Fuel Injection Conversion - Part 9

Titanium firewall retrofit
 

While safety is the top priority when engineering an airplane, one of the key players in keeping us safe is the firewall. Although not as glamorous as the engine or the instrument panel, the firewall is one of those parts you definitely want to get right, and while JT’s previous one was made out of aluminum with a heat rejecting paint, titanium is a much better material, making it perfect for this critical function. 

 

We’ve already discussed why the original aluminum firewall needed to be replaced in Fuel Injection Conversion - Part 3 - Engine Removal, so today, I’ll be diving into the process of manufacturing and installing a brand-new titanium firewall. Trust me, it’s not as complicated as it sounds, but it is a bit of a precision challenge.

 

Original aluminum firewall looking rough

Oil wicked up from the diffuser soaking the now flammable Fiberfrax "protection"

What’s a firewall anyway?
 

In simple terms, a firewall is a barrier that isolates the engine compartment from the rest of the airplane. It’s there to stop fires from spreading if something goes wrong with the engine, and a titanium firewall brings a ton of benefits over other materials like aluminum or steel.

 
Why titanium?
 

Titanium is great material for this job... it’s both strong and lightweight, meaning it gives you more protection without weighing down the aircraft, and in aviation, weight matters, so this is a big win. 

 
It’s also got a very high melting point (around 1,668°C or 3,034°F), which means it won’t melt or buckle under the heat that can come from an engine fire.
Furthermore, titanium is corrosion-resistant, which is perfect for planes that fly through harsh conditions like the saltwater air near the coast where I live.

 

The Installation Process
 

This is where things get a little tricky. When you’re installing a new firewall on an older airplane, the holes and studs are already there (on the fiberglass structure), which means you can’t just drill new holes and hope everything lines up perfectly, so I had to get super precise with the measurements.

Multitude of holes, threaded studs, and L channels projecting from the structure.

I ended up using a CAD (Computer-Aided Design) system, which allowed me to create a digital version of the firewall and manipulate it until I had the perfect fit. This way, I didn’t have to worry about making mistakes, and it gave me a blueprint I could use for future modifications (or if a future owner of the plane needed to replace it down the road).

 
To make it foolproof, I used a Cartesian coordinate system on the fiberglass structure to map out every existing feature of the old firewall, then recreated those features in CAD.

 

Using a laser to establish an arbitrary Cartesian coordinate system

The coordinate system was then transferred to the structure

Here the laser is aimed at the first feature I wanted to record

Measuring the feature's Y distance from the Y axis

Training the laser to an existing pass-through hole

Recording the location of the fuel supply to the engine compartment

Right rudder cable penetration

Future location of the engine grounding system

One of the three rudder pulley mounting bolts

These threaded studs were reused to fasten the firewall

The result was a virtual firewall that I could reproduce exactly, and at will, with Computer Aided Machining (CAM) programs on my CNC plasma table.

This view gives you a good idea of the many measurements that had to be taken

And this is the initial resulting virtual firewall

The design was enlarged to encompass every structure that needed protection

This is where things get a little nerve-wracking, because once you cut a piece of expensive titanium, there’s no going back. So, to make sure everything was on point before cutting, I borrowed a trick from my past projects. I swapped out the plasma torch on my CNC (Computer Numerical Control) table for a Sharpie marker (held in place by a 3D-printed holder). I then ran the firewall cutting file on semi-transparent paper, then attached it to the plane as if it were the actual firewall.

One of many transparencies used to verify the location of all relevant features

Working on the feature existing on the wing spar section of the firewall

 

 

 

 

 

Testing the firewall code

 

 

 

 

This way, I could verify that all the holes lined up exactly as planned. If anything didn’t match, I could tweak things in CAD and try again. I kept this cycle going for weeks, testing and adjusting until I was happy with the fit.

 

Many transparencies hanging on the wall, and 3D printed Sharpie holder (in red) on the plasma table.

Once everything was good, I marked the Fiberfrax ceramic insulation mat (which goes beneath the firewall) using the Sharpie CNC table trick, then cut it with scissors, and installed it on the back of the plane.

Marking the Fiberfrax using CNC before cutting it saved a ton of time

Later, I recycled the same file using the CNC plasma cutter to slice through the titanium sheet. A word of caution here, breathing in titanium fumes can be very detrimental to one’s health, so be careful out there!

 

 

 

 

 

Cutting the titanium firewall

 

 

 

 

Aluminum vs titanium firewall

Testing for fit

I left the Fiberfrax 1" off the bottom to prevent oil wicking up from the diffuser

Started sealing around the perimeter with RTV silicone

Since my CNC plasma cutter table wasn’t big enough to handle the entire firewall at once, I had to split the design and make two additional side firewall pieces separately. I oversize them by an inch to make sure they’d overlap with the main firewall for a clean, secure fit when installed. To make it extra fireproof, I sealed all the edges with high temperature RTV silicone, that’s the good stuff you use to create airtight, heat-resistant seals.

 

Nesting the two side protections on a single sheet of titanium (visible below the paper)

The 3 part firewall installed

There is a 1" overlap between the titanium sheets

The last bit of the job was creating a cover for the existing inspection hole. To do this, I sandwiched Fiberfrax between a titanium plate (facing the engine) and an aluminum plate (facing forward), then sealed the edges with RTV once again.

 

Cutting the aluminum access cover

Cutting the Fiberfrax for the access cover

Still dirty from cutting, titanium piece to complete the access panel cover sandwich.

Hole cover in place

Final look with cannon plug installed (more RTV sealing to come)

A closer look

The inspection hole cover wasn’t just for looks, I also used it to install a “cannon plug” for the engine monitor wiring. This was a game-changer because it allowed me to quickly disconnect 28 wires at once as needed for maintenance purposes.

 

Ran all engine monitor probe wires (and a few others) though a single disconnect point

The "cannon plug" greatly increase ease of maintenance

Firewall completely sealed with engine about to be installed.

Titanium firewalls might not be the first thing that comes to mind when you think about airplane safety, but they truly play a vital role in protecting both the aircraft and everyone onboard. Installing one isn’t just about slapping a piece of metal in place, it’s a process that requires precision, care, and a thoughtful approach to make sure everything fits just right.

 
This firewall upgrade project really highlights how modern technology and timeless materials like titanium can work together to make flying not only safer, but also more efficient, and it’s a reminder of how every little detail, no matter how small, contributes to ensuring we get to experience the joy and freedom of flight with confidence and peace of mind.
 

Cheers!

🍻