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Firewall Protection

macrafic

Well Known Member
For those of you who have read Dan Horton's testing of firewall materials and have implemented his suggestions, I have a couple of questions.

1. Dan suggests attaching the "sandwiched blanket" mechanically. How did you do that? safety wire? nuts/bolts/rivets? secured by all the "stuff" that attaches to the firewall (battery, contactors, etc.)?

2. Is the integrity of the "sandwiched blanket" compromised by compression? i.e. should standoffs be used to attach all the firewall "stuff" so the blanket is not compressed, or is compression OK.

3. Seems to me that the very thin SS covering would be extremely subject to puncturing/tearing/etc. while working on the engine. I guess I am thinking of aluminum foil. Is the SS tougher than I am thinking?

4. Did you put this on the firewall before, or after you put the engine mount on? Common sense would indicate to me that before is better.

Getting ready to mount my engine this winter. Need to get these types of tasks understood and ready!!! Thanks.
 
For those of you who have read Dan Horton's testing of firewall materials and have implemented his suggestions, I have a couple of questions.

1. Dan suggests attaching the "sandwiched blanket" mechanically. How did you do that? safety wire? nuts/bolts/rivets? secured by all the "stuff" that attaches to the firewall (battery, contactors, etc.)?
I have mine simply secured by all of the "stuff" that attaches to the firewall. It is working just fine this way going on 5.5 years now. I know Dan used pop rivets spaced out. That method creates a sort of patch quilt look. It looks great and If I were to do it again I would go this route. Truth be told the only reason I did not secure mine in this fashion was due to the fact I had already mounted ALL the firewall forward components, and I do mean ALL of them, before making the decision to install this insulation. I strongly recommend against doing it this way. :(

2. Is the integrity of the "sandwiched blanket" compromised by compression? i.e. should standoffs be used to attach all the firewall "stuff" so the blanket is not compressed, or is compression OK.
I do not believe it is compromised but that is just my opinion. I am not an engineer, scientist, or anything with any level of authority on this subject though. And no, I did not even sleep in a Holiday Inn last night. So take my opinion for what its worth.

3. Seems to me that the very thin SS covering would be extremely subject to puncturing/tearing/etc. while working on the engine. I guess I am thinking of aluminum foil. Is the SS tougher than I am thinking?
It is not like aluminum foil. Yes, it can be punctured but it is much tougher than aluminum. I have not had any issues what so ever concerning this at all in the 5.5 years I have been flying so far.

4. Did you put this on the firewall before, or after you put the engine mount on? Common sense would indicate to me that before is better.
Ok, as mentioned in question #1, absolutely you want to put this on BEFORE mounting your engine. However, DO NOT PUT IT BETWEEN THE ENGINE MOUNT AND THE FIREWALL. I had the misfortune of attempting to install the insulation after the engine was mounted and after every single firewall component was installed and wired. All I can say is working in this confined space with raw edges of stainless steel was like. . . well, it was like blindly sticking your arm up to your elbow in a box full of razor blades and feeling for a feather in the box. If you think cutting yourself while shaving is a pain, just go ahead and try to trim stainless steel foil around firewall components in a small space, around items that block your view and your access, all while trying not to cut a finger off! :eek:

Getting ready to mount my engine this winter. Need to get these types of tasks understood and ready!!! Thanks.
Read my thoughts below each numbered question above.
 
Rich,

Gotta keep the fiberfrax felt in place somehow, and a regular network of rivets is (in my opinion) the best way. Compressing any insulator will probably reduce its insulating properties. It means the insulating properties are compromised under each stainless pop rivet..but the rivet was already a heat path. As for battery boxes and other non-structural stuff, I'd probably install it over the foil/fiberfrax. You are the airplane builder; your call.

Installation is easiest with nothing installed on the firewall. That includes the engine mount. Caulk over all edges or use metallic aluminum duct tape. And wear gloves. Only an Okie would try to install stainless foil by feel ;)

Center%20Seam.jpg


Firewall%20Joint%20Caulking%20800w.jpg
 
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Rich,
I am doing the firewall insulation and can share some of the problems I had with you. Not flying yet. I used 0.002" SS foil.

