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Mixed aluminum and steel AN fittings

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  • Mixed aluminum and steel AN fittings

    I found a short thread on VAF about 8 years ago on the subject. I want to use steel bulkhead fuel fittings at the firewall. But I would prefer to use aluminum hose ends. Anybody have an opinion on aluminum fittings with a steel bulkhead fitting, using aluminum torque specs? The thread wasn't that long, or definitive.

    Is a steel bulkhead fuel fitting required? There are several threads on VAF where some people claim everything FWF should be steel fittings, and others say not required.

    For me, an engine fire would be be an immediate engine shutdown, on the ground or in the air. The glider vs Roman Candle thing.

  • #2
    I too couldn’t find anything definitive about the all steel fuel fittings FWF thing. I can say that both my core engines that came off certified planes had a mix of Aluminum, brass and steel fuel fittings on them. The hose ends were steel. I used aluminum bulkhead fittings, aluminum hose ends, steel fittings on the red cube and fuel servo, and left the bass fittings in the fuel pump. DAR didn’t bat an eye.
    Scratch Built 4-place Bearhawk. Continental IO-360, 88” C203 McCauley prop.


    • #3
      My Citabria uses steel fittings on the firewall. Steel fittings on hose ends. I elected to do the same. When you think about it however the carb is aluminum so in terms of fire not sure how much a steel fittings would buy you.


      • #4
        The certified airplanes referenced likely use steel fittings on the firewall to show compliance with FAR 23.1191 which requires the firewall to withstand a 2000 F flame for 15 minutes. It allows the use of steel fittings without a dedicated fire test. I know these regulations don't apply to homebuilts, but it provides good requirements for safety and preventing the fire from penetrating into the cabin. There are other regulations for components in the engine compartment, thus the use of aluminum in some places.

        Since aluminum and steel are not compatible from a corrosion standpoint, probably should not use different materials for hose fittings and bulkhead fittings.


        • #5
          Since I thought of the question, that probably provides the answer. I will probably just use either all steel or all aluminum on the firewall. Probably aluminum.


          • #6
            Steel is in contact with aluminum all over the place on the Bearhawk, and in commercial aircraft for that matter. In some places (like the lower wing strut attach) where water penetration is possible I'll be using anticorrosion paste. In a hot engine bay I'd be less concerned about that.

            Anyway I'm locating the aluminum firewall fuel bulkhead fitting just outboard of the tunnel, away from any sustained flame in the engine bay I could think of.
            Dave B.