Final Prep (Debur, Dimple, and Countersink)
5/6/2021 – 0.1 hours
The angle stiffeners that attach to the rear of the side skins were deburred and primed earlier in this section. The job for this session was to dimple each of the angle stiffeners where they will eventually attach to the side skins. This was a quick job since each stiffener is small and only has 6 holes.
[22” C-Frame, 3/32” Dimple Die Set]
5/10/2021 – 1.6 hours
5/18/2021 – 0.5 hours
The longerons, which run the length of the aft fuselage, are countersunk to accept the dimpled fuselage side skins. I set the countersink cage to a depth of 0.007” deeper than flush. There are 288 holes – 144 holes in each longeron – so it takes awhile to countersink all of them. The longerons provide a solid and flat base for the countersink cage, and countersinking didn't present any problems.
The J-Stiffener material is too thin to be countersunk, so the #40 holes in the J-Stiffener flanges are dimpled. The J-Stiffeners are long and narrow parts, so it is important to provide proper support to the parts during the dimpling process to ensure they don't warp or bend. The F-01486A left and right J-Stiffeners each have holes for two nutplates. The #40 holes to attach the nutplates are dimpled, and the #27 hole for the nutplate is optionally dimpled if you intent to use flush screws on the access covers. I elected to go with the flush screw, so I dimpled the two #27 holes in each J-Stiffener.
[Microstop Countersink Cage, #40 Countersink Cutter, Palm Drill, 22” C-Frame, 3/32” Reduced Diameter Dimple Dies, #6 Screw Dimple Dies]
6/3/2021 – 2.6 hours
6/4/2021 – 3.0 hours
The side skins are the largest single parts I've worked with so far, and one takes up my entire work bench. The side skins are relatively easy to debur since they have long, continuous edges and just four tabs at the forward edge of each skin. There are also a couple of small cutouts for an access panel and the rudder cables to debur, as well as lots of holes for rivets and the static ports.
[Hole and Edge Deburring Tools]
6/5/2021 – 4.3 hours
Dimpling the aft fuselage side skins takes some time since they are large, have a lot of holes (800+ between the two skins) in 3 different sizes, have curved sections with holes to dimple, and have several holes that are not dimpled. I started dimpling with the pneumatic squeezer and a reduced diameter 3/32” dimple die set to get all of the #40 perimeter holes and almost all of the #40 holes near the aft end of the skins. Each row of bulkhead holes has 3 or 4 holes in the curved edge at the bottom of the skin. I could dimple the first 1 or 2 holes in the curved area with the squeezer, but couldn't go further than that due to clearance issues. I successfully dimpled the remaining bulkhead holes in the curved areas with the pop-rivet dimple die set. I dimpled the interior flat-section holes with the 22” C-Frame and a standard 3/32” dimple die set, which left a row of holes in the center of the curve transition from the bottom to the sides. I switched to the reduced diameter dimple dies in the C-Frame, but the real trick is getting the hole to lie perpendicular to the dimple dies when the dimples are formed to avoid small dents at the top or bottom of the dimple. The best method for me was to rest the long, flat side of the skin against my chest to hold the hole perpendicular. There are a few that weren't completely flat, but that method worked for the majority of the dimples. I wrapped things up by dimpling the small number of #30 holes in the side skins, taking care with a piece of tape to not dimple the 4 holes called out in the plans. I also dimpled the bottom 6 #27 holes for the nutplates to flush-mount the access panels. The top 2 #27 holes do not get dimpled – they will be machine countersunk a few steps later.
[Pneumatic Squeezer, 22” C-Frame and Hammer, 3/32” Reduced Diameter Dimple Die Set, 3/32” Standard Dimple Die Set, 3/32” Pop-Rivet Dimple Die Set, 1/8” Dimple Die Set, #6 Screw Dimple Die Set]
Prime
5/17/2021 – 1.7 hours
5/18/2021 – 1.1 hours
5/20/2021 – 0.9 hours
5/26/2021 – 0.5 hours
6/5/2021 – 1.0 hours
6/7/2021 – 0.7 hours
Priming is generally the final preparation step for individual parts. Once parts are primed, they are ready for installation and assembly. My standard priming process started with the longerons followed by the F-01486A, B, and C J-Stiffeners. I also used this process to prepare and prime the aft fuselage side skins.
[Grey Scotchbrite Pads, Bon-Ami Cleanser, Dupli-Color Degreaser, Dupli-Color Self-Etching Automotive Primer (Green – Rattle Can)]
Assemble
6/6/2021 – 0.9 hours
6/7/2021 – 3.2 hours
The final mockup of the aft fuselage started by clecoing the F-01410 bulkhead into place and inserting the left and right channel stiffeners into the slots in the bulkheads. There isn't much support for the bulkhead at this point, so it is good to work on the assembly upside down on the saw horses to minimize any chances of bending the bulkhead tabs and flanges. I cleco'd the left and right longerons to all of the bulkheads, which provided enough support for the entire structure to be able to turn it upright on the work bench.
The WH-00057 aft fuselage wire harness and the WH-00059 phone cable are routed along the bellcrank ribs and then are nested in the top-left J-Stiffener through the #7 and #8 bulkheads. The initial routing is done before the left skin is attached to the aft fuselage assembly to provide access to the J-Stiffener gaps in the bulkheads. After labeling the WH-00057 connectors, I used twist ties to lay the wires in place and followed up with loosely installing the provided zip ties to hold the wires in place. I completed this step by clecoing the left and right side skins and angle stiffeners to the aft fuselage assembly. It took all of my 325 3/32” clecos spaced roughly every 3rd hole to attach both skins.