Header tank design and location

svyolo

svyolo

Junior Member
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.
 
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
 
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.
 
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.
 
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
 
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.
 
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, 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.)
 
svyolo said:
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.
Click to expand...
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.
 
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 said:
Why would you NOT use both the forward and aft tank outlets? Mark
Click to expand...

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.
 
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...
 
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.
 
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.
 
Bcone1381 said:
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.)
Click to expand...

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".
 
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
 
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.
 
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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
 
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.
 
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.
 
As noted, in a positive G coordinated turn the fuel distribution in the wing tanks should be even and level across both tanks.
You tube has several nice Bob Hoover videos that illustrate this point well.

A valid concern is a prolonged slip to landing
in a low fuel condition. Many production planes are placarded against this operating condition. The “saving grace” in this situation is the fuel consumption is down in the 1 to 2 gph range. So 1 quart of fuel should provide
15 min of slipping.

I postulate that if fuel is low beyond reasonable landing reserves, and a half hour
slip to landing is required the issue is not in the fuel system.

As part of Phase 1 testing,fuel unporting tests
and slips to landing, dry tank switchover, should all be conducted at altitude over a suitable landing site.

looking forward to that myself. : )
 
Well, I believe I had a disclaimer, "am I missing something"? In any coordinated turn (which is the goal), the lift vector (and load) is vertical with respect to the aircraft vertical axis. Most of us only try something different only in a crosswind landing. So my worrying about fuel being transferred to the low tank in a turn is.............somewhere between stupid, misinformed, or in my case, I think I will go back to stupid. I am an engineer by education, and I "missed something". I started this thread, and I learned a lot from it. Thanks to everybody. I think I will shut up now.
 
svyolo said:
Well, I believe I had a disclaimer, "am I missing something"? In any coordinated turn (which is the goal), the lift vector (and load) is vertical with respect to the aircraft vertical axis. Most of us only try something different only in a crosswind landing. So my worrying about fuel being transferred to the low tank in a turn is.............somewhere between stupid, misinformed, or in my case, I think I will go back to stupid. I am an engineer by education, and I "missed something". I started this thread, and I learned a lot from it. Thanks to everybody. I think I will shut up now.
Click to expand...

Don’t do that! Discussions like this are how we learn. There are no stupid questions and there is nothing wrong with being wrong or not knowing something. This is a great discussion, thanks for starting it!
 
Do not be too hard on yourself as these things being discussed leads to better information for everyone. I have learned from postings on this forum. And when Kevin D chimes in (Bearhawk272), it is always good info. Mark
 
I must admit that I have never quite understood the "need" for a return line with a FI system. I am currently running an RV-10 with an injected IO-540 with EDP and electric pumps. The electric pump has an idling circuit which deals with any excess fuel. No problems whatsoever...... For my Bearhawk, I have installed the Andair pump which has an internal bypass.

With a low-wing aircraft which generally switches tanks every 30 minutles or so, I see no issue with fitting a return - you just end up feeding off one tank longer that the other. But with a high-wing system designed to run on "Both", it just seems that you are building in potential problems........

As Svyolo said - "Am I missing something?"
 
I imagine there are several reasons why some FI systems need return lines and others don't. With the EFII system we are using one benefit is that there are zero vapor lock or flooded hot start issues. With the fuel contantly circulating when the system is powered up, there is cool fuel all the way to the injectors all the time. Even on a hot day, and hot engine restart, it starts immediately and runs smooth. I know the same cannot be said for some FI systems...
 
Hey Ed, it sure would be great if you'd do a write up about your experience with the EFII system. Installation issues? Good documentation? Good support? Teething pains initially? Any quirky operating requirements? A Beartracks article would be great, or a thread on the forum.
Systems like the EFII are cutting edge (for recip airplane engines) and it would be great to hear your thoughts about your experiences.

Bill
 
I believe the purpose of the fuel return was always to eliminate vapor lock. Cars used to always use it. I believe most have gone away from a return in the last decade or so for environmental reasons. Most now have an in-tank pump, and no fuel return. The tank is run at a slight negative pressure to reduce evaporative emissions.
 
Excellent discussion, and I'm learning a lot. And it's also stimulated my thinking on this subject. So, even though I am 99% likely to go with a carbureted engine for the simplicity of it, I'm still trying to think through the injected design side...

An FI system that "recirculates" the excess fuel would seem to either need a header tank (which I don't like for various reasons) or it would need one (or more) return lines to the fuel tank(s) themselves. I've heard some "interesting" stories from a friend with a Bonanza that had a total of 7 tanks (main, aux, and tip in each wing, plus a "baggage" area tank), but had a fuel system that aways returned the fuel to the left main tank... Fuel management seemed nightmarish to me, since he had to keep coming back to the left main to ensure it didn't overflow the returned fuel... Based on that, if I were using such an FI system, I would probably use a full-duplex fuel selector – plumbed such that the return fuel goes back to the same tank that is selected. Yes, that would require two return lines (one to each wing tank), but the additional weight would almost certainly be lower than the weight of a header tank, gauge, etc.

In Zzz's case, if a 1/2 inch fuel line is what is required to supply the "gravity-only" fuel flow rate to prevent "sucking" fuel with the pump, then I would use 1/2 inch fuel lines connected to both the forward and aft fuel pickup bungs. And agreeing with Zzz's (or was it Whee's?) about using the "T" or "Y" fitting for the returning fuel, it would probably be prudent to add an additional bung to the upper side of the fuel tank for the returned fuel.

