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  #1  
Old 11-04-2017, 11:43 AM
sritchie sritchie is offline
 
Join Date: Jun 2015
Location: Boulder, CO
Posts: 96
Default Ti and Fiberfrax Firewall Fireproofing Guide

Hey all,

I'm just about done fireproofing my firewall with titanium foil and fiberfrax -
Dave Paule suggested this method, and it turned out so well that I thought I'd document the process for y'all. Let me know if you'd like more detailed information!

Here's what the final firewall looks like:


The titanium doesn't crinkle at all, and is great to work with. This method is more tedious than the stainless foil method, but the results are worth it.

Bill of Materials:
You MIGHT be able to get by with 11' or so of foil by laying things out just right. Don't forget the firewall recess. I had to order a bit extra.

The Process
First, decide where you want everything on your firewall to go, add holes and nutplates, yada yada yada.

Then! Take it all off. Cut a big piece of cardboard so it fits onto the firewall inside the flanges. Do NOT cut out holes for anything other than the firewall recess in the center! Just create the big outline.

Next, use this template to lay out strips of fiberfrax. I managed to cover the firewall with two vertical strips of fiberfrax, side by side. I had no overlap between the two pieces of frax... I left a bit of overlap on the cardboard, then once I test-fitted the pieces against the firewall did the final cut to remove all overlap.

Then, lay out the Titanium foil on top of the fiberfrax. I used three horizontal strips, and cut the center strip to have roughly 1" of overlap with the top and bottom pieces. The Ti foil doesn't feel terribly sharp, but it WILL slice you badly if you let it!

Shears work just fine for cutting the Ti. You can use an exacto knife to cut out the firewall recess in the center. I'd recommend cutting out a square a little smaller, as you can use the dremel later to trim it back further.

Gluing on the Frax

First, lay your pieces of fiberfrax on the firewall to make sure they fit, mark any overlap between the two pieces with a sharpie and cut it off.

Next you'll want to clean your firewall off with some acetone.

Once it's dry, use a caulk gun with your Firebarrier 2000+ to lay out drizzles of firebarrier on the firewall. Stick one piece of fiberfrax on! It shouldn't move, it weighs nothing. Drizzle again on the other side and stick it down.

Next, you'll want to use an exacto knife to trim out all the holes for screws, nutplates, etc, anything that will penetrate. To find nutplate holes, get a partner to sit inside the cockpit and push a nail through the fiberfrax while you provide back pressure. Then, come at it from the firewall side with the exacto knife. For bigger holes you can run the blade around the edge of the hole and cut things nicely. For smaller nutplate holes you'll have to tear a little. Use your air hose to blow out any excess.

This is important - completely remove the fiberfrax from around the flanges of the oil cooler mount! I clecoed it on and used an exacto to trace around the edges, then took off the mount and completely removed the frax underneath and around the flanges. You could glue a piece inside here if you wanted; just make sure it doesn't sit under the flanges.

Adding the Ti Foil
Now that the frax is up and holes are all cleared out it's time to add the foil, one strip at a time. I started from the bottom.

Lay down some more firebarrier, this time on the Ti foil piece so you don't tear the frax dragging the caulk gun all over it. (Orient it so that the ends want to curl TOWARD the firewall so they don't lift up immediately!)

Place the Ti foil on the firewall, squish it down onto the frax and use some tape on the bottom edges to make sure it's held down. Run a strip of 3m aluminum tape along the TOP edge, taping the Ti foil directly to the fiberfrax.

Before you do the next strip you'll want to attach everything to the firewall that sits on top of this piece, including the bottom rivets of the oil cooler mount. Do that first.

Cleco the oil cooler mount through the fiberfrax using the top rivet holes. Then, use a #30 drill to match drill through the bottom holes, cleco-ing as you go. Remove the mount and give each hole a twirl with a countersink bit and make sure the hole's clear, then cleco the mount back on for support.

Clearing out the holes

Okay, now it gets sort of tedious! You'll want a partner to sit inside the fuselage with a nail or pop rivet shank or something. One by one, have your partner push the nail through various nutplate holes or larger holes to create a dimple on the front side while you provide back pressure. Mark the dimpled spot with sharpie.

Once you've marked all holes, take the nail from your partner and use a hammer to whack holes in the Ti foil at each sharpie-marked dimple.

Then, push an exacto knife into each hole so you slice across the full hole. On larger holes, like the holes for your heater boxes, you can cut all the way across and remove a good amount of material. On nutplate holes you're just trying to define the hole.

