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Bad Firewall Insulation Choice

DanH

Legacy Member
Mentor
Recently had an opportunity to remove the "firewall insulation" from an RV-7A. Although I can't determine a particular brand, the material type is common enough, a fiber mat backed with a fiberglass net and aluminum foil. It was a popular option 20 years ago, and I still see it under panels at fly-ins.

Trouble is, most of the fiber mat products are recycled polyester, Eco Fi being the major brand, and highly flammable, even when treated to be fire retardant (i.e. fire self extinguishes after the heat source is removed). I've tested similar materials and posted photos in the past; they were all uniformly awful. However, obviously not everyone got the memo. Here it is again...

An engine compartment fire heats the firewall. The red hot firewall ignites the insulation, bringing smoke and flame into the cabin. It is a fire transfer mechanism.

I had the firewall test rig set up anyway, so I ran two samples for video. Here's one of them: https://youtu.be/uwax7WNNKow. It was the least flammable fiber insulation yet tested.

There is no good insulation for the cabin side of a firewall. For any given heat source, even a completely inert insulation hastens the rise rate and increases the ultimate temperature of the firewall structure. In the case of an RV, the rivets and aluminum angles melt at 1100F.

Either insulate the engine side, or don't insulate at all.
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RE Bad Firewall Insulation Choice:

Dan,

Your posts are always very interesting. I was considering adding the Vans supplied sticky foil heat sheet to my RV-14 firewall, since I have a few rolls left over. I cannot determine the type, brand, or material, as it is not marked in any fashion. I have not tested the material with heat or flames, but am curious as to what happens to the glue when overheated.

Would you recommend this, and if so, on which side of the firewall?

v/r
 
Dan,

Your posts are always very interesting. I was considering adding the Vans supplied sticky foil heat sheet to my RV-14 firewall, since I have a few rolls left over. I cannot determine the type, brand, or material, as it is not marked in any fashion. I have not tested the material with heat or flames, but am curious as to what happens to the glue when overheated.

Would you recommend this, and if so, on which side of the firewall?

v/r

As a big 'ole general rule, there is limited downside to adding almost anything on the engine side of a firewall. Depending on material choice and installation details, it may or may not make things better, but it is unlikely to make things worse. There are caveats, #1 being the requirement to seal all openings gas tight, but you should be doing that anyway.

You can definitely make things worse with insulation on the cabin side.

Specific to your question, yes, the self stick foils generally use an acrylic adhesive, which would be a smoke/flame risk on the cabin side.

On the engine side, aluminum foil alone would be pretty useless. It works by reflecting radiant energy, and the bare stainless firewall already does a lot of that. Use the foil on the inside of your lower cowl.
 
Firewall rivets in my F1 are all steel, assuming they are NASM20427. Obviously a better choice for fire resistance.

I dunno Bob. They don't melt, but there's not much point if the supporting structure does.

Returning to the folly of cabin side insulation...in the attached photo, significant energy is being radiated from the "cool" side, the one facing the camera. If that side was covered with an insulation layer, the energy is retained, and the aluminum angle reaches melt temperature sooner than if it were left exposed. In this test, it took about two minutes for the 6061T6 aluminum angle to reach 800F, where it would remain intact, although with only about 10% of its original yield strength. Melt temperature requires 3 to 3.5 minutes. I've not yet quantified times with an insulation layer, but I'd guess half as much.

Point is, insulating the engine side protects the structure, while insulating the cabin side contributes to its failure.
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The best insulation for the Engine side is made by a Japanese company MAFTEC
https://www.maftec.co.jp/en/#blanket

Their blanket material is alumina fiber that is first needled and then heat treated for best mechanical properties. The heat treatment is at 1200-1400C, not F. I have used this product as a retention material on the huge substrates in the Caterpillar emission control systems that launched in 2012.

Im not sure if they have a US office for sales. Back in 2008-9 I had to buy sample material from Japan, but that might have changed. Back then they were part of Mitsubishi Chemical, in March 2022 they were spun off and are now an independent company.

The best way to use the product in an insulation capacity is to place the insulation between 2 sheets of stainless steel foil which are then spot welded together at the edges, this offers some mechanical protection and reduces the chance of dust, which because of the fiber diameter are very irritating to the skin, but cannot get into the deep lung. Fibers like asbestos are thinner and do not irritate the skin, but can be breathed in which is why they are carcinogens. Safety has been a very big focus with this product, along with absolutely the best performance from a heat transfer and mechanical retention for catalytic converter/DPF applications.

