Apr 24, 2023     21-12 - Flap Hardware - (0.4 hour)       Category: 21 Flaps

Assemble
4/24/23 - 0.4h
This turned out to be an abbreviated step, with a couple of items pushed to my “to-do” list later in the build. The only step I completed was to attach the control rod end to the inboard location on each flap. The rod end is secured with an AN4-11A bolt to the nut plate riveted to the inboard nose rib. The torque for the AN4 bolt is 50-70 in-lbs. I set my torque wrench for 60 in-lbs plus drag, which resulted in 70 in-lbs on the right and 68 in-lbs on the left. I also noted that Section 5 of the plans says to lubricate the shank of the bolt when you are torquing it rather than a nut. The other thing worth noting is the drawings show the thinner washer closest to the bolt head with the thicker washer closest to the threads.

Two items I did not complete at this point were press fitting the bushings in the wing hinge attach points and final attachment of the flaps to the wings. I plan to install the bushings after I attach the bottom wing skins. The bushings are wider than the hinge brackets, and could interfere with fitting the bottom skins over the hinge brackets. I'll complete the final attachment of the flaps after the wings are attached to the airplane. Until then, the flaps will go into storage with the wings at the airport.
[Torque Wrench]

  Apr 23, 2023     21-10/11 - Flap Assembly - Bottom Skin and Trailing Edge - (17.7 hours)       Category: 21 Flaps

Assemble
4/7/23 - 5.0h
4/8/23 - 3.6h
4/12/23 - 1.1h
4/13/23 - 0.8h
4/14/23 - 2.2h
4/15/23 - 1.3h
4/18/23 - 1.0h
4/19/23 - 0.5h
4/23/23 - 2.2h
I was worried about this step since the plans go into detail on how to avoid twist in the flaps and access to buck the bottom skin to spar rivets is extremely tight. I spent the time when I installed my workbench to ensure it was a level surface, and I confirmed the bench top is still flat and level. I also have a large, flat steel back-rivet plate (approximately 9” wide by 6' long) that I placed on top of the bench as a mount for the flap cradles. I put the flap in the cradles, cleco'd the bottom skin and nose skin to the bottom flange of the spar, and used a digital level to check the angles on the hinge brackets. With some very minor adjustments, both brackets on the right and left flaps came in at -4 degrees. I checked the angles periodically as I riveted the bottom flange of the spar to the nose and bottom skins, and the angles didn't change throughout the process. A final check after riveting confirmed no changes, so presumably I have no twist in the flaps.

The other worry in this step was actually setting the rivets along the spar on the bottom of the flap. I found that there simply wasn't enough clearance for me to reach the spar between the skins and maneuver the bucking bar into place. I've seen logs from builders who managed to do it, but I was not convinced I could get decent results with that approach. I decided to get creative, which generally is not a good thing, with my long elevator bucking bar. It had excellent access to the rivets, and the bar extended past the trailing edge of the flap about 3”, so I could easily maneuver the bar and apply appropriate pressure to set the rivets. I managed to align the flat side of the bar with the spar flange for evenly set rivets, and was extremely happy with the results using the long elevator bar. As a side note, I think this method put a lot of stress on my left wrist due to the way you have to hold the bar and then use your thumb to apply the pressure. I'll definitely use a wrist brace if I end up doing anything like that again!

One down side to the long elevator bar is it did not have good square access to the rivets inside the rib flanges. I needed another approach for those, so I used some gorilla tape to attach a small bucking bar to the end of some paint-stirrer sticks. I taped three stir sticks together to provide some rigidity to the handle, and then attached the bucking on top of the sticks at the bottom with about 3/4" of the bucking bar extending beyond the edge of the sticks. The portion of the bar sticking out fit into the rib flange to set the rivet, while the stir-stick handle provided enough leverage to hold the bar in place. This method worked really well for me, and I was happy with the rivets on the rib flanges.

According to Section 5 of the plans, “Building a truly straight TE is one of the more difficult things to do in aircraft construction.” I followed the recommendations in Section 5 closely to give myself the best chance for a straight trailing edge. That included using the recommended 3M VHB tape to bond the trailing edge components together before setting the rivets. Instructions for cleaning the parts and applying the tape are provided in Section 5. I allowed the tape to bond over night to give it a chance to completely adhere to the parts.

