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prkaye

Well Known Member
Reading a bunch of threads about fires, and firewall insulation etc, I came across one account of a fire (that ended without injury) where the fire actually apparently burned through the aluminum on the belly of the aircraft just aft of the firewall. I've seen such things mentioned on other threads too. When I think about it, I could imagine that a fuel leak around the mechanical fuel pump could spray fuel backwards towards the exhust pipes where the heat from the exhaust would ignite it. Seems to me this could end up creating basically a flame thrower directed towards the belly of the airplane.

We install a stainless steel firewall (some insulate this firewall), but even with the best firewall in the world, it seems to me a fire could still burn through the aluminum floor causing smoke and intense heat to enter the cabin that way.

Has anyone considered replacing the forward aluminum floor skin (under the area where your feet go) with a stainless steel skin? This would obviously have to be done at build-time. I guess this would imply a huge weight penalty.
 
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Stainless

I've seriously considered it after seeing and examining the RV-6 fire here at KFFC a few years ago that I wrote about. Perhaps even pop-riveting a thin layer of stainless under the fwd floor area behind the firewall would be fairly easy and effective.
 
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SS Belly Skin

I have an .020 SS overlay on the belly of my HR II that extends from the firewall overlap to approx. 20" aft of fw - I did it during the building process after another Rocket suffered a burn through of the forward floor boards and the owner succumed to his injuries. I also installed a fire suppression system, with its own dedection system (w/realtime temp monitoring in the affected areas), and have two smoke hoods hidden under the forward floor boards. Hope I never have to use any of it -- just like insurance!
 
Vern said:
I've seriously considered it after seeing and examining the RV-6 fire here at KFFC a few years ago that I wrote about. Perhaps even pop-riveting a thin layer of stainless under the fwd floor area behind the firewall would be fairly easy and effective.
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I've thought about that too and think the overlay technique would be the way to go. Even 0.020" SS would be a huge improvement and would <probably> allow plenty of time to turn off the fuel before a fire penetrated the floorboards.

On the -6 model, you could even extend the stainless forward and bend upward into an airflow smoothing radius to help with engine cooling...
 
This idea of a SS overlay is one of my many "someday" projects------I plan on putting a layer of fiberfrax under the SS.
 
Material swap/ add

I like the add on idea over the replace idea. By the time you get some Stainless that can replace aluminum structurally, you are likely to be in the 1/2 or full hard range. It is tough to work. Adding on using nut plates and 1/8" spacers with some insulation between that and the skin sounds really good. Insulation only on the inside needs some support, and that will melt away if it is aluminum.
 
I am not disagreeing about whether a SS belly might protect certain fire scenarios. Clearly it would. However, is it proportionate, or necessary, or could it be mitigated in another way?

Do certified aircraft have such protection? Is it really a problem? Are you trying to protect the occupant(s)? Or save the aircraft?

I would guess that if this area concerns you, there are some priorities you could apply in the design / build / maintain process that would be easier, take less overall time and redcue the overall risk more easily:
  1. Use well sourced / upgraded spec components in the fuel system firewall forward e.g. steel not Al. Wirelock everything.
  2. Be conservative in the design. Make bend radii larger. Eliminate unneceesary components / joins e.g. a fuel flow sender is a "risk", and by some accounts more so if mounted on the engine not firewall.
  3. Get 2nd or 3rd opinions / inspections on your design and build.
  4. Make the system easily inspectable e.g. through the oil door, exhaust outlet area.
  5. Provide drains from risk areas / components. Think drain paths. A fuel leak will not kill you, the risk is that leaked fuel then pooling and igniting.
  6. Considerably reduce the inspection interval e.g. to 25hrs, 10hrs, whatever. Enhance the inspection regime in these areas.
And of course, study the (few) applicable accidents carefully and really understand "why" they occurred, and what preventative measures would have worked.

I'm not asking for direct comments on the above - a short amount of research would see your knowledge exceed mine quickly. I just think you are looking at a lot of hassle / weight / cost to counteract the effects of a fire, when that effort could be better and more easily spent preventing the fire in the first place - and all that is after you have truly analysed the risk versus what really tends to kill pilots.
 
Not sure of the configuration of other aircraft but on the -10, the tunnel appears to be a high-risk area with fuel piping and electrics for the pump and flow sensor. I am sure we are all aware of the couple of serious incidents over the last year or so.

I am just completing the fuselage and am trying to work out some way of fitting a spring-loaded flap to the top of the tunnel. In the case of a fire, switch off the fuel and discharge the extinguisher into the tunnel. Doesn't really help with a FWF fire creeping back, though.
 