1. It is VERY tough and VERY sharp. Cuts like a sharp blade and bleeding does not stop easily.

2. You cannot drill though it. You have to cut all the holes with a knife. Larger holes, 1/4" and more, it is easily cut using the edges of the hole in the SS firewall to cut against. Smaller holes are more difficult. What worked for me is to cut a X through the small hole using the hole in the firewall as guide, then used a tapered grinding stone in the Dremel and grind the SS foil away, pressing against hole edges in firewall. Comes out nicely. I have not found anything that will punch a hole in the SS foil!!

3. I will compress the fiberfrax between the firewall mounted stuff and the firewall, limited to things that bolt or screw on. I have no fiberfrax behind oil cooler (riveted in place). That was installed before I decided to go with insulation.

4. Nothing between SS firewall and engine mount points.

5. I used SS vent valves on firewall, as well as steel for all other penetrations. Aluminum will melt and nullify the fire protection.

I have cut all the holes in the SS foil I know of at this point as well as cut the corresponding holes in the Fiberfrax. Because of the difficulty I anticipate cutting holes in the foil at later stage, I have decided to install all firewall forward stuff, all wire runs, cables etc with the firewall naked. When I have covered all firewall penetrations, I plan to remove the engine mount with engine as one unit, install the SS foil and fiberfrax as described by Dan Horton, then put back engine mount with engine when all is done. Probably a day's extra work when the time comes.

Johan
 
Rich,

Gotta keep the fiberfrax felt in place somehow, and a regular network of rivets is (in my opinion) the best way. Compressing any insulator will probably reduce its insulating properties. It means the insulating properties are compromised under each stainless pop rivet..but the rivet was already a heat path. As for battery boxes and other non-structural stuff, I'd probably install it over the foil/fiberfrax. You are the airplane builder; your call.

Installation is easiest with nothing installed on the firewall. That includes the engine mount. Caulk over all edges or use metallic aluminum duct tape. And wear gloves. Only an Okie would try to install stainless foil by feel ;)




Dan (and others) thanks! Understand that compressing will compromise the insulating capability. However, will it compromise the fire resistance capability? Or, is those essentially the same thing?
 
Insulation

What are builders trying to solve by adding insulation to the firewall ? I have a bare firewall and don't see the advantage of adding anything . What am I missing out on ?
 
another option

firewall fwd insulation is best. pictures of aft firewall insulation. ceramic batt, no binder, alum foil, taped the edges with alum tape. added a few securing brackets and taped on the backside. I also insulated the piece marked 601A. it's holding up well, 370 hrs.

100_5191.jpg


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100_5196.jpg
 
Firewall protection is not enough, IMHO. I personally know of two inflight fires in which the firewall did its job but the fire ate through the bottom of the forward fuselage. Both led to fatalities. One RV-8, one Rocket.
 
Dan (and others) thanks! Understand that compressing will compromise the insulating capability. However, will it compromise the fire resistance capability? Or, is those essentially the same thing?

Same thing.

What are builders trying to solve by adding insulation to the firewall ? I have a bare firewall and don't see the advantage of adding anything . What am I missing out on ?

Assuming your firewall is truly bare (no paint, just shiny stainless), you're doing fine. Expect the firewall itself to match the temperature inside the lower cowl during normal operations, and glow red hot like a toaster oven given a fuel or oil fed engine fire. Not a happy circumstance, but no open flame and no smoke, so you can at least pull your feet back and maintain control until you can get the fire out (shut off fuel flow, stop the prop to stop oil flow).

Insulating the engine side of the firewall will reduce cabin side surface temperature to bare skin levels in normal flight. Given an engine fire, the cabin side surface may get very warm if the fire lasts long enough (like ballpark 500~700F), but rudder pedal temperatures will be much lower. There may be hot spots due to high heat transfer at bolts and other fasteners, and well as at cables and fittings. Do not assume engine-side insulation allows the addition of dumb cabin side insulation (see below). I would also caution against allowing plastic brake fluid lines to contact structure.