Section 5 also goes into detail on “double-flush” riveting. I used special squeezer dies to double-flush rivet the rudder and elevator trailing edges, but I went with the Section 5 back-rivet technique for the flaps. Back-riveting allowed me to keep the flap trailing edge tight against the flat back-rivet plate, which resulted in a straight trailing edge! I used a small diameter rivet set in the gun to initially set each of the rivets, and finished with a larger flush set to finish the double-flush shop heads on the bottom of the flap. Per the technique detailed in Section 5, I used weights to hold the flap trailing edge tight to the back-rivet plate, worked from the center out starting with every 10th rivet, and used a low gun pressure of about 30psi.

After setting the trailing edge rivets, I finished the bottom of the flaps with pulled rivets along each of the ribs. The rivets called out for this step require the holes to be upsized slightly to #33. Access to pull the blind rivets is about as good as you can get, so there were no issues there. The rivets on the outboard and inboard ribs are squeezed solid rivets, with the exception of the aft rivet, which is a blind rivet due to limited access for a squeezer. I also couldn't get my squeezer into the adjacent rivet forward, so I set a blind rivet there, too.

[3x Rivet Gun, Small Diameter Flush Set, Regular Flush Set, Large Back-Rivet Plate, Clamps and Weights, #33 Drill, Blind Rivet Puller, Hand Squeezer, Flat Squeezer Set]

  Apr 07, 2023     21-09 - Flap Assembly - Top Skin - (7.5 hours)       Category: 21 Flaps

Assemble
3/28/23 - 1.4h
3/29/23 - 1.7h
4/4/23 - 0.7h
4/5/23 - 1.7h
4/6/23 - 2.0h
You may have noticed there is a gap of about a week in this step. That is because my fuselage kit arrived on March 30th! I spent the week unpacking and inventorying parts, and disassembling the shipping crate. The fuselage kit was delivered about a month earlier than expected, and approximately 2 months before I'll complete the wing tasks. I definitely won't complain about an early delivery, and I'm anxious to get started on the fuselage!

Flap assembly continues with the nose and top skins. The nose and top skins are riveted to the top spar flange. I started in the middle of the spar and worked outward in both directions from there with the rivet gun and bucking bar. I switched to the hand squeezer for the final rivet at each end of the spar. It's important to note that the rivets at the main ribs are longer than the ones between the ribs.

Riveting the top skins to the ribs involves three different techniques. The forward six rivets on each of the interior ribs are set with the rivet gun and bucking bar. A lot of care is required to avoid damaging the skins since there isn't much surface on the rib flanges for the rivet gun and bucking bar. The rivet squeezer has good access to the exterior ribs with good results. Finally, the aft two rivets on each rib, including the exterior ribs, are set by back-riveting. The ribs have gaps in the flanges opposite the holes for back-riveting, but the gaps are not large enough for the back spring-guard. I ended up using a very small diameter flush set, and held the rib against the skin during the process by hand. The back rivets turned out good, and it's on to the bottom skin!
[3x Rivet Gun & Bucking Bars, Flush (Mushroom) Rivet Set, Back-Rivet Set and Plate, Hand Squeezer, Flat Squeezer Set]

  Mar 27, 2023     21-08 - Initial Flap Assembly - Nose and Main Ribs - (6.9 hours)       Category: 21 Flaps

Assemble
3/25/23 - 1.4h
3/26/23 - 4.2h
3/27/23 - 1.3h
The nose ribs and main ribs are riveted to the spar to form the flap skeleton. I started with the nose ribs, which were mostly accessible with the pneumatic squeezer. The main ribs were also mostly accessible with the pneumatic squeezer. The exceptions were the second main rib from the inboard edge and the outboard nose rib/main rib combo. The second main rib flanges face the nose rib flanges, which obstructs squeezer access, and the squeezer is too large to fit in the inset area of the end nose or main ribs. I bucked the rivets with a double-offset cupped set on the rivet gun with good results. The trickiest part of the operation is figuring out how to secure the parts to the work bench prior to riveting. I clamped some 1x2's to the work bench with the ends extended about 6” past the edge of the work bench. That provided a stable surface, which allowed access above and below the parts for the squeezer and rivet gun.

