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Fiberfrax on Firewall Question...

idleup

Well Known Member
I was considering putting fiberfrax on the engine side of the firewall with a thin layer of steel over it to protect and keep it in place as was recommended in some other threads. I had read several people say they wish they did this before mounting items on the firewall (such as battery tray, contactors, etc.). They also talked about creating quarter inch stand-off's for these items. My question is how would mounting these items on 1/4" stand-offs effect the integrity of their mounting? I am concerned that it would compromise the security of them. For instance, the battery tray is currently flush on the firewall and bolted in three locations, if each of those bolts had a quarter inch stand off behind them it would not seem as stable.

Could you guys please give me your opinion on this? it would be nice to hear from someone who has actually used the stuff or researched it as well. Thanks.

Matt
 
It is true that more fiberfrax thickness means greater insulation value. However, two layers of 1/8" fiberfrax (1/4" total) may be overkill.

Remember, this is a system. Performance is a function of both the stainless foil and the fiberfrax. They each have a different purpose, and neither would do a great job alone. The foil is a reflector and a hot gas seal. Think of it as the layer which turns back most of the energy before it can ever reach the fiberfrax. The fiberfrax itself merely reduces the quantity of heat transferred from the stainless foil to the firewall structure.

Point is, the stainless foil does the heavy lifting. I doubt doubled fiberfrax thickness is twice as good

Standoffs and fasteners: One interesting test observation was the effect of fasteners. They create a small point hot spot on the cabin side, transferring heat by conduction and bypassing the insulation air space. A fastener assembly with more cross-section area (like a button standoff) would conduct more heat.

The point heat source effect of fasteners is why I don't think it wise to "double insulate", i.e. place fiberfrax/foil on the engine side and believe it is then safe to place some stupid plastic, rubber, or polyester fiber insulation choice on the cabin side of the firewall. If the firewall is bare (nothing, not even paint), the hot fastener head merely radiates a very small quantity of heat into the cabin. If that same fastener head is allowed physical contact with a flammable material, it can ignite it via conduction.

So, a standoff is unlikely to create a practical problem if the backside is bare, but will make things worse if the backside is in contact with something dumb. Take this thought a little further. A builder might think that nice thick insulation on engine side (requiring standoffs) would allow him to safely place sound insulation on the cabin side.....and that's not necessarily true.

§ 23.1191 Firewalls.

(f) Compliance with the criteria for fireproof materials or components must be shown as follows:

(1) The flame to which the materials or components are subjected must be 2,000 ±150 °F.

(2) Sheet materials approximately 10 inches square must be subjected to the flame from a suitable burner.

(3) The flame must be large enough to maintain the required test temperature over an area approximately five inches square.

(g) Firewall materials and fittings must resist flame penetration for at least 15 minutes.

§ 23.1182 Nacelle areas behind firewalls.

Components, lines, and fittings, except those subject to the provisions of §23.1351(e), located behind the engine-compartment firewall must be constructed of such materials and located at such distances from the firewall that they will not suffer damage sufficient to endanger the airplane if a portion of the engine side of the firewall is subjected to a flame temperature of not less than 2000 °F for 15 minutes.
 
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Dan;
Like Matt, I'm planning the same firewall insulation and I'm wondering the same problem.
In your consideration, if I understand well, the .125" fiberfrax plus stainless foil should be enough like heat insulation.

In this case I don't need to make stand off for battey, rele et... but would be nice if I bolt all together (ex battery rack + stainless foil + 1/8 fiberfrax + firewall) like sandwich, so I'll be able to avoid further fastener or glue, but I'll need just some sealant (like 3M fire barrier 2000) around holes and firewall edges?

If not, could you show us some pic where we can see how to keep this insulation to the firewall?

Thanks a lot for your time
 
Writing for the purpose of providing a data point. I have the fiberfrax with stainless steel sheeting on one side. I have no glues or mechanical fasteners holding it onto the firewall except for the existing bolts or screws that were already in place for the various components bolted to the firewall. There is some aluminum tape on all the edges and some insulation tape around the sensor wires that penetrate the firewall but they are not really holding the insulation onto the firewall as much as they are just cleaning up the edges. The battery box bolts, the brake master cylinder, the oil and fuel line manifolds, the relays, etc. etc. are all bolted with the insulation sandwiched between the component and the firewall. The one exception to this sandwiched insulation method is with the engine mount bolts. These have direct connection to the firewall and frame with no insulation between the engine mount and the firewall. This works great.