Most of the other fiber that is available in the US is RCF (Refractory ceramic fiber) and is made in a process similar to how candy floss is made from sugar and therefore it contains shot and also has a tail that gets thinner till it breaks off. Thus the fiber diameter distribution is horrible. Its also not nearly as temperature resistant, although the difference may be academic in the case of aluminum and composite airframes.
 
A key question about the MAFTEC blanket material is how conductive it is.
For firewall treatment, we need two things. 1) able to withstand the high temperatures, and 2) have a fairly low thermal conductivity.

If the blanket is able to withstand the high temperature, but is fairly conductive, then it is not going to delay the temperature rise on the cabin side of the firewall.

However, even if the blanket material is fairly conductive, then depending on its mechanical properties, it may be possible to perforate it into a mesh with mostly open space that would provide an air gap between two sheets of stainless steel foil, with the mesh providing separation but relatively little contact area for conduction.

The best insulation for the Engine side is made by a Japanese company MAFTEC
https://www.maftec.co.jp/en/#blanket

Their blanket material is alumina fiber that is first needled and then heat treated for best mechanical properties. The heat treatment is at 1200-1400C, not F. I have used this product as a retention material on the huge substrates in the Caterpillar emission control systems that launched in 2012.

Im not sure if they have a US office for sales. Back in 2008-9 I had to buy sample material from Japan, but that might have changed. Back then they were part of Mitsubishi Chemical, in March 2022 they were spun off and are now an independent company.

The best way to use the product in an insulation capacity is to place the insulation between 2 sheets of stainless steel foil which are then spot welded together at the edges, this offers some mechanical protection and reduces the chance of dust, which because of the fiber diameter are very irritating to the skin, but cannot get into the deep lung. Fibers like asbestos are thinner and do not irritate the skin, but can be breathed in which is why they are carcinogens. Safety has been a very big focus with this product, along with absolutely the best performance from a heat transfer and mechanical retention for catalytic converter/DPF applications.

Most of the other fiber that is available in the US is RCF (Refractory ceramic fiber) and is made in a process similar to how candy floss is made from sugar and therefore it contains shot and also has a tail that gets thinner till it breaks off. Thus the fiber diameter distribution is horrible. Its also not nearly as temperature resistant, although the difference may be academic in the case of aluminum and composite airframes.
 
I dunno Bob. They don't melt, but there's not much point if the supporting structure does.


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It seems like steel rivets may be a benefit. If the heads of aluminum rivets exposed on the engine side melt, or even soften severely, then the aluminum support structure will fall apart some time before the aluminum pieces melt or even lose significant strength. With steel rivets, the assembly would still stay together until the aluminum pieces actually do reach a high enough temperature to cripple the structure.

Another thought: if there are aluminum stiffening components on the cabin side of the firewall that are particularly critical, or in a particular zone of most-likely experiencing high temperatures (e.g. along the lower edge where the cooling exit flow goes) perhaps they could be replaced with lighter gauge stainless steel components with little or no weight penalty but an improvement in high-temperature performance.
 
It was used in a 12mm thickness in the CAT application because there was an external surface temperature requirement of I believe 210C while doing a regen which will have between 650-1050C at the substrate on the inside. It is definitely a low conductivity material. The installed density was something like 380kg/m^3 which is just more than 1/3 of the density of water and about 5% the density of steel. Now in an insulation only application (not having to hold an 80lb DPF in position), the installed density is probably 1/3 of that so less than 2% of the density of steel.

A key question about the MAFTEC blanket material is how conductive it is.
For firewall treatment, we need two things. 1) able to withstand the high temperatures, and 2) have a fairly low thermal conductivity.

If the blanket is able to withstand the high temperature, but is fairly conductive, then it is not going to delay the temperature rise on the cabin side of the firewall.

However, even if the blanket material is fairly conductive, then depending on its mechanical properties, it may be possible to perforate it into a mesh with mostly open space that would provide an air gap between two sheets of stainless steel foil, with the mesh providing separation but relatively little contact area for conduction.
 
