firewall insulation

[Mike D]

Couple of questions:

With the 1/4" insulation on the engine side, did you have issues mounting the accessories on the firewall?

Did you use spacers for mounting or did you just crush the insulation in that area?

How did you mount the insulation/stainless to the firewall?

What thickness of stainless did you use?

Any concern with the bolts transferring heat to the inside?

How about concerns with the interior carpet touching the firewall?

Thanks for the help!!!!!

My family will be flying in this aircraft, so it has to be done right. At least in the areas that concern safety. And the firewall is one of the big ones.

[RVbySDI]

Originally Posted by Mike D

Couple of questions:

With the 1/4" insulation on the engine side, did you have issues mounting the accessories on the firewall? No issues at all.

Did you use spacers for mounting or did you just crush the insulation in that area? I did not use spacers. I just crushed the insulation between the mounting object and the firewall.

How did you mount the insulation/stainless to the firewall? See post above and read through the threads mentioned below.

What thickness of stainless did you use? I do not know the exact thickness of the stainless foil. It was already attached to the material.

Any concern with the bolts transferring heat to the inside? I feel the material used will give me a larger window of time to deal with getting on the ground than I would have without this insulation. The bolts may transfer heat but they were all there already so I felt using them to my advantage instead of drilling additional holes and using additional fasteners was a good compromise.

How about concerns with the interior carpet touching the firewall? I have not directly considered the carpet issue. My carpet is not directly touching the firewall. It may be in close proximity to it and that may cause an issue but I did not address keeping the carpet from burning or off-gassing if a fire starts in the engine compartment. To tell you the truth, I am more concerned about those fuel lines running in the cockpit between my feet and through the firewall than I am the carpet off-gassing.

Thanks for the help!!!!!

My family will be flying in this aircraft, so it has to be done right. At least in the areas that concern safety. And the firewall is one of the big ones.

See my answers to your questions above.

This is a picture that was originally posted on post #4 in this thread:
http://www.vansairforce.com/communit...ad.php?t=97778
The picture no longer shows up on that thread though.


Here is a link to the material I used:
http://www.aircraftspruce.com/catalo...rewall2000.php
That material is discussed in some detail on this thread in posts #55-#59. This particular thread has quite a bit of detailed information from Dan Horton's testing. It is a good one:
http://www.vansairforce.com/communit...t=47587&page=6

Do a search on firewall insulation and you will find a great deal more info. To get you started, in addition to the threads mentioned above, here are a couple of more threads discussing firewall insulation that you might find interesting:
http://www.vansairforce.com/communit...hlight=RVbySDIpost #9

http://www.vansairforce.com/communit...ad.php?t=37012

[Mike D]

Thanks Dan and Steve. This is great info.

As for Nomex, just talked with a safety engineer who related that Nomex will not burn, but will decentegrate and fall off. This goes to the point of not adding fuel to the fire.

I understand the point of having the insulation on the engine side. My reluctance to going this way is the everyday maintaince, where a clean firewall surface makes life easier. I worry about the insulation soaking up oil and becoming ineffective. Anyone else have this concern? Any data to say one way or the other? Leave that dip stick loose just once and all this insulation has to be redone.

I really appreciate Dan's experiments. It is one thing t read a spec sheet, but quite another to have actually run the tests.

Just checked several certified planes. Guess what! No insulation at all. Either side. I'm sure the newer ones have something.
So for this reason, I love experimentals!

[RVbySDI]

Originally Posted by Mike D

Thanks Dan and Steve. This is great info.

As for Nomex, just talked with a safety engineer who related that Nomex will not burn, but will decentegrate and fall off. This goes to the point of not adding fuel to the fire.

I understand the point of having the insulation on the engine side. My reluctance to going this way is the everyday maintaince, where a clean firewall surface makes life easier. I worry about the insulation soaking up oil and becoming ineffective. Anyone else have this concern? Any data to say one way or the other? Leave that dip stick loose just once and all this insulation has to be redone.

I really appreciate Dan's experiments. It is one thing t read a spec sheet, but quite another to have actually run the tests.

Just checked several certified planes. Guess what! No insulation at all. Either side. I'm sure the newer ones have something.
So for this reason, I love experimentals!

Been flying for 4 years now with my insulation. Not a drop of oil anywhere. Don't think of your plane like you do those 40 year old rental planes you learned to fly in. Believe me, once you complete your build you are going to treat it far differently than those rentals. Think of it as your new baby. Take care of it and there will be no worries. Besides, if you do go with a material that has a foil surface front and back any contamination will have to make it through the foil before it gets to the fibrous material. I think this is a worry that will not come to fruition.

One point I want to emphasize because of my experience, the installation of the insulation material will work much better if you install it BEFORE you hang the engine. Trust me I have the scars to prove it!

[DanH]

Originally Posted by Mike D

As for Nomex, just talked with a safety engineer who related that Nomex will not burn, but will decentegrate and fall off. This goes to the point of not adding fuel to the fire.

Sheesh.

Not surprisingly, DuPont kinda tippytoes around the details. From the DuPont "Technical Guide for NOMEX Brand Fiber":

Flammability, Smoke and Off-Gas Generation

The Limiting Oxygen Index (LOI) of NOMEX® is
approximately 28. Thus, when exposed to flame at room
temperature in a normal air environment, NOMEX® will
not continue to burn when the flame is removed. At
temperatures above approximately 800°F (427°C),
NOMEX® carbonizes and forms a tough char.
The composition and quantity of off-gases varies widely
depending on rate of heating, presence of oxygen and
other factors. Burning NOMEX® brand fiber produces
combustion products similar to those of wood, wool,
cotton, polyester and acrylic. At combustion
temperatures, NOMEX® releases carbon dioxide and
carbon monoxide; and, sometimes traces of hydrogen
cyanide and nitrogen oxides are detected. Under less
stringent heating conditions, NOMEX® degrades very
slowly, releasing small quantities of a wide variety of
organic compounds. These may include carbon dioxide,
acetone, acetamide, acetaldehyde, benzene, butane,
toluene and many other compounds in trace amounts
depending on exposure conditions.