Steve Melton (above) illustrated the only reasonably safe cabin side insulation, ceramic batting with no organic binder, just pure ceramic fiber. It won't burn or smoke, although the acrylic adhesive on the aluminum duct tape might. The entire structure is exposed to engine fire, and because the cabin side is insulated, that structure will itself will get a lot warmer than a bare firewall structure. No predictions here, as I didn't test that detail after finding how well things worked by insulating the engine side. Be aware that ceramic fiber carries an inhalation warning for cancer, the reason Steve has his entirely encapsulated in foil.

Which brings us to the Darwin awards. I had no idea how bad some "firewall insulation" really was until folks started sending it for a check on the firewall test rig. For example, there are a few hundred RVs out there flying around right now with polyester fiber insulation in contact with the stainless on the cabin side. Given an engine fire, there's a very high probability of dying badly; a sample of that stuff torched up so violently that it melted the vinyl siding on my shop before I could drag the rig away. I walked into a hangar last year to speak with a fine young man building an RV-4, and found he had applied aluminized plastic bubble wrap to his firewall (Sorry...here's your sign). Likewise, paint, vinyl, Nomex, fiberglass, even fiberfrax felt are all bad choices for the cabin side. Don't do it.

Firewall protection is not enough, IMHO. I personally know of two inflight fires in which the firewall did its job but the fire ate through the bottom of the forward fuselage. Both led to fatalities. One RV-8, one Rocket.

Some others reports too, and an RV-10, reported here by its pilot because (1) he did a great job flying, (2) jettisoned a door to vent smoke, and (3) the burn-through was confined to the tunnel.

My own -8 has a stainless exhaust ramp replacing the aluminum ramp. For the flat-belly RVs, we've previously talked about a 0.010" stainless overlay on the skin, aft of the cooling exit. I saw a well done example at SERFI two weeks ago.
 
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See how it's done

Dan would you post a few photos of your firewall? I'm finally convinced it's the proper way to do it, I just want to see how you insulated around all that stuff that lives on the firewall.:D
 
Dan would you post a few photos of your firewall? I'm finally convinced it's the proper way to do it, I just want to see how you insulated around all that stuff that lives on the firewall.:D

I don't have all that much attached to mine.



Here's a mixed bag. Some stuff was installed prior to the insulation layers, some after. The square stainless patch is where I decided not to use a particular component.

 
What are builders trying to solve by adding insulation to the firewall ? I have a bare firewall and don't see the advantage of adding anything . What am I missing out on ?

Its for sound insulation and/or heat rejection during normal operations. May or may not be valid concerns depending on several factors. The way I understand it is this issue comes up when discussing a FWF fire event on an aircraft that has insulation on the back side of the firewall.

In my opinion, insulation on the back side of the firewall is not to mitigate risk in an engine fire situation. It will likely make things worse (smoke) or just kill you sooner which may not be all that bad if the outcome will be the same anyhow. However, if you want the insulation AND no additional risk from a fire, you probably should consider fireproofing the bottom skin of the fuselage first. This is aluminum skin and usually has carpet on it with your feet on top of that. This is where I believe the "blow torch" will burn through first.

My view is to learn to minimize the risk of FWF fires in the first place, and/or how to extinguish them should they occur. It's not like our airplanes are getting shot at.

Bevan
 
Nice

I don't have all that much attached to mine.



Here's a mixed bag. Some stuff was installed prior to the insulation layers, some after. The square stainless patch is where I decided not to use a particular component.


Very nice Dan. I can see you put a lot of planning and work into your firewall. :)
 
What are those fittings that the throttle and other control cables are going through? I've never seen those before.
 
What are those fittings that the throttle and other control cables are going through? I've never seen those before.

Inexpensive pass-throughs that work really well. Painted steel or stainless, about 0.030" is fine. Weld up whatever diameter, angle, or shape you need. The three on the right (throttle, mixture, prop) are ganged on one base plate. Insert the cable and pump it full of FireBarrier 2000 or other intumescent silicone sealant.