It seems like steel rivets may be a benefit. If the heads of aluminum rivets exposed on the engine side melt, or even soften severely, then the aluminum support structure will fall apart some time before the aluminum pieces melt or even lose significant strength.

Steve, maybe not. Observation from the burn rig...rivets provide a conductive path. Remove the rivet, remove the path. It's surprising how SS sheet begins to warp and physically separate itself from the underlying structure, leaving only the radiant path.

It's entirely possible to maintain reasonable structural integrity without using anything very exotic, simply by placing the insulation package on the engine side where it belongs. The photo below is an RV-7 firewall after being subjected to a burn run. The insulation package was removed and it was cleaned, but that's all. No melted rivets. I would replace the assembly if I were rebuilding the airplane post fire, but it remained intact.

Returning to focus, don't put insulation on the cabin side.
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Am I the only one who sees the guts of a weird TV set in that second photo?
 
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Unfortunately (for me) I had already assembled my RV7 befopre I learned of your research and advice. I have insulated the inside of my RV using fiberglass duck board (kind used in HVAC) cut to fit in between the angle supports at the firewall cover by aluminum tape to secure it to the firewall and then I used flame protective cloth (same as Oatley flame protective cloth for soldering/welding, can now be purchased at Lowes/Home Depot). At the time, it was supposed to be a pretty exotic, NASA invented, material but it now used by plumbers to solder pipe without damage to studs or drywall. I have taken a heat propane torch to get the cloth red hot while your hand is on the other side and only slightly warm. I cover the entire firewall which was covered with the duck board/aluminum tape (inside) with this NASA invented 1/4" heat shield cloth.

I am so old/inflexible now that I can hardly get under the tip up panel to reach the firewall. I have so much stuff attached to the engine side, I cannot imagine how I could insulate the engine side firewall.

I am fortunate enough to have a partnership interest in a YAK52 that we have owned since 1995, performed aerobatics, with parachutes and I have often said the only time I would even attempt to get out of that plane is, if it was on fire.

Have you tested fiberglass duck board? What, if anything, would be a plan of action for this scenario.

Have there ever been a report of a fire engine side in an RV resulting in death or serious injuries. If so, was a cause determined?
 
Question for Dan.

Since I have easy access to the firewall during the build….

How do you feel using 0.016 sheet aluminum and cut it to fit in areas of the firewall (cabin side), and put a layer of Fiberfrax under it making the Fiberfrax the middle of the sandwich? I found some 1/2” thick on Amazon that is enough for 2 firewalls for about $50 and rated to 2,400f.

Now would be the time since I don’t have to work around anything going thru the firewall yet and can make some tight fitting panels.
 
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What insulation package ?

Steve, maybe not. Observation from the burn rig...rivets provide a conductive path. Remove the rivet, remove the path. It's surprising how SS sheet begins to warp and physically separate itself from the underlying structure, leaving only the radiant path.

It's entirely possible to maintain reasonable structural integrity without using anything very exotic, simply by placing the insulation package on the engine side where it belongs. The photo below is an RV-7 firewall after being subjected to a burn run. The insulation package was removed and it was cleaned, but that's all. No melted rivets. I would replace the assembly if I were rebuilding the airplane post fire, but it remained intact.

Returning to focus, don't put insulation on the cabin side.
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Thanks DAN ….exactly what insulation was used in the video?
 
Have you tested fiberglass duck board? What, if anything, would be a plan of action for this scenario.

I stopped testing any insulation for the cabin side years ago.

Have there ever been a report of a fire engine side in an RV resulting in death or serious injuries. If so, was a cause determined?

Yes. Best known was Vern Dalman's Rocket NTSB ID# LAX99LA063. Our own Ted Chang was able to get his RV-10 down in a field by allowing a door to tear away, ventilating the cabin enough to maintain control. Luckily the burning insulation was inside the center tunnel. Both were fuel hose related. There have been others. I suspect fire transfer gets overlooked a lot when the airplane is destroyed, in particular when the impact site includes fire.

How do you feel using 0.016 sheet aluminum and cut it to fit in areas of the firewall (cabin side), and put a layer of Fiberfrax under it making the Fiberfrax the middle of the sandwich?

