What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Firewall

Scott Hersha

Well Known Member
I’m building another RV6 from a used kit I recently purchased. I am working on firewall component installation on this nearly completed airframe and I have a couple questions relative to firewall fire protection. First, is this kit from Spruce what I should be looking for as far as materials go?

https://www.aircraftspruce.com/catalog/appages/firewall2000kit.php?clickkey=1032084

Second question….. when should this be applied? I’m assuming it would be after all the firewall mounted equipment is installed (cutting around those objects), but before the engine is mounted, but there may be a better sequence. If the materials listed above are not adequate, please let me know what you recommend.

Thanks
 
First, is this kit from Spruce what I should be looking for as far as materials go?

https://www.aircraftspruce.com/catalog/appages/firewall2000kit.php?clickkey=1032084

I ordered some of that stuff more than 20 years ago when working on fire resistance for a mid engine design. Read the tech sheet, then pull up an MSDS and look at the materials by weight groups...it's not what you may assume. It works by releasing lots of water when the key ingredient, alumina trihydrate, is heated. The actual percentage of insulation fibers is kinda low, and the trihydrate makes it heavy, 1.83 lbs per square foot, before adding in the weight of the stainless steel sheet glued to the version Spruce sells.

There are fancy ways to do everything, but the best bang for the buck continues to be ordinary fiberfrax under stainless foil. Do the overlap seam in the middle with the aluminum tape. It's a vent...which, BTW, would be even more necessary with the alumina trihydrate.

Second question….. when should this be applied? I’m assuming it would be after all the firewall mounted equipment is installed (cutting around those objects), but before the engine is mounted, but there may be a better sequence.

Almost everything can be bolted on over the insulation, with the obvious exception of the motor mount points.
 
Fiberfrax

I used Fiberfrax and Titanium foil (.005"). Drill all the mounting holes. Install nutplates. Blah, blah, blah. Cut the fiberfrax and foil so seams are vertical. Cut out the holes for the engine mount so it is flush to the firewall. Secure the barrier and apply foil twpe over seams. Install the engine mount and bolt the parts right over. I applied the firestop to each hole before installing bolts. Engine mount goes on bare but you can smear some around after. Drill some holes for large flange stainless pop rivets to hole the barrier around the perimeter but be careful of substructure.
 
I can get fiberfrax at Spruce in 1/8” thickness.

https://www.aircraftspruce.com/catalog/appages/fiberfrax.php?clickkey=6977

Is that thick enough? I found SS foil at Grainger for about $50 for .002” thick 24” X 10 feet.

https://www.grainger.com/category/raw-materials/stainless-steel/stainless-steel-foil-rolls

If these are the materials I should use, my question is, how does this stuff stick to each other and how does the blanket stick to the firewall? Do you just ‘glue it on’ with Fire Barrier 2000? I’ve seen pictures of the completed firewall application, but didn’t see how it was done.
 
Barrier

I can get fiberfrax at Spruce in 1/8” thickness.

https://www.aircraftspruce.com/catalog/appages/fiberfrax.php?clickkey=6977

Is that thick enough? I found SS foil at Grainger for about $50 for .002” thick 24” X 10 feet.

https://www.grainger.com/category/raw-materials/stainless-steel/stainless-steel-foil-rolls

If these are the materials I should use, my question is, how does this stuff stick to each other and how does the blanket stick to the firewall? Do you just ‘glue it on’ with Fire Barrier 2000? I’ve seen pictures of the completed firewall application, but didn’t see how it was done.

I didn't bond anything. Two sections of Fiberfrax vertically oriented covered by three pieces of 15" wide titanium foil also vertical. Once all the components are bolted and a few rivets installed, it's not moving. I may have put a dozen rivets around the periphery. The only place where fumes can pass is bolt holes. I put a small dab of Firestop on each hole before installing the component. Same for the rivets. I got the stainless rivets from McMaster. 1/8" with a large diameter flange. I have a ton left if you need some.
.002 is pretty thin foil. You may want to bump up a little thicker. I got the titanium foil from Lite Outdoors.
Some builders make a template from the firewall to cut the foil. Don't ivertink it. I just cut it to fit the outer edges then taped it in place and poked the holes wirh an awl. Repeat with the next section. I did three sections with 15" wide titanium, overlapped 1". Any overage was easiely cut away with scissors.
Some builders also attach a section on the belly. I didn't.
 
Last edited:
Start by making sure the perimeter of the firewall is sealed gas tight, using a light wipe of 3M Firebarrier 2000 silicone.

The fiberfrax and foil are attached using SS pop rivets and small stainless washers. No glue required, but if you prefer to use a few dabs of Firebarrier to tack the fiberfrax to the firewall, no problem. Tape it up there until the Firebarrier cures. The tape can stay if aluminum.

When the foil are fiberfrax are riveted, apply a filet of Firebarrier over the foil edges at the firewall perimeter, and at any openings. Definitely bury the edges of the foil, both for sealing, and for your own safety. SS foil cuts like a razor.

0.002" foil is perfectly adequate from a practical standpoint. 0.005 will look better. Some have used Ti. I've recall one builder placed spacers under the foil at the rivet locations so there is no pillowing. Plenty of room for craftsmanship.

Note the lap seam down the center, sealed with aluminum tape. In the event of a serious fire, the tape melts and provides a vent for outgassing of the organic binder in the fiberfrax.

Firewall%20Joint%20Caulking%20800w.jpg


Center%20Seam.jpg


My%20Firewall.jpg
 
Thanks for all the help and good advice. Fiberfrax is easy to find. SS foil .005 thick is more difficult. The only place I’ve found so far is online metals, but it comes in 100’ rolls for about $550.00. A more common and obtainable gage is .002, available at several sources. If anyone has a source for heavier gage stainless steel foil, please let me know.

Thanks again.
 
Thanks for all the help and good advice. Fiberfrax is easy to find. SS foil .005 thick is more difficult. The only place I’ve found so far is online metals, but it comes in 100’ rolls for about $550.00. A more common and obtainable gage is .002, available at several sources. If anyone has a source for heavier gage stainless steel foil, please let me know.

Thanks again.

https://www.mcmaster.com/metals/stainless-steel/shape~foil/
 
McMaster-Carr, thanks. Should have looked a little deeper on their website.
.005 X 24” X 10’ is $170 and twice what I need. I’ll have to see if my hangar neighbor, RV7 builder Kevin needs some. I have a roll of fiberfrax that Steve Melton gave me, but it’s an inch thick.
 
.005 stainless processing ?

I have my .005 stainless on the way from McMaster. I recall some discussion regarding making clean holes for bolts and rivets but can’t find details. My questions:
* can you cut .005 with scissors ?
* can you punch rivet holes with an awl ( like .002 ) ?
-how to make larger holes clean for bolts without tooling a punch and die?
*suggestions for stand-off bushings to minimize pillowing ?
For 1/8” F’frax, two .062 washers are heavy and unnecessary OD.
Metal tubing would be good, but the lathe cut off would be laborious .
Aluminum or teflon would be good until serious fire developed. Ideas ?
 
Back
Top