Fire resistant firewall??

[Guest langted]

I am currently building an Arion Lightning, which has a fiberglass fuselage with a stainless steel firewall.  I will be paying attention to making penetrations fire resistant (e.g. not using plastic or aluminum pass-throughs), but I am wondering about the mounting of the firewall directly against the fiberglass fuselage flange.   It would seem that the heat of a fire, applied to the fiberglass via the thin stainless sheet, would quickly cause a lot of smoke and failure as the fiberglass overheats and burns.   I was reading about this on Van's forum, and looking at recommendations from (I think it was Dan Horton??) who did a lot of research and favored use of a high temperature insulation (like 1/8" of fiberfrax), covered with a thin (0.002") stainless layer to protect the fiberfrax, both on the engine side of the firewall.   This would seem even more critical on a fibrerglass aircraft than on a aluminum aircraft.  So, I was wondering what other fiberglass aircraft use in this area, or what other fiberglass aircraft builders are doing, if anything, to enhance fire resistance of the firewall?   

 

 

[facthunter]

  All a good idea. It's to give you extra time, not total protection. The underfloor and sides might be worth considering too. Nev

 

 

[M61A1]

You could also try having the stainless firewall on small standoffs to keep it from contact with the composite material. Seal any feedthroughs with PR812 sealant or BMS 5-63 as you are in Boeing country.

 

 

[fly_tornado]

a layer of carbon fibre would work well

 

 

[Guest langted]

Yes, as I understand it, the underfloor is another critical area becase the flames are initially swept against that area by the cowling exhaust air.   This is also often a big weakness in aluminum aircraft -- even though the SS firewall may hold, the aluminum on the belly can melt away very quickly and then the fire consumes your feet as you try to get down.   Aesthetically, it's harder to protect that area, since it's visible and it has compound curves that stainless sheet is hard to form around, and it's not pretty if you try.   I have located a few moderately high temperature (~1200F/649C) insulating materials that have some "formability", but these are mostly aluminum faced insulation, which limits their usefulness.  (They are generally made to reflect exhaust heat from nearby exhaust parts, not made as a fire-retardant material).  Still, they may slow things down a little to buy time, as Nev says.   I am thinking of using the aluminum stuff on the rear inside of the cowl to try to kept the cowl intact awhile and containing the flame, and maybe a small SS deflector under the cowl outlet just to keep the flames from making direct impingement on the belly skin, if  I can convince myself that it would work.  (might loose a couple knots on that).  

 

I would love to find some deeply "dimpled" thin stainless sheet, as dimples tend to allow the material to take compound bends, but I don't see any suppliers.   

 

I also like the idea of standoffs for the firewall, but these would obviously still need to be sealed.   I looked up those sealants-- 400F (204C) service temperature and "flash" temps as high as 2000F for one and the other at 3500F (1925C) !!!!   Great stuff but also PRICEY at $200-400 US for a small tube!!

 

Thanks for the thoughts -- keep them coming.

 

Ted

 

 

[Old Koreelah]

All types of fibreglass will burn, but worse than this, all resins lose their structural integrity as they heat up. As Nev suggests, anything that postpones this can save your life. Don't underestimate the value of wood as a fire insulator.  A SS-lined plywood firewall is easy to integrate into a composite aircraft and will keep its shape far longer than fibreglass resin, which will quickly turn to slop.

 

 

[Guest langted]

Interesting that nobody yet has said, "don't worry about it, just build it and go fly".  

 

Wood is an interesting thought.   I'll have to look into what temperature it starts to char vs Fiberglass turning to "slop".   Another advantage is that if it didn't delay the fire long enough, you would die to the pleasant smell of a campfire rather than toxic resin fumes. ;) 

 

 

[turboplanner]

All types of fibreglass will burn, but worse than this, all resins lose their structural integrity as they heat up. As Nev suggests, anything that postpones this can save your life. Don't underestimate the value of wood as a fire insulator.  A SS-lined plywood firewall is easy to integrate into a composite aircraft and will keep its shape far longer than fibreglass resin, which will quickly turn to slop.

You can look at the properties of fire retardant resin. There is a photo somewhere of a Shell gas tanker in England on fire after a crash, where the FRP tanker, constructed using fire-retardant resin was squashed and then rebounded to its shape with a large hole in the corner the spilled gasoline caught fire , but can be seen bubbling from boiling, still contained in the FRP.

