized. I made the targets by covering the pre-drilled probe holes with masking tape, and then tracing the outline of the holes with a pencil. I then inserted the probe into the mast and pushed the drill bit through the pilot hole to see where it broke through the tape below. That gave me an indication of how to adjust the location to drill the next size hole up. As the holes were upsized, the locations became more accurate; and the final holes were right where they needed to be. I completed the pitot mast by countersinking the holes by hand, and priming the drilled and cut areas.
[Hole Deburring Tools, Assorted Drill Bits (#53 to #27), Dremel with Metal Cutting Disk, Hack Saw, Files, Hobby Files]

The next task was the pneumatic connection to the pitot and AoA nylon tubing that was already routed through the wing ribs. The aluminum pneumatic tubing on the probe is very long, and must be sized to fit inside the wing cavity by trimming the aluminum tubing and/or bending the tubing to fit. I wanted to minimize trimming and bending as much as possible, while making it possible to insert the final result into the pitot mast.

The Garmin G3X Installation Panel states, “For heated probe installations where the installer desires to shorten the provided aluminum tubing, a minimum of 8 inches of aluminum tubing should remain between the probe and any transition to non-metallic tubing to protect the non-metallic tubing from excessive heat.” The aluminum tubing for the pitot and AoA lines are just over 13” long. That length is increased with the fittings to transition from the aluminum to nylon tubing, and I trimmed off about 5 1/2” from each tube. I then used a flaring tool to flare the ends for the fittings.

The tubes needed to be bent to ease the transition between the nylon tubing and the probe, so I used a 1/4" tube bender to put a 45-degree bend in the aluminum tubes approximately 6 inches from the end. Minimizing the bend, and strategically locating the bend made it possible to insert and remove the completed probe / transition fitting assembly in the pitot mast.
[Tubing Cutter, Flaring Tool, Tubing Bender, Deburring Tools]

The final task was setting up the wiring for the pitot heat. I ran 14 AWG twisted pair wiring from the wing root to the pitot tube for the pitot heat power and ground, which is connected with the power and ground wires on the probe. The probe has four wires (2 each power and ground), which are connected in parallel to the aircraft wiring for a 14V installation. I watched a couple of SteinAir videos, and decided to try a “window strip” and splice to set up the probe wiring. The window strip essentially creates a gap in the insulation away from the end of the wire, where another wire can be attached. I started by stripping about 3/4" of insulation from the end of one power wire and one ground wire. Next, I moved the stripping tool about 4 inches from the end and stripped about 3/8” at that location. The stripper essentially pushed the insulation toward the end of the wire, and I ended up with a 3/8” gap about 4 inches from the end and another 3/8” stripped section at the end of the wire. I cut the second power and ground wires to the length of the window strip, stripped the ends of those wires, and then made the parallel connection at that point with a solder sleeve covered with a shrink-wrap sleeve for some extra strength and protection. At this point, I essentially had one ground wire and one power wire, which could then be fitted with a connection fitting to match the ground/power wires installed in the wing. It sounds like a complicated solution, but it was not difficult to do, and I think it is a better approach than trying to crimp 2 wires together in a connector.
[Flush Cut Wire Trimmer, Wire Stripper, Solder Sleeves, Heat Shrink, Heat Gun, Red Faston Male and Female Connectors, Crimping Tool]

  Feb 26, 2023     20-06 - Wing Access Covers and Nut-Plates - (1.8 hours) Category: 20 Bot Skins

Initial Prep (Debur, Trim, Drill, and Cut)
2/26/23 - 1.1h
This step is out of sequence because I've decided to wait to rivet the bottom skins to the wing until the flaps and ailerons are built and I've done the initial installation of the aileron actuation parts. Most of page 20-05 is the rivet schedule drawings of the wing skins, but there is a very short step to final drill the holes in the six wing access covers. Sheet 20-06 continues the access cover preparation with deburring the holes and edges.
[Hole and Edge Deburring Tools, #19 Drill, #28 Drill, Bench Grinder with 6” Scotch Brite Cut and Polish Wheel]

Final Prep (Dimple, Countersink, and Shape)
2/26/23 - 0.2h
[Edge Forming Tool (Vise Grip Style), Hole and Edge Deburring Tools, 22” C-Frame with #40 Reduced Diameter, #30, and #40 Standard Diameter Dimple Dies, Pneumatic Squeezer with #40 Reduced Diameter Dimple Die]

