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Header tank design and location

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  • Header tank design and location

    I have read (by googling) the threads that popped up about header tanks on FI Bearhawks on this forum. I think I want to use one as well for the SDS EFI that I want to use. I have no experience with designing a header tank.

    Most tanks should be filled from the top, and "feed" fuel or fluid from the bottom. An aircraft header tank will also be vented to both wing tanks, with the vent lines coming from the top of the header tank, vented to the top of the main tanks.

    Is shape important? If the system is designed correctly, the header tank should remain full until 1 or both main tanks are empty. Would there be any problem "filling" the header tank from the bottom? That would make a few things easier. The returned fuel should be able to force the rest of the header tank up, and they should still vent upward. At least that is my thinking.

    Has anybody else put much thought into this, as well as what shape, and where to locate the tank. Tall/thin, mounted up by the firewall? Low, flat, under the floor or under the seats (front or rear). 3 gallons minimum si recommended by the EFI manufacturers to prevent excess fuel heating in the header tank.

    I won't let this delay the build. I am buying a rebuilt carburetor from Bob, and it will run on that first. If I think the EFI will delay the first flight, it will also fly on the carburetor first. I sort of want to do that anyway.

    Thanks for any input.

  • #2
    What some FI systems require is a return line to a tank. You should not need a header tank from what I have heard. On my RV8 injection system I just put in a loop that brought fuel back upstream of the boost pump. So I suggest looking at the different FI systems and the requirements for the system you want to use. Mark


    • #3
      Gerhard Rieger posted something recently about a brake system setup, but it prominently featured the header tank he put together for his Continental IO setup. Very similar to the way Maule does it. Take a look at this one and see if it will accomplish what you’re after. Perhaps Gerhard will answer some additional questions.

      Christopher Owens
      Bearhawk 4-Place Scratch Built, Plans 991
      Bearhawk Patrol Scratch Built, Plans P313
      Germantown, Wisconsin, USA


      • #4
        We have the EFII system on our Patrol with no header tank. We had to add a fitting to the fuel tanks for return lines and installed a duplex fuel valve that switches the return as well as the feed. Valve has left, right, both, and off settings. It was recommended not to use a header tank for the return to avoid fuel warming issues. Further, if the fuel is returned to a header that is vented up to the wing tanks you have no control over where fuel returns to. So far, our system works great. One more point is that switching from carb to EFI is not simple task in that carb needs no return nor fuel pumps nor fine filters that EFI requires.


        • #5
          I put a lot of thought into it and did the same and Ed. I studied many Cessna Illustrated Parts Catalogs, maintenance instructions, etc when making my decision. I do like Gerhard’s header tank under the floor and that is what I would have done had I decided to use a header tank.

          Actual shape isn’t important but it is important to keep the supply and feed ports separated so that warm fuel and vapor isn’t recirculated back to the engine. For this reason I would feed from the bottom and supply from the top. On the side near the top is actually where I’d place my supply/return ports.
          Scratch Built 4-place Bearhawk. Continental IO-360, 88" C203 McCauley prop.


          • #6
            I guess my reason for using a header tank is that is seems most high wing aircraft with fuel injection seem to use one if there are return lines, i.e. Continental, and now Rotax. I can think of ways to get into trouble using "both" on takeoff and landing with low fuel without a header tank. It seems like using a header tank in this set of circumstances is "convention". Cessna (Conti motors), Maule, and the newer fuel injected Rotax's all seem to use a header tank.

            Without a header tank, you need to run a full size fuel line from the duplex valve to each main tank. With a header tank, you STILL need to run two fuel lines to the top of both main tanks as vents.

            I am using the stock fuel feed to the fuel valve layout no matter what I end up with for as far as a header tank or not. It appears to work as designed, especially when run in "both". The valve with be in the stock location. SDS recommends a minimum of 3 gallon header tank (if using one) to avoid the problem of excess fuel heating of the tank.

            I still might start with a Duplex valve and no tank to start with. The feed side of the fuel system will be identical no matter what. There is plenty of room for the pumps and return lines to be added in the beginning, or later.

            I will contact Mr. Rieger


            • #7
              Something to think about is crash worthiness. I'm specifically putting all of my fuel system inside the fuselage tube structure so that if I crash and have the gear ripped off, my fuel system will remain in tact even if the airplane is sliding to a stop on it's belly.

              Given the cost of the fuel system, the cost complexity of the duplex fuel valve, the additional work to put it all together, I suggest you look at the airflow performance mechanical fuel injection and electric ignition. I suspect that will give you 90% of the engine smoothness and fuel economy without a complex fuel system.

              You could even run one side electric ignition and the other side mag. While this wouldn't idle as smooth because your mag is still way too advanced at low RPM, I suspect it would give you good lean of peak cruising performance because the EI would fire before the mag at higher RPM, making the mag wasted spark. This setup would probably get you 80% there, with a bit less cost, and it would run without battery power.

