Fuel hoses to/from fuel servo

[Nev]

Is there any requirement to have steel fittings on these fuel hoses ? Is it ok to use aluminium fittings ? Is there a preference between Stainless steel, Steel, and Aluminium?

Thanks.

[Rollie]

It's experimental so at least here in the US, you can do what you want. I think standard practice is to use steel fittings forward of the firewall on both fuel and oil lines. Any line that has fire sleeve on it shouldn't have aluminum fittings. That's how I understand it anyway. Stainless or not, I think would just be personal preference.

[Nev]

That was my impression too. But then I realised that large parts of the engine are made of aluminium, which upsets the logic I had been using up to this point. I believe even carburettors on Lycomings are made from aluminium. So now I’m wondering why I’m trying to protect the ends of a fuel and oil hose, when other fuel carrying parts aren’t going to survive anyway.

Where am I going wrong with my logic ?

[svyolo]

This is where the search function of VAF works great. I looked into this as well a while back. The mounts for my fuel injectors are aluminum. My oil cooler is aluminum (thin). Lots of the engine is aluminum.

Steel is better. Aluminum is lighter. I chose aluminum. Your choice may vary.

[JimParker256]

Small aluminum parts - especially relatively thin-walled tubing - would in theory be far more impacted by an engine fire than say a carburetor, which is much thicker, and attached to a much larger heat sink... I'm certainly no expert on this topic, but I've noticed that certified planes seem to use steel fittings forward of the firewall, and aluminum aft. Not sure if the weight difference is enough to really "make a difference" but I know some folks live by the "ounces count" axiom. Can't really argue that point...

[Battson]

Corrosion is another long-term consideration with aluminium fittings - probably more of a risk than a consideration - especially for planes in coastal areas or doing beach work. There is dissimilar metal corrosion and plain old oxidization to consider. If the fittings corrode it could lead to a minor leak in the worst case. Yes they come plated but that doesn't provide as much assurance as stainless steel.

It's a footnote at most. Not a big deal.

A fire hot enough to melt fuel line fittings - LOOONNNNG before it gets that intense, you are going to have bigger problems, like the fuel lines themselves melting (it's rubber inside after all), so I think this logic is not applicable here.

[svyolo]

One thing I noticed is that the smaller the fittings get (fuel injection on top of the engine), they tend to use steel, probably for strength of the thinner parts. My fuel lines going to the injectors are SS coated rubber lines with SS fittings. They attach to -3AN AL elbows, into the injectors. The mounts of the injectors are a mix of AL and SS.

The temp rating for the fuel line isn't much different than the non-SS covered rubber lines. It might be the same.