Couple comments.
Will an aluminum bulkhead fitting survive a fire? Quite possibly yes. An engine compartment fire will follow airflow, so if the fitting is located in some out-of-the-way corner of the firewall, it probably won't get very hot. In the hot spot however, it will melt.
The steel fitting is fireproof and you get a fatigue bonus. The price difference is about $3.50 (AN833-6). How often do you buy a sure thing for $3.50?
Regarding stainless vs aluminum heater boxes, my experiments agree with the observations on the planeinnovations.com site. Lifespan of a sheet aluminum firewall component is measured in seconds when placed in the 5" square (25 sq in) hot spot of a firewall burn test. Little more price penalty, $65 vs $98 for stainless. That's 33 wasted dollars if you never have a fire. You'd probably pay $3300 to close that 2" hole in the firewall if things go to ****.
Unsized ceramic insulation encapsulated in foil is a safe cabin side firewall insulation, "safe" meaning it will not ignite, unlike so many really dumb choices. A similar insulator placed on the engine side also protects the firewall structure itself. The use of aluminum rivets and aluminum structural angle becomes moot.
I can agree with all of this. Might even change my fuel fitting through the firewall.
What I'd really like to know more than anything, is statistics or testing of a FWF engine/compartment fire in which the fuel (100LL/Mogas) has been removed after a few seconds, but the fire has to be sustained by engine oil, and most likely not atomized, as it is with a modern day oil burner (furnace).
Oil flames can get up in the 3000 F. range too. But with most of it sitting in a pan below the engine, it certainly wouldn't be optimal for combustion, as with a flame thrower test. But.............I'm assuming this.
I do take airplanes and fire seriously. I believe I've already mentioned it on this forum...........I do live next to an airport. Six months before my house was built, a near new Commander (only 341 hrs.) crashed just across the street due to a failure of an exhaust pipe fitting. This is interesting because the fuel lines remained in place, but the fuel vaporized. I've copied below:
A few years ago, a Bonanza ended up with just a engine mount, door, wheel, and vertical tail laying against the street behind my home. Was about 1/2 mile away though. It was consumed by fire after a cartwheel, when the plane couldn't gain & sustain altitude.
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NTSB Identification: FTW98FA325 .
The docket is stored in the Docket Management System (DMS). Please contact Records Management Division
Accident occurred Saturday, July 18, 1998 in WEST JORDAN, UT
Probable Cause Approval Date: 12/1/1999
Aircraft: Commander 114TC, registration: N61174
Injuries: 1 Fatal.
The pilot had washed the airplane and said he was going to 'take it around the pattern.' Shortly after takeoff, witnesses heard the engine backfire, heard a muffled explosion, and saw flames and smoke coming from the engine area. The engine was 'sputtering' as the airplane descended and collided with terrain in a residential area. The stainless steel shroud around the turbocharger was scorched and discolored. The main fuel line showed signs of high heat distress, but had not been breached except where it attached to the separated engine.. The exhaust pipe was separated from the turbocharger, and the clamp that held it in place was broken. According to the metallurgist's factual report, there was a brittle transverse fracture of the circumferential tensioning band near one of two resistance spot welds, and had propagated to both edges of the band. There were preexisting cracks at both of the spot welds. The airplane had accrued only 343.1 hours since manufacture.
The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
A brittle fracture of the clamp that joins the exhaust pipe to the turbocharger. The pipe separated and hot exhaust gases escaped into the engine compartment. The engine lost power due to the high heat vaporizing fuel in the fuel line. Factors were inadequate quality control by the clamp manufacturer; the pilot's intentional maneuvering of the airplane to avoid houses and personnel, and the lack of suitable terrain on which to make a forced landing.
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L.Adamson - RV6A
). Anyone have any thoughts on this? (Optional follow-on question...is there such a thing as a steel AN Spacer a la the one's Van's sells?).
