Making a firewall

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Pops

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Pops you might be able to spray some high temp sealant onto that Fiberfrax to keep it from turning into powder. There is a thick goopy stuff called "Ocean" coating, very heat-resistant. It is used to seal firewalls IIRC.

I believe ACS has it. You could thin that down and spray it, or even roll it on the cabin side of the Fiberfrax???
Thanks, I'll check it out.
 

raymondbird

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You might also consider a firewall with galvanized on engine side, a flange, fluted or notched, with a layer of fibrefrax paper and a very thin piece of thin aluminum on the passenger side for the protection of the fiberfrax, all riveted together. (high temp ceramic paper)
Extra protection, a little sound deadening and heat barrier, easily drilled for pass throughs.


I was told (at least here in Canada anyway) that all you need is Intumescent Paint. Right over bare wood even . . . ?
 

dog

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I was told (at least here in Canada anyway) that all you need is Intumescent Paint. Right over bare wood even . . . ?
Interesting stuff.
My question before a purchase would be about
potential off gassing in a fire where the smoke
or fumes in a closed cockpit from the paint could be incapacitating, as say electricl fires can make
poisinous smoke, or blinding.
There are ceramic "cloths" for use in many high heat situations sometimes availible in local hardware stores that are completely inert and would definitely provide significant fire protection.
Reasonably priced, have seen 3 foot widths by nomnal 1/8 thickness, cut with a knife.
 

gtae07

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Dan Horton (DanH on VAF) has done some pretty good actual hardware testing (as in, hitting representative firewall samples with a blowtorch) of various firewall protection and insulation methods. I can provide some links if desired; yes, it’s VAF but Dan did a fine job of testing and showing his findings and definitely in the spirit of “experimental” and “education”. His findings largely mirror practices we use in big airplanes. To wit:

Your firewall should be some kind of fireproof material (as laid out in the old Part 23). Stainless steel, galvanized steel, or titanium; suggested thicknesses are given in the FAR.

Fiberfrax/ceramic wool should go on the engine side of the firewall, as it contains binders that will offgass under heat and could be toxic. This material should have a thin sheet (like .002 cres shim stock) over the top to protect it from direct flame impingement, fluids, and airflow. Seal around the edges with fire sealant (not proseal or RTV!). Some have encapsulated the fiberfrax in metal foil (or used loose fibers in metal envelopes) to address binder concerns, but those ceramic fibers might not be all that great for your lungs.

Backside of the firewall should be bare—no paint or insulation. At best, you get offgassing from stuff on the back; at worst, you’ve installed fire transfer material. Seriously, some of the products sold commercially as firewall insulation were tested on Dan’s burner and caught fire and emitted heavy smoke within seconds of the torch hitting the “engine” side of his test specimen.

Fluid fittings should be steel. Hardlines should be steel. Hoses should have firesleeve. A good wire/cable passthrough is a steel tube with mounting flange; once everything’s inside, stuff the space with firesleeve and plug the ends with fire sealant.

It’s also a good idea to add a heat shield (CRES/titanium sheet and maybe a thin layer of ceramic fiber) around your cowl/exhaust exit. Survivors of in-flight fires have noted burnthroughs at that location on aluminum airplanes.

Again, this is pretty much what we do on big airplanes. And it’s what I’m doing on my RV as well.


Remember, the point of the firewall is to keep the fire out of the cockpit and the rest of the airplane. The insulation helps buy you time to get on the ground and/or get out safely. Improper firewall construction can just about be worse than no firewall at all.
 

Geraldc

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I was told (at least here in Canada anyway) that all you need is Intumescent Paint. Right over bare wood even . . . ?
I tried some with a blowtorch and it did burn through so I put after a short time so I covered it with a thin layer of stainless.
 

n45bm

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Pops you might be able to spray some high temp sealant onto that Fiberfrax to keep it from turning into powder. There is a thick goopy stuff called "Ocean" coating, very heat-resistant. It is used to seal firewalls IIRC.

