Header tank design and location

[Ed.Meyer]

With Bob's design and the fuel valve set to both at least one tank port will be supplying fuel in any positive g configuration. Nose up, nose down, slip left or right. Using rear port only, nose down can leave both dry as Jim pointed out.

[Ed.Meyer]

In a coordinated turn one tank is is NOT higher than the other as felt by the g forces in the airplane which is what the fuel will react to.

[Mark Goldberg]

Bob's system has worked on both carb and injected engines. I am not sure why any modification is needed. I do not see it.

John - if you are in coordinated flight the tanks will draw down equally - even in a turn. At least it would seem that way to me. Mark

[Mark Goldberg]

It would seem to me that if you are in a coordinated turn the fuel would be flowing equally from both sides. Mark

[svyolo]

Kevin D;
Awesome info. Thanks. But I still see a problem that I described before.

Whether you return to both tanks, in "Both" or only return to the left tank all the time, I still see draining the high tank very quickly in a continuous, or mostly continuous turn. Assuming a left turn, fuel valve in Both, fuel returned to Both, or in you system, to the left, I see the right tank emptying fairly quickly when low on fuel.

Assuming a 35 gph pump, and 7 gallons in each tank, my high (right) tank is dry in 12 minutes, and the left wing lines are seeing only fumes.

Am I missing something?

I will be flying from the left seat. Given a choice, I will be making left turns in the above scenario for better visibility. If I was going to only return fuel to one tank, I think I would make it the right tank vs the left.

[AZBearhawk272]

A lot has been written and intimated on this thread and I will throw in a few nickels worth.
Just so happens I design fuel systems and components as my lively hood.
So here are a few points of note:

The system that Bob designed is simple and adequate for carb or fuel injected engines.
It works very well when implemented properly.
I have mocked it up in clear tubing to check flow and line refill, bubble formation and flow stagnation. I did this for two reasons: one to
investigate why A Bearhawk engine went quiet
and would not re establish fuel flow.
Two to make sure that in my installation,
IO-470 that fuel flow would be adequate and
un interupted.

Most general aviation aircraft that have a header tank have one for 1 reason.
to meet certification requirement that after engine fuel starvation of running a tank dry
that the engine can restart and produce power
within 10 seconds after switching to an available source.
The Bearhawk system as designed by Bob will go from a dry tank to fuel at the carb in 3
seconds!



Most production FI systems utilize an engine driven pump that is positive displacement pump some fixed displacement / some variable displacement. The pumps are sized to provide Approx 1/3 more fuel than needed
to support combustion. Fuel delivery is proportional to engine rpm. Un used fuel is returned to the “ system “

In most cases the header tank provides a means to capture the excess fuel bypassed and immediately make that fuel available for the combustion process.

I am not utilizing a header. Fuel will return to the left tank. Fuel selector will be R, Both, L, Off.
The primary flight mode is Both. Returned fuel
will level as the fuel seeks cross tank equalization. The fullest tank will have the highest head pressure and will drain the fastest.

Aircraft fuel pumps are not designed to
“ Suck “ and operation in that mode will destroy a pump quickly. Pump inlets should always be flooded by free stream supply.

A header tank is not a requirement but a means to meet a requirement.
Mock up and test your system with clear Tyron
tube to know before you build.

Kevin D # 272

[svyolo]

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.)

I originally was wanting a header tank because it seemed like that was the convention in high wing planes with FI, and I didn't know any better. I still feel that way. After lots of thought, my biggest concern with not having one is

1. Low on fuel, landing pattern, or looking for a place to land.
2. Turning in one direction for 15 or 20 minutes.

Because it is a side by side airplane, I will mostly turn left when given a choice for visibility reasons. While the engine may only be burning 7-11 gallons an hour, the FI is using a constant displacement pump, (25 or 35 gph I can't recall which at the moment). So I am feeding out of the high (right) wing at a rate of 35 gph, how long until that tank is empty, assuming I had 7 gallons in it to start?