Cabin side insulation? How do I feel?

banging-head-on-wall-bad-day.gif
 
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https://www.unifrax.com/product/fiberfrax-durablanket-s/

There are many grades of Fiberfrax product. The Durablanket S is a needled product that is "organic free" thus would not produce smoke when heated.

It is mainly SiO2 with just a little AL2O3, so not comparable to the Japanese stuff. Now Unifrax did purchase Saffil which gave them access to a proper Al2O3 product base but because it is more expensive its reserved for niche applications.
 
Question for Dan.

Since I have easy access to the firewall during the build….

How do you feel using 0.016 sheet aluminum and cut it to fit in areas of the firewall (cabin side), and put a layer of Fiberfrax under it making the Fiberfrax the middle of the sandwich? I found some 1/2” thick on Amazon that is enough for 2 firewalls for about $50 and rated to 2,400f.

Now would be the time since I don’t have to work around anything going thru the firewall yet and can make some tight fitting panels.

Ok, so I am not DanH, but I will answer with information on what I have done. I am sure Dan will chime in also.

So the problem I see with the .016 aluminum sheet is the low temperature at which it will melt. Your idea is exactly what I have done with the exception of using .016 stainless sheet. Bare Fiberfrax against the firewall and stainless sheet as the outer barrier. All can be acquired from McMaster Carr.
 
Unfortunately (for me) I had already assembled my RV7 befopre I learned of your research and advice. I have insulated the inside of my RV using fiberglass duck board (kind used in HVAC) cut to fit in between the angle supports at the firewall cover by aluminum tape to secure it to the firewall and then I used flame protective cloth (same as Oatley flame protective cloth for soldering/welding, can now be purchased at Lowes/Home Depot). At the time, it was supposed to be a pretty exotic, NASA invented, material but it now used by plumbers to solder pipe without damage to studs or drywall. I have taken a heat propane torch to get the cloth red hot while your hand is on the other side and only slightly warm. I cover the entire firewall which was covered with the duck board/aluminum tape (inside) with this NASA invented 1/4" heat shield cloth.

I am so old/inflexible now that I can hardly get under the tip up panel to reach the firewall. I have so much stuff attached to the engine side, I cannot imagine how I could insulate the engine side firewall.

I am fortunate enough to have a partnership interest in a YAK52 that we have owned since 1995, performed aerobatics, with parachutes and I have often said the only time I would even attempt to get out of that plane is, if it was on fire.

Have you tested fiberglass duck board? What, if anything, would be a plan of action for this scenario.

Have there ever been a report of a fire engine side in an RV resulting in death or serious injuries. If so, was a cause determined?

The danger from your situation with insulation on the cabin side is not so specific to letting the fire get into the cockpit. The danger comes from the out gassing, toxic fumes and smoke from the material inside the cockpit.
 
Ok, so I am not DanH, but I will answer with information on what I have done. I am sure Dan will chime in also.

So the problem I see with the .016 aluminum sheet is the low temperature at which it will melt. Your idea is exactly what I have done with the exception of using .016 stainless sheet. Bare Fiberfrax against the firewall and stainless sheet as the outer barrier. All can be acquired from McMaster Carr.

Webb, sorry that I miss understood what you were saying. What I described I did on my plane was on the engine side of the firewall. Nothing in the cockpit.
 
How would a FWF flame test look like with the heat/fire resistant blanket saturated with oil or avgas AND THEN ignited.

With a metal surface, there is little chance of accumulating any great amount of fuel or oil. A fire sleeve is a good example, it protects the fuel/oil line from fire, but will retain a significant amount of fuel or oil during a leak in the line that will ignite all at once if an ignition source is available.

It may be worthwhile to make sure that we greatly reduce (eliminate) any source of ignition, and just not have the fire to begin with.

Common sources of ignition would be...
1 alternator........ shield it and provide ram air from clean source.
2 mags.............. shield and provide ram air from clean source.
3 master relay.... make sure it is sealed.
4 exhaust pipes.. shield the top of horizontal pipes.
5 ??????

A fuel leak on top of the motor is a higher risk than a fuel leak at the carb.

In the Propane industry, a gas leak is insignificant without a source of ignition.
 
Fire suppression system

I may need a bit of weight forward and looking at a small fire suppression system …two nozzles forward of firewall and maybe one on pilot. ….anyone have experience with something like this ?
 
