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]