Test example here. Read the whole thing or start at post 38:

http://www.vansairforce.com/community/showthread.php?t=72087

 
My view is to learn to minimize the risk of FWF fires in the first place, and/or how to extinguish them should they occur.

Perfectly reasonable. Insulate or not is a personal choice. I hope the primary message has been to stop making bad choices....primum non nocere. Some of the "firewall insulation" products sold to the EAB community are truly awful, and builders seem to be endlessly creative with ways to transform an engine compartment fire into a cabin fire.
 
Just a little bit more....

Firewall protection is not enough, IMHO. I personally know of two inflight fires in which the firewall did its job but the fire ate through the bottom of the forward fuselage. Both led to fatalities. One RV-8, one Rocket.

Its sad to see someone go through so much effort to try and minimize the risk of fire penetration into the cockpit only to fail. I imagine that only a .020 or so thick stainless sheet bonded or riveted to the bottom forward fuselage would have given these folks the additional margin that they needed to keep the cockpit safer. I'm guessing the additional weight would have been maybe 2 to 3 lbs?

cj
 
Inexpensive pass-throughs that work really well. Painted steel or stainless, about 0.030" is fine. Weld up whatever diameter, angle, or shape you need. The three on the right (throttle, mixture, prop) are ganged on one base plate. Insert the cable and pump it full of FireBarrier 2000 or other intumescent silicone sealant.

Test example here. Read the whole thing or start at post 38:

http://www.vansairforce.com/community/showthread.php?t=72087


You mean I don't have to buy a $100 anodized gimbal thingy for each one?? AWESOME! Thank you!!!:D

I read that older thread from beginning to end. I am a lot less ignorant than I was. A great service to the community. My firewall is still bare so I have the opportunity to increase my safety margins based on this info.
 
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I imagine that only a .020 or so thick stainless sheet bonded or riveted to the bottom forward fuselage ...

0.010" is plenty, in particular over 1/16" fiberfrax felt. Even 0.003" stainless foil will block outright burn-thru.
 
For the flat-belly RVs, we've previously talked about a 0.010" stainless overlay on the skin, aft of the cooling exit. I saw a well done example at SERFI two weeks ago.

This is my plan using 24"x24" .016 stainless. It will remain unpainted.
 
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After reading all this and staring at my blank firewall my eye was drawn to the 3 holes dead center for the brake reservoir. It is aluminum, like all the other RVs. So in a fire after 30 sec or something it would leak brake fluid over everything. I would assume if things are hot enough it burns? So I could move it to the back side of the back side of the FW or I could make one out of stainless and run stainless hoses, or firesleeve them. What are others doing to address this?
 
Scott, I think that if you leave it on the front side of the firewall any fire will be contained there. DanH said that the firewall itself gets very hot in his test fires, so I'd wonder if mounting it on the back side would move the fire hazard (hydraulic oil is flammable) to the cabin.

Some alternative mounting other than the firewall might be appropriate for this, like Ron did, or just leave it on the front side and accept that this quantity of fuel could increase the duration or intensity of a fire.

Just my thoughts....

Which led me to this - I measured the brake reservoir and it seems as if roughly 3' of 1/2" tube would have the same internal volume. It would still need a vented cap but might be very easy to install and refill from time to time.

Dave
 
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I don't have all that much attached to mine.



Here's a mixed bag. Some stuff was installed prior to the insulation layers, some after. The square stainless patch is where I decided not to use a particular component.

Dan, it appears from the pictures of your attachment of the fireproofing to the firewall, that you used blind rivets/standard rivets/screws and some kind of decorative washer (or backing washer used on the manufactured head, rather than the shop head). Hard to tell. Can you verify what you used here? I like this method for securing to the firewall and would like to duplicate.
 
Fuel vents on belly...

One thing leads to another... my cam was bad so the engine had to come off and this thing is like an onion. I'm down to a few bolts holding the engine mount on and so I've decided to take it off and insulate the firewall with the Fiberfrax and stainless foil.