And from the MSDS:

NOMEX® fiber is inherently flame resistant, but can be ignited.
Burning normally stops when the ignition source is removed.

Note the "when the flame is removed" and "when the ignition source is removed". Here's the point to remember: You can't remove a red hot firewall.

Interesting master's thesis research at the link below. The researcher identifies the ignition temperature of Nomex as 1600F.

http://archives.njit.edu/vol01/etd/1...td1977-008.pdf

CONCLUSION
The gaseous products generated by flaming combustion of
Kynol and Nomex fibers under the same conditions (temperature
³00-700°C, in air) were quantitatively analyzed by infrared
spectrophotometry, gas chromatograph, mass spectrometer and
a colorimetric tube method. These four techniques were
chosen to examine the wide range of volatile and condensable
products because of the differences in capabilities, limitations,
and sensitivities of each method used. Combustion
of Kynol and Nomex produces copious amounts of smoke and
toxic gases which could cause asphyxiation to people trapped
in the area of a fire.

[Mike D]

Thanks Dan for the great information.

I typically don't trust student work. This thesis is no exception. The conclusion is not supported in the body. What I can take away, is that Nomex flashes at 1600 deg. And does not put off smoke or fumes that would cause an issue in the cockpit of an RV. If I were stuck in a test tube, that would be a different story.

Dan and Steve, I do agree the engine side is the superior placement. But it is not the only placement.

A gasoline flame is around 1650 deg At its hottest point.
Stainless steel melts at 2750 deg.
Aluminum melts at 1220 deg
Nomex is good to 700 deg and flashes at 1600 deg.
Ceramic insulation is good to 2300 deg.

So my theory is the SS firewall will hold off the fire.
The insulation is there only to keep my feet from being cooked by radiant heat.
The Nomex is there only to encapsulate the ceramic insulation so I don't get cancer.

If the firewall gets beyond 1200 deg (well below the Nomex and insulation critical temps), I will have big issues keeping the plane in one piece. The firewall and engine may (unlikely) depart the plane.

I think the biggest threat in an RV engine fire is the issue of flames coming through the NACA vents. (This does actually happen)

So, my next step is to buy some material and do a test. This will take awhile but I will report back.

[SMO]

Don't forget the floor area. I have heard of one RV with an engine fire where the floor under the pilot's feet literally melted away.

I have stainless foil wrapped ceramic fiber on the floor as well as on the engine side of the firewall. I believe the stainless foil is 3 thou, comes in a 2' wide roll. I used stainless foil tape to hold it together. This stuff is all available from McMaster Carr.

[DanH]

Originally Posted by Mike D

I typically don't trust student work.

I'm just a student, so you better do your own test. Set up a burner with enough heat flux to hold (per spec) a 5" x 5" area of stainless panel at 2000F. It's easy to calibrate with some pure copper sheet. Now attached a section of the test material to the side opposite the burner. I clamped most samples at the edges so fasteners would not serve as a heat path and skew the results. When it's ready, fire up the burner, with stopwatch and camera in hand. Here's a tip; stand upwind, and make sure the test rig is not too close to your shop.

This is Nomex felt, just before ignition of the main body.

If the firewall gets beyond 1200 deg (well below the Nomex and insulation critical temps), I will have big issues keeping the plane in one piece. The firewall and engine may (unlikely) depart the plane.

The anecdotal and documented fires all show the same pattern. Fire follows airflow; the hot spots are the lower firewall, and the floor aft of the cowl exit. I'm not aware of any single engine GA fire involving engine separation, so yes, it appears unlikely.

In any case, installing a stainless foil/ceramic insulation combination on the hot side protects the structure. I'll bet you don't wear your raincoat inside your clothing.

My reluctance to going this way is the everyday maintaince, where a clean firewall surface makes life easier. I worry about the insulation soaking up oil and becoming ineffective. Anyone else have this concern?

Stainless foil has held up well. It looks like this after three years of maintenance and experiments, and I've made no special effort to be gentle. The insulation can't soak up anything, as the perimeter is sealed with 3M Fire Barrier 2000 intumescent silicone.

[flyingriki]

Originally Posted by flyingriki

I have a two foot square of Firewall 2000 ceramic blanket I never used I'd love to sell....
http://www.aircraftspruce.com/catalo...rewall2000.php

Just a bump and to be clear. 2x2 square of this material that has all the components needed for soon applications. .....

[tgmillso]

Originally Posted by DanH

IF you really need a fireproof fabric, Bill's suggestion regarding 3M Nextel is a good one. It is sold with and without sizing, the lubricant added to the fabric for weaving.

Hey Dan, Bill, or anyone else,
Do you know where this 3M Nextel 312 can be sourced? Although you can find a good bit of information on it, the product seems hard to come by. I just thought it would be nice to have something that doesn't offgas deadly chem.
Also, another builder in Tas sent me a link to the Fiberfrax manufacturer in Australia. It appears they offer another product called Insulfrax (formerly know as Carbowool) also rated to more than 2000degF. It seems the upside to Insulfrax is that it has "enhanced in-vitro solubility" to meet European requirements, which I presume means it is less likely to cause mesothelioma than Fiberfrax if you breath it in, because your body will dissolve it. Anyone know anything further on this Insulfrax?
Cheers,
Tom.