Firewall insulation?

[aviator79]

From photos I have seen, it seems firewall insulation was common/standard on the model IV. I've seen some series V5-7 with firewall insulation, but most appear not to have any. I was chatting with a tech counselor at an EAA meeting tonight, and he put it in my head that I was going to die a terrible death with my feet on fire if I don't insulate my firewall and ditch the grommets for fireproof firewall feedthroughs for $60/pop.

I found a couple old threads on this, but I was curious if you guys are insulating, what you're using and how you're using it, and for those that aren't, why not?

[Wheels]

I have an older firewall with the original blanket on it. Over the years, it has accumulated spilled oil or cleaning agents or whatever and now just looks shoddy.
There are a couple of tears in the fabric that have allowed water or soap or spilled oil during an oil change to seep into the batting. I cant get it clean without removing it and that will be when I take the engine off the plane. NOT.
I really do wish I had a bare firewall so I could see any spray from fluid of any type and clean it to trace the source.
Just my two cents and probably not worth much if anything.

[David47]

Brian, the stainless steel firewall is the first line of defence but it's the cutout for cables and wires that causes a potential problem. What I'm doing is attaching flanged stainless steel bushes with s/s pop rivets, and coating the saying surface with a high temp resistant cement. The cables and wires that go through the bush will be sheathed in a fire resistant tubing and any gaps filled with fire resistant cement.

I suspect what you EAA TC was talking about was if you were using rubber grommets. In that case, in the event of a fire, your toes might get a little toast ... :eek:

[GMKman]

My firewall was bare when I bought the plane ( except for carpet inside). I used Lizard Skin ceramic coating on the inside and it made a big difference on the heat coming through. If I ever pull the engine, I’ll paint the engine side. Not the prettiest but it is effective.

[PapuaPilot]

I would beg to differ with your TC friend.

Here is what the FARs say about firewalls:

§ 23.1191 Firewalls
(a) Each engine, auxiliary power unit, fuel burning heater, and other combustion equipment, must be isolated from the rest of the airplane by firewalls, shrouds, or equivalent means.

(b) Each firewall or shroud must be constructed so that no hazardous quantity of liquid, gas, or flame can pass from the compartment created by the firewall or shroud to other parts of the airplane.

(c) Each opening in the firewall or shroud must be sealed with close fitting, fireproof grommets, bushings, or firewall fittings.

(d) [Reserved]

(e) Each firewall and shroud must be fireproof and protected against corrosion.

(f) Compliance with the criteria for fireproof materials or components must be shown as follows:

(1) The flame to which the materials or components are subjected must be 2,000 ±150 °F.

(2) Sheet materials approximately 10 inches square must be subjected to the flame from a suitable burner.

(3) The flame must be large enough to maintain the required test temperature over an area approximately five inches square.

(g) Firewall materials and fittings must resist flame penetration for at least 15 minutes.

(h) The following materials may be used in firewalls or shrouds without being tested as required by this section:
(1) Stainless steel sheet, 0.015 inch thick.

(2) Mild steel sheet (coated with aluminum or otherwise protected against corrosion) 0.018 inch thick.

(3) Terne plate, 0.018 inch thick.

(4) Monel metal, 0.018 inch thick.

(5) Steel or copper base alloy firewall fittings.

(6) Titanium sheet, 0.016 inch thick.

[jmodguy]

Brian,
The kitfox is a fabric covered airframe with a fiberglass cowl. If you have a serious inflight fire, dollars to doughnuts, the fire will burn through the glass and fabric before the firewall. My guess is that most kitfoxers wont be at 7 or 8000 ft and can get on the ground quickly.
As for firewall penetrations, I opted to run all my electrics through a single mil spec 38999 connector. They are pretty reasonable in cost for the simplicity and security they provide. All my firewall penetrations are located between the foot pedal bump outs. I minimized my penetrations by mounting all sensors behind the firewall as well. My 2 cents...

[aviator79]

Hi Phil,

I think you are more in agreement than disagreement with this TC. He's saying that in addition to a stainless firewall and fireproof penetrations, you should insulate the cabin. Side of the firewall to protect you from radiant heat. He cited the FAA design basis scenario of a 2000 degree flame for 15 minutes. The firewall will remain, but it will be glowing red hot, and cooking you. I do not find the design basis scenario to be credible for our airplanes, but it did get me thinking about my mode of mortality in the event of an engine fire. I would think that when firewall feedthroughs start to fail, the boot cowl is probably already burning, so the fire is already coming past the firewall.

Our kits come with plain rubber grommets for firewall penetrations. I can't even find properly sized fire resistant grommets. The stainless flanges with firesleeve and hose clamps are all I see for fire resistant feedthroughs. I feel like going great lengths to fireproof the firewall might be wasted time money and effort, but I also imagine my shoes catching on fire while I accept my imminent death and regret not having spent some more time, effort and money.

[jmodguy]

... I would think that when firewall feedthroughs start to fail, the boot cowl is probably already burning, so the fire is already coming past the firewall. ...

My point exactly...

For high temp grommets check mcmaster.com

[airlina]

Way back when I was building my Series 5, one of my go to publications was a 4 book series by a prolific builder named Tony Bingelis. Tony had a great solution, which was fabricating your own custom sized SS firewall pass thru's -which is what I did. Scrap stainless steel and tools you already have and you make your own to your specs. I highly recommend these books to anyone building as they were for me a tremendous reference library that I still use today. Check them out Bruce N199CL

[rv9ralph]

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

[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-Closet-Wardrobe-Support-Bracket/dp/B07BHJM1SB/ref=sr_1_3?ie=UTF8&qid=1535426406&sr=8-3&keywords=stainless+steel+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.
16287

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

16286

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

[n85ae]

It's probably the case that you don't need anything except to seal the feed
holes. Since if you have a serious fire in a Kitfox, you probably want a
parachute more than anything else ...

Jeff

[Av8r3400]

Excellent point, Jeff. All the extra weight of fittings, eyeballs and pass-throughs are a bit of a waste considering the cowl is fiberglass and its mated to a fiberglass boot cowl. This will all burn in the event of a fire.

An in-cowl fire means shut off the fuel and dive for the ground to get out asap.

[colospace]

This discussion has me once again considering use of a foam silicone tape (adhesive on one side only) to seal between the firewall and the boot cowl. Even though I can fold my panel down, being able to access from the top and sides would be super. Anyone have experience with using a foam tape on that interface?

[rv9ralph]

An in-cowl fire means shut off the fuel and dive for the ground to get out asap

True, but anything that adds seconds to the dive and dash protocol helps.

At my old airport base (KLVK,Livemore, CA) an A&P that build a 5151 Mustang had a inflight fire just after takeoff during testing. He did not make it to the ground in time, departed aircraft in flight and died in the fall.

Ralph