Engine Compartment Fire Prevention

All of us fear and inflight fire. There has been a ton of very good discussion on making the firewall as fire resistant as practical, to the point that someone following Dan H's designs will exceed anything that most certified airplanes has. But there has been little focused on the causes of firewall forward fires and how to prevent them, which in my opinion is even more valuable.

I could start of by saying that there are fires that happen due to problems somewhat beyond our control, like a catastrophic engine failure, but most are a result of poor design or implementation. Even in the case of a catastrophic engine failure like a connecting rod punching a hole in the crankcase spraying oil on the hot exhaust, there are measures that can be taken to minimize the chance of, or intensity of a resulting fire. FWF is an area of where we can easily control the design and the quality of the installation to minimize the chance of fire.

So with that introduction, it would be interesting to see posts about what folks think is important, and discussions on what techniques might be the best for prevention.

We should consider the basic requirements for fire- fuel, air (oxygen) and ignition source (heat), and how to keep from having all 3 in one place.

Go for it!

Fire prevention

There have been at least two Rocket fires that were caused by improper installation or improper torqueing of engine driven fuel pump fittings and hoses.
hard fuel injector lines(spider to injector) are very important and the Lyc service info should be carefully adhered to.
Stainless firewall bulkhead fittings are available in all common sizes but are rarely seen on EAB.
I have just four pass thrus on my firewall(not RV). Homemade stainless tubing about 2" long with flanges for four stainless screws and nuts. After the cables, wires etc are installed, the tubes are stuffed with fire sleeve and treated with fire barrier.
The most common and most dangerous failure forward of firewall is exhaust failure. If there is an indication of exhaust failure-excessive heat in the cabin, significant noise level change, smoke, etc., there is really only one option and that is to shut down the engine, shutting off the fuel first.
I do 25 hour inspections on everything firewall forward.

I put a wrench to all fluid and exhaust fittings FWF at regular intervals (ie oil changes), or anytime you've got all the cowls off for some reason. I hate fire.

Bevan

Airliner lavatories have trash can squibs that are good to about 77C. I'd love to have 2. One under the panel and another in the accessory compartment. I've looked for them, but because they are reusable, the don't come cheap.

did that once

Might cost more than what it gets you. As an in-flight fire survivor, I think getting down on the ground (any ground) is better than waiting to see if the "system" up front has done its job. I was at 14K plus and made it to the ground in under 3 minutes. The firewall did its job long enough though. It burned to the point NTSB could not find the source or cause.
The smoke was worse than the flames. I carry smoke hoods now... but will probably never see the need. (tempting fate by writing I suppose). The 737 captain that was riding along got bruised, but that was his own fault by not getting the seat belt cinched well enough.
Others will see the engineering challenge here... and come up with some things to build. I just hope the sense of urgency is kept at the forefront if a situation occurs.

Proper fabrication, installation and maintenance of any system is the most important step. There are plenty of factory built airplanes flying with materials that are now considered "dangerous". Aluminum hard lines for the oil cooler, copper, brass, no fire sleeve, etc. Whatever you use, do it right and keep it maintained.

I will also agree that the exhaust scares me the most. A failure here can do a lot of damage without much (if any) forewarning. Listening for a change in engine note is important, but ANR headsets and on board entertainment systems are making that increasingly difficult.

Having the ability to shut off the fuel suply quickly is vitally important. A fire is not going to burn very long without fuel. If the fire is oil fed, I would imagine that an immediate engine shutdown is going to stop the "supply" and remove the heat source quickly. Just curious, anybody have any experience with an oil fed fire continuing after engine shutdown?

The other thing that popped into my head the other day was the proximity of the fuel injector lines to the spark plug wires. With the prevelence of electronic ignition and "automotive" style wires, its not too hard to imagine a break in the dielectric shielding of the wire and have the arc finding the injector line instead. Remember back in the "old days" when your car had a miss and it was because the wires were old and the spark was snapping against the valve cover?

