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firewall insulation

Mike D

Well Known Member
At the point of making the firewall insulation choice.
I have the Dan Horton tests and recommendation.

I plan on following the basic idea on material choice.
- should not catch on fire
- should not produce toxic fumes or smoke
- should meet the 2000 deg requirement

Seems fiberflax had an issue of out gassing when under high temp or fire.
This leaves me with the cerablanket. ( now known as superwool 607). Will get this from McMastercarr.

So the last two issues are how to cover the superwool and how to attach it to the firewall.

My idea is to use Nomex fabric and thread to sew covers for the superwool. This will not survive over 600 deg, but the superwool will. The only reason for the nomex is to contain the superwool fibers. Would not want them in my lungs.

So this leaves the attachment method. Thinking of using screws and nutserts. This way when the Nomex desintegrats the superwoll will still be attached to the firewall.

I know this is going to open a lot of debate, but does anyone see an issue with my idea?

Should the insulation be separate sections between the angle aluminum, or cover the whole firewall in one piece?
 
I know this is going to open a lot of debate, but does anyone see an issue with my idea?

No debate. Fact: Nomex burns rather well when placed against red hot stainless.

Here's a quote:

Fabrics woven of Nomex fiber have a low level of flammability and do not melt or flow at high temperatures. Above 700?F (370?C), they will degrade rapidly to a friable char.

So, Nomex looks like this when placed against the cabin side of a red hot firewall:

PA050005.JPG



Should the insulation be separate sections between the angle aluminum, or cover the whole firewall in one piece?

It should cover the whole firewall on the engine side.
 
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No debate. Fact: Nomex burns rather well when placed against red hot stainless.

Here's a quote:

Fabrics woven of Nomex? fiber have a low level of flammability and do not melt or flow at high temperatures. Above 700?F (370?C), they will degrade rapidly to a friable char.

So at the FAA standard 2000F we have:

2h5sg1y.jpg





It should cover the whole firewall on the engine side.

When it gets to that point and you are not on the ground, RUNNING away from the plane.. You are already dead...
 
Dan, is there a better way to cover the cerablanket?
My intention is to use the Nomex to encapsulate insulation. As long as the Nomex does not add fuel to the fire, put off toxic fumes, or smoke, it should be okay. Correct?
 
I cannot comment on the functionality of the system, but 3M's Nextel fiber is woven in to cloth and blankets. It is good to 2500F. You might investigate that. It is a premium ceramic material and might be expensive. Also, coatings that used in the weaving process might outgas as well. A supplier should be able to address such questions.

I worked on a project with 312 fiber to filter diesel particulates then heated them to burn off the carbon. It and variants are quite durable under high temperatures.

Google away . . .
 
I cannot get to any pics at this moment but I can try to get to some showing my insulation material I used on the engine side of the firewall tomorrow and post here. Dan has done a great deal of testing and knows of which he speaks! DO NOT INSULATE ON THE COCKPIT SIDE OF THE FIREWALL! I used an insulation that I purchased from McMasterCarr that has a ceramic fiber material rated to 2000 deg F sandwiched between stainless foil on both sides. It is on the engine side of the firewall and I used no additional fasteners other than what items were bolted to the firewall (i.e. brake master cylinder, battery box, etc.). I did not install the material underneath the motor mounts! There is a thread on this forum with pics of my install on here somewhere, probably on one of the threads Dan started when he did his tests. If I find it I will come back and post the link. Think long and hard about installing on the cockpit side!
 
I used an insulation that I purchased from McMasterCarr that has a ceramic fiber material rated to 2000 deg F sandwiched between stainless foil on both sides. It is on the engine side of the firewall and I used no additional fasteners other than what items were bolted to the firewall (i.e. brake master cylinder, battery box, etc.). I did not install the material underneath the motor mounts!

+1, I did exactly the same on my Rocket - not flying yet, final inspection tomorrow.
 
