Bearhawk Aircraft Bearhawk Tailwheels LLC Eric Newton's Builder Manuals Bearhawk Plans Bearhawk Store

Announcement

Collapse
No announcement yet.

Return fuel lines

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    Originally posted by Battson View Post
    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.
    Based on this approach, no one would bother taking math classes because numerical analysis is a complete waste of time. I was going to say that we'd all still be flying Wright Flyers, but that is wrong. There would have been no Wright Flyers. You are flying an airplane with fuel injection and extended wingtips of non-stock shape. Why not a carburetor and stock tips?

    Everything we are flying is an advancement over what came before it. We all have different priorities on where to step a little further than the mainstream. I can't recall it in enough detail to find it, but I've read some sort of statement about pigs attacking the one that tries to get out of the pen. ...not a real event, an analogy of human behavior.

    It is not true that "they all end in the same place". There are Bearhawks flying with EFII. We don't hear a lot about it because there its a lot of hostility. You'll note that the OP felt the need to reply, "I tried to ask it without creating a big debate."
    Last edited by kestrel; 03-17-2023, 08:49 AM.

    Comment


    • Battson
      Battson commented
      Editing a comment
      I did 400 level "theoretical fluid dynamics" amidst a range of other fluid dynamics papers, so I feel qualified to talk about the value of calculation - particularly for flow within a pipe. It is hugely valuable and useful, but not required when deciding on your fuel line diameter in this specific case.

      I think you mistake my comments to encompass more than they do, I only refer fuel line diameter.
      Last edited by Battson; 03-19-2023, 03:10 PM.

  • #17
    Well,
    Made sure tubing runs were straight, smooth,
    bends not ovaled in cross section. Used two Bob gascolators, located one on each side behind and
    below the struts. Fuel selector modified on the lower body for better fitting position and cleaner tubing hookup with less bends, located in front floor adjacent to flap handle. Then flowing through an electrical pump with bypass, lower firewall mounted and then on to the inlet of the standard engine driven Continental
    mechanical fuel pump. Measured at the pump inlet.

    Return from the pump goes directly to the left fuel tank.
    via a 3/8 line.

    And…… each tank has TWO, (2) vents of .280 ID.
    Fuel will not flow out well if air cannot get in.

    Flow from a single side with fuel level down to about 3 gallons is 48 gph.

    OH! Correcting typo in my original post.
    fuel flow is 78 GPH! When in both…

    Kevin D
    #272
    KCHD


    Comment


    • #18
      jaredyates, Do you want to move the supply lines discussion, or is it OK here? I didn't expect to get this involved when I high jacked the OPs topic.

      Comment


      • #19
        Originally posted by Battson View Post
        I did 400 level "theoretical fluid dynamics" amidst a range of other fluid dynamics papers, so I feel qualified to talk about the value of calculation - particularly for flow within a pipe. It is hugely valuable and useful, but not required when deciding on your fuel line diameter in this specific case.

        I think you mistake my comments to encompass more than they do, I only refer fuel line diameter.​
        Ok, you are close to saying things that I want to hear. Why are calculations (estimations with expected error value) not required (useful?) for fuel line diameter? Am I incorrect that a 1/2 line will flow at twice the gph under otherwise same conditions as a 3/8?

        Note that I am not trying to predict flow rate from "scratch". I am trying to estimate the relative performance of the two line sizes and then apply that to experimental/measured data.

        Comment


        • #20
          I once got 400-level science credit for going to the Ozark National UFO conference in Arkansas, so I'm not qualified at all. But I suspect the value of calculating line flow is less useful, if our flow rates are more primarily limited by the non-line members of the system, like fittings, valves, sensors, bends, etc. Sort of like using the straight part of the car racing track to calculate theoretical top speed when it's merely the slowdown prior to the next curve and the speed-up after the last one.

          Comment


          • Battson
            Battson commented
            Editing a comment
            This is exactly the point. It's the restrictions which create most of the losses. Orifice calculations would be more material overall.

            We have so much practical experience - and the first thing you learn about calculations and models of fluids is: you must validate calculations / models with practice tests. The practical test results are king.
            Last edited by Battson; 03-20-2023, 03:14 PM.

          • kestrel
            kestrel commented
            Editing a comment
            Practical, real world data are what I'm looking for. The orifice of a 1/2" fitting vs. a 3/8" fitting scales with the tube diameter. I know the fuel flow sensor and pumps won't, but they are not part of the sub-system I'm asking about. As for validating calculations... well... no $hIt... That doesn't make the calculations stupid. Do the calculations to make an informed design. Then run the test.

        • #21
          Originally posted by jaredyates View Post
          I once got 400-level science credit for going to the Ozark National UFO conference in Arkansas, so I'm not qualified at all. But I suspect the value of calculating line flow is less useful, if our flow rates are more primarily limited by the non-line members of the system, like fittings, valves, sensors, bends, etc. Sort of like using the straight part of the car racing track to calculate theoretical top speed when it's merely the slowdown prior to the next curve and the speed-up after the last one.
          I've considered that, at least as best I can. The fittings will also scale with the line. For an EFI type system, the fuel pump is often right after the selector valve. So, there are no extra bends, sensors, etc.

          Maybe I should back up a little and better define the problem.

          I'm not sure of the exact FAA wording on the 125% flow rate requirement. I've read it, but can't recall exactly. I also don't think that is the right requirement to be looking at.

          If the pressure in line drops below ambient, then you are "sucking" on the line. In this case, if there is a Y in the supply line, it will prefer to pull from the one with air in it instead of the one with fuel. This is bad(tm). Bearhawk systems with fuel pumps have Y's supplying the pump. IMHO, these systems need to have 150% flow if disconnected just below any Y (or T). If all Y/T junctions can get 150% flow, then the final single line can have a pump sucking on it, for the consideration of preferring to flow fuel instead of suck air. This final comment doesn't consider cavitation concerns.

          The systems that are flowing 30 gph before the fuel pump have not demonstrated 150% flow rate where it is needed. I also believe that they almost certainly have 150% where it is needed and most of the restriction is after the selector valve. After the selector valve, I think that the 125% requirement (23 gph * 1.25 = 28.75 gph) is appropriate.

          The EFII System32 pump flows 40 gph. That system needs to flow 40*1.5 = 60 gph through the selector valve. I don't think that 125% should apply to that part of that type of system. I also feel that that flow should be from a single tank when "low on fuel". When low, feed lines will un-port.

          Data:
          2 cases of 30 gph feeding from both tanks through the selector, pump and flow sensor.
          1 case of 48 gph feeding from one tank or 78 from both. Also feeding through the whole system.

          Conjecture: Most of the resistance to flow in the 30 gph cases is downstream of the selector valve. I expect that these systems will still flow nearly 30 gph from a single tank. If not, they may not be safe, but I think they will.

          We have the one example demonstrating that 48 gph is possible from a single tank with 3/8 lines.

          From this and my calculations of cross section area and circumference, I conclude that a system that is identical to Kevin's except for being built with 1/2 inch lines will flow at least 80 gph through the selector valve from a single tank. Jarred and Johnathan's should flow something greater than 60 gph through the selector valve. Since there is much less variation before the selector valve, they may well flow through the selector valve just about as much as Kevin's.

          Can we address the engineering/math here rather than jumping to conclusions and projection our own decisions and preferences? It is only a question of how much flow might be expected through the selector valve.
          Last edited by kestrel; 03-19-2023, 07:36 PM.

          Comment

          Working...
          X