I believe ACS has it. You could thin that down and spray it, or even roll it on the cabin side of the Fiberfrax???
Why and how would Fiberfrax turn into powder? I can't see that happening.
 

gtae07

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Has a standard single sheet of stainless been a issue in the past? I don’t hear about many firewall issues.
Not as such (provided your penetrations like fuel fittings and cables are made of the right stuff and properly protected); that will keep the fire from burning through. However, that’s about all it will do. A bare stainless sheet may well keep the fire from coming through, but it can still get pretty darn hot on the “cool” side and if your feet are anywhere close, so will they. And as I noted above, anything on the backside of that firewall (like paint, cloth, insulation, or what have you) is likely to also get really hot and start smoking or burning. That’s why many of us recommend the ceramic fiber on the engine side—it buys you additional time before things start getting really uncomfortable in the cockpit (well, beyond the discomfort that dealing with an engine fire and forced landing already brings). It also provides some small measure of sound and thermal insulation during normal operations.

We don’t hear about many firewall issues because we generally don’t see too many bad engine-compartment fires in flight. I know of two fire incidents in RV-10s where both survived (at least one had a burn-through on the belly as I noted earlier); I know of one unfortunate incident in an RV-8 where the poor pilot chose to jump from the burning airplane without a chute. I think Ron Alexander died in an engine-fire-related crash.

Engine fires don’t account for too many accidents—or more to the point, there are a lot more accidents from other causes. But if one does happen, it’s a very serious thing, so it’s worth protecting against. Fortunately, doing it right isn’t hard or expensive. Build a real firewall without paths for fire to get through (like aluminum fluid fittings or rubber grommets for cables and wiring) and without flammable stuff on the cabin side (like the “FAA-approved firewall insulation”, which is really just for general cabin use and NOT on firewalls), and use proper practices on your engine to help keep a fire from happening in the first place, and you’ve gone a real long way. The fiberfrax isn’t strictly necessary, but it’s cheap insurance and additional comfort.
 

dog

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This is only a half remembered thing I read but isn't galvanized real nasty when it burns?
Yes,nasty,oxiized zink,makes a white smoke that
is toxic,though it takes a very high heat to
do it,add a very,and you could consider seeing it as a reminder that NOW would be
a good time to CLOSE the tank valves.
The more I learn about all of the failure modes involved with fuel,the more I want to know about building the best possible fuel system,and unfortunately it appears that fuel and electric subsystems, can not be engineered and quantified
in the same ways that wings and landing gear can.
So the experience gained from "big airplanes" is the best we have,anecdotal or not.
 

TFF

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Everyone has different thoughts on why to add insulation to the back side of a firewall. I am more worried about heat with normal flying. If my feet are getting hot in the summer, I’m not going to want to fly. Lots of factors inside engine compartment and how close feet are to firewall. A thermal break is important however it is made; material or distance. Race only plane, you would burn your feet to win, every day. Sport flying, I want to be comfy.
 

gtae07

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A few threads with actual testing results, illustrating why things like aluminum firewall fittings and cabin-side insulation are not good ideas:
Firewall sealant and Fire Safety - Page 2 - VAF Forums (start at post 38 for testing results; later in this thread it shows an example of foam insulation on the back side of an otherwise-decent firewall becoming fire transfer material)

A good layer of ceramic fiber on the engine side will help with normal-flying heat—if that’s even really a concern.

As a data point, Dad’s RV-6 has no firewall insulation and even in summer conditions, feet warmth isn’t a problem. That big greenhouse of a canopy, OTOH...
 

Victor Bravo

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Why and how would Fiberfrax turn into powder? I can't see that happening.
The stuff I played with some years ago would start to flake apart or "shed" if you were folding it or forming it with your hands, or with any abrasion. It gave me the immediate impression I wanted it to be contained in something, for the same general reason as you would want for the heat insulation inside your oven.

I've seen Fiberfrax-type stuff that had an aluminized foil on one side and self-adhesive fabric on the back, which you can easily form around curves and tuck into corners.
 

TerryM76

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Piper Tripacer firewall. Appears to be galvanized with a shrink formed aluminum edge. Looks like a Fiberglas backing on the interior side.
 

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TiPi

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Yes, if the heat insulation is fragile (woven, brittle etc), it is better sandwiched between 2 metal sheets. Only one of them really needs to meet the FAR23 requirement, the other is just to preserve the integrity of the insulation.
I'm building a plane with a wooden firewall, so the heat insulation and protection of the insulation is even more important. My plan is a 4mm fibrefrax sandwiched between the plywood firewall and protected by a 0.6mm gal sheet. The structural firewall is the ply (with bracing), the gal sheet is only protection for the fibrefrax and to mount various components, incl the cable glands.
 
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