Which insulation from McMaster did you use? I am thinking the Ultra High Temperature roll, 1/4" x 24" x 20 feet.
 
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. They actually weave it, then burn off the sizing to remove it if you order unsized. Unsized Nextel doesn't even smoke when you apply a torch.

That said, applying even the best fire protection insulation to the cabin side of a firewall is inferior (in every respect) when compared to insulating the engine side of the firewall.

Here's what you get when you do it the right way. You're looking at the cabin side of a simulated Vans firewall; same aluminum angle and rivets (which melt at 1100F, BTW), same stainless material. The engine side is well insulated with a layer of ceramic felt and stainless foil. The same burner is operating on the other side, running at 2000F over 25 sq inches. This 5 minutes into a burn. The small black sheet is a radiant heat target positioned 6" from the back side of the "firewall". It simulates the soles of your shoes, which have just passed 200F. The small dark brown spot is an AN3 bolt, an experiment to look at the heat transfer capability of a fastener. As you can see, it makes a hot spot. We can expect any steel fitting to do the same, which is why it would be dumb to think insulation on the engine side makes adding bad insulation on the cabin side "safe". Note that the firewall structure, complete with its aluminum components, is entirely intact. It will remain so no matter how long the fire lasts.

5%20minutes%20small.jpg


Same setup, night shot, no flash. Sure do like that (relatively) cool, dark cabin side:

Night%20Shot%20Backside%20small.jpg


§ 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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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.
 
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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/community/showthread.php?t=97778
The picture no longer shows up on that thread though.
image.jpg


Here is a link to the material I used:
http://www.aircraftspruce.com/catalog/appages/firewall2000.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/community/showthread.php?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/community/showthread.php?t=62381&highlight=RVbySDIpost #9

http://www.vansairforce.com/community/showthread.php?t=37012
 
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. :eek: I'm sure the newer ones have something.
So for this reason, I love experimentals! :)
 
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. :eek: 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! :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/1970s/1977/njit-etd1977-008/njit-etd1977-008.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.
 
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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.
 
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.
 
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. Want to be inside a closed space with this?

PA050004.JPG


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 many 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.

Firewall.jpg
 
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3M Nextel Source and Insulfrax

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.
 
Hi Dan,
I've now worked out why you think 3M Nextel 312 is a bad "practical" choice for a firewall product. It's because for 1/16" cloth in a 30" width it is $140 per linear foot!!! Ouch. That really makes fiberfrax look cheap at $7.50 per foot for a 24" width of the same thickness. I guess that's the downside of using a product that normally spends it's time stopping asteroids from ramming into spacecraft (at least per the data sheet). The larger fiber diameter of Nextel and and lack of carcinogenic status was sure attractive compared to Fiberfrax, but it looks like I'm going to have to don the mask and hack into the Fiberfrax instead.
Tom.
 
+1 for Fibrefrax

Hi Tom,

Very happy with the Fibrefrax :

I installed the firewall doubler on my RV-10 using .016 stainless sheet and Fiberfrax.
Making the stainless box around the control cables was not difficult but stainless does not bend as easy as the materials we are used to working with.

The stainless/Fiberfrax sandwich used on the firewall and the tunnel ,along with the stainless heater boxes has resulted a very cool to touch tunnel and very little radiated heat at my feet.

My aircraft has a very effective A/C unit installed from Airflow-Systems and the low cabin heat from the firewall area was one of my goals.

I am very happy with how it looks and performs .

I used 1/8" Fiberfrax and Type 301 1/42b .016" Stainless Sheet. Thinner sheet would of been better,but it was all that was readily available to me at the time.

3M Fire Barrier 2000 was used to fill in any gaps.

The Eyeball fittings are available from Aircraft Spruce.

http://www.aircraftspruce.com/search/search.php?s=EYEBALL+FIREWALL+FITTING&x=0&y=0


Very happy with the smooth and maintenance free finish on the inside and out of the firewall.