 

 

[M61A1]

Some useful information here:

 

https://www.experimentalaircraft.info/articles/aircraft-firewall-preparation.php

 

 

[Guest langted]

M61A1:  Thanks for the link.   That link suggests using the same material as I have purchased to insulate my firewall, but thinner stainless steel, and no overcover for the Fiberfrax, because it says to put the Fiberfrax between the firewall and the composite.   (I was planning to put the stainless steel firewall directly on the composite flange per the plans, but then overlay with Fiberfrax and very thin stainless sheet (0.003 inch) to protect the Fiberfrax.  That is, the insulation on the engine side vs the cockpit side of the stainless firewall.   However, I think the link might be describing installation on a full composite bulkhead, vs a flange.   In my case, I think cockpit side material would compress too much between the flange and the firewall (loosing insulation effectiveness) especially since the motor mounts go on top of the firewall, compressed against the flange with four AN7 bolts.  

 

I can also get save a few pounds compared to the uninsulated kit material weight if I use .018 inch stainless steel instead of the 0.030 supplied with the kit.   I called the kit manufacturer, and he confirmed the kit does not require the thicker stainless for any structural reason.   But no information on fire-resistance improvement of sides and bottom of the fuselage.   Guess I'm still on my own for that.

 

 

[flyvulcan]

Hi Ted,

 

Did you complete the entire two weeks of builder assist with Nick?

 

Could you post a few pics of your aircraft?

 

Mine is still with Nick having the interior fitted.  It should be on its way to Australia shortly.

 

Dave

 

 

[Guest langted]

Dave:. I did about 7 days of build assist.  I wanted to get major structures done and the canopy, then trailered it back home.  I'm surprised you don't have yours yet -- hope it's worth the wait.  My fuselage arrived a little late, and (long story) I ended up with an epoxy fuselage instead of vinyl ester.   Anyway, Nick (for others, Nick is the Arion Aircraft owner) worked with me over Saturday to catch up the lost time.   I've never posted pictures on this forum, but I'll add a couple once I figure it out.

 

 

[Guest langted]

Dave:  Here are a few.  Just like yours, except trip home.

 

 

Classic Arion photo while being flipped over after wing and tail mount (about day 3)

 

 

Last time the wings were fitted, on mains, canopy in place, flaps, ailerons, but no elevators/rudder (about day 5) 

 

 

Getting ready to go home, day 7.   (No, not tailwheel, just no place for training wheel yet)

 

 

Arrived home, in shop (also showing forward flange without firewall)

 

 

[facthunter]

 Suitable heat insulation will also act as sound deadening. I don't know what engine you are using but any oil tank or cooler holds oil that burns extremely well.  If you fly at heights rather than low you will take longer to get down if you are alight. Consider underfloor as well. and cowl gills /flaps to seal it up and reduce the oxygen available (and increase cruise speed).. . Heat shield and safety all oil and fuel lines. Nev

 

 

[rgmwa]

Dan Horton also did some practical tests on fire retardant sealants that were written up on VAF. His conclusion was that 3M Fire Barrier 2000+ performed best.

 

Not expensive either.    https://www.3m.com.au/3M/en_AU/company-au/all-3m-products/~/3M-Fire-Barrier-Silicone-Sealant-2000-/?N=5002385+3293123941&rt=rud

 

 

[Guest langted]

Yes indeed, protection for hoses!  Fire barrier 2000+ looks like a reasonable choice, available, and not extremely pricey.  

 

FWIW:  My engine is a Titan 340 (experimental) with vertical induction, Airflow Performance fuel injection, and twin E-mag electronic ignition.   I went with low compression pistons since I don't trust the future fuel options.   I will be using a Prince fixed pitch prop.   Great props and built locally.   I can literally ride my bicycle to Prince Propellers.  

 

The Arion Lightning was really designed originally for a Jabiru 3300, and perhaps I should have stuck with it (the kit is more complete if that option is used, and there is a lot to be said for the Jab.   However, market penetration in the US is much stronger with Lycoming clones, and of course I have more horsepower with this option.   

 

 

[Yenn]

One thing to bear in mind is that when you realise you have a fire, the normal thing to do is shut off the fuel to the fire. Remove the fuel, by which I mean petrol and what is left to burn?

 

It won't make improve your outcome to leave the fuel on and burn faster. Either way you want to be on the ground as soon as possible.

 

 

[johnm]

don't worry about it, just build it and go fly langted

 

do you know of intumescent paints - don't know how they would peform in aviation and as a top coat on your fire wall - see link below ?

 

http://www.permax.com.au/intumescent-information?gclid=EAIaIQobChMIrueMyZzu3wIVRAwrCh22ZAITEAAYAyAAEgI1RfD_BwE

 

 

[onetrack]

If I was building an aircraft (but I'm not), I would be paying attention to shielding of high temperature areas, location and protection of potential fire sources, such as oil and fuel hoses, and ensuring that every feature of the cabin interior design was as fire-resistant as possible.

