This weekend I spent two days at the hangar in order to finish the firewall. I could see that I was close, and didn’t want to return to it next weekend for some minor finishing task (aka riveting). So the following takes place over the 13th and 14th (cue Jack Bauer music).
There are two side stiffeners that run diagonally down each side of the firewall. There’s a set of pre-drilled holes that locates their position and so I drew a line on the back and matched it with the holes, clamping it in place.
After drilling through all of the holes, I trimmed the top and bottom of the stiffener to remove any overlap of the firewall base.
The plans call for 40mm to be removed from the bottom flange of each end of the rear reinforcement. Not entirely sure why but I do what I’m told.
Two gear gussets run down the centre stiffener. The flange in each will line up with some pre-drilled holes in the top stiffener but thanks to the latter’s curve you need to bend the corners of the flange over for it to fit.
It then clecos in place quite nicely and you can clamp the end of the gusset to the stiffener making sure that there is the correct clearances.
There are pre-drilled holes down the sides and I pilot drilled through these into the centre stiffener.
Inside the bottom of the stiffener, there is clecoed and drilled a stiffener doubler.
Next up was to drilled the hole for the bungee pin, this has to go up to 5/8″ and my heavy duty unibit drill was required. I also had to bring out my electric drill, the other two couldn’t handle the power needed to make the cuts. In this picture you can also see that I have laid out the locations of four rivets that surround the hole.
Here’s a picture with the bungee pin in the hole.
Next up was to locate and drill two slide covers that will keep the slide plates in place when they are installed.
The top stiffener gets two side braces. These are clamped in position over the pre-drilled holes and back-drilled.
The final components to be assembled were a couple of l-angles that go on the rear.
I wasted a couple of pieces of metal trying to get the proper diagonal cut on the bottom edge so that it fit square. No matter how hard I thought about it, I kept making the cut in the wrong direction. Sad.
At this point I disassembled everything and did the tedious task of deburring and priming the surfaces. As part of this work I countersunk the rivet holes that go around the bungee pin. I used a drill bit for this, turning it by hand to make the sinks. We want the rivets to be as flush as possible so that they don’t interfere with the bungee cord.
Per the video’s suggestion, I riveted the firewall in subsystems, starting with the top stiffener. The upper bearing gets four bolts to hold it in place.
And before I knew it, I had the whole firewall together.
From the back. Note that I pulled some rivets from the back as there is just no way to get a rivet gun on the head from the front.
And here’s a view looking along the gear channel.
So that completes the firewall and it really is the last of the sub-kits, everything else is adding something to a pre-existing kit or joining things together. Of course there is still the major item of the wheels but from here it really is “downhill”.