There are plenty of General Maintenance Practices that the homebuilder may not be aware of, but is second nature to a trained mechanic or Engineer. If you can help it, don't safety wire an electrical component to a fluid line/component; don't route a fluid line so that it can leak on something electrical or hot; do maintain adequate clearance between components (passthroughs, fluid and electrical runs, etc). There are plenty of sources for basic design principles available. Certainly AC 43.13 is one, but so is a good old military Technical Order: T.O. 1-1A-8. Great stuff in that last one.

Much is discussed on this forum concerning "protection" from fire. But if we spent as much time on "prevention", we'd be a whole lot better off.

Toobuilder said:

Much is discussed on this forum concerning "protection" from fire. But if we spent as much time on "prevention", we'd be a whole lot better off.

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Mike, sorry, but that's just nonsense. Why should anyone believe folks who (1) think about risks and (2) eliminate them by design are any less conscious of good maintenance practice?

I'm not suggesting that it is a "one or the other" situation. My point is that this forum tends to obsess on making sure we use the "best" magic bullet - firesleeve, steel fittings, etc. and then fabricate it incorrectly or do something dumb like zip tie the battery cable to a fuel line in the cockpit.

My only suggestion is that we pay attention to doing something properly in the first place so that we don't need to test if the fire protection is effective.

Engine fire

3 yrs ago i had an engine oil fire fail on my RV6 over KHFD at night vfr and was lucky enough to glide to HFD airport. Vibration then smoke via the heater duct, was at 6,500' a few miles away and dove at 200 which kept the flames under me. Must have looked good to the TWR, upon touchdown i noticed them around the cowl and got out PDQ. Also had an exhaust pipe break on a Bonanza, very loud but was able to land under power at the nearest airport, no other damage. P.S. Insurance don't pay for the part that came from the all together, ie. Motor$

hawker said:

3 yrs ago i had an engine oil fire fail on my RV6 over KHFD at night vfr and was lucky enough to glide to HFD airport. Vibration then smoke via the heater duct, was at 6,500' a few miles away and dove at 200 which kept the flames under me. Must have looked good to the TWR, upon touchdown i noticed them around the cowl and got out PDQ. Also had an exhaust pipe break on a Bonanza, very loud but was able to land under power at the nearest airport, no other damage. P.S. Insurance don't pay for the part that came from the all together, ie. Motor$

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What caused the RV 6 fire?

Fire

Not 100% sure, oil starve via a line and blew the case apart, but fire damage was severe and they could not say. No leaks on preflight, no warning lights.

Link to source of smoke hood?

bkthomps said:

Link to source of smoke hood?

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http://www.aircraftspruce.com/menus/ps/survival_smoke.html

I also pay very close attention to things simply nearby the exhaust. Rubber or worse poly motor mounts and other such things.

tj

Exhaust wrap?

what are your thoughts on wrapping the exhaust pipes with a thermal insulator to keep the surface temps down? i have this on the headers in a kit car where the engine is closely surrounded by fiberglass and it works well.

Jasonm said:

what are your thoughts on wrapping the exhaust pipes with a thermal insulator to keep the surface temps down? i have this on the headers in a kit car where the engine is closely surrounded by fiberglass and it works well.

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Makes inspection impossible. Hides problems, like cracks, really well. It also can render the exhaust system un-repairable/weldable due to the elevated temperature of the stainless. Something in the physics of the metal changes.
Been there, won't go there again.

Jasonm said:

what are your thoughts on wrapping the exhaust pipes with a thermal insulator to keep the surface temps down? i have this on the headers in a kit car where the engine is closely surrounded by fiberglass and it works well.

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Dont.

Your car headers are a different material than aircraft units.

Value of a CO detector

My CO detector went off when I had an exhaust crack. Excellent insurance in my opinion.

LeRoy Johnston RV-6A Esperanza 980 hours

An aircraft exhaust system builder once told me that coatings cause the pipes to run too hot causing degradation. They need the cooling from the air going through the cowl.

Bevan