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Sound proofing

GrinchF16

Well Known Member
While rebuilding the panel, I have discovered that my sound proofing material is in awful shape. The stuff that was in the plane appears to be sold at ACS but doesn’t ship until 01 August…. Any thoughts or other material / suppliers that you have used?

Thanks
 
If you are referring to "Super Soundproofing", they are having a difficult time getting the material from their suppliers. A direct call to them would be beneficial.
 
Brian, the black soundproofing foam may be fine on a cabin sidewall ("meets FAR 25.853a Appendix F, Pt1"), but I sure hope you're not placing closed cell nitrile foam in contact with a firewall.

FAR 25.853a Appendix F, Pt1 materials are merely required to be self-extinguishing within a specified time period after the heat source is removed, unless the claim is based on paragraph (v), in which case it's not even required to be self-extinguishing. The heat source for the test is a Bunsen burner adjusted for a 1.5" flame. Think little Johnny in an airline lav with his dad's Bic lighter. Nothing about the standard applies to a firewall, and in fact, the black foam burns with vigor when in contact with red hot stainless.
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Dan,
This could be an interesting conversation. I'm learning all sorts of new things about my RV as I'm changing this panel. More than on my initial CI in fact. The builder had the black soundproofing adhered to the aft portion of the firewall (ie the forward wall of the cockpit). Are you telling me that is no bueno? If so, what is the solution?
 
Dan, I'm planning on doing the ceramic mat/stainless sandwich on the front side (engine) that many have done.

Having said that, if you do that on the engine side, what does your testing show, if a person does the soundproofing foam mentioned above on the cabin side firewall? Enough heat come through on your test rig to cause issues with the adhesive and foam? I'm leaning towards putting nothing on the cabin side, but was curious what your thoughts and testing indicated.

Thanks,
Lance
 
Dan,
This could be an interesting conversation. I'm learning all sorts of new things about my RV as I'm changing this panel. More than on my initial CI in fact. The builder had the black soundproofing adhered to the aft portion of the firewall (ie the forward wall of the cockpit). Are you telling me that is no bueno? If so, what is the solution?

I'm telling you no bueno, for sure. And remove the glue too. No paint either.

The firewall standard is 2000F over a 5" x 5" area. So imagine a 25 sq in patch glowing like the broiler element in an oven. Now imagine what sort of materials might tolerate contact with red hot stainless steel, without ignition or smoke.

There are such materials, mostly ceramics without sizing or adhesives (a smoke problem) holding the fibers together. However, loose ceramic fiber tends to be a lung cancer risk, and insulating the inside of the firewall is dumb anyway. It's pointless to heat the structure while trying to isolate the cabin. Testing showed insulating the engine side of the firewall to be far superior.

As for sound insulation, I recommend an in-ear headset.
 
Dan, I'm planning on doing the ceramic mat/stainless sandwich on the front side (engine) that many have done.

Having said that, if you do that on the engine side, what does your testing show, if a person does the soundproofing foam mentioned above on the cabin side firewall? Enough heat come through on your test rig to cause issues with the adhesive and foam? I'm leaning towards putting nothing on the cabin side, but was curious what your thoughts and testing indicated.

Thanks,
Lance

Bare stainless is safest. No paint, no glue, and darn sure no rubber.

Temperature on the cabin side varies with thickness and type of insulation on the forward side, exposure time, and of course the severity of the fire. I intend to re-run some old tests to more closely quantify, but 400~500F is entirely possible on the rear surface with practical (i.e. thin) insulation types and thickness.

The real risk is point heating, for example a AN3 bolt passing through the insulation and firewall. It may glow red. Not a problem in terms of radiant heating risk for the pilot. However, it could easily cause something to smoke or ignite.

My own cabin below. No paint on the stainless, or the floor near the firewall. All pass-throughs are steel tube filled with intumescent sealant. Bulkhead fuel fitting is stainless, as is the line connecting it to the electric pump. Brake lines are braided SS with nylon liners and 83282 fluid. I like comfort as much as anyone. If I thought there was a safe sound insulation with the forward side insulated, you would be seeing it here.
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Dan,
This could be an interesting conversation. I'm learning all sorts of new things about my RV as I'm changing this panel. More than on my initial CI in fact. The builder had the black soundproofing adhered to the aft portion of the firewall (ie the forward wall of the cockpit). Are you telling me that is no bueno? If so, what is the solution?