 

In addition, I'd be paying attention to ensuring cabin exit ability after a crash is easy, and there can be no confusion with regard to door or canopy latches.

 

There are two major scenarios that obviously worry most pilots in the back of their mind - smoke, then flames, in the cockpit - and being trapped in an aircraft that is on fire.

 

As a large majority of aircraft end up inverted after a crash, one has to remember that confusion is the primary problem when inverted, everything is upside down, and you lose precious seconds trying to re-establish your orientation.

 

I understand the commercial aircraft designers go to great lengths to ensure any fire activity on aircraft is slowed down at every possible point, thus enabling people to gain additional time to calculate their options and ways out.

 

 

[Bruce Tuncks]

When I was building my SK Jabiru, I thought that the weight of the galvanized iron sheet firewall was excessive. Fibrefax and thin stainless would have been better over the plywood bulkhead and I wish I'd done that. Mind you, the 3M silicon stuff looks good too and might have been lighter again, but how would you know you had applied it properly?

 

But one thing about tractor engines, they are better for fire. Much better than having the engine behind you.

 

 

[RFguy]

I searched for 'fire' in titles and this was the most useful forum topic.

I had been wondering what happens to a fire and a fibreglass monocoque body, knowing what happens to fibreglass when it goes over Tglass.... The wood firewall barrier is a good one IMO. And self extinguishing materials for everything.

Automatic fuel cutoff ? hmmmm maybe not, maybe not always. Although rockets usually INHIBIT all the automatic shutdowns from when they start moving until they are at least 30 seconds into flight.

 

I don't have any experience and informed opinions with understanding how much fire say a 2 cups of AVGAS can make in a engine bay ? (IE thinking a 2 cups is thrown in before fuel cutoff occurs) .

 

As a electronics person who knows what happens when there are many amps available, I don't see any excuse for an in-cabin electrical fire if precautions for fusing, suitable wire gauges , and wiring integrity (damage to insulation) are followed .

 

-glen

[Old Koreelah]

...I don't have any experience and informed opinions with understanding how much fire say a 2 cups of AVGAS can make in a engine bay ? (IE thinking a 2 cups is thrown in before fuel cutoff occurs)...

 

Glen you've done well by bringing this thread back to the fore.

I start my wood stove each afternoon and often use an outside wood-burner. City people might not realise that most of us farm boys are crap at lighting fires because we grew up with woof-water.

I cup of metho makes a small "whoosh". A cup of petrol makes a much more violent "woof!"

It's sobering to think of a spray of petrol loose in your engine bay, where there's also oil, rubber and wire insulation to catch fire.

 

The more quickly you can shut down the fuel and the closer to the fire, the better.

It's probably the only time altitude is not your friend.

[RFguy]

Let us assume the wiring doesnt catch fire. All teflon, or silicone right ? AND encased in a braid or other armour. Although the gas from burning Teflon is bad. leaving oil, rubber, cable ties, and a shop rag that was left in the engine bay along with a 10mm ring and a couple of sockets. From memory in rally car days a fire was most likely to occur with fuel hose failure or something falls out of carb body. pinned/wired screw joint hoses were not that common in low end auto circles. The manned rocket program people learned early with all their computer control and auto engine shutdowns even if it was about the blow up NOT to shutdown the engine , when the launch vehicle was the most vulnerable.

 

I dont really know much about aviation and engine fires, but I would be pretty sure pixel- bolometer sensors could tell the differences between a fire and the usual red hot engine parts.

 

Does the exhaust header shine a dull red for a engine at 100% in climb out ?

 

I am sure there are readers here that could comment on approximately what goes on with a fire in a light aircraft engine bay ?

 

glen

Edited August 12, 2020 by RFguy

[Thruster88]

As an avid reader of ATSB accident reports I can say that INFLIGHT fire is very rare in certified (VH) aircraft. Unfortunately the ATSB doesn't investigate RAA types where there appears to be a slightly higher rate. One difference I can see is carburetor venting, in the event of a float malfunction VH types vent into the intake whereas Bing carbs used in most recreational types vent over board. I work part time at an aircraft maintenance organisation.

[RFguy]

seems that is known. jezuz. the rotax man on the rotax-owner suggested - vent into a larger tube with clearance, and take elsewhere (this preserves pressure location)

 

https://www.rotax-owner.com/en/general-tech-discussion/1390-bing-carb-breather-over-flow

https://www.recreationalflying.com/threads/bing-carby-altitude-compensation.6548/

 

we are probably generating unwanted thread topic drift away from "fire resistant firewall". not sure here how tight the board likes to run on that ?