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  • Return fuel lines

    For those that ran return fuel lines to the tanks for fuel injection did you run the lines up the front at the window or in the rear? I can see benefits to both. Front is defiantly shorter and less tubing. The rear location would be potentially less visible.
    Thanks
    Travis M
    Kentucky
    Bearhawk 5 Quickbuilt Kit Plane #5041
    Received December 2022

  • #2
    Disclaimer - I didn't run return lines, but I did run a lot of stuff down the front door post and wanted it to be out of sight and well protected.

    I just used offcut aluminium from the kit to make these box sections you see in the image. They are one piece and slip over the door post, very rigid and strong once secured to the window frame tabs. It also makes a tidy finish for the window and the door seals.

    As pictured, the screws aren't installed to hold the frames to the window. I used nut plates on the window tabs, with short truss-head screws.
    20130608_163150.jpg

    Comment


    • FFTravism
      FFTravism commented
      Editing a comment
      Thanks for the picture. I like the concealer trim on the A post.

  • #3
    Travis, only some fuel injection systems require a return line to the tank. The legacy injection systems, Bendix & Airflow Performance, do not. While we are free in our planes to do largely whatever we want - I prefer the legacy fuel injection systems for the Bearhawks. If you want fuel injection.

    Not trying to start an argument here. Or even a discussion about fuel injection systems and which are best. But I know you are a first time builder. So I thought to chime in. Mark

    Comment


    • Battson
      Battson commented
      Editing a comment
      It's a good comment, simple fuel systems are so important for safety, and return lines do not make the system simpler.
      Not to mention the challenges with not overflowing one side, when you want to fill both tanks.

    • triumphantduke
      triumphantduke commented
      Editing a comment
      Some passive thoughts to share from my personal decision process, this is not to discourage you..just to share.

      My driving reason originally to chase return type fuel injection AND ignition was fuel efficiency, engine longevity(less carbon build up), and cooler fuel (because it returns, so vapor lock is reduced).
      -Fuel efficiency is taken care of with a lambda gauge if you want to be precise, this will also reduce chances of carbon buildup from overly rich mixtures(there are tests done comparing carb to fuel injection for efficiency, where the BSFC was essentially equivalent). From what I gathered, the primary factor that makes us “think” fuel injection is way better becomes clearer when there’s a control for the ignition type used for the comparison. So theoretically, after a baseline, I’d like to eventually swap one ignition out to get the majority benefit while keeping a non-electrically dependent setup(mags for the 2nd). This is all thrown out the window if you like negative Gs or are trying to have a performance setup (max hp available no matter the increase in fuel usage)
      -cooler fuel/vapor lock risk reduction can be achieved with proper down hill flowing lines, insulation, heat shielding, and a carb if you’re extra concerned (b/c of mechanical injection worries of fuel heating around the spider in the heat of summer after shutdown or at a low idle/taxi)

      The appraised value of these thoughts is 2 cents. Just trying to relate, injection is cool though but ended up with too many caveats for my comfort. I think discussion is healthy and reduces the risk of choices made in a vacuum.
      I do not have a completed Bearhawk.
      Last edited by triumphantduke; 03-15-2023, 03:48 PM. Reason: incorrect thought process presented..

    • FFTravism
      FFTravism commented
      Editing a comment
      I am looking at both options. I evaluated my mission with the plane and what we want to do and really the option of running any fuel would be really nice. Mogas/Rec Fuel/100LL and 100GAMA.

  • #4
    I ran my return lines up the front door post. Shorter lines, away from passengers that might accidentally damage them, easier routing and easy to cover. Routing my rear supply lines was a little challenging and sharing that space with return lines would have made it more so. I intended to cover the fuel lines and wiring I ran up the front door posts but I never have.
    Scratch Built 4-place Bearhawk. Continental IO-360, 88" C203 McCauley prop.

    Comment


    • #5
      One consideration: I believe the bank attitude (in exclusion) doesn’t drive the scenario you describe. In the left turn wouldn’t you would generally be in balanced flight (ball centered)? Theoretically then, the remaining fuel would remain level in the tanks, regardless of the bank attitude. It would require a slipping turn to cause fuel to move to the down-side and un-port the pickup at the wing root for a sustained period.

      The slipping turn is of course a common technique, which might need to be avoided at low fuel levels. Conversely, a skidding left turn (which pilots are taught to avoid) would potentially un-port the right pickup. In fact, any unbalanced flight in any normal flight attitude could cause these effects.

      Perhaps this is a case for using a “both” selection? Im not arguing against compelling reasons not to use both-just theorizing. Personally, I’ll be careful if I am doing much maneuvering at low fuel levels. I’m going carbureted as another part of my mitigation strategy.

      Comment


      • triumphantduke
        triumphantduke commented
        Editing a comment
        you're totally right - thank you for catching that! (edit made)

    • #6
      ​Poor Travis, looking for an answer to a simple question.

      What’s 2+2? Everyone: PURPLE!​

      image.gif
      Scratch Built 4-place Bearhawk. Continental IO-360, 88" C203 McCauley prop.

      Comment


      • FFTravism
        FFTravism commented
        Editing a comment
        You feel me on this. Not to offend any of the answers as the info is good but yes. I know fuel injection is a topic with different opinions. I tried to ask it without creating a big debate.