Here is a pic during installation of the insulation. I would suggest installing the insulation prior to mounting anything to the firewall. One could die of a thousand cuts if one has to install it with the components already in place. Ok, go ahead, ask me how I know. :eek:

 
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Here is a pic during installation of the insulation. I would suggest installing the insulation prior to mounting anything to the firewall. One could die of a thousand cuts if one has to install it with the components already in place. Ok, go ahead, ask me how I know. :eek:


Yep. I used .003" SS foil and the 1/4" insulation from mcmaster, with the engine mounted, but pretty much everyhting else removed. It, bluntly, sucked, but I got it done. If you have a chance to do it early in the build, it'll be easier and look better. I don't have insulation outside the frame of the engine mount, only the foil and the fire-seal silicone stuff (firestop 2000, or whatever it is that spruce sells). If you did before mount goes on, you could get the fiber insulation everywhere pretty easily.

I used standoffs for the battery box (3x #10's) and fuel flow transducer (4x #10's on an angle) and everything is pretty solid feeling. If you were really nervous I think you could use large diameter teflon or delrin standoffs to spread the load more without being overly heavy (they might melt in a big fire, but a saggy battery box doesn't matter at that point).

DO remember to mount EVERYTHING you want mounted on the firewall before permanently installing the insulation, I don't think it'd be possible to cut a clean hole after that. I glued the standoff's to firewall with RTV and a cleco, and that was more than adequate to allow them to live under the insulation, then later get a bolt in them. I closed all the seams in the stainless with aluminum foil/speed tape, looks good and should seal. It might come off in small areas in a big time fire, but most seams are overlapped, so I don't think the insulation would be greatly compromised.

Buy some good mechanics gloves.
 
DO remember to mount EVERYTHING you want mounted on the firewall before permanently installing the insulation, I don't think it'd be possible to cut a clean hole after that.


I was wondering if you could do this. Thanks for mentioning it.
 
I was wondering if you could do this. Thanks for mentioning it.
Indeed, this is what I did. I Installed the insulation after everything was mounted on the firewall. I have the scars to prove it! Working with this stainless steal foil was like sticking my hand into a hole in the lid of a box of rattle snakes. There were many times when I was unable to see where my hand was in relation to the foil. Once contact was made Freddie Kruger's "knife" fingers could not have inflicted more damage!

I would suggest you drill all holes for cables, wires, bolts, screws or any other protrusions you will need in the firewall prior to installation. "Dry mount" everything on the firewall to make sure everything will work properly. Then remove all of those things and install the insulation, cutting out for all the needed penetrations. Then methodically bolt everything in place with the insulation in its proper place. I am sure there will be no way to completely avoid the sharp edges of the foil but I do believe this method will be much better than what I had to endure.
 
....and the....??

Guys;
Very interesting your experience about skin cuts I'll follow your advice :) but

I've some more question

Ground in the engine side:
the battery, engine case and other few things needs some metal contact directly on firewall so ground forest inside, I'm wondering if just the pass thru bolt should be enough to make a solid ground, or you left some part off insulation, how did you solve this question?

Fuel;
For the fuel line pass thru, did you fit the usual AN833 bulkhead sandwiching the insulation? or.... I ask so because I'm pretty fearful about fuel :confused:

Alu tape;
The edge of fiberfrax and steel coil, ends really where the firewall make the radius flange .... or you left 1" or 1/2" or... to allow the tape grip?

Control cables;
I've eyeball in aluminum TTP but, before decide to fit this kind of insulation, I tough to switch to steel one, someone said "its firewall!!!", so now that kind of cable pass is designed for thin bulkhead.... You?

Any advice or suggestion will be appreciated
Thanks
 
Ground in the engine side:
the battery, engine case and other few things needs some metal contact directly on firewall so ground forest inside, I'm wondering if just the pass thru bolt should be enough to make a solid ground, or you left some part off insulation, how did you solve this question?

Cut a 19mm hole in the foil and insulation. Drill a hole for the brass ground block stud. It has two nuts. The first clamps the block to the firewall and the second clamps the engine ground cable.