Looking down the belly at the path of the fire stream should the worst thing happen, I see two fuel vents staring me in the face. They are just in front of the spar carry-through. Is there a better place to put these? Seems to me that if there was a fire this direct route to the tanks would just contribute to the bad day. The RV-3 plans are quite vague in this area.

On my husband's Panther, with folding wings and wing fuel tanks, his vent tubes are simply coiled up inside the wing root. Not the greatest place because they can't get any higher than the top of the tank, but a necessity for the wing folding mechanism. AND out of the flame/exhaust path. Is there any reason to not reroute these the way of the Panther?

0219161611.jpg
 
Katie,

The vents are fine. No, they should not lead fire to the tank.

Since you have it down this far, take the opportunity to add a stainless overlay with a curved leading edge wrapping up and around that bottom cross tube. The result would look like an RV-8.

 
Bonded with what?

Its sad to see someone go through so much effort to try and minimize the risk of fire penetration into the cockpit only to fail. I imagine that only a .020 or so thick stainless sheet bonded or riveted to the bottom forward fuselage would have given these folks the additional margin that they needed to keep the cockpit safer. I'm guessing the additional weight would have been maybe 2 to 3 lbs?

cj


Curious what bonding agent you'd use to attach the SS sheet? McMaster-Carr carries a 24x24 sheet of .016 321 Stainless Steel for ~45 bucks.

Cheap enough, for what it's protecting.

Having an easy way to attach it to the fuselage bottom without creating more holes in the skin or having it come detached would be much appreciated.

Rob S.
 
Katie,

The vents are fine. No, they should not lead fire to the tank.

My concern with this would be the opposite: that a hot tank would cause vaporizing fuel to be vented right into the hot gas stream exiting the cowling, which could introduce [additional] fuel to a potential source of ignition.

Unlikely? Maybe. I'm curious as to people's thoughts on this.
 
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My concern with this would be the opposite: that a hot tank would cause vaporizing fuel to be vented right into the hot gas stream exiting the cowling, which could introduce [additional] fuel to a potential source of ignition.

Unlikely? Maybe. I'm curious as to people's thoughts on this.

You'd have to be dumping enormous amounts of fuel vapor out the vents to make a combustible mixture at flying speeds - not likely unless you've got a fire IN the wing, in which case the burning fuel vents are not your biggest concern.
 
Katie,

The vents are fine. No, they should not lead fire to the tank.

Since you have it down this far, take the opportunity to add a stainless overlay with a curved leading edge wrapping up and around that bottom cross tube. The result would look like an RV-8.


Dan,

How big does the radius on a curved exit like that need to be to make an appreciable difference in exit airflow?

A stock RV-6 just has a protruding firewall flange there (like the RV-3), which is a simple solution on the construction side, but not an efficient solution from an airflow standpoint.
 
One thing leads to another... my cam was bad so the engine had to come off and this thing is like an onion. I'm down to a few bolts holding the engine mount on and so I've decided to take it off and insulate the firewall with the Fiberfrax and stainless foil.

Looking down the belly at the path of the fire stream should the worst thing happen, I see two fuel vents staring me in the face. They are just in front of the spar carry-through. Is there a better place to put these? Seems to me that if there was a fire this direct route to the tanks would just contribute to the bad day. The RV-3 plans are quite vague in this area.

On my husband's Panther, with folding wings and wing fuel tanks, his vent tubes are simply coiled up inside the wing root. Not the greatest place because they can't get any higher than the top of the tank, but a necessity for the wing folding mechanism. AND out of the flame/exhaust path. Is there any reason to not reroute these the way of the Panther?

0219161611.jpg


I am using these in the root fairings with three big loops, from JDair.

DSC02747.jpg
 
Dan, How big does the radius on a curved exit like that need to be to make an appreciable difference in exit airflow?

I dunno. We eagerly await your flight test data ;)

Seriously, here I would make it just large enough to wrap neatly around that lower cross tube, as progressively larger probably is a case of diminishing return.
 
