Firewall Forward: Aluminum versus Steel

[Rob Erdos]

I just noticed that my plans specify aluminum pipe fittings forward of the firewall. Why does Van specify aluminum (e.g. AN822-4D) when steel fittings are not-quite-as-cheap? Wouldn't steel fittings be safer?

Awaiting enlightenment,

Rob Erdos

[vlittle]

I have an opinion (not necessarily correct). I try to use steel fittings when:

-the fitting is screwed into the engine or other expensive part such as the oil cooler. This should minimize cold welding.
-the fitting carries fuel (also use steel fitting on the fuel lines). It won't melt during the fire (maybe too late!)

Al to Al fittings work well, as do Al to Steel. Apparenty, steel to steel fittings need more torque because the steel is hard and does not seal as well.

V

[frazitl]

and recommend steel, stainless steel, or fire-sleeved flex lines for all fuel and oil lines and fittings FWFD. It's a little heavier and a little more expensive, but the time to burn through aluminum lines and fittings has to be much less than for steel. Sure, the oil cooler is aluminum, and so is the fuel injection servo body and spider. Nonetheless, fuel or oil under pressure spraying around FWFD scares me enough to take every reasonable precaution I can...

Call me chicken

[NDrv8r]

another reason to use steel fittings on fluid carrying lines firewall forward is that they are more crack resistant.

[Wayne Gillispie]

I am using what is provided, using fuel lube, torqing, and supporting lines properly. If we have a fire hot enough to melt alum ftgs with oil/fuel inside of them then your cowling/bottom skin/oil cooler/fab are in big trouble. All we can hope for is to be in the flare over a lake close to shore.

[L.Adamson]

Originally Posted by Wayne Gillispie

I am using what is provided, using fuel lube, torqing, and supporting lines properly. If we have a fire hot enough to melt alum ftgs with oil/fuel inside of them then your cowling/bottom skin/oil cooler/fab are in big trouble. All we can hope for is to be in the flare over a lake close to shore.

That's been my take for a long time. I figure the cowling and windscreen won't be around too long. My plan is to shut off the fuel. I do have a steel fitting connected to the carb.

L.Adamson --- RV6A

[Walt]

I prefer steel fittings FWF for the extra strength they provide, this is especially true on the engine which is subject to significant vibration.

[DanH]

Originally Posted by Walt

I prefer steel fittings FWF for the extra strength they provide, this is especially true on the engine which is subject to significant vibration.

Exactly.

Engines shake. Aluminum has no knee in the SN curve.

[Alan Carroll]

Originally Posted by Rob Erdos

I just noticed that my plans specify aluminum pipe fittings forward of the firewall. Why does Van specify aluminum (e.g. AN822-4D) when steel fittings are not-quite-as-cheap? Wouldn't steel fittings be safer?

We can only speculate on Van's motives, but it could have something to do with the fact that aluminum fittings are considerably lighter.

Personally I'm skeptical that steel fittings help much with fire safety. Surely the rubber hose will be gone long before the aluminum fitting to which it is attached? Fatigue strength is another matter however.

[jtrusso]

I was just going to ask this question.

I just bought into a share of a Glassair and all the fittings FWF on the fuel and oil lines are Al. All the fuel and oil lines are braided stainelss over teflon and fire sleeved, which is good.

I was wondering what the brain trust thinks about leaving it alone vs replacing with steel. I think it's better to leave them alone because the system has been tested and has no issues. If we tear it apart (assuming I could get the partner to go for that) we run the risk of building in a problem. Seems like the risk to reward ratio doesn't pan out. These lines were installed about 7 years ago when a new O-360 was installed.

I know, it's not an RV...but it's close enough for now. I'll still get that RV someday!