Prime
2/26/23 - 0.5h
[Grey Scotchbrite Pads, Bon-Ami Cleanser, Dupli-Color Degreaser, Rust-Oleum Automotive Self Etching Primer (Green – Rattle Can)]

  Feb 25, 2023     20-03 - Wing Skin and ADAHRS Bracket Preparation - (28.9 hours)       Category: 20 Bot Skins

Initial Prep (Debur, Trim, Drill, and Cut)
2/6/23 - 1.6h
2/7/23 - 0.8h
2/18/23 - 3.3h
2/19/23 - 2.9h
2/20/23 - 1.6h
2/21/23 - 1.7h
2/22/23 - 0.5h
The first task on this page is to match drill the ADAHRS mounting zee to the left inboard J-channel. The flange of the mounting zee where it attaches to the J-channel is slanted, and there aren't any specifics in the plan on how exactly to match drill the holes. I looked at several builder sites, and didn't get any hints there, either. My main concern was the eventual level installation of the GMU-22 magnetometer on the ADAHRS mounting bracket. In the end, I realized that the leveling would have to come after the wing was attached, and it would likely take some washers to shim the ADAHRS mounting plate to achieve a level installation. I decided to draw a line down the middle of the J-channel, and use that as a guide to match drill the holes.
[Hole and Edge Deburring Tools, 12” #30 Drill, Cleco Clamps]

Final Prep (Dimple, Countersink, and Shape)
2/9/23 - 0.8h
2/12/23 - 0.6h
2/16/23 - 0.7h
2/20/23 - 3.0h
2/22/23 - 0.3h
2/23/23 - 2.2h
2/24/23 - 3.3h
The dimpling description in the previous log mentioned taking a moment to visualize the final build and ensure the dimpling orientation is correct. That applied to this step as well. Dimpling the wing box J-Stiffeners is straight-forward, but the ADAHRS parts needed just a little thought to get things right. The six holes on the bottom of the ADAHRS mounting zee are dimpled inward to mate with the lower wing skin, and the middle three holes on top of the mounting zee are dimpled the opposite direction to mate with the ADAHRS mounting plate. The corresponding center three holes in the mounting plate are also dimpled to fit with the mounting zee. The outer two holes on the mounting plate and mounting zee top are not dimpled, because there is a flat part that mates above those parts. That brings us to what I think is an error in the plans. The plans say the ADAHRS retainers should be countersunk, but those are very thin parts and would be impossible to fully countersink without enlarging the rivet holes. The retainers sit on top of the ADAHRS mounting spacers, which are very thick parts. My solution is to machine countersink the top of the thick spacers to fit the dimpled retainers, dimple the thin retainers to nest with the spacer countersinks, and leave the plate and mounting zee below flat.

Several holes are final drilled from the inboard bottom skins to the inboard ribs for nut plates that will eventually be used to connect the wing fairings. The nut plate screw holes are final-drilled #19 as well as the #19 screw hole for the access plate attach locations. The newly drilled holes all need to be deburred after removing the skin from the wing.

This step references Section 16 of the plans to modify the lap joint between the inboard and outboard bottom wing skins to be the same thickness as the adjacent leading edge skins. Section 16 says to remove material thickness from the top outboard forward edge of the inboard wing skin and the bottom inboard forward edge of the outboard wing skin to be of equal thickness with the fuel tank skin upon installation. This task is a little easier for the bottom skins since the fuel tank is already installed making it easy to check your progress.

I took this opportunity to ensure the leading edges of the inboard and outboard bottom wing skins didn't overlap any of the leading edge skins at the spar. Some light filing and sanding made everything fit properly. Finally, section 16 instructs you to put a slight break in the leading edge of both inboard and outboard top wing skins, and the inboard edge of the outboard top wing skin. There is no instruction in this section to do that for the bottom skins, but I expanded the instruction to modify the lap joints to include putting the same edge break on the bottom skins prior to dimpling the holes.