Finally, get out your dremel tool with its cutting bit:


and start cutting away to the perimeter of the hole. With nutplate holes you can do a pretty good job with the tip of the cutter, then go in and clear out the very thin foil with the exacto knife, then go back for a final pass. The results look like this:


For larger holes, make sure to hold the cutter perpendicular to the edge so the dremel doesn't kick and tear the foil. It's not that fragile so you should be fine!!

Finally, secure the foil by bolting or screwing on any components that below the top inch of this stretch of foil. (That was only the EFII fuel regulator in my case.)

Next Foil Strips

Okay, time for the middle strip. Same drill as before. I recommend an inch of overlap, a strip of aluminum tape along the bottom to join the strip to the bottom strip, and another strip on top to secure this middle strip to the fiberfrax.

DON'T cut out the outline around the heater boxes. You'll want to bolt them through this fiberfrax and Ti sandwich.

Cleco the oil cooler mount on to the new, cleared out bottom holes, and match drill the top holes, clear them out with the countersink and cleco back on.

It's the same drill for the top strip as well! Bolt on firewall components as you go.

Last edited by sritchie : 11-04-2017 at 01:53 PM.
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  #2  
Old 11-04-2017, 11:44 AM
sritchie sritchie is offline
 
Join Date: Jun 2015
Location: Boulder, CO
Posts: 96
Default Continued...

Firewall Recess
As you can see, I'm not done with the recess Ti yet. I've cut out squares and rectangles of fiberfrax and glued them on with firebarrier. That worked great. My plan with the Ti is to cut out a square for the back - it'll be secured by the throttle, mixture and alt air cable passthroughs - and then for the sides and top, I plan on bending little almost-Z channels. I'll tuck the back end of the foil pieces under that back square, and aluminum tape the outside edge over the middle Ti foil strip. This should be really secure. I'll fill any gaps with firebarrier and call it a day!

Engine Mount Pads
It's important to mount the engine mount directly to the firewall, NOT through the sandwich.

After I mounted all the foil, I put the engine mount on for a test fit, then traced around the pads with a sharpie. I removed the mount and used the tip of the dremel cutting but to trace along the sharpie and cut out the various mount pad shapes. I put the engine mount on again for another test fit, marked what I'd missed, and repeated that a couple of times before the mount was fully clear of the sandwich.

Basically you're thinning out the Ti until you can use an exacto knife to cut through the very thin foil and frax to clear out that section.

Edges
I'll finish up the outer edges with a fillet of firebarrier over the edges of the Ti foil. I'm waiting to do that until I get my camloc flanges mounted and my engine mount installed. Once those are in, I'll tape off the edges and get a fillet down... and that will complete this process!

Pic of the completed firewall once again:

That's all I've got. Let me know if you find this helpful, or if I can clarify any details of the installation! Hopefully I'll never have to test out whether this thing actually does its job

Last edited by sritchie : 11-04-2017 at 01:51 PM.
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  #3  
Old 11-04-2017, 11:49 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Personal research.....
Can anyone that has done this on an airplane that has now been flying for a while, where the metalized tape was needed to seal joints in the metal overlay, comment on how that held up over time with exposure to engine compartment heat and (in particular) oil exposure (I.E. have you had an instance of a major oil leak and had it not effect the tape... if so please indicate the tape used).
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  #4  
Old 11-05-2017, 08:10 AM
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DanH DanH is offline
 
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Location: 08A
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Weight savings compared to SS foil? Just curious. Any savings is a plus.

Application notes:

Given fire exposure, the binder in the fiberfrax and some volatile components in the Firebarrier 2000 sealant will outgas. That gas needs an escape path. We want it to go into the engine compartment, where it is harmless.

So, before applying any fiberfrax, be sure the firewall is sealed at the perimeter flange, as well as around any openings, like under the mounting flanges of the heater boxes. No leak paths into the passenger compartment.

Fixating the fiberfrax to the firewall with a few beads of FB2000 is not a bad idea, and convenient for fabrication, but I'd keep it to a minimum, depending instead on mechanical fixation with SS pop rivets through foil, fiberfrax, and firewall. You simply can't depend on sealant to remain highly adhesive when hot.

