Header tank design and location

[svyolo]

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.

[svyolo]

Schu;
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.

[svyolo]

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

[whee]

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.

[Ed.Meyer]

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.

[Chris In Milwaukee]

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.

https://bearhawkforums.com/forum/bearhawk-general-discussion-news/37603-brake-system

[Mark Goldberg]

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

[svyolo]

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.