For the fuel line pass thru, did you fit the usual AN833 bulkhead sandwiching the insulation?

Again, just cut an appropriate clearance hole in the foil and insulation. Caulk to seal the edge of the foil. See below.

Alu tape; The edge of fiberfrax and steel coil, ends really where the firewall make the radius flange .... or you left 1" or 1/2" or... to allow the tape grip?

No tape at the perimeter. First caulk the firewall flange radius (to close the many little holes) with a smooth filet of FireBarrier 2000 before installing any insulation. Fit and trim the fiberfrax and foil so the edges are against the firewall flange. Fasten with SS pop rivets. Now run another bead of FireBarrier to seal the edge of the foil to the flange.

Aluminum tape will melt instantly in a fire, so tape is not used to hold anything. Tape is only used to seal foil overlaps which would be fireproof even without the tape.

Control cables;I've eyeball in aluminum TTP but, before decide to fit this kind of insulation, I tough to switch to steel one, someone said "its firewall!!!", so now that kind of cable pass is designed for thin bulkhead.... You?

So trim an opening in the foil and caulk it smooth after installing the eyeball. Or make up simple steel tube pass-through fittings for just a few centesimi. They can protrude through a hole in the foil or sandwich over the foil.

BTW, cutting a hole in stainless foil is easy. Just use the corner of a razor blade to make a series of connecting punctures...poke, poke, poke.
 
BTW, cutting a hole in stainless foil is easy. Just use the corner of a razor blade to make a series of connecting punctures...poke, poke, poke.

Yep, recognize that ALL your foil edges will be covered in firestop caulk or tape, and really any method of cutting is fine, you'll never see the edge once you're done.

For the pass throughs, I did the tube and sheet with firesleeve, but made them myself. Here is a picture before the foil went on:

IMG_20130421_151654_493.jpg


The white insulation is just held up with a bit of RTV at this point, eventually the firesleeve/firestop caulk and the various items mounted will hold the foil on, which will support the insulation.

And here's an "after" picture:

IMG_20130508_184231_153.jpg


I'll install hose clamps and more firestop to seal everything once I know I'm done pulling wires. I have lots of small passthroughs, rather than a couple large ones, just because I was working with existing holes. If you were building a new airplane, I'd recommend two large (1", maybe more) ones.

You might be able to see in the second picture that I slid the firsleeve over the stainless tube and used a bit of firestop to bond the end of the firesleeve to the foil. This seals it, but also turned out to be a really good "mount" for the foil, helping to stabilize it.

I'm considering making up a batch of pass-throughs for my hangar neighbor who is building a -9A. If anyone else wants some, let me know what size we can come up with a price, I guarantee they'll be cheaper than the ones spruce has (which are absurd, at $45 a pop).
 
I'm considering making up a batch of pass-throughs for my hangar neighbor who is building a -9A. If anyone else wants some, let me know what size we can come up with a price, I guarantee they'll be cheaper than the ones spruce has (which are absurd, at $45 a pop).

I would buy two or three. And am ready for them pretty soon.
 
Count me in on the pass-troughs as well .. I have no holes yet - so maybe a few in 1" and in 1/2" would do ... What material are they made off ? looks like 4130 tube welded to a plate .. which you then rivet on with Monel rivets ?? What is a good source for the insulation material ?
 
Count me in on the pass-troughs as well .. I have no holes yet - so maybe a few in 1" and in 1/2" would do ... What material are they made off ? looks like 4130 tube welded to a plate .. which you then rivet on with Monel rivets ?? What is a good source for the insulation material ?

I used 304 stainless, .032" thick and #8 screws to do the passthroughs, but rivets would obviously work just as well.

The insulation is mcmaster part # 93315K51 (1/4" ceramic insulation 2'x20') the foil is 3254K16 (.002" 321 stainless 20"x10' roll). Mcmaster also sells aluminum standoffs (ex: 92510A642 for a spacer with a clearance hole for a 3/16 screw, 1/4" thick, 3/8" OD).

I've got plenty of insulation and foil left (more than half of each), if someone wants to buy it off me, though mcmaster ships it so much cheaper than I can that it may not make sense....maybe for someone local?
 
The insulation is mcmaster part # 93315K51 (1/4" ceramic insulation 2'x20')?

Hmmm...a low density wool.