I also planned to modify the bottom left outboard wing skin for my pitot mast. The pitot mast came with location and installation instructions, which I modified to suit my installation. The pitot mast goes just outboard of the rib that is outboard of the bellcrank inspection plate. My mast has a joggle to allow it to attach inside the spar flange with the mast plate on the bottom wing skin. I match drilled the pitot mast joggle to the spar first, and then transition to the skin to cut the hole for the mast. The trickiest part of the installation by far was ensuring everything was aligned before cutting the hole in the skin and match-drilling the top holes. My hole in the skin for the pitot mast isn't perfect, but it is really close, so overall I was happy with the way it turned out. I countersunk the holes in the aft side of the pitot mast plate and dimpled the corresponding holes in the skin. The end result will rivet the mast forward-edge joggle to the skin and spar in 3 places, and rivet the aft portion of the plate to the skin in 2 places.
[22” C-Frame with #40 Reduced Diameter, #40 Standard, #30 Standard, and #19 Dimple Dies, #40 Drill, #19 Drill, Micro-Stop Countersink Cage, #30 Countersink Bit, #40 Countersink Bit]

Prime
2/8/23 - 1.1h
2/10/23 - 0.8h
2/17/23 - 0.1h
2/22/23 - 1.2h
2/25/23 - 1.5h
[Grey Scotchbrite Pads, Bon-Ami Cleanser, Dupli-Color Degreaser, Rust-Oleum Automotive Self Etching Primer (Green – Rattle Can)]

Assemble
2/17/23 - 0.9h
The ADAHRS mount assembly is essentially a mini practice project and a lot of fun to put together. I reviewed the assembly steps in the plans, and decided to back-rivet the majority of the parts together. I started with the center 3 rivets that attach the mounting zee to the mounting plate, and then went up a layer to back-rivet the mounting spacers and retainers to the mounting plate. I deviated from the plans by countersinking the mounting spacers dimpling the ADAHRS retainers rather than countersinking the thin retainers. That ended up working very well, and they all came together nicely.

I set the final three universal head rivets that attach the latch to the mounting plate with the pneumatic squeezer. It took a second to figure out a good way to clamp the assembly to the workbench before setting the rivets. I started with the center rivet with the holes on either side cleco'd, which worked fine. I had a little trouble getting a tight fit between the parts on the 2 outer rivets since there was nothing on the outer side to hold the parts together. I partially setting the rivets and noticed a small gap between the parts. I squeezed the parts back together using a nylon spacer with a hole slightly larger than the shop head of the rivets. The partially set rivets held the parts tightly together while I finished the final squeeze. I wasn't sure that method would work, but decided to try it on a non-structural part that could be easily replaced if things went bad. The experiment ended up working really well, and I'll keep it in mind if I run across similar situations down the road.
[3x Rivet Gun, Back-Rivet Set, Back-Rivet Plate, Pneumatic Squeezer, 1/4" Cupped Rivet Set]

  Feb 17, 2023     20-02 - Flap and Aileron Gap Fairings - (13.6 hours)       Category: 20 Bot Skins

Initial Prep (Debur, Trim, Drill, and Cut)
2/5/23 - 1.3h
2/6/23 - 1.2h
It is really nice to be back into the “normal” build routine with no tank sealant in sight! Working with the sealant really wasn't too bad, but it added a layer of complexity to the process, which slowed things down. This section starts with the flap and aileron gap fairings that run the length of the wing and encloses the area from the aft edge of the wing skin to the aft spar. Each wing has a flap gap stiffener that gets trimmed to shape and deburred, and the flap and aileron gap fairings for each wing are also deburred.
[Hole and Edge Deburring Tools, Band Saw, Bench Grinder with Scotch Brite Wheel]

Final Prep (Dimple, Countersink, and Shape)
2/9/23 - 1.2h
Dimpling is a standard skill at this point in the build, but it is not without challenges if you don't pay close attention to the end goal. I have found it is a good practice to nest parts together whenever possible to confirm the orientation of all the dimples. The flap gap fairing is a good example. The plans say to dimple the fairings, and refer to a drawing of the fairing with an instruction to “DIMPLE THIS SIDE”. The figure does not mention that the dimples on the inboard edge of the fairing stiffener and the 6 inboard dimples for the rear spar doubler are opposite of the dimples along the upper skin. The orientations are not hard to figure out, but you need to take a beat and think about how the part is ultimately installed to ensure you have it right!
[22” C-Frame with #40 Reduced Diameter and #30, Dimple Dies]

Prime
2/8/23 - 0.8h
2/10/23 - 0.8h
[Grey Scotch Brite Pads, Bon-Ami Cleanser, Dupli-Color Degreaser, Rust-Oleum Automotive Self Etching Primer (Green – Rattle Can)]