The final task on this sheet was to cleco the nose and top skins in place. The nose skin takes some maneuvering to get in position, but it eventually fit really well. I was also very pleased with how well the rivet holes in the skins and flap skeleton parts lined up. Clecoing everything together was easy for both flaps!
[Pneumatic Squeezer, 1/8 Cupped Squeezer Set, 3x Rivet Gun, Double-Offset Cupped Set, Tungsten Bucking Bar]

  Mar 25, 2023     21-07 - Flap Hinge and Nose Rib Assembly - (4.3 hours)       Category: 21 Flaps

Assemble
3/24/23 - 2.7h
3/25/23 - 1.6h
Flap assembly starts by building up the nose rib parts. The inboard rod end ribs each get doublers, and the outboard rod end ribs each get doublers and nut plates. Van's specifies the direction of the rivets in the drawings. In this case, the manufactured head goes against the ribs, and the shop head is set on the doubler. The nutplate rivets are set in the opposite direction to attach the nutplate inside the rib with flush rivets on the doubler. The pneumatic squeezer had good access to set all the rivets.

The hinge assemblies start similarly to the rod end ribs. The hinge brackets are riveted to their corresponding rib, with the manufactured head against the ribs, and the shop head set on the hinge brackets. The pneumatic squeezer had good access to set all of these rivets as well.

The final task in this step is to rivet left and right hinge/rib pairs to each other. This is a little different than previous riveting tasks because the rivets are set double-flush. The process starts by clecoing the hinge sub-assemblies together, and inserting the flap hinge bushing to keep the hinge brackets aligned properly. I was concerned that the clecos didn't hold the hinge pairs tight enough, which could lead to setting bad rivets, so I supplemented the clecos with c-clamps. The other thing to keep in mind is setting the pneumatic squeezer too tightly will prevent it from generating the maximum compression on the rivets. The shop head of the double-flush rivets completely filled the countersink, and ended up just very slightly proud. I sanded the flanges smooth, and was very happy with the results.
[Pneumatic Squeezer, 1/8 Cupped Squeezer Set, Flat Squeezer Set]

  Mar 24, 2023     21-06 - Flap Parts Prep - (30.9 hours)       Category: 21 Flaps

Initial Prep (Debur, Trim, Drill, and Cut)
3/9/23 - 1.5h
3/10/23 - 3.8h
3/11/23 - 0.7h
3/17/23 - 0.4h
3/18/23 - 2.4h
Final preparation of the flap parts includes some match and final drilling. The upper flanges of the nose ribs get each get 2 holes match drilled to the pre-drilled holes in the nose skin. The joggled flanges in the hinge brackets also get match drilled to the holes in the opposite hinge brackets that were drilled earlier. The hinge brackets are aligned by inserting the hinge bushing on the hinge bolt at the bottom of the hinge. I also used a cleco clamp as I worked my way up the flange, and then cleco'd each hole as I went. The top hole is very close to the nose skin, so I used an angle drill attachment to get a straight shot at that hole. A 12” #40 drill bit would also work for the top hinge flange hole.

The trailing edge wedge is final drilled along with the trailing edge of the top and bottom skins. Just like the rudder trailing edge, the holes are match drilled at an angle to the skin rather than perpendicular. An 84-degree angle to the skin gets the drill perpendicular to the centerline of the wedge. I held an angle gauge set to 84-degrees against the drill to align the drill properly.
[Hole and Edge Deburring Tools, #40 Drill, Angle Gauge, Angle Drill with #40 Bit, Cleco Clamps]

Final Prep (Dimple, Countersink, and Shape)
3/6/23 - 1.1h
3/12/23 - 0.5h
3/14/23 - 1.7h
3/15/23 - 1.8h
3/17/23 - 3.1h
3/18/23 - 0.7h
3/19/23 - 0.6h
3/20/23 - 2.1h
3/22/23 - 0.6h
A couple of different countersink techniques/tools are required for the flap parts. The trailing edge wedge is countersunk on both sides perpendicular to the wedge. I have a wedge drill and countersink jig that makes it easy to countersink the wedge correctly.

The hinge brackets are the other parts that need to be countersunk for double-flush rivets. This is different because the countersinks are on the joggled flanges, which prevents directly using a microstop countersink cage. The plans have you fashion a drill jig to help countersink the joggle. I tried to use the joggle jig, but struggled to set up the countersink cage correctly. I eventually decided to countersink the holes on the joggled flanges by hand with the countersink cutter on an electric screw driver. This method was effective for me, but it takes time since you need to frequently check the countersink to ensure you don't inadvertently go too deep. I typically stopped countersinking when a rivet head would sit just proud of the surface (maybe a couple of thousandths), and then I finished the countersink with a hole deburring tool.

