Steel AN fittings - some questions

Flying Scotsman · #1 03-02-2010, 04:23 PM

Thinking of using a steel AN bulkhead fitting for the fuel line at the firewall (hey, everything else there is steel, why not this fitting, too?

). 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?).

Just wondering about the possibility of dissimilar metal corrosion in the aluminum-to-steel interfaces, etc.

erich weaver · #2 03-02-2010, 04:42 PM

Dont forget to replace all the aluminum rivets in the firewall with steel ones as well

Steel rather than aluminum fittings at the firewall arent high on my priority list, but if it makes you more comfortable, I dont see any strong reason why not to use them. Are you concerned about heat tolerance? If you are at the point where it would make a difference, I dont think a fitting or two is gonna make or break you. Galvanic corrosion shouldnt be an issue unless you get persistent moisture caught between the two metals. Im not aware of any steel spacers available, but you may be able to make your own using a fender washer as a starting point

erich

Flying Scotsman · #3 03-02-2010, 05:02 PM

Yeah, I know, it's probably way overkill, especially given the (as you noted) bunches of aluminum rivets

. I just figured if you replaced the cabin heat valve with a steel one to prevent a great big blast of flame and smoke and fumes, why not replace the fittings to prevent a smaller one? Of course, then there are all those rivets to melt away and create hundreds of tiny little jets of flame and smoke! LOL!

Steve

GAHco · #4 03-03-2010, 10:07 AM

Quote:

Originally Posted by erich weaver

Dont forget to replace all the aluminum rivets in the firewall with steel ones as well

Steel rather than aluminum fittings at the firewall arent high on my priority list, but if it makes you more comfortable, I dont see any strong reason why not to use them. Are you concerned about heat tolerance? If you are at the point where it would make a difference, I dont think a fitting or two is gonna make or break you. Galvanic corrosion shouldnt be an issue unless you get persistent moisture caught between the two metals. Im not aware of any steel spacers available, but you may be able to make your own using a fender washer as a starting point

erich

I used Cad plated Monel rivets for the engine mount corner brackets. That was one area I thought would not be overkill; and increase the safety factor. A little stronger and much more heat resistant.

I will be using steel or stainless steel for all fuel penetrations.

aerhed · #5 03-03-2010, 10:19 AM

I was taught to use steel on fuel FWF. Vibration is the biggest reason. You get hot enough to melt aluminium you got other problems. I'm using a 6D fitting on the firewall but probably shouldn't. ****, now I gotta take it off. I hate this forum.

L.Adamson · #6 03-03-2010, 10:31 AM

Quote:

Originally Posted by Flying Scotsman

Yeah, I know, it's probably way overkill, especially given the (as you noted) bunches of aluminum rivets

. I just figured if you replaced the cabin heat valve with a steel one to prevent a great big blast of flame and smoke and fumes, why not replace the fittings to prevent a smaller one? Of course, then there are all those rivets to melt away and create hundreds of tiny little jets of flame and smoke! LOL!

My first thoughts regarding an engine fire... will be immediately turning the fuel selector to off, which will eliminate a major fuel source for an ongoing fire.
I'm a furnace guy by trade, and it's amazing of what turning off the gas will do!

I have a hunch that if a raging engine fire is getting through the penetrations of a firewall..............then the fiberglass cowling and windscreen are going to be having some major problems as well. At this point, we'll assume the fuel source is just oil.

In the meantime, I've used aluminum AN fittings at the firewall, but a steel fitting on the carb, since it's small & has a better chance for the shakes. My larger fittings for the oil cooler are aluminum AN.

L.Adamson --- RV6A

DanH · #7 03-03-2010, 11:12 AM

FAR 23.1191 (3)(g): Firewall materials and fittings must resist flame penetration for at least 15 minutes.

But hey, fire is no big deal.

The Feds were just being cautious when they wrote the FAR, and the Mil specs for fire resistance are just a fantasy. The fire test handbooks? They just flat made up all that stuff....sorta like the moon landings.

All you need to snuff a fire is superior pilot skill.

Anyway, everybody knows homebuilts are less safe, so why bother with details?

Auburntsts · #8 03-03-2010, 11:28 AM

Just curious. For the firewall has anyone substituted steel rivets for all of the standard aluminum ones that come with the kit? How difficult are they to set vs aluminum?

L.Adamson · #9 03-03-2010, 12:33 PM

Quote:

Originally Posted by DanH

FAR 23.1191 (3)(g): Firewall materials and fittings must resist flame penetration for at least 15 minutes.

But hey, fire is no big deal.

The Feds were just being cautious when they wrote the FAR, and the Mil specs for fire resistance are just a fantasy. The fire test handbooks? They just flat made up all that stuff....sorta like the moon landings.

All you need to snuff a fire is superior pilot skill.

Anyway, everybody knows homebuilts are less safe, so why bother with details?

Getting back to "reality"...

Yes, my superior pilot skill will at least snuff the major source of a FWF fire. I'll turn off that stinkin fuel supply.

The 2000 degree flame thrower test for 15 mins certainly doesn't take into account........all that fiberglass surounding it either. And speaking of fiberglass, that "certified" Cirrus descending by it's parachute last month, didn't look too safe either. I felt just horrible for it's occupants. At the same time, I guess we should be thrilled that our RVs are a lot more metal! Burning fiberglass boats evaporate in just a few minutes too. The FAA might have to ban fiberglass planes, and Boeing could be on the wrong track too.

Yes, I'm spouting off a bit. Perhaps I shouldn't. But in the meantime, my 3/8" fuel fitting that penatrates the firewall is about 4" from my fiberglass cowling. It's also an aluminum AN fitting. Worse than that, I can't remember if my heater duct is aluminum or stainless steel, as it's been much too long since I installed it.

So again, looking at the whole situation in a realistic way, at what point is it all overkill? At what point has the complete fiberglass cowl gone up in smoke before my AN fitting at the bottom of my firewall has melted.

This is the exact reason I don't go for the flame thrower test. Yes, it proves the durability of stainless steel and possible firewall insulations. But that's all it does! It doesn't take into account the rest of the aircraft firewall forward, and what's left when temps reach that high. What's happening to everything else!!! And yes, I'm a furnace guy. Have been looking at flames for nearly 40 years. Maybe I'm just num.

Perhaps the whole shell firewall forward (cowl & all) should be stainless steel. Or we can just stay on the ground, and forget it all! End of rant...

L.Adamson --- RV6A

SMO · #10 03-03-2010, 12:59 PM

I noted the new Aerosport Power engine for my -4 was supplied with all steel fittings. On my Rocket the FW rivets appear to be stainless. I have steel fittings for all the FWF stuff and anything going through the FW. I will also use a stainless heater box. And I will put some fireproof ceramic material on the floor and inside the firewall.

Overkill? Maybe, but fire in the air scares me. I firmly believe a few extra seconds of protection could make the difference between running away or becoming a crispy critter. I am definitely not numb!