I like the look of the wrapped stainless, but if I cover the bottom cross tube, how do I inspect it regularly? Is it screwed on or riveted?
 
I Want to know too!

Also building an RV-3B like KatieB and will be starting firewall shortly.

Cleaning behind it is also a concern.

Dave
 
OK, I'm working on the firewall this weekend. I've got my roll of Fiberfrax in hand and I see that it's got a slightly different texture on one side. Which side is best to put against the firewall? I'm guessing the fire properties are the same on each side, but one provides "tooth" for an adhesive. Just thought I'd ask.

Also-- I have several pop rivet tails sticking forward through the firewall. Is there reason to think these might wear holes in the fiberfrax after a while? I'm thinking of just putting a blob of 3M Fire Barrier 2000 on each one to soften the hard edges and letting it dry before putting the fiberfrax layer down. Thoughts? Am I overthinking this as usual? :p

(Bret, I love that fitting for the fuel vent, btw!)
 
I like the look of the wrapped stainless, but if I cover the bottom cross tube, how do I inspect it regularly? Is it screwed on or riveted?

Usual choice...if you think you might want to take it off later for some reason, use nutplates.

Me? I'd leave generous areas uncovered around the welds where the crosstube meets the gear tubes, and just rivet it on.

I've got my roll of Fiberfrax in hand and I see that it's got a slightly different texture on one side. Which side is best to put against the firewall?

Doesn't matter.

Also-- I have several pop rivet tails sticking forward through the firewall. Is there reason to think these might wear holes in the fiberfrax after a while? I'm thinking of just putting a blob of 3M Fire Barrier 2000 on each one to soften the hard edges...

Good idea. I'd do it to protect the stainless foil.
 
0.010" is plenty, in particular over 1/16" fiberfrax felt. Even 0.003" stainless foil will block outright burn-thru.

This is my plan using 24"x24" .016 stainless. It will remain unpainted.

It seems natural (RV8/4) to extend the stainless back to the fuse bottom, and in the cooling flow exit, but what about 6/7's?

How far back from the firewall - 6"? 8"? Width - same as the shovel exit? I have some .016, and 1/16 fiberfrax. The plan is to screw the exit radius to the FW lip. It would overlay a joggle of the aft SS barrier to have steel screws holding it all together.
 
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Fixing a SS belly skin?

I have done the FW engine-side insulation per Dan's recommended scheme (installed on a bare FW). Now I am planning on putting a roll of SS over the bottom tube of my engine mount and also fixing a second skin of SS extending back past the rudder pedals.

How would I fix these in the case of a tail dragger 9? Could I use a bonding agent on the belly skin without mechanical fastenings? Which one might work best?
 
It seems natural (RV8/4) to extend the stainless back to the fuse bottom, and in the cooling flow exit, but what about 6/7's?
How far back from the firewall - 6"? 8"? Width - same as the shovel exit?

Nobody knows for sure. All we have to work with is anecdotal evidence and a few photos. Here's one I saved from Ted's account of his RV-10 fire, which was (IIRC) due to fuel from a loose nut at the mechanical fuel pump.



Looks like it melted back more than 12" from the firewall, but realize that insulation inside the tunnel caused the skin temperature to skyrocket there...energy in less energy out = temperature. Insulation inside the aluminum belly skin is a bad idea for several reasons, but it's hard to convince everybody.

Took this photo at SERFI, Joel's RV-10. IIRC, 0.010" stainless foil over fiberfrax, attached with SS pulled rivets, perimeter sealed with Firebarrier 2000.

 
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Just about finished...

Thanks to Dan's info and diagram and Dorfie's experience posted here, I was able to insulate my firewall over a long weekend. Total cost was under $100. Total weight is a pound or less. I didn't do it because of fire paranoia... I did it because I've been flying almost exclusively in composite Jabiru-powered aircraft for the past 8 years and I'm used to flying in comfort. The Jab runs about 100 degrees cooler than a Lycoming in both CHT and EGT. The firewall on our aircraft is a sandwich of stainless steel, ceramic felt, plywood, and padded carpet that extends to the entire fuselage. Cabin temperature is never a problem. When DanH says he can fly his RV-8 in sock feet, well, that's what I'm going for here! The added layer of fire safety makes it a no brainer.