Now, very important...the desired outgas path is provided by one of the foil overlaps. Those overlaps are sealed with aluminum tape in normal service. We want the tape to melt so the outgas can pass through the overlap, thus at least one section of overlap should be located in an area with a high likelihood of 1100F or more. The likely hot spot is down at the base of the firewall, so the surest bet is a vertical overlap seam right up the center. Horizontal overlaps higher on the firewall may not get hot enough. Is it critical? Maybe not, but the vertical overlap should make it predictable.
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Last edited by DanH : 11-05-2017 at 02:24 PM.
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  #5  
Old 11-05-2017, 10:40 AM
David Paule David Paule is online now
 
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The .005 titanium foil weighs about 1/2 ounce MORE than .002 stainless steel foil. But of course it's lighter than thicker stainless steel foils.

I suggested the titanium not for weight savings, but for ease of working it after reading a few stories about how the edges of the stainless steel would cut people's fingers. I bought some of the titanium foil and played with it and thought it was a reasonable alternative in that regard. Sam lives nearby and when I took a look, he showed me some of the cuts he had from the titanium foil, so it's not as benign as I had thought. Still, since it's about eight times stiffer in bending and 2.5 times the thickness, the titanium is probably more controlled and less sharp overall.

The extra bending stiffness gives a smoother look to the firewall, if that is important you you.

Dave
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  #6  
Old 11-05-2017, 12:37 PM
RVDan RVDan is offline
 
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Location: Frederick, MD
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Id be curious how Ti does under Dan Hs burner test. It autoignites at 2200 degrees f and powder or grindings ignite at 480 deg F. http://archpdfs.lps.org/Chemicals/Titanium%20metal.pdf

I have watched Ti burn in a machine shop where they didnt observe proper machining processes. Quite interesting and lots of heat. I do know some helicopters that have used Ti for firewalls and it does eventually tended to fatigue from vibration and start cracking.
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  #7  
Old 11-05-2017, 01:16 PM
David Paule David Paule is online now
 
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Default Sec. 23.1191 Firewalls.

Sec. 23.1191 — Firewalls.

....some sections omitted....

(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.

(h) The following materials may be used in firewalls or shrouds without being tested as required by this section:

(1) Stainless steel sheet, 0.015 inch thick.

(2) Mild steel sheet (coated with aluminum or otherwise protected against corrosion) 0.018 inch thick.

(3) Terne plate, 0.018 inch thick.

(4) Monel metal, 0.018 inch thick.

(5) Steel or copper base alloy firewall fittings.

(6) Titanium sheet, 0.016 inch thick.


===========

Not having Dan's pet dragon, I cut a strip of .005 titanium foil and attempted to ignite it using a MAPP fuel torch. I was unsuccessful. I concluded that as a protective layer for the fiberfrax, the .005 foil was satisfactory.



Please note that the stainless steel firewall is still in place on Sam's RV-10.

I'm using some .020 titanium for some firewall-related things on my RV-3B.

Dave

Last edited by David Paule : 11-05-2017 at 03:27 PM.
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  #8  
Old 11-05-2017, 03:18 PM
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SMO SMO is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
Personal research.....
Can anyone that has done this on an airplane that has now been flying for a while, where the metalized tape was needed to seal joints in the metal overlay, comment on how that held up over time with exposure to engine compartment heat and (in particular) oil exposure (I.E. have you had an instance of a major oil leak and had it not effect the tape... if so please indicate the tape used).
I have 185 hours on mine. I used stainless tape to seal up the stainless foil encasing ceramic fiber. I had a major oil exposure event at about the 60 hour mark - left the dipstick in the hangar - that resulted in hot oil everywhere including the firewall (quick turn around and land when I noticed oil seeping out the oil filler door on take off). The stainless tape is holding up fine.
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  #9  
Old 11-05-2017, 04:51 PM
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maniago maniago is offline
 
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Default eh?

So just as a lesson for us poor unwashed non-RV folks, why are you guys doing this exactly? Is it part of your build sequence? Do you not have firewalls as Dave Paule noted ie .015 SS? Or is this something above and beyond the book build?

For the M2 we put sound insulation on the back side of our SS firewall....and ok some annoying heat transfer in the summer months. But not for fireproofing.

Just curious. I learn a lot from you guys by asking the assumed stupid questions.
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Last edited by maniago : 11-05-2017 at 04:59 PM.
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  #10  
Old 11-05-2017, 05:03 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by maniago View Post
For the M2 we put sound insulation on the back side of our SS firewall....and ok some annoying heat transfer in the summer months. But not for fireproofing.
You installed fire transfer material.

Search "firewall insulation".
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