    • #7
      Originally posted by whee View Post
      ​What’s 2+2? Everyone: PURPLE!​
      Ha!
      Ha!​
      Ha!​
      Ha!​
      Ha!​

      Comment


      • #8
        Does anyone know the gravity feed flow rate of a Bearhawk with 3/8 inch fuel lines? A 540 burns about 23-24 gal/hr at full power and I think that some people run that without a fuel pump? Mine is equipped with fuel pumps so I can't make any assumptions from aircraft.

        EDIT: Maybe I can make some assumptions?

        The spec is 125% of flow rate to a pump. On a Bearhawk with feeds from both front and rear of the tank, it really should be 150%, but I should be able to expect that it was tested to at least 30 gph?
        Last edited by kestrel; 03-16-2023, 10:20 AM.

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        • #9
          I never tested it without a fuel flow meter in the circuit, but found on both airplanes around 30gph as I recall. Bob ran his 540 without any pumps but I didn't feel like I could meet the spec without them. Maybe not having a fuel flow meter would help, but for me it's a required item to manage the engine.

          Comment


          • #10
            Maybe someone can check my numbers:

            A 3/8 inch OD fuel line has a wall thickness of 0.035" (I'm uncertain here, I found the spec for 1/2 line) so and ID of 0.305", an ID cross section area of 0.0731" and an ID circumference of 0.958".

            A 1/2 inch OD fuel line has an ID of 0.430", a cross section area of 0.1452" and an ID circumference of 1.351"

            The cross sectional area of the 1/2" line is 1.99 times that of the 3/8" line. So, for the same flow "speed", it should flow about twice the GPH.

            However, it is going to be somewhat better than that because the circumference is "only" 1.4 times that of the 3/8 line so while it has twice the cross section area, it has only 1.4 times the surface area to slow it down. So, a fuel system made from 1/2 inch line should flow more than 60 gph.

            Did I miss anything?

            Comment


            • FFTravism
              FFTravism commented
              Editing a comment
              Friction loss for each one. It doesn't go up or down at a proportional rate typically. Calculating friction loss is something I have to do for my job.

          • #11
            My system flows 78 gpm with 3/8 in lines.
            Aircraft at 17 deg nose up with 5 gal in each tank, selector in both, feeding only from the aft feed ports on the tank.

            Kevin D
            #272
            KCHD

            Comment


            • #12
              Originally posted by FFTravism View Post
              Friction loss for each one. It doesn't go up or down at a proportional rate typically. Calculating friction loss is something I have to do for my job.
              I didn't forget friction, but I'm also not expert in it. I tried to address it by pointing out that the ratio of cross section area vs. circumference was more favorable for the 1/2 line.

              Comment


              • #13
                Originally posted by kestrel View Post
                I didn't forget friction, but I'm also not expert in it. I tried to address it by pointing out that the ratio of cross section area vs. circumference was more favorable for the 1/2 line.
                That makes sense. I may try to find it but it may not be readily available.
                Travis M
                Kentucky
                Bearhawk 5 Quickbuilt Kit Plane #5041
                Received December 2022

                Comment


                • Battson
                  Battson commented
                  Editing a comment
                  No point calculating it, theory and practice are only the same in theory. Just go with a simple system with 3/8s lines and old school injection - everyone goes through the exact thought process you're doing now, at the start. They all end in the same place... Practically, it just makes sense.

              • #14
                Originally posted by AZBearhawk272 View Post
                My system flows 78 gpm with 3/8 in lines.
                Aircraft at 17 deg nose up with 5 gal in each tank, selector in both, feeding only from the aft feed ports on the tank.

                Kevin D
                #272
                KCHD
                Wow! That's higher than I would have expected. Can you expand what the fuel was flowing through for this? Any chance you tested with fuel in one tank only? ...thinking of uncoordinated flight and or one tank run dry before the other.

                Jared's test seemed to include at least the fuel selector valve and fuel flow sensor? I'm not sure where his test point was and if the fuel was flowing through any idle fuel pumps?

                For an EFII system, the fuel pump is often under the floor or front seats, so that would be a shorter, less restrictive run than all the way through the firewall to the engine.

                Comment


                • #15
                  Originally posted by kestrel View Post

                  Wow! That's higher than I would have expected. Can you expand what the fuel was flowing through for this? Any chance you tested with fuel in one tank only? ...thinking of uncoordinated flight and or one tank run dry before the other.

                  Jared's test seemed to include at least the fuel selector valve and fuel flow sensor? I'm not sure where his test point was and if the fuel was flowing through any idle fuel pumps?

                  For an EFII system, the fuel pump is often under the floor or front seats, so that would be a shorter, less restrictive run than all the way through the firewall to the engine.
                  I suppose if you tested it at the output port of the fuel selector, that number would probably be fairly universal. It's all the other stuff downstream which slows down the flow rate, and which varies between builds.

                  I got something like 125 L/hr from memory (33 Gal/hr, very similar to Jared's numbers) - less than half what Kevin measured - after flowing through all the usual obstructions (selector, gascolator, filter, transducer, electric pump, flexible hose, plus countless corners / elbows, fittings). That's without the electric pump running, so it's flowing through the pump's bypass valve.

                  The IO-540-A4EXP "Bob" engine requires about 90 L/hr (23 Gal/hr) at full power / sea level, developing around 270 to 275 hp with ram air and fuel injection.
                  Last edited by Battson; 03-16-2023, 09:48 PM.

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