Fiberfrax is a Unifrax trade name covering a whole range of ceramic insulation products. Among homebuilders the word means Fiberfrax 970 felt (the manufacturer calls it "paper"). I think it was Rutan who introduced it to us.

http://www.fiberfrax.com/files/Fiberfrax-Papers.pdf

It is a dense felt (about 10 lbs per cubic foot) held together with an organic binder. It forms a nice firm sheet, easy to trim to exact dimensions and smoothly cover with metal foil or fiberglass fabric.

The organic binder (glue) makes it more durable than a wool blanket product which is simply tangled long fiber. The durability issue is perhaps important given that firewalls vibrate.

Spruce, Wicks, etc all carry 970.
 
It's pretty well secured, but if it doesn't hold up, (the only failure mode I could see is it pilling up on the bottom) it won't be that bad to start over and try something else.
 
Inside FW treatment

I've been reading up on all the old threads about FWF insulation and sound dampening... I've got foil and fiberglass on order with McMaster. But just curious, is the general guidance to leave the inside surface of your firewall completely bare? No paint, no insulation?

Since this SS and fiberglass mat will buy extra time to protect the pilot if a FWF fire ensues, you don't want anything inside the cockpit smoldering and chocking you as you make an emergency landing. So I'm thinking I need to break out the paint stripper and remove the paint in this area, right?
 
Thicker SS Option No Interior Firewall Paint

I used .005 SS Shim Stock, 1/8" FiberFrax, 3M Barrier 2000+. No wrinkled tinfoil look like the thinner stuff but some oil canning is to be expected around the areas where you attach items over it but still easy to work with, gloves still a must. Also a hydraulic punch works great for making nice clean round holes. Ordered everything from McMaster-Carr.
All steel or stainless purchased or custom made fittings used for any pass through items. No painted surfaces on the cockpit side.

https://lh3.googleusercontent.com/R...GJQD81wdoO90saoV1Pbr1MnQCBg35eGM=w800-h450-no

https://lh3.googleusercontent.com/7...L-2ChtwrEGq8MTDIDYG3bn233ujPs85M=w450-h800-no

https://lh3.googleusercontent.com/x...EK1kuaY-fx9d_6PEfp9zWuMKVmIsqnHg=w800-h450-no

https://lh3.googleusercontent.com/B...1Z-paZaB1csLKGe7ZZkWzxFsRHsbtgYk=w800-h450-no
 
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Broken Web Links

[/QUOTE]

Ed,
Your web links don't work for me. Are you using the Chrome browser?? I'm using Firefox with uBlock Origin pop up blocker.

I tried using MS Edge. It asked me to sign into my Google account, which I did. Still no joy on those links.

Charlie
 
Sorry about the link but it should work now. Using Google account and Chrome for a browser

I used .005 SS Shim Stock, 1/8" FiberFrax, 3M Barrier 2000+. No wrinkled tinfoil look like the thinner stuff but some oil canning is to be expected around the areas where you attach items over it but still easy to work with, gloves still a must. Also a hydraulic punch works great for making nice clean round holes. Ordered everything from McMaster-Carr.
All steel or stainless purchased or custom made fittings used for any pass through items. No painted surfaces on the cockpit side.

https://lh3.googleusercontent.com/R...GJQD81wdoO90saoV1Pbr1MnQCBg35eGM=w800-h450-no

https://lh3.googleusercontent.com/7...L-2ChtwrEGq8MTDIDYG3bn233ujPs85M=w450-h800-no

https://lh3.googleusercontent.com/x...EK1kuaY-fx9d_6PEfp9zWuMKVmIsqnHg=w800-h450-no

https://lh3.googleusercontent.com/B...1Z-paZaB1csLKGe7ZZkWzxFsRHsbtgYk=w800-h450-no
 
forward floor

It seems to me that the goal of mitigating fire penetration should be on the forward floor rather than the firewall. If the cabin side of the firewall is free of flammable sound deadening material and unpainted, is not the forward aluminum floor the greater risk in the event of a significant firewall forward fire event? I recall one or more posts suggesting cladding the exterior of the first 18 inches or so of the floor with thin stainless sheet to prevent fire penetration into the foot well. Easier to do than cover the stainless firewall, and perhaps more benefit.
Thoughts?
Bill
 
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