Dimpling also requires several different tools and techniques. The C-Frame is effective to dimple the top and bottom skins. The C-Frame is also good on the nose skin aft edge holes, and for the forward 2 or three holes on the top side of the nose skin. The other top and bottom holes on the nose skin are accessible with a hand or pneumatic squeezer. The pneumatic or hand squeezer is also required for the holes in the rib and spar flanges.
[Edge Forming Tool (Vise Grip Style), Hole and Edge Deburring Tools, 22” C-Frame with #40 Reduced Diameter and #40 Standard Diameter Dimple Dies, Pneumatic Squeezer with #40 Reduced Diameter Dimple Die, Trailing Edge Wedge Drill and Countersink Jig, Microstop Countersink Cage, #40 Countersink Cutter]

Prime
3/13/23 - 2.0h
3/19/23 - 2.0h
3/20/23 - 1.0h
3/21/23 - 0.7h
3/22/23 - 0.7h
3/23/23 - 1.5h
3/24/23 - 2.0h
[Grey Scotchbrite Pads, Bon-Ami Cleanser, Dupli-Color Degreaser, Rust-Oleum Automotive Self Etching Primer (Green – Rattle Can)]

  Mar 06, 2023     21-05 - Flap Trailing Edge Prep - (3.4 hours) Category: 21 Flaps

Initial Prep (Debur, Trim, Drill, and Cut)
3/5/23 - 2.2h
3/6/23 - 1.2h
Trailing edge wedges, like the one on the rudder, are provided for the flaps (and ailerons). The flap is longer than the wedge, so a long piece and short piece are trimmed to form a but joint approximately 10 inches from the inboard edge of the flap. The initial cut locations are measured and marked, and then the wedges get cleco'd to the bottom flap skin for fine-tuning. The problem I had was deburring the cut ends of the wedges. The deburring process led to a small, but noticeable gap (less than 1/32” between the wedge pieces. I plan to try again and leave the wedges a little long so the deburred wedges fit closer.

The final task on this step is to put a slight bend in the long edges of the leading edge skins. This is a little tricky because the skins are hard to clamp to the workbench without damaging the bends in the skins. I ended up holding the parts in place by hand, and going very slowly with the edge forming tool. The bend is very subtle and even down the length of the skins, which is what I was going for. I also took this opportunity to debur the edges of the leading edge skins.
[Hole and Edge Deburring Tools, Dremel with Metal Cutting Disk, Edge-Forming Tool]

  Mar 05, 2023     21-04 - Flap Skeleton - (1.1 hours)       Category: 21 Flaps

3/5/23 - 1.1h
This may be the quickest step in the build to this point. All of the flap parts, with the exception of the skins, spars, and trailing edges have been drilled, cut, and deburred as specified. The primary task in this step is to bend the spar flange of the inboard ribs to be parallel with the forward edge of the bottom skins. The inboard edge of the flaps flares out just a bit, which changes the angle of the inboard rib. The most challenging part of this step for me was figuring out the orientation of the bottom skins. The forward edge is shorter than the trailing edge, the square edge is outboard and the angled edge is inboard. Once I had that figured out, I cleco'd the inboard ribs to the angled edge of the skin and adjusted the spar flange angle.

The final task of this step was to cleco the flap skeleton together. The drawings in the plans are very clearly marked to show the orientation and location of each part. I marked each of the nose ribs (L-1 through L-8 and R-1 through R-8) from the inboard end of the spar to the outboard end. I did the same for the main ribs to help me maintain this orientation throughout the remainder of the build.

  Mar 04, 2023     21-03 - Nose Rib, Hinge Bracket, and Rib Prep - (5.5 hours)       Category: 21 Flaps

Initial Prep (Debur, Trim, Drill, and Cut)
3/3/23 - 1.5h
3/4/23 - 4.0h
All of the nose rib holes are final drilled in this step, and the remaining modifications for the rod end rib subassemblies are completed in this step. All of my nose ribs were delivered with final-sized holes, which made quick work of this step. The main task was final-drilling the 1/4" hole in the outboard rod end subassemblies. I also had to do some final-drilling for the webs of the hinge pair subassemblies. The plans were not completely clear on whether or not all four (two left flap and two right flap) hinge pair subassemblies received the same treatment. There is a note after this step that says remaining steps refer just to the left flap, but I think that note also applies to the hinge pair assemblies and I final drilled all four sets.

