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  • #16
    Post #7 and #13 is a request for the designer of our aircraft and the EFI supplier (SDS), to collaborate on setting a design standard for using his EFI system. That means a very simple drawing similar to the gravity fed carb fuel system in the Patrol Book. Then Experimentation in this arena can move from mandatory to optional.
    Brooks Cone
    Southeast Michigan
    Patrol #303, Kit build

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    • #17
      I would not expect the designer to collaborate with a single supplier for a "standard" for any system. The designer of an EAB designs his aircraft and systems to fullfill certain requirements. Bob does that really well. Bob designed and built the BH with no electrical system, CS prop, carbs, and magneto.

      I have no expectation that he design an electrical system, fuel system, ignition system, or prop to work together seamlessly, with ANY aftermarket supplier. If he CHOOSES to do that because he believes in a specific product, that is up to him.

      Talking to him several times, I don't believe he expects us to build our aircraft systems to comply with his requirements. This is EXPERIMENTAL aviation. He embraces it, including making his own CF blades for a constant speed prop. I am impressed.

      Van's does a great job of selling phenomenal kits. Very standardized. Brilliant. BH and Avipro sell a less standardized kit. No RV-4 will ever be a great Bush Plane. A Patrol might be a great cross country cruiser.

      I do hope SDS looks at our market and tries to make some recommendations on how their fuel and ignitions system work with what we are trying to build.

      The last 2 years, Ross has been very forthcoming with me on how to make things work. SDS has probably fuel injected more different types of motorized things than any company than I can think of.

      But I don't have any expectation, or personal requirement, that SDS and Avipro/Bob, come up with a "standard" system to run EFI on a BH.

      I bought a kit from Avipro, plans from Bob, a rebuilt engine from Bob. I bought EFI/EI from SDS. All of them have been very helpful in me trying to make them all play well together. But at the end of the day, I consider that, my responsibility.

      If I flameout on my first takeoff, it is my fault.
      Last edited by svyolo; 05-17-2020, 11:10 AM.

      Comment


      • #18
        Just a point of clarification on my setup: When in a low fuel situation I can do a prolonged skid with the airplane which unports both of the fuel pickups and causes the engine to quite. Returning to coordinated flight results in an almost immediate restart. The same thing will happen in a plane with a header tank but it will take much longer to use up the fuel in the header tank. I’ve never experienced vapor lock even when running mogas on a 100deg summer day.

        I agree with svyolo that following Cessna’s designs is a solid plan. Most of their designs use two header tanks (one for each main tank) mounted under the floor beneath the pilot/copilots feet. I didn’t want tanks below the airframe structure, I also didn’t want tanks under my butt. The Cessna 337 uses “sump” tanks that are mounted in the wing roots. The main tank drains into the sump tank via front and rear ports. The sump tank has a single outlet at its low point. It’s just wing root mounted header tank. I couldn’t fit a tank in the BH root but this design is what eventually lead me to where I’m at and so far I have zero issues.

        If I were to do it again I would fabricate a small tank that would take the place of the fuel line at the forward door post.
        Scratch Built 4-place Bearhawk. Continental IO-360, 88” C203 McCauley prop.

        Comment


        • svyolo
          svyolo commented
          Editing a comment
          Zenith chose something similar. For EFI engines they put a header in the left rear doorpost. Tall and thin. They even tested it with the outer wall in either lexan or polycarbonate so they could watch what goes on inside.

      • #19
        Originally posted by Archer39J View Post
        Main idea with header or without is to keep the stock fuel system supplying only what the engine burns, no different than carb or mechanical FI.

        I'm going the headerless route, don't see the need for heat with good routing, vapor lock isn't an issue if the inlet is at a positive pressure head. Air is a concern so keeping those runs short is the goal, but with BOTH that risk seems minimal. Thinking I might make use of those extra ports and put the regulator on the pump outlet and return right to the inlet manifold. Has anyone else run this kind of setup or something similar? That pump seems almost made for it
        I wouldn't return fuel to the pump inlet as, if air is introduced, it has no way to escape except by being processed through the engine. Think running a tank dry here. With EFI, fuel with air mixed in, will cause a lean condition and in serious cases, engine stoppage.

        Headerless can be fine if laid out well. My RV6 feeds from either wing tank, through a filter, Duplex selector, pumps, fuel rails, regulator, back through selector to selected wing tank. I've tested at some fairly extreme bank angles with some decent skid/ slip on with 1/4 fuel and have never had a fuel interruption. A high wing aircraft should be even better in this regard.

        That being said, every aircraft and layout is different and only flying it like this will prove how well it works. A BH can probably generate more of a sideslip than an RV so you'd want to test these extremes at altitude.