The firewall is one side of forward baggage hold on a RV8. The combustible items that touch the firewall from time to time takes on a new level of concern from Dan’s work.

Paper, plastic, the sleeping bag going to Oshkosh, the edge of the carpet that is on the floor, duffle bag, etc…. Not to mention not metal items of a smoke system may be present (talk about smoke!).

Paper ignites around 480F but burns hot enough to melt aluminum.

Adding insult to injury, that nice pass thru that is sometimes cut out to access the rear of the avionics would be a potential for smoke leakage unless it had a fire seal and was screwed in place should a fire occur.

Not trying to thread drift but was thinking about insulation of this area in particular.

BTW - there is a good article in Aviation Safety on fire in flight. https://www.aviationsafetymagazine.com/features/fire-in-flight/
 
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Firewall side

I’ve wondered if a Ceramic coating applied to the engine side of the stainless firewall would be effective at buying some time or is the ceramic too brittle for the flexible stainless firewall.
Another idea is maybe a stainless sandwich with some sort of insulation between stainless sheets with a coating of ceramic?
 
How would a FWF flame test look like with the heat/fire resistant blanket saturated with oil or avgas AND THEN ignited.
With a metal surface, there is little chance of accumulating any great amount of fuel or oil.

Yes, engine side, 0.002 or 0.005 stainless or titanium foil sealed at all edges.

...looking at a small fire suppression system …two nozzles forward of firewall and maybe one on pilot.

In flight, an RV's cooling air flow is roughly 30 to 35 cubic feet per second. Consider how many cubic feet of suppression gas can be stored in a practical system, and at what rate it can be discharged.

The firewall is one side of forward baggage hold on a RV8. The combustible items that touch the firewall from time to time takes on a new level of concern from Dan’s work.

Yep. Remember, this interest started because I was building an -8. I've thought about it a few times in the last 1100 hours.

In general, when in flight we can assume fire follows airflow, meaning down and out near the bottom of the firewall. Remember, we're talking 30 to 35 cubic feet per second. So far, all the cases for which there is information have followed that pattern, with one exception, and frankly I suspect the investigator drew the wrong conclusion.

A static fire (aircraft stationary, prop stopped) is quite different, following the pattern taught to every fire investigator...hot air rises, with dramatic heating near the ceiling first. The upper firewall components and top cowl get the most exposure. The good news is you can watch it burn from across the ramp.

A fire on the ground with the engine running is going to be a hybrid, with low cooling flow, so more upper zone heating. Even so, the anecdotal evidence has been that it melted the belly skin aft of the exit...fire follows flow.

In the case of the RV-8 baggage compartment (and again returning to topic), the goal should be to minimize temperature rise in the structure. Insulating the inside doesn't do that. It's like wearing your raincoat inside your clothes.

I’ve wondered if a Ceramic coating applied to the engine side of the stainless firewall would be effective at buying some time or is the ceramic too brittle for the flexible stainless firewall.

As before, you can add nearly anything to the forward side of a firewall, and even if ineffective, it probably won't make things worse.

A thin ceramic would slow heat transfer, but I wouldn't think enough to be practical.

I have tested one intumescent paint. Most of those work by forming an insulating char. Vibration and airflow makes the char fall off the stainless steel just when you need it most.

Hey Dan have you ever tested this stuff or anything like it? The 200 series is roll on, so could be “painted” on the firewall (engine side).

Not tested. I do have an interest in the 100 series joint sealant, as 3M FireBarrier 2000+ is currently in short supply. I'll call them later today and see if there are test samples available.
 
Yes, engine side, 0.002 or 0.005 stainless or titanium foil sealed at all edges.



In flight, an RV's cooling air flow is roughly 30 to 35 cubic feet per second. Consider how many cubic feet of suppression gas can be stored in a practical system, and at what rate it can be discharged.



Yep. Remember, this interest started because I was building an -8. I've thought about it a few times in the last 1100 hours.

In general, when in flight we can assume fire follows airflow, meaning down and out near the bottom of the firewall. Remember, we're talking 30 to 35 cubic feet per second. So far, all the cases for which there is information have followed that pattern, with one exception, and frankly I suspect the investigator drew the wrong conclusion.

