Header tank design and location

[Bcone1381]

I am doing MFI with Bob's original fuel system design due to the issues I am reading about here. My conclusions mirror almost exactly with what schu described. But please allow me to offer what I think might be a reasonable design improvement....way off from Bob's design. So its worth what you are paying for it.

I am installing my fuel system in accordance with Bob's Patrol Book. The electric fuel pump on my installation will between the gascolator and the firewall. I am not running EFI. I am not installing a header tank. My term "Design Improvement" was a poor choice of words. I intended to offer something to consider for those who are installing EFI with its large volume pump/fuel return. A header tank installed under a seat concerned me.

For those who are using EFI, be sure that its simple to operate without having special operating limitations.
My preference at this juncture in time would be to use a single 5 gallon header tank located aft of the cargo area with an on-off fuel valve.

Bill, its been decades since I last flew a low wing injected aircraft. I sense I may be missing something due to your post...

[svyolo]

I have been trying to figure out how I wanted to do a header tank. One of my assumptions was wrong. Reading some of the documentation for EFII's system, they recommended a header tank of at least 3 gallons, because of fuel heating, if I remember right. I assumed SDS, the system I bought, was the same. Bad assumption.

EFII uses a classic fuel rail EFI delivery. There is a common fuel rail on each cylinder bank, and fuel is returned from a pressure regulator on the end of that rail, AFTER the injectors. The fuel is heated, and that heat returns to the tank, or header tank. SDS uses a fuel divider, similar to the Bendix style I think. The FP regulator is mounted to this divider. Little heat is absorbed by the fuel so a large header tank is not required, according to the owner of SDS.

So a bit of searching for "small header tank" yielded a few results, and also I found the term "surge tank" and "swirl pot". They are very common in racing applications, and converting an old car from a carburetor to EFI, kind of like I am doing. They come in lots of shapes and sizes, 1/2 gallons to 1.5 gallons. Some are just a tank, some with 1 or more internal pumps. A few even have a pressure regulator built in, and the "return fuel" never leaves the tank.

If I can't find one I like I will just make my own. I like the idea of internal pumps to keep it all compact, and most leaks will be internal to the tank. Although keeping the tank itself from leaking (pump mount uses O rings) might be just as hard. If I rolled my own I could probably even put both the primary and secondary fuel filters in the tank. The only external fittings would be 1 or 2 outputs, 1 input form the main tanks, 1 return, and one vent. I could put the whole thing in a very thin CF (1 layer of 5 oz) sump with a drain line to the bottom of the aircraft.

[Chris In Milwaukee]

I’d considered something like this I the past:

https://www.summitracing.com/parts/rci-2010a

may have to add another connector or two depending on ventilation and return lines.

[svyolo]

Early on I noticed a lot of High wing airplanes had a header tank. The Bh system is obviously so well designed that I haven't heard of an issue, including feeding a 300hp engine on takeoff at very steep climb angles.

With EFI, without a header tank, the system would be required to flow 35-45 gph, or whatever the pumps are pumping, 100% of the time. The tanks also have to vent that much air. It just kind of makes me tilt my head a little.

With a header tank, the gravity feed only has to feed engine demand. Return fuel goes easily and quickly to and from a header tank. It makes me feel a bit better. Even if the header tank is less than a gallon in size. A gallon is a bit over 2 minutes of fuel at takeoff power, and 4 minutes at cruise.

I will probably start with what is easy, and easy to pass DAR inspection. That is probably a small tank, and the two pumps from SDS.

[Gerhard Rieger]

Hi, My header tank take 2,2 gal and have an 3/8' inlet (top) and outlet (bottom), and two 1/2' vents to each tank,I also fitted a drain at the low point of the tank to clear out any chance of water before flight. ( there should not be any water because the gascolator is fitted before the header tank .The IO 540 Lycoming do not require a return to the header tank, so, I do not have the hot fuel problem. I opted for the 1/2' vents to have the vent of double 1/2' to single 3/8 inlet. This will cause fuel to flow freely even if you un-ported a tank for a moment, it will refill that 3/8' fuel line in no time.

[svyolo]

I will post a pic of my choice when it is installed.

[whee]

I've beat this drum before and I probably will again. Something about experiencing multiple fuel starvation engine failures due to a design flaw tends to leave a lasting impression.

Sorry for the slight, but relevant, tangent svyolo.

23.975 Fuel tank vents and carburetor vapor vents.

(a) Each fuel tank must be vented from the top part of the expansion space. In addition -

(1) Each vent outlet must be located and constructed in a manner that minimizes the possibility of its being obstructed by ice or other foreign matter;

(2) Each vent must be constructed to prevent siphoning of fuel during normal operation;

(3) The venting capacity must allow the rapid relief of excessive differences of pressure between the interior and exterior of the tank;

(4) Airspaces of tanks with interconnected outlets must be interconnected;

(5) There may be no point in any vent line where moisture can accumulate with the airplane in either the ground or level flight attitudes, unless drainage is provided. Any drain valve installed must be accessible for drainage;

(6) No vent may terminate at a point where the discharge of fuel from the vent outlet will constitute a fire hazard or from which fumes may enter personnel compartments; and

(7) Vents must be arranged to prevent the loss of fuel, except fuel discharged because of thermal expansion, when the airplane is parked in any direction on a ramp having a one-percent slope.

This goes all the way back to CAR4:

Car4.jpg This is one of those regulations that was written in blood. My blood was almost added to it twice.

I recognize that there are many BHs flying and pretty much all of them do not comply with this regulation nor is it required that they do but it is a design flaw that should be recognized even if you don't plan to change it. It needs to be recognized so that if you ever encounter its failure mode you'll know how to mitigate it.

[way_up_north]

Hi guys, I`m no where near thinking about fuel systems and such..I`m not sure if the following is applicable to this... ive been watching some of the Viking Engine(auto conversion) videos....They have 4 or 5 videos about header tank placement and they sell tanks and pumps....Their engine is fuel injected so I thought it might be worth a mention.....I was thinking maybe their tanks could be used with your application and save you some money over general aviation offerings..

[svyolo]

I saw them several months ago and made a couple of inquiries. I really liked their "mini-header tank", as it was what I was wanting to make myself. It is very expensive, as are replacement pumps. It is also internally regulated, but not with a reference to MAP, which is what SDS said they prefer. It also has plastic fittings. It is very slick, and I really like it at first.

Walbro pumps are 1/6 the price. I would probably replace one every 5 years/1000 hours as a maintenance item.