        The attraction of the header tank is that you don't need a Duplex selector valve and long return lines back to the tanks.
        Last edited by rv6ejguy; 05-17-2020, 12:57 PM.

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        • #20
          Originally posted by svyolo View Post
          The Rotax, was, well, Rotax. Why use 4 parts when you can use 24. But I bet it works well. The one thing I really did like about the Rotax was it comes standard with an electrical system to run the engine electronics, ignition, pumps. I think having that come from the factory reduces risk for a lot of installations. The thing that made little sense to me was they had 2 fuel injectors per cylinder for redundancy. Massed produced electric fuel injectors are probably some of the most reliable things every made. Maybe they wanted bragging rights for "most redundant". Their 100 hp EFI engine is only 3k more than their carburated version and burns a bunch less gas. I bet it is a very good engine.
          According to the guys who teach the Advanced Pilot Seminars (and Mike Busch, who probably learned from them), clogged or partially clogged fuel injectors are a fairly common problem in fuel injected Continentals and Lycomings. Busch feels so strongly about it that he advocates against having your injectors cleaned during routine maintenance. With that in mind, and recognizing that Rotax owners burn a LOT of MoGas (which may or may not be filtered as well as AvGas, depending on the source), means that dual-injectors would tend to mitigate the "leaning" of a cylinder with a clogged (or partially-clogged) injector. Thus, increased reliability. Apparently, there are something like a bazillion military drones using that Rotax engine, and they have racked up well over a million hours in flight...

          But then, I'm no expert, and I did not stay at a Holiday Inn last night...
          Jim Parker
          Farmersville, TX (NE of Dallas)
          RANS S-6ES – E-LSA powered by 100 HP Rotax 912ULS

          Comment


          • svyolo
            svyolo commented
            Editing a comment
            Continental and Lyc/Bendix don't have a fuel filter after the engine driven pump. Debris from the engine driven pump itself (impeller or seals?) could definitely plug an injector or the fuel divider. EFI always has a fuel filter after the pump. There are no moving parts after the filter.

        • #21
          Originally posted by rv6ejguy View Post

          I wouldn't return fuel to the pump inlet as, if air is introduced, it has no way to escape except by being processed through the engine. Think running a tank dry here. With EFI, fuel with air mixed in, will cause a lean condition and in serious cases, engine stoppage.

          Headerless can be fine if laid out well. My RV6 feeds from either wing tank, through a filter, Duplex selector, pumps, fuel rails, regulator, back through selector to selected wing tank. I've tested at some fairly extreme bank angles with some decent skid/ slip on with 1/4 fuel and have never had a fuel interruption. A high wing aircraft should be even better in this regard.

          That being said, every aircraft and layout is different and only flying it like this will prove how well it works. A BH can probably generate more of a sideslip than an RV so you'd want to test these extremes at altitude.

          The attraction of the header tank is that you don't need a Duplex selector valve and long return lines back to the tanks.

          My goal is to avoid having to run anything back to the tanks, either a full return or a vent line from a header tank with no need for a duplex valve either.

          I'm willing to accept that air will need to be processed through the engine which is why I want the regulator at the pump outlet, and I'll for sure be testing how long it takes to come back if you run a tank dry. But running BOTH seems to me if you run a tank dry, you're out of gas.


          The issue for many of us I think is that if we use a full return the stock BH system can't supply sufficient flow via gravity, so the pump is then sucking fuel and with multiple pickups in the tanks that presents a possibly dangerous problem at a low fuel condition where a pickup could be unported. Hence folks looking at using header tanks and, in my case, looking at just returning to the pump inlet.
          Last edited by Archer39J; 05-17-2020, 06:44 PM.
          Dave B.

          Comment


          • #22
            Originally posted by Archer39J View Post


            My goal is to avoid having to run anything back to the tanks, either a full return or a vent line from a header tank with no need for a duplex valve either.

            I'm willing to accept that air will need to be processed through the engine which is why I want the regulator at the pump outlet, and I'll for sure be testing how long it takes to come back if you run a tank dry. But running BOTH seems to me if you run a tank dry, you're out of gas.


            The issue for many of us I think is that if we use a full return the stock BH system can't supply sufficient flow via gravity, so the pump is then sucking fuel and with multiple pickups in the tanks that presents a possibly dangerous problem at a low fuel condition where a pickup could be unported. Hence folks looking at using header tanks and, in my case, looking at just returning to the pump inlet.
            Another reason we like the reg after the fuel block is for hot starting. When you turn the pump on, all hot fuel and air is removed from the fuel block in the first second.