A static fire (aircraft stationary, prop stopped) is quite different, following the pattern taught to every fire investigator...hot air rises, with dramatic heating near the ceiling first. The upper firewall components and top cowl get the most exposure. The good news is you can watch it burn from across the ramp.

A fire on the ground with the engine running is going to be a hybrid, with low cooling flow, so more upper zone heating. Even so, the anecdotal evidence has been that it melted the belly skin aft of the exit...fire follows flow.

In the case of the RV-8 baggage compartment (and again returning to topic), the goal should be to minimize temperature rise in the structure. Insulating the inside doesn't do that. It's like wearing your raincoat inside your clothes.



As before, you can add nearly anything to the forward side of a firewall, and even if ineffective, it probably won't make things worse.

A thin ceramic would slow heat transfer, but I wouldn't think enough to be practical.

I have tested one intumescent paint. Most of those work by forming an insulating char. Vibration and airflow makes the char fall off the stainless steel just when you need it most.



Not tested. I do have an interest in the 100 series joint sealant, as 3M FireBarrier 2000+ is currently in short supply. I'll call them later today and see if there are test samples available.

Do let me/us know , I’m very interested since it meets the FAA20135
 
Lower mount weldments, RV-7A. Here the fiber insulation pictured in the first post and below was applied to the sidewall and overlapped the weldment, with the insulation edge on the bolt heads. The result is a clear corrosion line across the heads where there was contact. You can still see fiber on the second bolt.

I don't know if the corrosion was due to some chemical content in the insulation, or simply holding moisture over the years. Probably both, given the usual need for an electrolyte. Doesn't matter very much really. Just don't install dumb things on the inside of firewalls.
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Follow up on the RV-8. I replaced the aluminum cowl exit ramp with a piece of 0.015” SS. Using the aluminum part as a template it is not hard to fabricate this replacement. On the sides of the ramp use the same firewall sealant Dan recommends for the firewall insulation/SS cladding sandwich.

While not a perfect way to protect from flames following airflow out of the cowl I consider this a simple way to gain some margin.

Carl
 
Example.....

Edit: Unlike the other RVs, the 8's have a box recess in the belly, so the aluminum or stainless ramp is non-structural, and has a degree of separation from the floor.
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On my RV-3B, I added 1/16" Fiberfrax and .020 titanium overlay (underlay?) to the belly aft of the firewall. Some of the rivets were per plans, left open for this, but most of them were just for this.

Where I wanted to support the titanium in the middle area, I glued down some .063 spacers, cutting out the Fiberfrax at the spacer. The end result lays down nicely.

Dave
 
Removal

I have aforementioned “insulation” on the 6 I bought a decade ago. The need to replace my carpet and the **** under it brings me to the question at hand which is what helps in breaking down the nearly invincible glue holding it on?

I know there are a number of glues the builder could have used but I’m looking for any suggestions to make this easier. My best guess based what the small sections I’ve been able to remove are a 3m spray on adhesive or similar.

Craig
 
A long time ago I did some formica work and used contact cement. Nasty flammable smelly stuff but it was cleaned up with lacquer thinner. Wear a quality respirator and have a fire extinguisher close by if you try it. Maybe GoofOff?
 
Progress!

It looks like lacquer thinner is by far the most effective solvent to dissolve the glue that was used on my insulation.

I’ve got a large fan blowing, masked up, and taking frequent breaks to minimize the exposure.

Thanks for the suggestions. Goo gone and acetone were ineffective to say the least.
 
cowling insulation?

It looks like the fire has escaped the engine cowling. Note how the heat has apparently burned through the external fresh air intakes, yikes! The pilot was fortunately able to land.
Methinks cowling insulation is worth considering, at least for the aft part.
 

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It looks like the fire has escaped the engine cowling. Note how the heat has apparently burned through the external fresh air intakes, yikes! The pilot was fortunately able to land.
Methinks cowling insulation is worth considering, at least for the aft part.

Fire follows airflow. RV cowls typically leak air along the cowl-to-fuselage seam, so post-incident we'll always see at least some soot staining.

Teal's RV-9, being Yamaha powered, does not have a conventional upper plenum space. Given a fuel leak on top of the engine (see the other thread), a conventional rear baffle wall and seal strip would force flow downward through the fins, rather than directly aft to the seam in front of the windshield. Eventually the baffle seals or plenum lid might burn out, allowing flame to flow directly aft, but it would take time, and fire protection is all about buying time.