Andy Hill said:
I am not disagreeing about whether a SS belly might protect certain fire scenarios. Clearly it would. However, is it proportionate, or necessary, or could it be mitigated in another way?.
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Andy's approach is valid. I'd like to add one item. After ensuring fuel security the single most important step you can take to improve fire safety is to not place the wrong materials in contact with the back side of the firewall, or the inside the forward floor panel. Nothing at all is much better than a bad insulation.

Please note that materials meeting FAR 25.856, Appendix F, Section VI are NOT suitable for contact with metals at 2000F. When a vendor quotes this section to sell you an insulation, the kindest view is to consider it a stupidity test....his or yours.
 
I added a layer of .016" stainless to the floor of my Rocket, covering the belly skin from the outside. I riveted it on with standard AN426 rivets, but would like to drill those out and replace them with stainless rivets. Stainless AN426 rivets do exist but I have not been able to get a hold of any. Anyone know where I can get them?
 
Rivets

MS20427*M* I think the M is for monel
How many and what size? I have access to a few of the shorter sizes. PM me.
 
rocketbob said:
I added a layer of .016" stainless to the floor of my Rocket, covering the belly skin from the outside. I riveted it on with standard AN426 rivets, but would like to drill those out and replace them with stainless rivets. Stainless AN426 rivets do exist but I have not been able to get a hold of any. Anyone know where I can get them?
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Monel at GAHCO.

The RV8 has a cowl exit ramp inset into the belly. Replacing the built-up aluminum ramp with a 0.020 stainless ramp improved several issues. The price is one pound.

24vogac.jpg


Bob's use of thinner (0.016") stainless as a belly overlay is a good call. I suspect you could go a lot thinner and still have all the flame protection benefits.

You should not expect a stainless belly overlay to allow placing foam rubber or plastic insulation in the cockpit, above the aluminum belly skin. The stainless overlay and the aluminum skin will still get hot. It may even melt the aluminum, but the stainless will exclude flame from the cockpit.

I realize many builders want carpet. If you must insulate or fill the floor, at least lay down a layer of unsized ceramic batt to isolate the hot belly from whatever you have above it in the cockpit.
 
DanH said:
Nothing at all is much better than a bad insulation.

Please note that materials meeting FAR 25.856, Appendix F, Section VI are NOT suitable for contact with metals at 2000F. When a vendor quotes this section to sell you an insulation, the kindest view is to consider it a stupidity test....his or yours.
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Since we are one of the vendors that offers insulation meeting FAR 25.856, I must disagree with Dan H's "stupidity" comment quoted above. Dan can have his opinion, but that doesn't make his view correct for everyone.

We never claim that any of our insulating materials are fireproof. Anyone who assumes that any material is fireproof is a fool. The information regarding the FAR 25.856 is listed to give the buyer a point of reference. Surely, it is better to use a material that is a least minimally tested than something unknown from the local auto store or refrigeration supply house.

Dan H can advocate lining the inside of all RV cockpits with space shuttle tiles if he wants. That is up to him. However, having flown many RVs, I find that the main cockpit heat problem is hot feet, not fire.

Our insulation products were chosen to minimize heat and sound infiltration and be cost effective, durable, and as safe as is reasonably possible, not to protect against fire.

Besides, any serious fire is going to burn through the belly skins in short order as others have rightly pointed out. For that possibility, I have a parachute and an aqueous based fire extinguisher in my Rocket. I hope to never need either of them.

While I applaud Dan H's work with firewall material choices, I disagree with taking his data as gospel and using it to the point that your airplane becomes unnecessarily hot, noisy, expensive, and heavy. Everything else on an airplane is a compromise. The firewall is no different.

I sincerely hope that Dan will continue to do his normally GREAT job for the RV crowd. His work is very helpful. But I also hope that he is more careful at choosing words that might imply that others have ideas that are less viable than his.
 
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SS foil

Slight amount of thread drift here but,
Enco sells stainless steel foil that is 2 mills thick and could be used to wrap ceramic blanket.
Stainless foil would be a little bit heavier, but would help with the heat.
Would it be worth while?
Also, how much ceramic batting is necessary to work, 1/2" or less?

Dave A.
6A build
 
Just did a cooling ramp upgrade 2 months ago with my annual. After reading about the rash of RV/Rocket fires it made me realize it could happen to me too.

I used .016 ss with a layer of Fiberfrax in between the fuse and fireshield and attached everything with ss blind rivets.

I then sealed around my transponder antenna and fuel vents with Biotherm 100...I know its not the best stuff but is what I had and should be sufficient in that application.

Hopefully it will never be tested but it still makes me feel safer.

Glenn Wilkinson
 
vfrazier said:
Dan H can advocate lining the inside of all RV cockpits with space shuttle tiles if he wants. That is up to him. However, having flown many RVs, I find that the main cockpit heat problem is hot feet, not fire.

Our insulation products were chosen to minimize heat and sound infiltration and be cost effective, durable, and as safe as is reasonably possible, not to protect against fire.