            3/8 lines gravity fed to pumps on the floor should easily feed them.The pumps flow about 3-4 quarts per minute each.

            Others have found out the hard way that's it's a bad idea to return fuel to the pump inlet. It could take as long as 30 seconds to process the air through the engine with a windmilling prop. Not so good if this happens at low altitude.

            Comment


            • #23
              Originally posted by rv6ejguy View Post

              Another reason we like the reg after the fuel block is for hot starting. When you turn the pump on, all hot fuel and air is removed from the fuel block in the first second.

              3/8 lines gravity fed to pumps on the floor should easily feed them.The pumps flow about 3-4 quarts per minute each.

              Others have found out the hard way that's it's a bad idea to return fuel to the pump inlet. It could take as long as 30 seconds to process the air through the engine with a windmilling prop. Not so good if this happens at low altitude.
              I haven't looked back for the posts, but actual flow test seem to show the stock BH system cannot feed 45-60 GPH. And I think it's suspected that a sucking pump has been an issue before.

              Were those people running returns from the fuel block, or straight from the pump outlet? I really don't see running dry on BOTH unless you're completely out of gas.
              Last edited by Archer39J; 05-18-2020, 07:25 PM.
              Dave B.

              Comment


              • svyolo
                svyolo commented
                Editing a comment
                After going through all of the published fuel flow tests that builders have posted, I came to the same conclusion. I think Whee did as well on his Conti IO-360. Whee used 1/2" fuel lines which hopefully fixed it for him.

                Each tank has a fore and aft pickup that meet at T's close to the fuel valve. If the pump is "sucking" on the fuel lines, and one fuel pickup gets un-ported, you might be sucking air.

                The fuel system will gravity feed the pump for engine demand for a 540, but 3/8" lines won't gravity feed 40+ gph for a fuel pump. The pump will be sucking somewhat.

                1/2" fuel lines for full return, header tank return, or return-less. I have installed the header tank solution as that is what Mr Cessna did. I am also going to brake my engine in on the ground so I will also test the return-less, just for my own education.

            • #24
              Originally posted by Archer39J View Post

              I haven't looked back for the posts, but actual flow test seem to show the stock BH system cannot feed 45-60 GPH. And I think it's suspected that a sucking pump has been an issue before.

              Were those people running returns from the fuel block, or straight from the pump outlet? I really don't see running dry on BOTH unless you're completely out of gas.
              Most of our Lyconental installations run -6 lines and the 393 pumps with return lines from the far side of the fuel block. We caution people not to use 90 degree fittings on the pump inlet side on low wing aircraft to minimize the chances of vapor lock, especially when running mogas on hot days. The flooded inlet available with a high wing configuration should work fine feeding a 540. We've had customers with 400 hp supercharged ones feed the pumps with -6 lines with no issues on low wing aircraft.

              Comment


              • Bcone1381
                Bcone1381 commented
                Editing a comment
                Do those installations you sight here on this post have a single -6 fuel line supply or do they have two....one in the front of the tank and one in the rear of the tank...to accommodate fuel supply at various pitch attitudes with a small amount of fuel in the tank?

            • #25
              Ross;
              Yeah the big difference with the BH is each side has 2 fuel lines, and "Both" seems to be the preferred position on the valve. So 4 fuel lines feeding the pump. 1 -6 line in a low wing aircraft will definitely flow 40+ gph of gas when scavenged by a pump. But if you have multiple lines, and 1 gets un-ported, you might suck air if the pump is "sucking". If the fuel lines are big enough to gravity flow fuel to the pump inlet, hopefully that won't happen. The fuel flow tests published by BH builders don't show any single -6 fuel line flowing anywhere near 40 gph.

              That is why I want to return to a header tank. I think 1/2" fuel lines would also work, but they are a bit harder to install. I tried a piece.

              Comment


              • #26
                RVs and most other low wing aircraft have a single feed line from each tank, against the forward side of the spar.

                On an aircraft like the BH which is likely to be slipped vigorously once in a while, my opinion is that the header tank is the safest bet and never return fuel to the pump inlet. Might as well stack all the cards in your favor and follow best practice on what's been proven over the last 25 years with EFI fuel systems. A big slug of air into the high pressure side will almost certainly kill the engine for a bit which is something you don't need at 100 feet.

                Comment


                • #27
                  So the BH system is significantly different than any low wing system and cannot provide 40+ GPH. It is also dangerous to have a pump pulling a negative relative pressure at its inlet given the multiple pickups and BOTH position. So the part of the SDS instructions that say "you must use a return" is not at all what you want to do in our system, which is why we're having to figure something else out...
                  ​​​​​
                  I understand the issue of air in the system. But, to reiterate, I don't think that's really a concern when running BOTH. Even if I were running a single tank at a time I've never come close to running a tank dry and really don't understand those that do, save uncoordinated unportings which we've discussed before.