Of particular interest here is the obvious fire trail directly forward of the cabin air inlets. There's a good lesson here. Note the original builder did not incorporate any form of cowl fastening along that section of upper cowl. The edge of the cowl would have been pillowed outward in flight due to normal in cowl pressure, so those sections of seam were really cowl outlets, same as the big cooling outlet on the bottom. Fire follows flow, here bad juju.

The lesson is to keep the cowl edge fastened as tightly as possible all the way around. Odds are you'll never catch fire, but sealing off seam leakage is a drag reduction just the same.

Break.

The main theme remains "Don't install stupid insulation inside the cockpit".
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Fire follows airflow. RV cowls typically leak air along the cowl-to-fuselage seam, so post-incident we'll always see at least some soot staining.
...
Of particular interest here is the obvious fire trail directly forward of the cabin air inlets. There's a good lesson here. Note the original builder did not incorporate any form of cowl fastening along that section of upper cowl. The edge of the cowl would have been pillowed outward in flight due to normal in cowl pressure, so those sections of seam were really cowl outlets, same as the big cooling outlet on the bottom. Fire follows flow, here bad juju.

The lesson is to keep the cowl edge fastened as tightly as possible all the way around. Odds are you'll never catch fire, but sealing off seam leakage is a drag reduction just the same.

Break.

The main theme remains "Don't install stupid insulation inside the cockpit".
.

I checked my cowl installation and it is the same - there is no hinge in that section, this is per the Van's plans. Teal's thread post is a good lesson in prevention (root cause). And also to not insulate on the aft side of the firewall.
It might be an idea to incorporate some sort of inner lip on that section of the cowl, given the proximity to the plastic NACA inlets.
 
Remember this photo next time someone advertises FAR 25.853 insulation as a safe material for the cabin side of your firewall.

Japan Airlines Fire.jpg
 
If you find the initial images, the fire is visible only in the aft two windows. They may have fought the fire only externally?

...which doesn't say much for any innate fire resistance of an FAR 25.853 material.

The detail missed by most is that "fire resistant" is not even remotely fireproof. It merely means the test subject will self-extinguish in a certain period of time after a Bunsen burner-sized heat source is removed. Jack up the heat flux, or make the heat source difficult to remove, and it becomes fuel.

When placed on the cabin side of a firewall, the heat flux is far larger than specified for a fire resistance test, and there is no immediate shutoff.
 
...which doesn't say much for any innate fire resistance of an FAR 25.853 material.

The detail missed by most is that "fire resistant" is not even remotely fireproof. It merely means the test subject will self-extinguish in a certain period of time after a Bunsen burner-sized heat source is removed. Jack up the heat flux, or make the heat source difficult to remove, and it becomes fuel.

When placed on the cabin side of a firewall, the heat flux is far larger than specified for a fire resistance test, and there is no immediate shutoff.

All 379 people onboard the JAL A350 evacuated without a fatality. So it was resistant enough to give people time to evacuate.
 
Perhaps I was too cryptic.

The best fire resistant materials perform far better than materials with no rating. Below are examples. One is Orcotek, the other is Thermozite.

Orcotek is a legitimate aircraft sidewall insulation. Best I know, it's not marketed as firewall insulation, or represented as "fireproof". It performs exactly as I would expect for good fire resistant material. If I wanted to insulate behind a sidewall in my RV, it would be on the short list.

Thermozite is a polyester fiber insulation. The manufacturer represents it as environmentally friendly, as it's made from recycled plastic bottles. Unfortunately, it was heavily sold into the RV market specifically as firewall insulation. Walk the lines at OSH and you'll still see lots of it.

Here's the point. Orcotek is legit aircraft material when used properly. Thermozite is suitable for insulating under a carpet in your car. Neither is a good firewall insulation. When exposed to red hot stainless, the Orcotek is performs far better, but you would not want to be in the cockpit with either at 8000 ft.
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It doesn't matter how flame-resistant the materials are if they are soaked in fuel. I encountered this first-hand in an attempt to rescue occupants in a burning PA32. There is nothing worse than that fate. I couldn't sleep for weeks.

In the JAL case they were in position and holding short on the runway in low viz where the other aircraft landed on top of them. Likely fuel everywhere.
 
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