Assemble
2/10/23 - 0.9h
2/12/23 - 2.0h
2/13/23 - 1.1h
2/14/23 - 1.1h
2/15/23 - 2.0h
2/17/23 - 1.2h
I may be reading too much into the plans at this point. For example, the plans say to “Rivet the gap fairings to the Rear Spar Assembly and the top skins.” The plans didn't explicitly state that the rear spar rivets are first, but its mentioned first in the instructions, so that's where I started. I'm glad I started with the spar rivets, because there are a couple that are a little tricky. I also found that I could set the rear spar rivets with the wing in the cradle, but I had to take the wing out of the cradle and lay it flat to set the skin rivets.

I decided to start with the longest rivets, and work my way to the shortest rivets. The six inboard rivets go through a couple layers of doublers, the rear spar, and the two inboard ribs, and are very long AN426AD4-8 solid rivets. I was nervous about working with the long rivets, since they are very easy to tip, but all of the rivets on both wings went in without any issues.

The next rivets to go in were the AN470AD4-5 rivets. That's a pretty standard length, so I wasn't as worried about successfully setting them without tipping. These rivets go through the areas on the rear spar with doublers near the flap and aileron hinge brackets. The pneumatic squeezer with a longeron yoke can get to most of the rivets easily, but not the rivets on each side of the inboard aileron hinge bracket. I decided to buck those rivets. The one on the inboard side of the aileron hinge bracket went fine. The real trouble came with the outboard rivet, which ends up right next to the hinge bracket doubler assembly. I did the best I could with the edge of the bucking bar pressed up against the doubler assembly, but as you can see in the picture the rivet did not set well at all. I only managed to “set” the outboard 2/3rds of the rivet, which I was not happy with. In a moment of insanity (trying the same thing and expecting different results), I tried to buck the rivet on the other wing. I was disappointed to end up with another poorly “set” rivet. I researched some builder log sites as well as the Van's Air Force threads, and found other builders had the same issue. Van's apparently said the ugly rivet is OK, but also weighed in on an alternate solution using pulled rivets. Van's said the MSP-42, and the lower-strength LP4 pulled rivets are acceptable substitutes in this instance for the AN470AD4-5 solid rivet. I also noted that the instructions for the quick build wings say, “When attaching the flap gap fairing, use CR3212-4-6 rivets for the six inboard locations and MSP-42 rivets elsewhere.” It appears there is good precedent and recommendations for going with the MSP-42 pulled rivet, so I drilled out the bad solid rivets to give it a try. The pulled rivets worked beautifully, and I'm very happy with the final result. I sent a note to Van's to recommend changing the plans to the MSP-42, since I can't see any way to get a solid rivet to set properly with almost no clearance from the hinge bracket doubler.

The rivets on the skin are all AN426AD3-3.5, which are probably the most commonly used rivets to this point in the build. I tried to set a couple of rivets while the wing was in the cradle, which essentially put me beneath the rivet and unable to see or control the squeezer on the manufactured head side on the top wing skin. The rivets went in very poorly, and it was clear I needed to take a different approach. I pulled the wing out of the cradle and laid it face up on a work surface. I had much better luck setting the rivets that way, and all the rivets for both wings went in without incident. The bad rivets were also easy to drill out and re-set with the wing out of the cradle.
[Pneumatic Squeezer with Flush and 1/8” Cupped Rivet Sets, 3x Rivet Gun with 1/8” Cupped Rivet Set, Tungsten Bucking Bars, Blind Rivet Puller, #30 Drill]

  Feb 05, 2023     20-01 - Wing Bottom Skins (Plans) - (3.0 hours) Category: 20 Bot Skins

2/5/23 - 3.0h
The plans to prepare and install the bottom wing skins don't appear to be overly complicated, but I have a feeling that execution will be a bit tricky given the limited access to buck rivets as the skins get attached. I did not see any revisions and changes to the plans, notifications and letters, or service bulletins related to the wings. I did find a typo on sheet 20-04, which refers to the W-00005-L Bottom Inbd Wing Skin (should be Bottom Outbd Wing Skin). I also plan to review some builder sites to see when they actually rivet the skins to the wings. It seems like at least some builders wait until all of the control and wiring systems are complete before riveting the bottom skins on to have unimpeded access to finish the internal work.