The stainless foil (.002" thick, 24" by 10-foot roll), stainless rivets and rivet washers are from McMaster Carr. The FiberFrax and 3M FireBarrier 2000+ is from Aircraft Spruce. I used 1/16" thick FF on the belly and 1/8" FF on the firewall. I started with the belly and made posterboard patterns first. All edges are folded around the Fiberfrax when possible. The front side overlaps the belly and is secured by screws for the battery box, rivets and aluminum tape. I didn't use a whole lot of rivets on the belly because my belly skin is also my floorboard, so I didn't want a bunch of rivet tails sticking up where my feet go. I was able to use the screws that hold the removable battery box for several anchor points.

If I were to do it again, I think I'd use a thicker sheet for the belly pan similar to what Dan did. Mine is sort of wrinkly. I hope it holds up over time. We shall see!

By the way, the steel conduit fittings in the firewall are for my wiring bundles. They will be lined with firesleeve and caulked with the 3M Firebarrier. I still need to drill out some stainless large area washers to go around them for support. Cost? 64 cents each at Lowes. :cool: You should've seen the guy's face at Lowes when I walked up and asked him how to tell what these fittings are made of, because I wanted steel, not zinc, because zinc melts at a low temperature. He just looked at me like, "What planet are YOU from?" Turns out the steel ones say STEEL on the bag label. (He didn't know that, though!)

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Katie, that's good work.

Two notes for observers;

(1) The overlap seams (firewall, about 1/3 up from the bottom, and belly, just aft of the exit) appear to be well position to melt the aluminum tape (given an engine fire) and vent the organic binder which will be out-gassing from the fiberfrax. My overlap is vertical, right up the center of the firewall. Either way, the venting is important.

(2) I'm a big fan of the steel tube type pass-throughs, as they are cheap, gas tight, and fire test as very effective. Mine were pumped full of FireBarrier 2000 after all the wires, cables, etc were in place. I recently had the need to remove the FireBarrier from a wire bundle pass-through, as I wanted to rewire for a new ignition; out with the P-lead, in with some signal and power wires. Anyway, it was not real fun. Needed to make a half-moon semicircular cutter blade to slide in alongside the tube ID (a half moon cut from the next size smaller tubing), separating the cured FB from the tube. That part worked as planned, and was no trouble at all. However, it took about an hour to peel the 1-1/2" long cured plug of FireBarrier out of the wire bundle to separate the wires!

So, the moral of the story; I think your plan to pack Fiberfrax around the wires inside the conduit, and then seal just the ends of the conduit with a cap of FireBarrier is a good idea. At worst, if you need to pull the bundle later, you'll only have very short plugs of FireBarrier to clean away. Big single cables (like a battery lead or throttle cable) are not an issue to clean up, so I'll probably continue to simply pump them full in the future.
 
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The comments about stainless steel foil cutting fingers made me think that there might be an alternative for overlaying the Fiberfrax ahead of the firewall. I ordered some .005 titanium foil from www. titaniumgoat.com to see. While I was at it, I ordered a bit of .020 titanium from www.mcmaster.com to evaluate it for belly protection behind the firewall, since the belly otherwise has no fire protection.

Both pieces are Grade 2, which can be bent cold and which has about 40,000 psi ultimate tensile strength. Here's a shot of the .020 after I bent it using about a .12 radius on a brake.

zveyf.jpg


Why titanium? It's resistant to elevated temperatures and has a lower density than stainless steel. It tends not to corrode. And I checked FAR Part 23.1191 and found that these materials were acceptable as firewalls:

Stainless steel sheet, 0.015 inch thick.
Mild steel sheet (coated with aluminum or otherwise protected against corrosion) 0.018 inch thick.
Terne plate, 0.018 inch thick.
Monel metal, 0.018 inch thick.
Titanium sheet, 0.016 inch thick.