Besides, any serious fire is going to burn through the belly skins in short order as others have rightly pointed out. For that possibility, I have a parachute and an aqueous based fire extinguisher in my Rocket. I hope to never need either of them.

While I applaud Dan H's work with firewall material choices, I disagree with taking his data as gospel and using it to the point that your airplane becomes unnecessarily hot, noisy, expensive, and heavy. Everything else on an airplane is a compromise. The firewall is no different.
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That's my take on it also. My business is gas furnaces. I've seen flame after flame for over 40 years now. I don't see a continual source of fuel for the sustained flame thrower effect at 2000 degrees........when a fuel valve is within reach. Oil would also have to be atomized.

I'm convinced, that if the firewall & belly is hot enough to burn through, or cause materials on the other side to reach a combustable temperature, then the cowling, and windscreen will also have major problems.

As has been previously discussed, careful plumbing of the fuel lines, and properly securing them, is of most importance.

L.Adamson --- RV6A
 
L.Adamson said:
Unless it's truely going un-noticed.............turn off the fuel supply.

L.Adamson --- RV6A
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Good advice, however if I remember correctly the fire in the RV10 that burnt through the floor went unnoticed for some time. It seems to me that an effective fire warning system would be the first priority and would make a stainless steel floor largely redundant as the pilot would quickly stop the fire by turning the fuel off.
Also if I remember correctly the fire in the RV10 originated at the fuel pump but the flames and heat were carried by the air-stream straight down to the cowl exit with no damage to the adjacent firewall components.

With these two points in mind I have installed a cowl exit air temp probe mounted through the cockpit floor on the aircraft centre line just aft of the firewall to hopefully detect an engine compartment fire (EGT probe to a stand alone instrument with an over temp alarm). Hopefully I will never have to put this alarm to the test but I am confident it would warn me of an engine compartment fire before any serious damage is done including to the aluminum floor.

Fin
9A
 
Fin,

Good idea. The Dynon has provisions for a couple "general purpose" thermocouples (which I never found use for), so I may follow suit and install some sort of temp probe in/on the belly area.

cheers,
greg
 
rocketbob said:
...Stainless AN426 rivets do exist but I have not been able to get a hold of any. Anyone know where I can get them?
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The Monel AN426M rivets that someone else suggested are probably the best and most elegant solution. But an alternative for some areas might be Monel pop rivets such as the MK319BS and MK419BS. I'd be inclined to put a bead of RTV or similar seal on the stem of each one before pulling it.
 
Fusible links in a series circuit

Is what i am installing in a few weeks in addition to the fiberfrax/ss combo on the bottom. L. Adamson has seen many in use too as we are both in the hvac field. Simple, lightweight and reliable.
 
From a corrosion viewpoint Al and SS are not that happy together. Direct contact with each other with difficult to examine assemblies probably ought to be avoided.
 
Rivethead said:
From a corrosion viewpoint Al and SS are not that happy together. Direct contact with each other with difficult to examine assemblies probably ought to be avoided.
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Like where the firewall and fuse meet on our planes???
 
Dissimilar metals

For smaller overlaps like the firewall, a good epoxy prime and sealant is sufficient. Between skins I have had excellent results on gulf coast off shore helicopters by laying a layer of packing tape over primed aluminum and installing with wet sealant. The tape trick also works good on nutplates as the cad plate eventually is sacrificed and aluminum corrosion can start unless electron flow is halted. Also keeps sealant out of threads.

Will MS20427-3M4 rivit be long enough?
Cherry Monel CR3522 and CR5352 are nominal and oversize. I don't know if they make a NAS1097 style head like the CR3214 in Monel, anyone know?
 
Wayne Gillispie said:
[Fusible links in a series circuit] Is what i am installing in a few weeks in addition to the fiberfrax/ss combo on the bottom. L. Adamson has seen many in use too as we are both in the hvac field. Simple, lightweight and reliable.
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Wayne,

At the risk of contributing to thread drift, could you elaborate on where someone might find fusible links appropriate for this purpose? Or maybe you'd make your own out of fine-gauge wire? I understand the principle, just not sure where or how to select the parts. It does seem like cheap insurance, and since I have some unused switch inputs on my annunciator panel (and EFIS) I was thinking I would try to source some and make my own simple fire detection loop.

thanks,
mcb
 
Matt, search thermal cutoff and look at bottom of this page http://catalogs.johnstonesupply.com/3128_johnstone_202/full.asp?page=381 from Johnstone Supply. I am using an 1A fuse, 18 ga wire(for durability) with those soldered in and heat shrink applied. I am using 262F limits. If you have a fire the limit opens, takes power away from my 5 terminal relay which then brings on my led above the grt efis. I will put one near the spider, near rear of fab, and at cowl exit which is below mech fuel pump.

