Wing Flap 22-8-4 to 22-8-14

In preparation to install the trailing edge wedge using tank sealant, I first scuffed the wedges and skin interior trailing edges with 150 grit sandpaper, and wiped all parts down with acetone.

I also positioned both flaps and trailing edge wedges so that I could easily work with them while applying proseal. In order to keep the trailing edge flat while curing, I used my previously prepared square aluminum tubes, with holes that I had match drilled to the trailing edge. By clecoing the trailing edge to these jigs, the edge is not only kept straight, but the clecoes keep both skins pressed firmly against the wedges while the sealant cures.

Both flaps and wedges cleaned and positioned for easy application of sealant

After mixing the proseal components, and carefully applying a thin layer to each wedge in turn, I was able to easily cleco the wedges and skins to the aluminum alignment jigs, and leave the sealant to cure for several days.

After about 5 days of curing, during which the weather was quite warm and the garage temperature rose into the mid 80s, I felt the sealant had cured sufficiently to allow me to remove the trailing edge clecoes. The clecoes came out easily, and I was also able to remove the alignment jigs fairly easily using a utility knife to trim away sealant that had squeezed out from the trailing edge and adhered to the jig.

After putting the flaps back in the cradles, I was very happy with how straight the trailing edge had come out. Above is the left flap... 

...and this is the right flap

Both flaps back in the cradles, ready to start cleaning away excess proseal from the trailing edges and holes

Next I used a #40 drill bit, spun by hand in each hole to remove proseal from the holes. I also used the deburring bit to cut away any proseal in the trailing edge dimples. I also found that a sharp razor blade run along the trailing edge made quick work of removing any proseal that had squeezed out between the skins.

Finally, I carefully wiped the skins near the trailing edge with a shop rag and acetone to remove any smudges of proseal around the holes. Here I paid attention to not let acetone seep into the holes and potentially weaken the sealant holding the skins tight to the wedges.

Running a razor blade along the trailing edge easily cut away any proseal that had squeezed out

Once the trailing edges were clean, I reattached the jigs to the trailing edge of each flap to hold everything in alignment and proceeded to blind rivet the bottom skin to the ribs.

Flap ready for bottom skin to be blind riveted to the ribs

The bottom skin to end ribs on each flap use (mostly) solid rivets, so here I used the pneumatic squeezer to set those. The only rivet that took a little more thought was the second from the aft edge because the standard 3" yoke does not fit in the space between the rib flanges. I switched to the 4" no-hole yoke and the 1/2" thick flat set and was then able to squeeze that rivet without issue. 

The final bottom skin aft end rivet closest to the trailing edge requires a blind rivet because there is no room for a solid rivet.

Using the 4" no-hole yoke and 1/2" long flat set to set the end rivets where space is limited

Bottom skin fully riveted on the left flap. One more flap to go.

Squeezed rivets came out nicely. Note the blind rivet closest to the trailing edge

Right flap on bench ready for riveting the trailing edge

To rivet the the trailing edge of the flaps, due to the unwieldy nature of maneuvering the flaps over a back riveting plate given their length, I decided to approach the riveting slightly differently from the published technique in plans section 5.

After placing all the rivets into the holes along the trailing edge, I used my pneumatic squeezer to perform the initial set of each rivet by partially squeezing it between two flat sets. By working my way out from the center, starting with every 9th rivet and splitting the difference as I had done before, I was able to partially set each rivet while maintaining a perfectly straight edge.

Rivets positioned along the flap trailing edge. There were a few holes where the rivet didn't quite sit flush prior to riveting, but that was easily remedied by cleaning out some leftover proseal that remained in the hole

Using the pneumatic squeezer to partially set each rivet along the flap trailing edge

Next I switched to the Cleaveland trailing edge dies in my pneumatic squeezer and this followed the same riveting pattern to fully squeeze each rivet so that the shop head (along the bottom trailing edge of the flap) was flush with the skin.

Trailing edge dies in the pneumatic squeezer used to fully set the trailing edge rivets. I used a piece of wire to hold the dies aligned with the yoke and prevent any spinning of the dies while squeezing

Flap was placed top side up on some 2x4s to finish setting the trailing edge rivets. This was easier for me than riveting with the flap in the cradles due to a better view of the dies over the rivet head

With each flap fully riveted, I then proceeded to temporarily attach them to the wings. 

I first inserted a brass bushing into each of the hinge bracket flap attach holes using a pair of Knipex pliers to push the bushing through, I was then able to hold each flap over the hinge brackets and install the bolts, washers and castle nut to hold the flaps in place.

After hand tightening each castle nut, I held each flap securely and checked that they swung freely on the hinges and sat well in the recess. I'll make final adjustments later after attaching ailerons and necessary control tubes and motors.

Using Knipex pliers to push the brass bushing into the flap hinge bracket attach hole

Flap hinge brackets with bushings inserted, ready for flap to be hung

Right flap seen from the bottom as it sits close to the flaps up position. I used some foam under the leading edge to prevent the flap from resting on the wing rear spar

Left flap seen from the bottom side

Both flaps hung and they sit well in their somewhat "flaps up" position. Final positioning will be done once the ailerons and all necessary control hardware are installed

With the flaps temporarily hung on the wing, section 22 is COMPLETE!

Build Hints:

• 8ft square aluminum tubes make perfect jigs for keeping the trailing edges tight and straight while the sealant cures. Prior to dimpling the flap bottom skin trailing edges, I used them to match drill #40 holes into the aluminum tubes.
• Riveting the trailing edges using only the pneumatic squeezer worked very well. However, I still folowed the recommendation to first perform a partial set (using flat sets) and then finish with the Cleaveland trailing edge dies.
• Knipex pliers make quick work of squeezing bushings into tight spaces.

Time Taken:     10.7 hours

Dates:                September 28 - October 9 2024

Wing Flap Total Time:        80.1 hours

RV-10 Build Total Time:   825.8 hours

Priming Total Time:                     102.2 hours (not included in build time totals)