I was inspired while I was building by Deems Davis (RV-10 ) and Dan H's though testing on his burn rig.

In-flight testing with my insulated firewall,showed that the hottest spots on the firewall are now the engine frame mounting bolts.
There is still an elevated temp area around the closed heat boxes so a diverted valve up stream of the heat boxes would help.

With two summers of North Australian flying,the cabin temps have been very comfy with the A/C consistently being able to have a 10 deg C drop at the vents over outside ambient temps. ( Happy wife = Happy life )

https://goo.gl/photos/Lo9W1kiobwgEUCr5A

The FLIR camera is an attachment to the iphone from,
http://www.flir.com.hk/flirone/content/?id=62910

Very useful for finding failed insulation points and confirming where the heat flows around an aircraft.

Thank you to all that post their collective knowledge on this site to pass on to the next builder.

I'll be visiting Oshkosh for the first time this year and hope to meet many of you that are on these forums.


https://photos.google.com/share/AF1...?key=bUo4WlQxc2x2d0w5RWRUSjJuRzJyTlp0UUxFVnN3

Cheers,
 
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What thickness of Fibrefrax are people using, 1/16 or 1/8? I have been searching but can't seem to find a reference.
 
Belly.

Hi Ashley, thanks for your comprehensive overview. My fiberfrax arrived in Tas yesterday, so I'll be at it shortly.
Bill. 1/16" seems to the the general norm for the belly fiberfrax thickness, then covering with 5 thou 16" wide titanium sheet (from Titanium Goat) or stainless steel, and as Ron said, 1/8" for the firewall, followed by a covering of 0.002" stainless foil. I'm a little hesitant about using titanium 5 thou sheet on the firewall even though the weights will be similar as titanium is almost exactly half the density, because if you need to add a hole through the firewall in the future it is easier to punch a hole through the 0.002" foil with successive pokes with a knife. Cutting 5 thou titanium in place could be a bit of a dog, unless someone else could offer up an alternate experience with this?

Tom.
 
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Bad web link

Hi Tom,

snipped
The Eyeball fittings are available from Aircraft Spruce.

http://www.aircraftspruce.com/catalo...ickkey=3026635

snipped

Ashley,
No joy on the web link you provided above. I found the two links below. First is a SS plate with a steel ball. See

http://www.aircraftspruce.com/catalog/appages/eyeballfw2.php?clickkey=268034

Less desirable from a fire protection stand point would be the units below, which have an aluminum ball. See

http://www.aircraftspruce.com/catalog/appages/eyeballfw1.php?clickkey=268034

Which did you use?

Charlie
 
....I'm a little hesitant about using titanium 5 thou sheet on the firewall even though the weights will be similar as titanium is almost exactly half the density, because if you need to add a hole through the firewall in the future it is easier to punch a hole through the 0.002" foil with successive pokes with a knife. Cutting 5 thou titanium in place could be a bit of a dog, unless someone else could offer up an alternate experience with this?....

You can drill a hole easily enough in the .005 Ti foil, but in my limited experience it's somewhat difficult to get it smooth and without a burr. Perhaps I just haven't found the secret sauce. I prefer using a Whitney Roper punch but that's limited to size and location.

I just tried using an X-Acto knife to puncture some .005 Ti foil and was not successful. Haven't tried a real knife with a sturdy blade, though.

I plan to use the .005 Ti foil on my firewall but will use .020 Ti for the belly, where it'll be the primary fire barrier since the aluminum floor won't work for that. According to the FAA, .016 is the minimum thickness for a titanium firewall. I'll have the Fiberfrax between the belly Ti and the belly aluminum floor.