The primary task on this sheet, other than deburring all of the nose and main ribs, is removing the small tab at the aft end of the upper rib flange. This is done to gain access to the hole just across from the tab on the lower rib flange. The task doesn't look overly complicated, but I learned a lesson from another builder that it is very easy to accidentally trim off the lower tab with the hole while trimming off the upper tab. I planned to clamp the rib to the work bench and use a Dremel with a metal cutting disk to remove the tab. I clamped a thin piece of steel under the tab to act as a backstop to protect the bottom tab. The backstop worked great, and I managed to remove all of the upper tabs without damaging the bottom flange of the ribs. I filed each cut even with the curve in the notch, put a small radius on the end with the file, and deburred each rib.
[Hole and Edge Deburring Tools, #30 Drill, #40 Drill, 1/4" Drill, Dremel with Metal Cutting Disk]

  Mar 03, 2023     21-02 - Nose Rib and Hinge Bracket Prep - (5.0 hours)       Category: 21 Flaps

Initial Prep (Debur, Trim, Drill, and Cut)
3/1/23 - 1.9h
3/3/23 - 2.1h
The flap, like all the other build steps, starts with preparing parts for assembly. The first job is to lay out a 4-hole pattern in the joggle of a left hinge bracket, drill the 4 holes, and then use that hinge bracket as a template for the other three left hinge brackets. Note that the right hinge brackets do not get drilled in this step.

Preparation of the nose ribs comes next. The faceted curved forward-edge flanges get buffed with a 6” Scotch Brite Cut-and-Polish wheel to “minimize the tendency for them to appear faceted instead of curved.” I didn't need to flute any of the ribs since they were all straight, so I moved directly to deburring the holes and edges.

The final parts that get some attention in this step are the rod-end assembly doublers. The doublers don't have any complex curves or crevices to complicate deburring, and I did most of the edge deburring with the 6” Scotch Brite Cut-and-Polish wheel since it was already out to buff the nose rib flanges. After I deburred the doublers, I cleco'd one each to the outside of a left and right nose rib to form the outboard rod end rib assemblies. There is a nut-plate pattern in the doubler that is used to match drill the holes in the ribs. The center hole of the nut-plate pattern is also match drilled with a 1/4" drill bit.
[Hole and Edge Deburring Tools, #40 Drill, 1/4" Drill, Bench Grinder with 6” Scotch Brite Cut-and-Polish Wheel]

Final Prep (Dimple, Countersink, and Shape)
3/2/23 - 0.7h
3/3/23 - 0.3h
The final task for this step was to countersink the nut-plate holes in the doublers flush on the exterior side. The rod end rib subassemblies are then disassembled to clean and debur the holes, and then reassembled with the clecos inside the flange of the ribs.
[Bench Grinder with 6” Scotch Brite Cut-and-Polish Wheel, Microstop Countersink Cage with #40 Countersink Cage]

  Feb 27, 2023     21-01 - Flaps (Plans) - (2.5 hours) Category: 21 Flaps

2/26/23 - 10h
2/27/23 - 1.5h
A quick review of the service information and revisions section of the Van's website confirmed I have the latest copy of the flap plans. I did, however, download an update to Manual Section 5. Section 5 updates include a note on cracks in dimpled holes, tips on nut-plates, a caution on isopropyl alcohol near acrylic edges and holes, and an additional set of torque values for shear-type nuts.

The plans start with a note on special tools required for this step of the build including #33 6 in. long drill bit, back riveting plate, and duck-bill pliers. I'm good with the back riveting plate, but I'll have to look into sources for the other specialty tools. The plans for the flaps also deviate from other wing build plans by recommending building both flaps at the same time to “help prevent mistakes and speed up the construction process.” Other sections leave it up to the builder if you want to work on the left and right sides together or consecutively. I've completed the other sections to this point at the same time for both left and right assemblies, so this isn't really a change for me. The other thing I noticed for the flaps is an emphasis on building flat and square assemblies to minimize twist in the flap. That will require some careful planning and additional preparation to keep things as square and level as possible. I have a friend who took extraordinary care building his flaps, and they still had some twist; so I'm not real optimistic on my chances for a flat flap. There are also a lot of instructions about the specific order in which parts are drilled, cleco'd, riveted, …; which will require a lot of care during the assembly to get it right.