Corrosion Risk - Insulation

I've previously posted regarding the fire transfer risk inherent in poor insulation choices on the cabin side of a firewall. Fiber insulations can also promote corrosion.

The components below were removed from a rebuild underway in my shop. They were in contact with a common aluminum foil faced fiber insulation still seen in a lot of RVs. Here the insulation was on the cabin side of the firewall and the underside of the upper boot cowl skin.

Note these parts are primed, or powder coated, or cad plated. Didn't help. This airplane is only a little more than 10 years old.
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It looks a bit rusty Dan! I dont have anything hidden on my plane with insulation but wouldn't that be something that should be checked at each annual? Maybe not completely removed but pulled back enough to see critical parts.

It is all the things people dont realize or know that cause us costs and mishaps. Thanks for the reminder.

Rust

Wow! Those are some pretty important parts.
The insulation was wet quite a while.
Good save Dan.

Insulation

Well to ditto Dan's post.
I bought an RV-6A a few years ago and one of the first things I did was remove all the foam from the sidewalls, floor, and here and there, Because I didn't feel I would do any good. Maybe just kill me with smoke during a fire.
I did find light rust on a few bolts though. No corrosion. Smart decision.
Nothing to worry about, But Dan's post brought the thought back.
I Won't fly without ANR hear sets anyway and the foam didn't make any noise difference from before and after flights.
Good call.
My three cents worth Art

rockwoodrv9 said:

...wouldn't that be something that should be checked at each annual? Maybe not completely removed but pulled back enough to see critical parts.

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Consider how hard it would be to replace these parts on a flying airplane.

Insulation on the cabin side should be removed, period.

Similar experience from certified world

Mooneys originally had fiber insulation in the cabin; big time moisture magnets. Leaky plexiglass or pilot service window would load up the fiberglass. This played h3ll with the tubular steel fuse structure of course. SB M-208 (IIRC) was issued to inspect the tubular steel, change the insulation to closed cell, reseal windows with tank sealant, etc.

Corrosion on that structure can easily economically total the aircraft. Since it was “only a Sevice Bulletin”, many weren’t done. Many became parts aircraft in short order.

Any open cell insulation in an aircraft is unacceptable IMO. A spilled soft drink, accident with a Jiffy John, etc can kick off some aggressive chemistry. Why make the things worse for no real benefit?

My two cents.

Dan, what insulation do you recommend?

I am observant enough to keep it off the firewall, but what about the sidewalls? Thinking of certified aircraft and sound reduction/minimizing heat transfer

NTex said:

Dan, what insulation do you recommend?

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My own has none, except the engine side of the firewall.

NTex said:

Dan, what insulation do you recommend?

I am observant enough to keep it off the firewall, but what about the sidewalls? Thinking of certified aircraft and sound reduction/minimizing heat transfer

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I am not Dan but I do know him.

Anyway, if you do a little research on what effective materials are needed to insulate for sound you would discover that effective sound insulation does so by dampening vibrations. Dampening vibration mostly involves heavy material that “absorbs” the vibrating sound waves. So, (1) we don’t want additional weight in our airplanes. (2) The additional materials inside the cockpit can produce toxic fumes in the event of fire. (3) the aviation industry has some very good headsets from multiple manufacturers that address noise.

There is little (some may say no) benefit to installing insulation in the cockpit of our airplanes.

My guess would be that this was an aircraft that spend a lot/ some time in a cold climate. If the engine side of the firewall is cold and the cabin side is humid, (how many times have you have the windscreen fog on the inside on a cold morning due to your breath). This insulation is not sealed well enough to keep the humidity from hitting the cold firewall and then is sealed well enough not to vent and dry.
Even if it were not a fire thing, it seems insulating on the outside ventilated side is best.

RVbySDI said:

I am not Dan but I do know him.

Anyway, if you do a little research on what effective materials are needed to insulate for sound you would discover that effective sound insulation does so by dampening vibrations. Dampening vibration mostly involves heavy material that “absorbs” the vibrating sound waves. So, (1) we don’t want additional weight in our airplanes. (2) The additional materials inside the cockpit can produce toxic fumes in the event of fire. (3) the aviation industry has some very good headsets from multiple manufacturers that address noise.

There is little (some may say no) benefit to installing insulation in the cockpit of our airplanes.

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(mostly) Yes and (some) No.

Gonna talk in very general terms so that the acoustical engineers that happen upon this don't have a heart attack. I work with several talented ones and combustion dynamicist (here = attenuation experts).

Sound waves are pressure waves. Less than rigid surfaces transmit this energy fairly efficiently. Lower frequency waves tend to carry more energy than higher frequency ones, so on, so on. The subject frequencies can cover a wide range. All of this combines to equal a less than accommodating, very complex environment in GA cockpits.

The issue with most counter measures -> they tend to be tuned to/effective in a very small frequency band. They all add weight. The wider the spectrum, the more "types" of attenuation are required. As for the low freqs, nothing more effective than mass. Since you can't do much to attack the sound power level, it comes down to dampening. It's a loosing battle in my opinion.

You can spend a lot of effort and money to half the cockpit noise and you'll still be disappointed. Sound power level doubles (or halved) every three decibels. Because of human ear physiology, you don't perceive this until ~ every 10 dB. While the reduction is still good for you (hearing loss is associated with the actual, not perceived noise), the associated comfort benefit isn't very noticeable.