              If I was running EFI and felt that the pros outweighed the cons, I'd probably install the left/right/both/off duplex fuel valve in the vertical structure under the pilot seat between the pilot stick and flaps, then build the header tank under the co/pilot seat, then mount the fuel pumps under the pilot seat with another cutoff valve between the pumps and engine. I'd run a duplex valve and vent it to to the wing tank.

              Here is why:

              1. You can turn off wing tank fuel, or header tank fuel.
              2. The weight is more or less on the CG
              3. It's super easy to inspect.
              4. The header tank isn't under much pressure, just head pressure, which is less than fuel pumps pushing fuel into it, which forces fuel back up the main fuel feeds.
              5. The whole thing is above the floor so it will almost certainly stay together in a crash.
              6. Tubing is fairly minimal, front/rear mains to T under the door to fuel valve to header tank to engine back to valve back to wing tank.
              7. Fuel won't get hot there.

              Con is that you will have a lot of fuel in the cockpit with you. But then again, lots of airplanes that way, and if I'm going to be riding with my fuel, I'd like to smell it if it starts leaking, inspect it on preflight, and have it protected.

              Thoughts are worth pretty much what you paid for them.....

              Last edited by schu; 04-29-2018, 08:46 PM.


              • #8
                I was leaning toward putting the header tank under/right behind the pilot seat, or under the rear seat for the reasons you mentioned, including crashworthiness and ease of inspection. Header tanks are not normally pressurized, although the ones that they seem to use on the FI Rotax's are shaped like a pressure tank, so maybe they are pressurized. the BH already has 4 gravity fed fuel lines running through the cockpit. What additional risk is another small tank?

                With or without a tank, you need to run two lines up the the mains for either vent or full flow return. If using a tank, it is best if the tank is in a convenient location to run the two lines, with no low spots, up to the mains.

                For some reason high wing airplanes use header tanks a lot, and I think most if not all injected Conti motors use them. I am not 100% sure why, but I think the engineers that chose to do that know something about fuel systems that I haven't thought of yet. All that being said, the fuel feed side of Bob's fuel system appears to function perfectly, and I will utilize that layout.

                I was even thinking about putting in a very small header tank in just the feed side of either the front or rear fuel lines.

                As for ultimately, why EFI? Other than personal preference, which is big. I almost talked myself out of it, and using MFI. But I finally was able to justify it to myself. I have spent an adult lifetime leaving home for 6 months to 2 years, and coming home. It didn't take long for me to learn to disconnect the battery before I left. Old tires used to "flat spot" and be ruined when you came back (this was fixed). When I came back to a carburated vehicle, I was never sure if it would even start, let alone how it would run. A few years later I was running modern EFI vehicles. 6 months or 2 years, it doesn't matter. As long as the battery can crank the engine over, the engine starts, and runs perfectly, every time.

                My airplane is going to sit unused 6-8 months a year, unless I take on a partner in the plane. I want to know that when I come back, connect the battery, and turn the key, that it will start and run perfect.


                • #9
                  If there was more room up in the boot cowl, I would probably go with that location. Some applications use a tall, thin, flat tank. That still might work as well, situated above the rudder pedals. I think from a crashworthiness perspective, I would rather have it somewhere between beneath me and slightly behind me.

                  If I haven't sorted it out within 3 months, I will fly it first with a carb. That is the last major system I haven't sorted out in my mind.


                  • #10
                    The idea behind a header tank is pretty simple, you basically get 2-3 gallons of fuel that will never un-port because it will never be empty enough until you are down to your last 2-3 gallons and if you are putting a fuel injected engine in, you can push your extra fuel back to a header tank without needing a duplex valve.

                    This is why most fuel injected engines use a header tank, because they don't have a duplex valve, and need somewhere to put the extra fuel. If you have the duplex valve, you don't need a header tank, unless you think that you will run into situations where the main tanks will un-port, but that's not a known issue on the Bearhawk.

                    This is why I like airflow performance. No return line needed and it's mechanical fuel injection. I get a smooth running engine without the complex fuel system.

                    Also, I'm not sure that EFI will be more reliable in a sit and wait situation. With a carb you can turn off the fuel at the fuel valve and run the system dry, but you can't do that with fuel injection because the moment you turn off the fuel valve you will loose fuel pressure because the pump has no where to draw from, and it will probably kill the engine before the fuel is consumed.

                    As for disconnecting the battery, I'd get a battery maintainer that will float charge it and make a harness so you can plug it in easily. I've lost many batteries in motorcycles, riding mowers, motorhomes, etc that died because they were not maintained while sitting. (Note, this is for a wet or AGM battery, probably not a good idea on a lithium)



                    • #11
                      Svyolo, May I ask a question out of curiosity? Ed Meyer in post #4 has is flying an EFII installation without a header tank. It functions as it is designed and as you hope to have yours function. What aspects of a header tank installation is appealing, or what concerns do you have about a headerless fuel system design? I am curious, have no intentions to stir up controversy, nor am I trying to persuade you for or against. Just trying to understand. (I use to lean towards a header tank install in this type of system, but Ed's report has me doubting myself now.)
                      Brooks Cone
                      Southeast Michigan
                      Patrol #303, Kit build


                      • #12
                        Originally posted by svyolo View Post
                        I was even thinking about putting in a very small header tank in just the feed side of either the front or rear fuel lines.
                        I considered something similar. I was going to replace the AN T fittings at the forward door posts with a 1ish gallon tank. The was primarily to prevent un-porting a tank when low on fuel and maneuvering. I decided I didn't need this or a header tank in my airplane.