Might I suggest a quick search on “firewall insulation”. Along with a great slew of DanH’s experiments on the subject, you can spend hours exploring the previous “conversations” on the subject. A second suggestion, is to perhaps start thinking about this as a conversation about “insulation” and not “soundproofing”.
 
I removed all of mine back to bare metal on my new to me RV. It wasn't fireproof. Saved a few grams. Apple watch says the cabin is 95 dB so I just bought Bose A20s. Problem solved.
 
I have no idea.... so this is just thinking "out loud"
maybe fiberglass?
or maybe even better..... those carbon fiber felt soldering/welding blankets. You can just about put a blow torch to your hand with nothing but a thin little piece of felt shielding.
Don't know the acoustical insulation value but it's gotta be something.
 
I'm with Dan

Dan is correct. Nothing on the firewall. The reality is RV's can't really be sound proofed to any measurable degree. The 10 might be a different animal.
 
i was thinking more about it...that felt is probably too light to do much good for acoustic reductions. Probably mostly higher frequency stuff so more mass would be needed, right?
 
I don't understand why firewalls are only vertical and do not extend a ways aft on the belly of the plane. If there is a fire, it could follow the cooling air out the belly and there would be nothing to slow it from chewing up the aluminum.

IIRC, I've known of two cases of inflight fires where an aft firewall extension might have helped. One was a Harmon Rocket where there was burn through into the cockpit, and the elderly pilot only lived for a week with his burns. The other was an RV-8 where the pilot bailed out without a parachute at 200' because of the fire.
 
For the very reason mentioned by Ed_Wischmeyer I replaced the kit supplied aluminum cooling ramp with a stainless steel one and extended the bottom edges about an inch below the fuselage. Hopefully I’ll never need to find out if it performs as expected.
 
I added a stainless panel, with fiberfrax under it, to the area aft of the cowl, on the underside of the aluminum floor.

So, while we're at it, time to get all that foam rubber off the floor. And the synthetic carpet...

I think it is time that the Lindy contestants at Osh get dinged for having a whole bunch of whiz bang upholstery up against the firewall. Might help get the message out there.
 
Inflight fire is one of the 2 reasons I and my passenger wear a parachute on every single flight. That, or structural failure are the no-brainer reasons to jump out. Engine failure over inhospitable terrain is the third, but I do my absolute best not to put myself in that position if at all possible.

That said, my airplane does have insulation on the cabin side of the firewall...it's a foil with some type of insulation beneath it...guess it'll be removed at some point. Is replacing said insulation on the engine side a hard requirement?
 
A little different situation on composite but I used 1/2” fiberfrax covered by .020 SS engine side. Back in the day stoddard hamilton called for AL over fiberfrax! Not that brave. Nothing on inside like dan h mentioned. Addition of SS cost 2lbs. Worth it.
 

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Along the lines of previous post I used 1/2” fiberfrax with .020 SS on exhaust tunnels. Considering fire suppression for FF.
 

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RV-8 Baggage area

For RV-8 owners, consider what you put in the forward baggage area. Probably not the right place for very flammable items. Unfortunately this is a convenient and popular place for smoke systems, engine oil bottles, and light bags of clothing. :(
 
That said, my airplane does have insulation on the cabin side of the firewall...it's a foil with some type of insulation beneath it...guess it'll be removed at some point. Is replacing said insulation on the engine side a hard requirement?

If it's a gray fiber, chances are it is Thermozite Plus, made from "Eco-fi™ polyester fiber...specifically, 100% post-consumer recycled plastic bottles. It was sold by a popular RV upholstery vendor back in the bad old days, because the manufacturer (Ozite at the time, IIRC) claimed it was a "firewall insulation". It's still available all over the net, including Amazon and Ebay, still claimed as ok for a firewall.

Absolutely the worst insulation I ever tested. Had to drag the burn rig away from my shop because it flared up so bad I thought it would melt the vinyl siding. If you have any of this stuff in your cabin, please remove it as soon as possible. Given its former popularity in the RV and Rocket community, there a pretty good chance it is what killed Vern Dallman. From the NTSB report, passenger's observation:

As the airplane turned wings level onto final, thick black smoke that smelled like burning fiberglass or plastic filled the cockpit. After the airplane came to rest, he observed flames around the pilot and felt high heat.