To reiterate, it is what it is. Carefully weigh the trade-offs. Don't expect too much from you efforts.

Finally, let me step in it one more time. If you fly with your pets, please protect their ears. Most are far more sensitive to the actual sound than we dumb humans. "My dog loves to fly", etc. is probably isn't true. They want to be near their people and will gladly suffer to do so; one of the reasons we luv 'em.

Requesting pics of front firewall insulation/soundproofing installed on an RV with cutouts for all the attached items. Trying to visualize how that works.
Oh, and spec of materials used.
Thanks.

corrosion

Dan-
That is an A model, correct. I think on an A model waster trapped in those corners could be a possible factor. I am working on a RV3 that had insulation around those fittings and NO corrosion.

jrs14855 said:

That is an A model, correct. I think on an A model waster trapped in those corners could be a possible factor. I am working on a RV3 that had insulation around those fittings and NO corrosion.

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Yes Jim, a 7A.

Check the photo of the other lower weldment. You can draw a line across the bolt heads where the insulation was in contact and where it was not. It could be something corrosive in the insulation fiber, but probably just where the fiber held dampness.

Doesn't matter. Never going to see it in anything I fly. Photo below is only 30 seconds into a test. The front side of the firewall isn't even up to full temperature yet, but it has already transferred the fire to the cockpit side by igniting the fiber insulation.

BruceW said:

Requesting pics of front firewall insulation/soundproofing installed on an RV with cutouts for all the attached items. Trying to visualize how that works.
Oh, and spec of materials used.
Thanks.

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Cutouts are not necessary. You can sandwich the insulation material between the firewall and the various items.



I will leave it up to Dan to reply to your request for detail specs of materials used. Perhaps you can just request he send you a firewall insulation kit for your airplane.

DanH said:

Fiber insulations can also promote corrosion.


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Dan,
Any idea what the source of moisture/water was to cause this level of corrosion? Was this plane hangared, tied down, cold climate, warm humid…

That far right "insulation" looks like 100% cotton sound deadening mat.

"Cotton fibers can hold water 24–27 times their own weight"

Consider that the insulation around the center spar on C-210s caused a lot of the problem. Expensive AD.

Yup, some folks still not getting the message...
Recently saw a bunch of insulation glued down to the entire "floor" as in under the seat trays and baggage floor. Not on the *bottom* of those panels, but on the top of the bottom skin. As in... where the water will collect from every little leak.

Maybe it helps my imagination that I used to live where lots of salt was used on the roads.

Timely topic.... I've got my plane torn apart for a panel upgrade. Bought it last year from the dry plains of eastern washington state. Never stored outside nor flown in the rain. See all the black stuff on the floor? That's thin rubber insulation. Reflective stuff on inside of firewall? Similar insulation to what was shown burning. White stuff on floor under pedals - more closed cell foam insulation. Thankfully what little I have pulled up in my work has not revealed anything. Can't imagine the smoke this would create in a fire. Guess I will have to remove the other floor panels now.... Wonder how much weight I'll remove from the plane?

Can I ask what people are using on the engine side of the firewall?
I read a thread where DanH was going to start selling kits, but can’t find anything.

Jonnyb said:

Can I ask what people are using on the engine side of the firewall?

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Reflector/gas barrier over an insulator, with edge sealing and mechanical fasteners.

I read a thread where DanH was going to start selling kits, but can’t find anything.

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Ok, an update...

I am selling kits...sort of. The RV-8 kit is a finished product. The 6's, 7's, 9's, and 10's present a problem with the overlap seams for the center recess. As currently configured, the kit will extend cabin fire protected time from seconds (no, I'm not kidding) to roughly 3 ~ 4 minutes. I am not entirely satisfied with smoke performance.

The primary issue is the use of proseal in that seam. As temperature rises, it tends to liquify, boil out of the joint, and ignite...on the cabin side. Do not use polysulfide sealant in the firewall seams, period.

I have tested a variety of firewall sealants. The current market is divided between rubber based and silicone based. Any of them is better than polysulfide. None are entirely fireproof. My favorite at this time is Dapco 2100...single component (no waste), with good performance. The budget choice remains 3M FireBarrier 2000+.

The insulation package does eliminate a fundamental failure mode, gapping of the seams, with or without melting of the aluminum rivets, and significantly improves the structural integrity of the firewall support angles. No sealant is effective given gapping and/or rivet failure.

The current 6-7-9-10 packages are at least an order of magnitude better than none, and light years better than bad insulation on the cabin side. Is it good enough? I've discussed investment, risk, and reward with some smart folks. The universal opinion is that 3 to 4 minutes is a big win given an engine fire, and given normal operating temperatures, the comfort aspect of the current package is fine. Still, I'm trying to improve it, smoke performance in particular, which is why you've not seen any marketing.

Current status? I've put out a few beta installations, and continue to work on improvements. If current performance is good enough, send an email. If not, stay tuned. The big factor for most builders is their progress status. The insulation package needs to go on after all driven rivets are in place, but before populating the firewall with bolted components.

Yes, the folks at Vans are aware of developments, and have been extremely helpful. Enough said.

Thanks for the update Dan. PM sent regards an RV-8 kit.