                        Maybe worth noting:

                        The Cessna 206 doesn't have a "both" position on the fuel selector valve. There are two header tanks under the floor and the fuel selector valve is a duplex valve that returns the fuel to the appropriate header tank.

                        The Cessna 185 has a single header tank has a simple On/Off fuel valve that in placed after the header tank. The fuel tanks all feed the header tank with no valve in between.

                        The Cessna 337 does not have a header tank or a 'both' position on the fuel valve. Fuel from the front engine is always returned to the left main tank and the fuel from the rear engine is always returned to the right main tank.

                        I plan to primarily use mogas in my airplane and after a conversation with Peterson Aviation I determined that a fuel injection system with a vapor return line was necessary on my airplane. Peterson spent a lot of time and money trying to develop a mogas STC for fuel injected Lycomings (no vapor return) and eventually gave up. He couldn't keep the fuel from vaporizing in the fuel lines. I know many RV guys successfully run their fuel injected Lycomings on mogas but after talking with Peterson that was one experiment I wasn't willing to test.
                        Scratch Built 4-place Bearhawk. Continental IO-360, 88" C203 McCauley prop.


                        • #13
                          Whee, learned a few things from your post:

                          1. Cessna 185 having an on/off header tank setup. Interesting. That sure makes fuel management easy for the pilot, but no way to manage left/right fuel.

                          2. Peterson couldn't make mogas work with mechanical injection without a return line. I wonder how the airflow performance people do it? They don't have a return line, and the fuel lines up to the servo are pressurized. I'll need to do more research.



                          • #14
                            I'm building my 4-place as a FlyEFII machine. I have an Andair duplex valve, and am returning fuel to the tanks. In this kind of system, the header tank is really only good for the unporting issue. I am using only the rear pickups on the tanks, with fuel returning through a newly added bung near the top of the tank, more forward to keep it further from the pickup.

                            One benefit of returning fuel to the tanks is that the extra travel gets you good cooling. A header tank can accomplish cooling as well, but needs a minimum volume of like 5 gallons. I don't want a 5 gallon tank in my fuselage. I figure if I'm totally dependent on the fuel pumps anyway, might as well just go with return lines. The header tank does nothing for you if you lose both high pressure pumps.

                            I got over my need for a BOTH selector after flying old Pipers and a Bonanza.


                            • Mark Goldberg
                              Mark Goldberg commented
                              Editing a comment
                              Why would you NOT use both the forward and aft tank outlets? Mark

                            • JimParker256
                              JimParker256 commented
                              Editing a comment
                              I have the same question as Mark G... My concern about not using the forward wing pickup is that in a descent, with the nose-low, the aft pickup may be surrounded only by air because the fuel is sloshed forward in the tank, while the forward pickup point should be awash in fuel. By feeding from both fwd and aft ports, the nose-up / nose-down attitude of the airplane becomes a non-issue.

                              I attended a "fuel systems design" seminar at OSH a couple of years ago. The instructor (whose name escapes me) was an engineer who designed the fuel systems for several military aircraft, as well as consulting on many homebuilt designs. When I received my Patrol plans, I was pleased to see that Bob's design was EXACTLY identical to the "optimal design for high-wing homebuilts" that the instructor provided us. Right down to the gascolator being the lowest point in the fuel system... And he highlighted the importance of using two fuel pickups per tank (forward and aft)

                              By the way, his personal pet peeve (he's a DAR as well) was those small in-line fuel filters that: A) have no automatic "bypass" provision in case the filter becomes clogged), and B) have non-transparent bodies (so you cannot even see if fuel is flowing or if it is totally clogged). He simply won't sign off an airplane with those installed, because of the high danger of fuel starvation in the event of a clogged filter. He doesn't much care for the non-bypassing "transparent" filters, either, but reluctantly approves them, after extracting a promise from the builder that they will include "replace fuel filter" in their 50-hour preventive maintenance schedule, along with oil and filter change...

                          • #15
                            Okay, I see, many of them mix fuel to keep the vapor pressure down, or they test to make sure it's not winter blend, most report that turning on the boost pump resolves the issue, and others eliminate the engine driven pump and use two electric pumps on the cold side of the firewall so that everything on the hot side is pressurized.

                            I already have an andair boost pump, so I suppose I could just put a walbro GSL392 between it and the firewall and use the walbro all of the time, and the andair as a backup since the walbro can pull through it.

                            That would certainly make my airplane mogas capable, especially if I mix 50/50, and the pump is $250 cheaper, but back to depending on electricity. I'll have to think about that.....