Is replacing said insulation on the engine side a hard requirement?

No, it is not, and it's an important point I'd like to stress. The danger here is generally self-inflicted. Builders place all kinds of bad choices in contact with the cabin side of the stainless steel firewall. Doing so can easily create a fire transfer mechanism...engine fire heats the stainless, stainless heats the flammable material on the cabin side, the result being fire in the cabin. Given an engine fire, a bare steel firewall will glow red, and it won't be comfortable, but it should be survivable.

Bottom line? Adopt “Primum non nocere”...first do no harm. Insulate the forward, engine side, or don't install anything at all.
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Inflight fire is one of the 2 reasons I and my passenger wear a parachute on every single flight. That, or structural failure are the no-brainer reasons to jump out. Engine failure over inhospitable terrain is the third, but I do my absolute best not to put myself in that position if at all possible.

That said, my airplane does have insulation on the cabin side of the firewall...it's a foil with some type of insulation beneath it...guess it'll be removed at some point. Is replacing said insulation on the engine side a hard requirement?
A few years ago I was upgrading a panel on a 9A. The new owner had recently bought the plane. The builder had installed the type of insulation described by RhinoDrvr. Over the prior year or two the plane developed a brake fluid leak somewhere inside the cockpit. The brake fluid had pooled on the floor at the firewall on numerous occasions over multiple months before they could find the leak. Eventually the leak was repaired. They continued flying the plane as is until I got it for the upgrade.

When I started working upside down under the panel my head kept getting wet as it laid on the floor. Investigation found that the carpet and the firewall insulation had wicked up a voluminous amount of the brake fluid. The insulation was saturated from top to bottom of the firewall from floor to top with brake fluid. It would have been a horrible situation had an engine fire started. Needless to say, I removed all of that insulation during that upgrade.

It is not just the fire that can kill you! It is the noxious fumes and/or smoke that is more likely to kill you! Don’t put any insulation material on the cockpit side of the firewall! It is not a “hard requirement” for any insulation. Vans does not call for it in the build instructions. Many are installing but before DanH displayed his experiments on this forum a few years back there was little guidance on effective installation.

Live Long and Prosper!
 
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How about some discussion on putting out the fire. At the first sign of engine fire, turn off the dang fuel valve. It was always common sense to me, but when I asked students and some licensed pilots what to do in case of an engine fire, that didn’t always enter their consciousness. Ya there is oil and brake fluid on the hot side, but a fuel leak is no doubt the biggest threat. I’d rather fly the “glider” than depend on the ss firewall saving my butt.
 
How about some discussion on putting out the fire. At the first sign of engine fire, turn off the dang fuel valve. It was always common sense to me, but when I asked students and some licensed pilots what to do in case of an engine fire, that didn’t always enter their consciousness. Ya there is oil and brake fluid on the hot side, but a fuel leak is no doubt the biggest threat. I’d rather fly the “glider” than depend on the ss firewall saving my butt.

Could not agree more!
 
How about some discussion on putting out the fire. At the first sign of engine fire, turn off the dang fuel valve.

Absolutely.

That said, building in a fire transfer mechanism can easily result in loss of control well before a shutdown is effective. Again consider the Dallman accident. The survivor reported light smoke on downwind, and the pilot "secured the master switch" and turned base. Yet the cabin was full of thick black smoke by the time they turned final, and open flame at or just after touchdown.

Point is, good pilot skills may not successfully compensate for bad builder choices.
 
D Horton - Thank you

Dan - Thank you for scaring the **** out of me.

Seriously, I never thought about the heat transfer through the firewall from an engine compartment fire. Now that I'm building an 8, I promise nothing on the interior firewall.
 
Heat Transfer

Dan,
What kind of temperatures did you measure with the fiberfrax sandwich in place?
 
DanH,

Any chances you could ID the insulation pictured from your experience? I’ll start removing it if it’s nasty stuff. Probably won’t insulate the firewall side though.
 

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Yep, that looks like foam rubber. Maybe grab a small chunk and hit it with a lighter and see what it does. The stuff my Rocket builder used was wildly flamable. Not only did it readily burst into flame, but the choking, black smoke it produced would have been debilitating in flight.
 
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