Aug 24, 2023     Firewall pt 2       Category: C15 Firewall

I have two tasks - the firewall needs to fit the engine, and I have to patch the gaps and then extend onto the strakes. On the first, see the attached Word document with embedded pictures. On the second, see the following.

First builder Chad planned on a Mazda engine, and I'm using the wide deck angle valve Lycoming. The Lycoming is wider, requiring a wider cowl matching to a wider fuse. I defined the fuse shape as I made the cowling, and now I need to expand the area covered by the insulation and firewall. Also, Chad skipped covering the fuel sump and the wing root / aft wall of the fuel tanks out past the wing attach bolts. I want to cover that area and, separately, add the wing root heat shields. See attached photos showing the fuse area I need to cover.

I have a big sheet of stainless that I could cut, but I'm hearing about some modern products that do a better job at lighter weight. Les Laidlaw came up with a high tech product out of Italy: Teknofibra, now a subsidiary of Volkswagen. It is described as "Can manage temperatures up to 800'C only transferring through 35'C on the reverse of the panel it is mounted to." Les used FiberFrax against the composite bulkhead, then the Teknofibra, then stainless steel tool wrap. I'll follow his lead, substituting ceramic felt for the fiberfrax - it is easier to work with and has a higher heat resistance. (Commonly used for kilns and fireboxes, as it has a 2300F temperature rating. I used the same product for the heat shielding of the gear legs near the brakes.) I had a choice of SS alloys for the tool wrap (cut with shears as it is thicker than foil, too thin to rivet or weld). I went with 321, an alloy with extra corrosion resistance. The spend is $150 for Teknofibra + $60 for tool wrap + $20 for the ceramic felt = $230. The three products are shown below. The commerically available products leave me with a lot of left over foil and felt. I'll try to find another builder who can use the products.

  Oct 17, 2021     Fuel pump, gascolator and filters Category: C15 Firewall

This work is described in Chapter 21

  Apr 30, 2009     Rudder Cable Brackets - (8 hours)       Category: C15 Firewall

The plans included instructions on how to fabricate the rudder cable brackets, and I even have the basics already from Brock. However, the CozyGirrrls make such nice parts that I decided to buy the angled brackets for the rudder cable pulleys.

2009-04-29 (3.00 hours):

First Bracket

Metalworking isn't my favorite task, so I ordered the angled brackets from the CozyGirrrls to save time. But the vertical brackets are pretty easy, so I made those myself. I was careful to make sure I found the grain direction before cutting and bending the brackets. I had to tweak the holes a bit after drilling, but it worked out OK.

If I ever did this again, I would change how I installed the screws for the brackets way back in Chapter 4. I would mark and drill a block of wood as a template, then use it as a drill guide to install the screws. I would then clamp the brackets (which I would also make in Chapter 4) to the block to drill the holes in those. That would give you a perfect drill pattern without as much measuring and layout later.

I was pretty confident when I completed Chapter 4 that my screw heads wouldn't turn. FAIL. One did on my first bracket. Fortunately, it's the one on the far outside corner, nearest to the fuselage wall. I can drill through the side with a small drill bit into the screw, and then use that bit to keep it from turning. I may even flox in a bit of wire (or the drill bit!) to create a permanent solution. To prevent any of the other screws from turning, I'll also grind a slot into the end of each one so I can hold it with a flat-head screwdriver. Some builders have reported success with this method. I can think of a million better ways to do this step than the way the plans call for, but I guess it doesn't matter that much. Just another setback.

While I was at it, I taped down the rudder cable tubing so it pointed perfectly at the brackets, then used 5-min micro and a tiny swatch of BID over it to give it some protection where it exits the electrical channel.

2009-04-30 (4.50 hours):

Brackets Installed

Making the brackets wasn't too bad. I came up with a good way to mark the holes accurately for drilling, although I was halfway through before I hit on it. It's simple. Just drill one of the starter holes for alignment, then dab a tiny bit of black grease on the other screws. Gently line up and press the bracket against the screws, and the grease will accurately mark the holes to drill. Installing them was another matter entirely. I had three screws that spun, and it was a royal pain getting everything installed. Flox just doesn't grab hold of plywood edges - the plans method for installing the screws is terrible! They should have just had you install nut plates or something. Oh well.

What ended up working for me is the trick others have used of using a Dremel and cutting wheel to notch the end of each screw. A flat-head screwdriver then serves to keep the screw from turning as you tighten the nut. Oh well, at least it's done now.

After the installation, I put a vinyl glove over each pulley and wrapped it in duct tape. That should keep them clean for later.

  Apr 16, 2009     Firewall Insulation and Liner - (7 hours)       Category: C15 Firewall

01/11/2009 (1 hour):

I started this step by making a template of the firewall out of cardboard. I laid the cardboard against the firewall, with two holes cut in the center to duct-tape it against the glass. I then carefully cut around the edges with a razor blade to get a perfect fit, leaving some extra material in front of the spar. Finally, a few taps with a mallet on each screw head gave me the exact screw hole locations.

Next time I'll actually cut the stainless. John suggested leaving 1/8" or so of margin since a to-theedge fit isn't COMPLETELY critical, and trimming it later is a pain. I still need room for the cowl lips.

04/02/2009 (1 hour):

OK, instead of cutting the stainless I realized that my template didn't allow for the lower cowl lips... because I hadn't installed them yet. So I did that today. It wasn't rocket science, although I did allow for a slightly larger indentation (1/8" rather than 1/16") than called for in the plans to make it a bit easier to fair in the cowl. When I first attached the firewall onto the fuselage, I had had trouble making the depressions properly - specifically, I hadn't made them at the right angle, or deep enough. This will help make up for that. To finish the lips I still need to knock out the foam blocks and do the inside layups.

04/05/2009 (1 hour):

Today I trimmed the previous layup, then made an inside layup of two more layers of BID. This will give me the 4 plies of BID called for in the plans on my cowl lips.

04/07/2009 (1 hour):

The cardboard template wasn't rocket science - hopefully the stainless will fit as well! I'm going to start cutting it on my next trip out.

04-16-2009 (3 hours):

Tonight I installed the Fiberfrax and firewall. I was actually pretty pleased with myself. Working with this stuff, and the stainless, has given some builders some trouble. I spent some time researching this step and had a pretty decent time with it.

To cut the firewall I used tin snips, which was hard on the hands but worked out OK. A nibbler would have been better but I wasn't buying one just for ONE USE. I filed and Dremeled all edges smooth, then worked on the holes. I center-punched each hole, then worked my way through a variety of bit sizes until I was happy with each hole. A step drill is really the #1 choice for this work, but although I have one, I couldn't for the life of me find it. I used a hole cutter for the torque tube holes, which was a bit more work. I wasn't using a bimetal hole saw, just a cheap-o from a $5 set. It took a bit of doing, and I think I killed the hole saw, but it worked OK.