                  I asked earlier, but were those who had issues returning to the pump inlet running returns from the fuel block or the pump outlet? Also were they low-wings? That would have a significant effect on how much line there is to purge air from and would be good to know.

                  Have there been any high-wing, cross-linked at the fuel valve (BOTH), planes that have had issues returning to the pump inlet?

                  I'd accept the limitation of no uncoordinated low-level maneuvering, while at minimum fuel, while on only one tank, if it means not putting a reservoir of fuel in the cabin and having a vent line return to the tanks.

                  ​​​​

                  ​​​
                  Last edited by Archer39J; 05-20-2020, 12:53 PM.
                  Dave B.

                  Comment


                  • Russellmn
                    Russellmn commented
                    Editing a comment
                    another issue with returning to the pump inlet is heat. you see more fuel heating issues from the pump than from engine heat radiating to the fuel lines. Repeatedly recirculating fuel through the pump is going to rapidly increase fuel temp, increasing the chances for detonation, vapor lock, and ultimately engine failure.

                  • Archer39J
                    Archer39J commented
                    Editing a comment
                    Not an issue with the pressures in the SDS system even at idle flow rates.

                  • Russellmn
                    Russellmn commented
                    Editing a comment
                    archer, what kinda pressures and flow rates are you talking? 30psi? 50? 80? I don't know what pressure SDS runs at, but it looks like a fairly typical automotive type injector, so I'm guessing 45psi or more. At low flow rates, such as at idle, constantly recirculating fuel through the pump will absolutely increase fuel temps to an unacceptable level. This is one of those scenarios where automotive experiences really do transfer over. Dumping the return fuel back into the inlet of the pump is just asking for trouble. Even a small, 1/2 gallon or so, surge/header tank will help tremendously, 2 gallons or more would be much better though.

                • #28
                  Maybe I'm missing something, but why not run the return line to the header tank itself? If the header is gravity fed from the mains, seems like the issues are all handled... But then again, I am NOT an expert on fuel systems or fuel injection, either...
                  Jim Parker
                  Farmersville, TX (NE of Dallas)
                  RANS S-6ES – E-LSA powered by 100 HP Rotax 912ULS

                  Comment


                  • #29
                    Originally posted by JimParker256 View Post
                    Maybe I'm missing something, but why not run the return line to the header tank itself? If the header is gravity fed from the mains, seems like the issues are all handled... But then again, I am NOT an expert on fuel systems or fuel injection, either...
                    I believe that's the idea actually. From Ross's site, described as a "surge tank", it's the same thing. Size of the tank is per your comfort level, I reckon:

                    http://www.sdsefi.com/techsurge.htm
                    ​Christopher Owens, EAA #808438
                    Project "Expedition"
                    Bearhawk 4-Place Scratch Built, Plans #991
                    Bearhawk Patrol Scratch Built, Plans #P313
                    Germantown, Wisconsin, USA

                    Comment


                    • svyolo
                      svyolo commented
                      Editing a comment
                      The automotive world calls them surge tanks. They have 2 main uses - one is maintaining fuel pressure under high G/extreme attitudes. The other is converting a formerly carberated vehicle to EFI.

                      Sounds kind of familiar :<)

                    • Russellmn
                      Russellmn commented
                      Editing a comment
                      Even better would be to run that surge tank with the pumps submerged in the tank. Keeps them MUCH cooler and they'll last longer.

                  • #30
                    I had a little time this morning so I started fabricating the header tank and working on the layout. The tank is 9 x 5.75 x 4. This works out to .89 gallons or 3.35 liters. There is room to make it larger but I made it to keep some space between it and the bottom of the seat. If I go with this layout I will run either a rigid aluminum tube or possibly a PTFE flex line, to better handle vibrations and make filter removal for cleaning easier, from the tank to the filter. Either will be -8AN. -6 would probably work but bigger should be better. I upped the line from the aft left main tank feed to -8 all the way to the Andair valve. I will have a -8 line from the valve to the header tank. The valve will be the choke point. When in both or on the left tank there should be good flow only limited by the valve.

                    It looks like I will be able to fit everything under the left seat, including a pitch servo. I want it clear under the right seat so that I can take the seat out for long cargo.

                    Feel free to criticize.

                    John

                    Comment


                    • svyolo
                      svyolo commented
                      Editing a comment
                      That is pretty close to what I did but under the right seat.
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