For about 1 lb in materials it may give you a little heads up. Then you can look at fuel flow/pres, oil pres/temp, circle to check for smoke behind you, etc.

On the bottom ss... like others said prime, paint, use fiberfrax except on riveted joint, seal joint with proseal(as smoke will be outside the cabin). On my mostly finished -10, I will have to use MSP-42 or ss sheetmetal screws as I cannot get to the back side under my floor pans.
 
Wayne Gillispie said:
Matt, search thermal cutoff and look at bottom of this page http://catalogs.johnstonesupply.com/3128_johnstone_202/full.asp?page=381 from Johnstone Supply. I am using an 1A fuse, 18 ga wire(for durability) with those soldered in and heat shrink applied. I am using 262F limits. If you have a fire the limit opens, takes power away from my 5 terminal relay which then brings on my led above the grt efis. I will put one near the spider, near rear of fab, and at cowl exit which is below mech fuel pump.

For about 1 lb in materials it may give you a little heads up. Then you can look at fuel flow/pres, oil pres/temp, circle to check for smoke behind you, etc.
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Thanks Wayne. Looks like those are the same thermal fuses used in coffee makers and the like, so they should be easy to source. I was also just looking at some linear fire detector wire like this: http://www.protectowire.com/products/protectowirelhd.htm Clever idea, maybe worth checking out.

mcb
 
Wayne Gillispie said:
I am using an 1A fuse, 18 ga wire(for durability) with those soldered in and heat shrink applied. I am using 262F limits. If you have a fire the limit opens, takes power away from my 5 terminal relay which then brings on my led above the grt efis. I will put one near the spider, near rear of fab, and at cowl exit which is below mech fuel pump.

For about 1 lb in materials it may give you a little heads up. Then you can look at fuel flow/pres, oil pres/temp, circle to check for smoke behind you, etc.
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Hey Wayne, I like this idea...it even sounds easy to retro-fit, since I can't really retrofit the stainless steel on the belly. One question, though...is the 262 F limit high enough? I'm assuming that you'll get radiant heat from the exhaust higher than that. For fire detection, wouldn't you want it much higher, like over 600 F?
 
Rash?

"After reading about the rash of RV/Rocket fires it made me realize it could happen to me too."

Glenn654: I'd like to hear about the rash of Rocket fires.

Carry on!
Mark
 
Sonny, I am starting at a low temp limit until I start flying and will get some actual temps with my 4 probe thermistor temp tool that I use to check hvac systems. Then I will increase until 50F or so higher. I will try to shield it from radiant exh heat as much as possible. My solder joints won't withstand over 350F or so. Of course I could use male and female terminals or butt splices.

As with most sensors/indicators, we don't want to panic with just one indication of a problem. At least this is something to alert me. After hearing about my friend's fire going unnoticed for a few minutes I am going to take as many precautions as possible including someone flying beside me on first flight.
 
Rash of RV/Rocket fires.

Of three I know about two were due to failure to tighten firewall forward fuel line connections. 100% preventable

The third was in a non-standard fuel system...cause unknown to me.

Use quality components. Check and double check (triple check) all connections. If this is done fires would be a rarity more so than now.
 
Wayne,
Could you post some photos of your SS install on the belly. I am headed this way also. Maybe after you complete it I should fly over and check it out.
Bill
 
Monel is better! IMHO

rocketbob said:
I added a layer of .016" stainless to the floor of my Rocket, covering the belly skin from the outside. I riveted it on with standard AN426 rivets, but would like to drill those out and replace them with stainless rivets. Stainless AN426 rivets do exist but I have not been able to get a hold of any. Anyone know where I can get them?
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We stock monel and stainless, I prefer the Monel. The drive easier and will take alot of heat too. They are more compatible with aluminum and fine with the sheet stainless.

My thought is that the aluminum will remain the primary structure and the stainless is just an overlay for extreme heat emergencies.

To see some tech info http://www.gen-aircraft-hardware.com/images/pdf/solidrivets.pdf

Figuring out how to attach after the fact will take some thinking!
 
To F-1 Boss...

After reading this site thoroughly for approximately 10 years, I can't remember a period when there has been three inflight fires within a month and a half.

Seems like a "rash" to me but could have substitued "several" or "series" or some other preferred term.

I certainly did not expect to offend anyone and didn't mean to and these fires are not a reflection on any particular design, I see it as a firewall forward problem.

I am certain each builder/pilot was as careful as possible but no man or man-made thing is beyond error or failure.

And that was my intended point and reason for my added safety feature.

Also, whoever made the point about possible corrosion between Al and SS...Thanks, I didn't realize there was much of a problem between those materials, may replace the SS self-sealing blind rivets I used with Monel.

Anyway YMMV....


Glenn654
 
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