Inside of firewall: bare, paint, other?

[birdus]

I'm putting a new panel in my Luscombe. While I'm in there with good access, I want to clean up the inside of the firewall. It looks awful now. There was definitely something on it before and it's peeling off now. I want to clean that off and get it looking nicer before getting the new panel put in.

Does one generally leave the cabin side of the firewall bare? Paint it? Apply something else to it?

 

[NordicDave]

Figuring where to stop on restoration is a difficult choice. For me the tipping point might be when is my next best low cost opportunity to do this again? With the panel out, kind of a one time opportunity. Blistering or peeling paint would be a trigger for strong consideration. I'd probably strip and apply the proper anti-corrosion treatments in this case.

 

[Ed Haywood]

I would be careful stripping it, on the off chance it contains asbestos.

There are various firewall blanket materials to lessen heat and noise. Browse Aircraft Spruce for ideas.

 

[kyleb]

I wouldn't add insulation on the inside of the firewall. It will add weight and also put something potentially flammable against the inside of the firewall and in the cockpit with you. With modern headsets, cabin noise isn't a big issue, so I wouldn't try and solve that issue with a firewall blanket. Heat? Is heat a problem with your current situation?

On my Rv-6, which probably has 2.5x the HP of your Luscombe, I kept the firewall bare and really don't notice a heat issue.

But that's just me.

 

[Jdm]

It’d be a job alright, but I would consider stripping it and treating as previously suggested. I would go with the foiled foam insulation on the inside. It’s a quality product. We recently completed a new panel also and put the soundproofing insulation from the door posts forward. It helps with both sound reduction and insulating from the heat and cold.

 

[kyleb]

I would go with the foiled foam insulation on the inside.

if you have a leftover piece of the insulation, set it on fire and consider if you really want it against the firewall. All those products (at least the ones I’ve seen) are huge smoke sources when burned.

 

[Jdm]

Same is true for any if the other interior pieces. Original insulation is horrible. At least this stuff has a metal barrier. A lot of the other items in a certified aircraft would already be up in flames before the foiled insulation begins to smoke.
I had to remove a piece from the side wall to get to some wiring the other day. The thickness of the metal is impressive. It’s so thick I probably shouldn’t even refer to it as foil.

 

[kyleb]

Same is true for any if the other interior pieces. Original insulation is horrible. At least this stuff has a metal barrier. A lot of the other items in a certified aircraft would already be up in flames before the foiled insulation begins to smoke.
I had to remove a piece from the side wall to get to some wiring the other day. The thickness of the metal is impressive. It’s so thick I probably shouldn’t even refer to it as foil.

The difference is this stuff is on the FIREWALL. Putting semi-flammable, smoke generating stuff on the firewall is rarely in your best interest.

 

[3393RP]

The difference is this stuff is on the FIREWALL. Putting semi-flammable, smoke generating stuff on the firewall is rarely in your best interest.

It's also on the side of the firewall that doesn't have an engine next to it.

 

[kyleb]

It's also on the side of the firewall that doesn't have an engine next to it.

Stainless is an excellent heat transfer mechanism. If you get a fuel or oil fire in the engine compartment, it is possible to heat the firewall enough it ignites whatever touches the other side of the firewall or at least causes it to smolder.

 

[Jdm]

If you’re smoking the best certified metal firewall insulation available I suspect you’ve already experienced a cabin fire that is beyond human control. The HP of your RV has no correlation to the heat of the firewall of this Luscombe. I don’t understand the 2.5X HP correlation? Firewall heat has more to do with the proximity of the engine to the firewall and it’s ventilation.
It’s very common to have firewall insulation on certified airplanes. Some of the new technologies are a definite improvement over previous certified production. I’ve been flying and A&Ping for 32 years now. I’ve never been involved in a situation where certified firewall insulation was the source of cabin smoke.

 

[Dan Thomas]

Cessna used a fiberglass mat on the firewall that had a black vinyl facing the cabin. The fiberglass won't smoke and it insulates the vinyl from the heat if there's an engine compartment fire.

I sure wouldn't paint anything on the firewall or use anything plastic against it.

Before the FAA put a bunch of FAR 23 into ACs, FAR 23.853 had this in it:

(f) Airplane materials located on the cabin side of the firewall must be self-extinguishing or be located at such a distance from the firewall, or otherwise protected, so that ignition will not occur if the firewall is subjected to a flame temperature of not less than 2,000 degrees F for 15 minutes. For self-extinguishing materials (except electrical wire and cable insulation and small parts that the Administrator finds would not contribute significantly to the propagation of a fire), a vertical self-extinguishing test must be conducted in accordance with Appendix F of this Part or an equivalent method approved by the Administrator. The average burn length of the material may not exceed 6 inches and the average flame time after removal of the flame source may not exceed 15 seconds. Drippings from the material test specimen may not continue to flame for more than an average of 3 seconds after falling.

 

[kyleb]

If you’re smoking the best certified metal firewall insulation available I suspect you’ve already experienced a cabin fire that is beyond human control. The HP of your RV has no correlation to the heat of the firewall of this Luscombe. I don’t understand the 2.5X HP correlation? Firewall heat has more to do with the proximity of the engine to the firewall and it’s ventilation.

There's a lot more energy (heat) released under the cowl of a 160 hp airplane than a 65 or 85 hp airplane. That's the point of the 2.5x figure. That said, there's no doubt there are other under-cowl factors which contribute to the amount of heat potentially passed through the firewall into the cabin.

As rare as serious engine fires are, if you are unlucky enough to have one, the last thing you want is smoke in the cabin fed by smoldering insulation. Can you point to a certified insulation you would recommend for the cabin side of a firewall?

 

[biplanebob]

The Rutan Vari-EZ and Long -EZ builders use a ceramic fabric called "Fiberfax" as part of their firewall sandwich. Available from Aircraft Spruce.

 

[kyleb]

The Rutan Vari-EZ and Long -EZ builders use a ceramic fabric called "Fiberfax" as part of their firewall sandwich. Available from Aircraft Spruce.

In most cases, the firewall is fiberglass covered plywood, with fiberfrax bonded to the fiberglass, and a thin sheet of aluminum or stainless foil to protect the fiberfrax. The foil is on the engine side of the whole stackup.

 

[Dan Thomas]

As rare as serious engine fires are, if you are unlucky enough to have one, the last thing you want is smoke in the cabin fed by smoldering insulation.

Or flaming insulation. Or smoldering epoxy paint....very toxic.

 

[Jdm]

Can you point to a certified insulation you would recommend for the cabin side of a firewall?

I’ll check with the repair station who conducted the installation on this certified airplane. They regularly use the product during panel upgrades. Hopefully they can provide documentation. If so, I’ll be sure to pass it along.

 

[Jdm]

Ok, after doing some research and actually putting my hands on it, I realize that was a slightly incorrect. I recently provided a photo of some soundproofing insulation (1” think) with metal on one side and black cushion on the other which I thought was used on the sidewalls and firewall. It was indeed used for the sidewalls. The metal blanket that was actually used on the firewall is slightly different however. It looks the exact same from a side profile but it has metal on both sides with a thinner cushion that is sandwiched in between. Appropriately 1/2 inch thick cushion. They are both made by the same company, SoundEx.
The certificate of confirmation lists the following item numbers.

SX-1000 (sidewalls)
SX-580F (firewall)