Firewall insulation?

[David47]

Brian, I don't recall any single engined GA aircraft I've ever flown or worked on having thermal or fire insulation on the cabin side of the firewall. I don't believe that's what the FAA expects, nor is it necessary IMHO. If you have fire coming past the f/wall, you have bigger problems than insulation. That, to me, is where a handy fire extinguisher comes in. At least you have a fighting chance then. FWIW.

[jmodguy]

Brian, I don't recall any single engined GA aircraft I've ever flown or worked on having thermal or fire insulation on the cabin side of the firewall. I don't believe that's what the FAA expects, nor is it necessary IMHO. If you have fire coming past the f/wall, you have bigger problems than insulation. That, to me, is where a handy fire extinguisher comes in. At least you have a fighting chance then. FWIW.

My ‘68 E33A Bonanza had a thermal blanket on the inside of the firewall. Came from Beech like that. Maybe it was an “old school” idea...

[aviator79]

Brian, I don't recall any single engined GA aircraft I've ever flown or worked on having thermal or fire insulation on the cabin side of the firewall. I don't believe that's what the FAA expects, nor is it necessary IMHO. If you have fire coming past the f/wall, you have bigger problems than insulation. That, to me, is where a handy fire extinguisher comes in. At least you have a fighting chance then. FWIW.

The stated concern is not so much that fire comes past the firewall, it's that the firewall gets really hot, and the radiant heat sets your shoes on fire. A guy name Dan Horton on the Vans forums has actually subjected many products sold to insulate the firewall to the design basis fire, and the results are not good. Almost all materials sold as firewall insulation on the cabin side will ignite, smoke, and/or emit noxious fumes when the firewall heats up due to a 2000 degree flame on the engine side. You can insulate the firewall side with certain materials that will protect you from radiant heat but it's an involved job, and in my opinion probably not worth it in our airplanes.

It turns out fiberglass ignites at 820 deg F. So it actually resists fire better than I would have thought. It's still burning quite enthusiastically when subjected to the design basis fire of 2000 deg. F. When selecting fireproofing materials, this is probably a good design number. If you have Fiberglass cowls that traverse the firewall, then the firewall cannot stop a fire burning above 820 deg F, even if the firewall itself is good to 2000 deg F.

[Clark in AZ]

Hey Brian, me not being a Kitfox guy, what does Kitfox recommend?


Clark

[aviator79]

I sealed my throttle pass throughs by buying Stainless Steel Flanges on Amazon. Cutting one side to get it around the already installed cable. Wrapping the cable and flange with firesleeve the wrapping with self sealing vinyl tape and closing with stainless clamps.
I tried to upload pictures, but every time I tried to reduce the size, they were still too big. (.jpg files must be smaller than 97 kb.)

Ralph

Do you have a link to the flanges you bought on Amazon? I'm not seeing anything suitable. What you describe is basically the same thing they sell on spruce for $56/fitting. If I could find suitable flanges, I think I could do it a lot cheaper.

[PapuaPilot]

My ‘68 E33A Bonanza had a thermal blanket on the inside of the firewall. Came from Beech like that. Maybe it was an “old school” idea...

I believe that is correct. It was probably both for fire and soundproofing. As was mentioned they easily get dirty with oil.

I built my plane with the black rubber grommets and used 3M Fire Barrier 2000+ sealant that I purchased readily online.

I just saw that ACS has firewall penetration kit that uses high temp silicon grommets (orange colored). The kit is made by SPT, but you can buy the grommets individually for about $3 each. This seems like a good low cost solution if you just get a few grommets. I would fill the holes with the 3M fire barrier mentioned above. I may upgrade my grommets to these.

If I were to ever have a fire in the engine compartment I would be pulling the mixture and turning off the fuel selector. Next is to dive the plane to get down fast and extinguish the fire. I carry an aircraft fire extinguisher that I would use if needed.

[aviator79]

Hey Brian, me not being a Kitfox guy, what does Kitfox recommend?


Clark

I haven't asked them specifically, but the manual does not suggest any insulation, they provide standard rubber grommets for firewall penetration, and don't mention anything specific regarding fireproofing. There are also plastic brake lines right against the firewall in the Kitfox design. The designers do not appear to have considered a prolonged gasoline or oil-fueled engine fire a design-basis event. I believe the way the design is, if you have an oil-fueled fire in the engine compartment that you cannot extinguish, a fatal accident is likely. I think your protection from this event is purely statistical: it happens rarely.

[aviator79]

I built my plane with the black rubber grommets and used 3M Fire Barrier 2000+ sealant that I purchased readily online.

I just saw that ACS has firewall penetration kit that uses high temp silicon grommets (orange colored). The kit is made by SPT, but you can buy the grommets individually for about $3 each. This seems like a good low cost solution if you just get a few grommets. I would fill the holes with the 3M fire barrier mentioned above. I may upgrade my grommets to these.

If I were to ever have a fire in the engine compartment I would be pulling the mixture and turning off the fuel selector. Next is to dive the plane to get down fast and extinguish the fire. I carry an aircraft fire extinguisher that I would use if needed.

This is what I'm leaning toward as well. If you want more size selection in the grommets, McMaster has a large selection. They are rated to 500 deg F, so depending upon the safety margin, they may fail before your fiberglass ignites. Still, it's probably a good low-cost measure to buy you a little more time to get on the ground.

[rv9ralph]

Ok, I am trying again. The link to an option for the flange is:
https://smile.amazon.com/Stainless-C...el+flange+19mm

The images failed again. File size has been reduced to below listed size. Steve, help fix this.

Ralph

[rv9ralph]

The image gods are smiling on me today. I was able to upload the images of my firewall pass through. Here they are:
The Stainless Flanges after I made the cut to fit them around the throttle cable.
SS Flanges.jpg

Here is the completed item. Fire sleeve over the cable and flange, self sealing vinyl tape over that and Clamps.

Pass Through.jpg

As a next level, I was going to use fireplace sealant caulk, available at most big hardware/home inprovement centers, good to 1500 to 2500 degrees depending on selection, I was going to fill the cockpit side with the caulk.

Ralph