So these thicknesses of titanium would certainly be acceptable for these applications.

The .005 titanium, because of its thickness, is slightly heavier than the .002 stainless foil. It's .53 oz. per square foot heavier, or .033 pounds heavier per square foot. The .020 titanium is .16 pounds per square foot lighter than .015 stainless, and lighter still compared to the .018 that seems to be more commonly used.

Drilling takes a slow speed (I used 900 rpm) and slightly more pressure than aluminum. The added pressure is not significant for this soft titanium. In the .020, I consistently got 3-lobed holes using twist drills. Reamers cleaned them up. I used twist drills and a Unibit, with the Unibit worked best. They all left burrs. I could remove the burrs with a file, filing flat to the metal, and the reaming the hole.

I didn't have a reamer to clean up the 1/2" Unibit hole so I used a normal deburring tool and that worked. Here are the holes in the .020:

2nbg8w2.jpg


In the .005 material, the titanium would try to climb the twist drill. The only way I could get a decent drilled hole was to sandwich the titanium foil between two pieces of plywood and press them together and drill through that. That worked reasonably well, even with the Unibit. Filing flat deburred these holes:

2rzx55g.jpg


I tried grinding a hole and that worked fine. It would have worked better if I had a sharper Dremel grinder bit.

The very nicest holes were punched. I tried a 3/16" hole in both with the Roper-Whitney hand punch and that was sweet. Nice round holes with minimal burrs. Next to the hole in one piece, you can see a center-punch mark I made. It takes more force to do the .020 than the .005, but both were ok:

29m0tqf.jpg


The throat depth of my Roper-Whitney punch will be the limiting factor for these.

I could cut the .005 foil with ordinary kitchen scissors. It took my usual hand shears to cut the .020 titanium. The cutting was easy for both.

In both cases, the burr was not something that was at all likely to cut me. And I could file the burr off or use a Vixen fine. Both worked well.

Bottom line, I'm planning on using larger pieces of both of these on my RV-3B.

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Dave
 
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Took this photo at SERFI, Joel's RV-10. IIRC, 0.010" stainless foil over fiberfrax, attached with SS pulled rivets, perimeter sealed with Firebarrier 2000.


Dan, I stand corrected. I thought I used 0.010" at the time we were discussing this but I looked back when ordering material for this -7a and we used 0.005" on the belly and the firewall. No adverse effects that I know of with over 300 hrs since I put this on.

Joel
 
Dan,

On the subject of packing the pass-through tubes, I've played with this idea. Using an old tube of the latex based firestop (it was available locally), I was able to lay out multiple runs of ~1/4" 'fingers' of the material on a non-stick surface. My idea (using the good stuff) would be to pack the empty space with the cured fingers of firestop, then use firesleeve clamped over the outside of the pass-through & wire bundle for CO block.

The idea is that as long as there's no fire, there's no mess; if there is a fire, the fingers will swell up & fill whatever airspace was left in the pass-through.

Thoughts?

Charlie
 
what about firesleeve

Is there a downside to using a piece of firesleeve with some trimmed out lengthwise then wrapped around the wires and slid inside the tube? Similar to how the commercially available stainless pass-throughs recommend. You can then firebarrier the exposed end. Firesleeve that is manufactured to the FAA TSO can withstand 2200 deg F for 15min.
 
Why titanium? It's resistant to elevated temperatures and has a lower density than stainless steel.
Dave

I don't think I would do that if I were you. Titanium might have a nice listed melting temperature in the 3000F range, but that will never actually occur because it will burn at about 1100F. Having started a titanium fire on a lathe once when I wasn't using enough coolant, once it starts burning, it will not likely stop until it is consumed. I'd sure hate to have an engine fire, and then have my firewall literally catch fire and not stop until it was completely gone.

Stainless steel will not exhibit this behavior, and is quite fine up to the melt temperature of about 2500F.
 
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