If I am running the fuel valve in "right", and all the fuel is returned to the right tank, no different than a carb or MFI. If I am running in "both" as recommended, I simply don't know.Assuming that the fuel follows the path of least resistance, I could be feeding 35 gph out of the right tank, and returning 28 gph to the left tank, as it is several feet lower when in a 15-30 AOB turn to the left. I could possibly run the right tank dry in as little as 10 or 12 minutes when running in both. At the moment, this is a concern, but I don't know if that will happen for sure. I could fly for 500 hours with no problem. Then, at 501 hours, I am having a hard time deciding where to land, or am practicing touch and goes, and ......................

Which gets me back to "why a header tank". Some engineers with a lot more experience than me designing high wing airplanes thought it was a good idea. Mostly I am not 100% either way, and am leaning toward following "convention".

[whee]

Jim, The issue is the amount of fuel being drawn from the tanks by the fuel pump. It is entirely possible that the fuel pump will actually be sucking the fuel out of the tank because head pressure will not deliver fuel fast enough to keep up with the pump. If the pump is pulling fuel from the tank and one of the pickups un-ports then the pump will suck air and not fuel. You’ll be left with whatever fuel gravity can supply through a single pickup which may not be enough.

Also, simply having the return line T’d into one of the supply lines at the tank isn’t sufficient. The returned warm fuel and vapor needs to be cooled and vented in a tank.

Z, we discussed this at length a while back. You also talked to a buddy of yours in AK that suffered a partial power loss because he un-ported one of the pickups on his EFI cub.

The Continental IO360 fuel system flows 30-35gph pretty much constantly, it varies a little with rpm, but the max that is supposed to make it to the cylinders is around 20gph. The remainder is returned. I wanted to use both ports in the tank to supply fuel so I did some testing and decided that I would be comfortable with using both ports if I used 1/2” fuel lines at the rear port. After installing the lines we performed a preliminary flow test. As we hoped the 1/2” line alone will meet the 125% flow requirement. In my system, which is basically what Bob specified except the 1/2” rear fuel lines, gravity should provide more fuel at the fuel pump than required. The pumps should never have to suck fuel from the tanks making un-porting a nonissue.

[JimParker256]

If you explained the issue, Zzz, I must have missed it. You mentioned you were using a "bung" near the top to return the fuel, and only using the rear pickup to deliver fuel. It would seem to me that you could use both front and rear bungs (at the bottom of the tanks supplied with the QB kit, and shown in the plans for scratch-builders) for your fuel pickup, and add one near the top to return the fuel. If absolutely necessary, I suppose one COULD even use a "Y" or "T" fitting and use either the front or rear pickup point as the "return" point as well.

To reiterate my concern, there are TWO situations you will encounter on many flights: The first is the high-angle climb-out, where the fuel will shift aft, and (especially in low-fuel situations) the front pickup point may be uncovered for the duration of the high-angle climb. The second is a descent from altitude, where the nose is lowered, and the fuel will shift forward, and (again, especially in low-fuel situations) the aft pickup point may be uncovered for the duration of that descent. The steeper the descent, the greater the likelihood.

[JimParker256]

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...

[Zzz]

Why would you NOT use both the forward and aft tank outlets? Mark

It's not as if it didn't cross my mind also as the ideal solution. I can't remember where I discussed this, but I did at length, about the potential to suck air in the unported forward pickup. Would the rear pickup and line keep everything primed? When the two lines are Y'd or T'd together, it gets a little more head-scratchin'... This isn't just atmosphere or even an engine-driven fuel pump, it's high pressure, target being 35 psi. Suckage of air could happen fast and a lot of it.

I figured the most likely scenario, and the most deadly, for unporting would be in a steep climb, so the rear pickup is the primary.

I'm all ears if someone can figure out how to incorporate the front pickup too without the complication I mentioned.

[Mark Goldberg]

Why would you NOT use both the forward and aft tank outlets? Mark

[Zzz]

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.

[whee]

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.

[Bcone1381]

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.)