Dave
 
Hi Dave,

Thanks for the feedback on the titanium drilling. With respect to the belly skin in mind that Dan Horton's testing has shown that 0.002" stainless foil backed with fiberfrax can successfully meet the 2000 degree flame requirement, so going to 20 thou is pretty significant overkill. The most important thing is the layer insulation before your airframe structure so that you don't simply transfer the heat from one layer of metal to the next (and then to your carpet/paint/feet etc). Take a look at this post for further details on a 0.005" belly skinning. I'm not far away from doing mine, and will use monel MK319-BS rivets in the middle (sealed with 3M Fire Barrier), and simple AN426 rivets around the perimeter where heat is less of an issue. This will allow me to keep everything flush and make cleaning the belly easier.
http://www.vansairforce.com/community/showthread.php?p=1063167

Tom.
 
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.

That's what I suspected, but it's good to see such a well written and informed conclussion.
 
Holes in .005 Titanium Foil

More about this... with the firewall insulation now covered with the Ti foil and all the through-holes in it, I've more experience. Remember, I'm using Grade 2. The stronger grades might act differently. They'll certainly cost more.

Holes are a real pain!

It's easy to drill holes to 1/4" with normal drills. No problem at all.

Unibits, I use Harbor Freight's version, tend to leave a burr. They form a partial cylinder, a shot one, around the hole. The second-best way I've found to remove those is with a coarse mill file. The best way is with a Dremel sanding drum, which does it quickly.

I tried Harbor Freight's 95547 punch set and it was terrible. It did work for some 1/2" holes with a lot of swearing and some burrs, but wasn't worth the trouble. I recommend against it. The smaller holes made by my Whitney Junior punch work fine, but that has a short throat depth and so can't put holes everywhere they are needed.

Dave
 
Holes in titanium

More about this... with the firewall insulation now covered with the Ti foil and all the through-holes in it, I've more experience. Remember, I'm using Grade 2. The stronger grades might act differently. They'll certainly cost more.

Holes are a real pain!

It's easy to drill holes to 1/4" with normal drills. No problem at all.

Unibits, I use Harbor Freight's version, tend to leave a burr. They form a partial cylinder, a shot one, around the hole. The second-best way I've found to remove those is with a coarse mill file. The best way is with a Dremel sanding drum, which does it quickly.

I tried Harbor Freight's 95547 punch set and it was terrible. It did work for some 1/2" holes with a lot of swearing and some burrs, but wasn't worth the trouble. I recommend against it. The smaller holes made by my Whitney Junior punch work fine, but that has a short throat depth and so can't put holes everywhere they are needed.

Dave

I used Fibrefrax covered with .005” Ti foil. I must have used a softer grade than you did. After some experimentation I found that a sharp 3/32 bit would easily drill a clean hole and it could be upsized with a 1/8” bit, but anything bigger would tend to grab the foil and twist it like a wet towel. Solution was to use a small cone shaped grinding stone in a dremel to enlarge holes to desired size. Didn’t leave much of a burr, but when it did a sanding disc or flap wheel easily cleaned it up. I used the firewall components for clamping everything in place but needed about 10 pop rivets in strategic locations. In those spots I ground the holes just big enough to accept the dimpled countersink of a #8 SS CS washer and used a sealed SS 1/8” universal head pop rivet.

Don Broussard
RV9 Rebuild in Progress
57 Pacer
 

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I used Fibrefrax covered with .005” Ti foil. I must have used a softer grade than you did. After some experimentation I found that a sharp 3/32 bit would easily drill a clean hole and it could be upsized with a 1/8” bit, but anything bigger would tend to grab the foil and twist it like a wet towel. Solution was to use a small cone shaped grinding stone in a dremel to enlarge holes to desired size. Didn’t leave much of a burr, but when it did a sanding disc or flap wheel easily cleaned it up. I used the firewall components for clamping everything in place but needed about 10 pop rivets in strategic locations. In those spots I ground the holes just big enough to accept the dimpled countersink of a #8 SS CS washer and used a sealed SS 1/8” universal head pop rivet.

Don Broussard
RV9 Rebuild in Progress
57 Pacer

Thanks for the info, Don! I have decided to add Ti to my firewall with the 1/8" fiberfax.
 
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