Catalytic Converter

Why Aviation Manufacturers Choose Custom Catalytic Substrate Carriers (Not Off‑the‑Shelf)

Walk into any automotive parts warehouse, and you'll find a shelf full of catalytic converter substrates. Round. 400 cpsi. Aluminum or stainless. Pick a size, grab one, go.

Now try that for an aircraft. You won't find a shelf. Because there is no standard.

Every aviation manufacturer I've worked with – APU builders, ECS suppliers, even ground support equipment makers – they all need something different. Different shape, different cell density, different material, different mounting. Off‑the‑shelf doesn't exist.

Why? Because aircraft aren't cars. And the substrate carriers have to fit the aircraft, not the other way around.

Here's why they always come to us for custom.

Space Is Never Standard

A car has room under the floor. Not a ton, but enough for a round can.

An aircraft has no spare room. The APU is crammed into the tail cone. The ECS is buried in the belly, surrounded by ducts and valves and wiring bundles. The space left for a catalytic converter is whatever happens to be leftover after everything else is designed.

That leftover space is never round. Sometimes it's oval. Sometimes rectangular. Sometimes a weird D‑shape to clear a structural rib.

One customer sent us a cardboard template they'd made by pressing it into the cavity and tracing the edges. That was their "drawing." We built a custom oval substrate carrier to match.

Off‑the‑shelf round parts wouldn't fit. They'd have to redesign the whole compartment. That's not happening. So they call us.

Heat Is Higher and More Constant

An aircraft APU runs for hours at high power. No coasting. No stop‑and‑go. Just steady, hot exhaust.

Temperatures hit 650, 700, sometimes 750 degrees Celsius. That's way above what a car converter sees.

Standard automotive substrates – even the stainless ones – start to creep at those temps. The foil sags. The cells distort. The carrier loses shape.

So we build custom with higher alloys. 347 stainless. Inconel when it's really hot. Not off‑the‑shelf. The customer tells us their max temp, and we pick the material.

One APU builder tried a standard 304 stainless substrate from another supplier. It sagged after 500 hours. They switched to our custom 347 part. No sag at 2,000 hours.

Vibration Is a Different Beast

A car engine vibrates. But an aircraft APU vibrates at different frequencies, and the airframe adds its own shaking.

Standard mounting mats – the fiber wrap that holds the substrate in the can – aren't always enough. They can take a set, or they can loosen up over time.

For aviation, we add mechanical retention. A ring or a lip inside the can that holds the substrate even if the mat fails. That's not standard. That's custom.

We also adjust the foil thickness. Thicker than automotive – 0.08 mm or 0.1 mm – to handle the shaking. The weight penalty is worth the durability.

One customer had a vibration issue that kept cracking their substrates at the brazed joints. We went to a thicker foil and a softer, more flexible brazing filler. The cracking stopped.

Flow Requirements Are Different

An aircraft ECS moves a lot of air. Hundreds of pounds per hour. The substrate can't create much backpressure, or the whole system loses efficiency.

Standard 400 cpsi is often too restrictive. So we go custom with lower cell density – 200 or 300 cpsi. Bigger cells, less restriction.

But lower cell density means less surface area for the catalyst. So we have to balance. Sometimes we lengthen the substrate to compensate. Sometimes we use a more active coating.

There's no standard recipe. Every application gets its own calculation.

Weight Is Always Watched

Aircraft manufacturers weigh everything. A few grams here, a few there – it adds up.

Standard substrates are designed for durability, not weight. They use a certain foil thickness, a certain mat density, a certain can wall thickness.

We can shave weight by using thinner foil, lighter mats, and shorter lengths – but only if the operating conditions allow it.

One ECS customer needed a substrate that weighed under 200 grams. Our standard version was 280 grams. We went to 0.04 mm foil, a lightweight mat, and shortened the length by 10mm. Got it down to 185 grams. Passed all their tests.

That's custom. You don't find that on a shelf.

Materials Must Match the Environment

Not every aircraft application needs Inconel. Some are fine with 304 stainless. Some need 316 for corrosion resistance. Some need aluminum for weight, but only if the temperatures are low.

Standard suppliers stock one or two materials. We stock many, and we'll use whatever the customer's environment demands.

We had a customer building an ECS for a seaplane. Salt air everywhere. They needed 316L stainless for corrosion resistance, not 304. We built it. Off‑the‑shelf suppliers didn't even offer 316L in their catalog.

Certification and Traceability Aren't Optional

Aviation manufacturers don't just want a part. They want a paper trail.

They need to know the foil supplier. The batch number. The braze cycle. The test results. They need a certificate of conformance for every shipment.

Standard substrate suppliers often don't keep that level of traceability. They buy foil in bulk, run production, and ship. If something fails, they can't tell you which coil it came from.

We can. Every custom batch gets a unique number. We record everything. When an auditor asks, we have the answers.

That's a big reason aviation customers stick with us. Not just the part – the paperwork.

Testing Is Never "Standard"

A car substrate gets a flow test and a visual. Maybe a thermal cycle if the manufacturer is thorough.

An aviation substrate gets thermal cycle to 500 or 700 degrees, hundreds of cycles. Vibration testing at aircraft frequencies. Sag testing under load. Coating adhesion testing.

We don't have a "standard" test package. We ask the customer what their qualification requires, and we run those tests.

One customer needed a substrate that could survive 1,000 thermal cycles from –50°C to 650°C. That's insane. But we built a batch, tested it, and it passed. The data went into their certification package.

Real Examples

An APU manufacturer needed a custom oval substrate to fit between two structural members. Standard round wouldn't fit. We built a 300 cpsi, 0.08 mm stainless 347 part with a heavy‑duty mat and retention ring. They've ordered over 1,000 pieces.

An ECS supplier needed a lightweight substrate for ozone conversion. Space was tiny. We used 0.04 mm stainless, 400 cpsi, 60mm long. Weight was under 150 grams. They tested it to 500 thermal cycles. No cracks. They're on their third production order.

A ground support equipment maker needed a high‑flow substrate for a diesel APU simulator. Low backpressure was critical. We used 200 cpsi, 0.05 mm stainless, and a low‑density mat. They measured backpressure at 2% of their previous supplier's part. Engine ran cooler. They switched all their production to us.

Aviation manufacturers choose custom catalytic substrate carriers because off‑the‑shelf doesn't work for them.

Different shapes for tight spaces. Higher alloys for high heat. Thicker foil for vibration. Lower cell density for flow. Lighter construction for weight. Full traceability for certification. Testing that matches their requirements.

We don't have a catalog. We have a shop and a set of tools. When a customer calls with a sketch and a list of requirements, we listen. Then we build.

If you're in aviation and you need a substrate carrier that doesn't come from a shelf, give us a call. Bring your space constraints, your temperature specs, your vibration data. We'll figure it out. We've done it before. We'll do it again.