Firewall 27-1 to 27-4-3

While working around my daughter's school schedule to slowly rivet the bottom skins to the mid fuselage, I decided to start work on the firewall.

After reading stories of other builders easily cutting themselves on the sharp edges of the firewall stainless steel, the first thing I did was to debur all edges and holes in the firewall and recess.

The V-shaped deburring bit did a good job of cleaning the edges of the firewall flanges and larger hole edges. I used Boelube paste every few minutes to minimize dulling of the deburring bit.

The standard hole deburring bit worked well to debur rivet holes in the stainless steel, but I did have to push harder to get the bit to bite the edge. Boelube was also used regularly here, however, I did decide to purchase a new deburring bit for future aluminum use and keep this one only for use on steel

The edge deburring bit worked well enough to debur within the flange notches. However, as with the other deburring bits I used on steel, I'll dedicate these bits for use on steel only from now on

Firewall fully deburred. The edges were now very smooth

Next I dimpled the holes in the corners of the firewall recess and riveted those together.

Dimpling firewall recess holes with the squeezer. I dimpled through two holes at the same time as it would be hard to separate the sides without deforming the recess. I also used a cleco to help keep the holes in alignment while dimpling and riveting

The hole nearest the corner in the firewall recess that will be used to attach the rudder pedal brace needs to be dimpled using a rivet. The dimple turned out surprisingly well, and I'll keep this technique in mind for future dimpling in tight spaces

Firewall recess dimpled and ready to be riveted together

Firewall recess was riveted using the squeezer. I did have to drill out a couple of rivets due to some leaning, but overall the recess riveted together fairly easily 

I then pulled together all the angles and brackets that will be used to stiffen up the firewall as well as provide points for mounting the engine once I get to that stage.

Angles and brackets that will attach directly to the firewall

After deburring all edges of the aluminum angles and brackets, I clecoed everything to the firewall to check the fit and make sure I didn't miss anything.

At this time, I decided to countersink the rudder pedal brace attachment holes in the F1001E-L angle to fit against the dimpled holes in the recess

All aluminum angles and brackets clecoed to the firewall

Engine mount brackets clecoed in place after reaming some holes to clear out the powder coat

Next I placed the firewall assembly vertically on the workbench using wing jigs to support it, and then final drilled those nutplate screw holes that were undersized in the firewall stiffener angles.

Firewall assembly secured on the work bench. It rested quite happily on the nose gear tension fittings. The jigs were just there for additional support from tipping

With the nutplate screw holes final sized, I put the firewall assembly aside, and worked on drilling holes into the F-1048-R for the scat tube support

Scat tube support holes marked, drilled to #19 and dimpled

Dimple was flush on the outside of the forward fuselage rib

The nutplate holes in the scat tube support bracket also required dimpling. This was difficult due to the proximity of the holes to the bend in the flange. I improvised countersinking a #8 hole in a scrap piece of aluminum bar stock, and used the rivet gun with the male dimple die to dimple the scat tube support screw holes into the countersink. The dimples seemed good enough, with no deformation of the support flange, but still did not look quite as good as regular dimples!

Items used to dimple the nutplate screw holes in the scat tube support bracket

I then removed the nose gear tension fitting from the firewall and match drilled the holes to the F-1048 tunnel ribs. The holes are already final sized, with the match drilling involving mostly just reaming out the powder coat in the rivet holes of the welded parts.

As match drilling continued, clecoes were used to keep all parts in close alignment

F-1048 tunnel rib clamped securely to the workbench, again with the help of wing leading edge jigs

After match drilling the nose gear tension fittings to the tunnel rib, the F-1001E angles are also attached at the leading edge of the rib. The angle holes were already final sized, so didn't require match drilling, however, I did have to trim a small portion off the bottom edge of the angle in order to have it fit flush inside the rib angle.

Bottom portion of F-1001E angle trimmed away to fit while maintaining edge distance for the #30 hole nearest the bottom edge

The last step before priming the firewall stiffeners involves countersinking all the rivet holes that lay against the firewall. It took a little while, but wasn't particularly difficult.

Countersinking holes close to the edges of the stiffener with proper support for the countersink cage to avoid tipping

Using various items to ensure that I had a good surface for countersinking tricky holes near the edges of stiffeners

The same techniques worked well to get good countersinks on the #40 holes of the brake bracket

Time Taken:     13.2 hours

Dates:                February 27 2025 - March 18 2025

Firewall Total Time:               13.2 hours

RV-10 Build Total Time:      972.2 hours

Priming Total Time:             126.0 hours (not included in build time totals)