But in any case, I would NOT do away with the "dual" fuel pickup points, for the reasons discussed earlier.
 
I agree with Jim's comment and would that I would NOT do away with the forward tank pickups. We plumbed the fuel lines as Bob designed all the way to the gascolator. The dual fuel pumps (redundant) and filters are after that. We put in a duplex fuel valve and return lines to both tanks. Of course had to add fittings to the tanks which we placed at about the center of a rib lightening hole for easy access and about the center fore and aft. I don't think it much matters whether high or low.

An interesting observation occurred yesterday and I had noticed i before but this thread came to mind this time. When I first powered up for start and the fuel pump came on, I could hear bubbles in the fuel tanks for a couple seconds as air was being purged out of the system.

I gave many hours of tought and some lost sleep over many of the concerns and ideas, including header tank, expressed here before deciding on the final design.

As to the concern regarding sucking air from an unported tank outlet, I worried about that as well. Apparently it does not suck hard enough to overwhelm gravity. Tested this before first flight by measuring fuel flow in hard nose up attitude with only 5 gallons in each tank. Was the same whether selector was on both or either individual tank. This is with 3/8 lines throughout.

As others have said, interesting thread...
 
I am using Bob's design with 3/8 tubing for my FI engine except I am only using the forward bung on the left tank where the return goes. I have a lot of time in Bonanzas with the return to the left main only and am very comfortable with the operation. Just takeoff and land on the left main. If there is a problem, the left main always has some fuel in it. Low wing planes do not flow any fuel without a pump and do fine with 3/8 inch tube. I have an Titan engine and understand the return is less than a couple gallons an hour, similar to the Bonanza.

Newer RANS aircraft have a header tank under the baggage compartment and skip the forward tank drawoff.
 
I am starting to like Whee's idea of 1/2 inch lines as well. If nothing else, extra capacity, stored in the lines itself. Sort of a built in small header tank in each line.

Lots of great responses. I learned a lot.

I still haven't quite come to closure over forgetting how loading works in a coordinated turn. 30 years of flying for a living hasn't taught me much I guess. LOL
 
Not clear to me but sounds like you are using the left forward bung for the return. Interesting idea. I would think though that if you select the left tank only then you feeding from only one bung, the left rear. Wounldn't you then risk sucking air to that one feed with low fuel and nose low or left slip? I would think it would be better to select both for critical operations.
 
svyolo said:
I am starting to like Whee's idea of 1/2 inch lines as well. If nothing else, extra capacity, stored in the lines itself. Sort of a built in small header tank in each line.
Click to expand...

I’d wait till empirical data suggests my solution is suitable. Hopefully within the month I’ll be performing actual flows tests with a complete system. Testing the fuel system will be part of my phase one testing.
 
I chose to have Left, Off, Right. With the FI system And my header tank with two 1/2 “ vents back to the wing tanks. I placed one vent on the rear left and the other front right., no matter what attitude your in you always have a vent facing up for any air to escape back to the main tanks. The Header tank will fill up super fast with the two 1/2 vents. No matter if you slip for an extended period with low fuel it will not cause fuel starvation or air to enter the FI system. I only added the header tank and two 1/2 “ vents to what Bob shows on the plans.
 

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This has been a funny discussion, kind of like "Who's on first." We're not talking about the same things.

EFII systems are much more akin to car electronic fuel injection, which utilize a pressurized fuel rail to provide supply to the electric injectors. If you decide to go down this road, you have to throw what you know about the Bob fuel system out the window. Like schu said, it is great for a carb or mechanical drip fuel injection. But when you go with a system that utilizes high pressure fuel pumps to pressurize your fuel rail to 35 psi, there is no consideration of "will my engine continue to run on gravity feed alone?" It will not. So why worry about it? At that point you focus on the reliability and failover of your electric pumps.

The fuel return is mostly to keep fuel cool that is running over the top of, or along side hot cylinders. You could also use a header tank to accomplish that, but you need a minimum volume tank to effect the cooling. I have chosen to return to the tanks because I just don't want to use a header tank in my aircraft.

You cannot return fuel to both tanks at once using a BOTH selector. You have to use a duplex valve and operate on LEFT or RIGHT; supply and return are set to one tank at a time. The header tank can get you around this limitation, so that's a plus for the header tank. But if you've flown old Pipers or Bonanzas, you get used to managing your tanks. No big deal.

Those of us choosing to go with EFII aren't modifying our fuel systems just for the hell of it. I would stick with the Bob design if I was using a carburetor. But if you commit to EFII, it is a different approach and so you modify the fuel system to support the paradigm of electronic everything. The guidance on the fuel system design has come more from the system engineers, and is the same for RVs, Cubs, etc.

To Kevin D: I'm not sure I understand your claim that an electric fuel pump doesn't "suck." ? With fuel upstream and downstream of the pump regulated to 35 psi, how can you avoid drawing fuel at an equivalent flow rate? There's always going to be a positive pressure, given the tanks are above the pumps (in the Bearhawk), so it's not fighting gravity.
 
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The duplex valve we have does have a 'both' setting for supply and return. Fly set to both most of the time.
 
Ed.Meyer said:
The duplex valve we have does have a 'both' setting for supply and return. Fly set to both most of the time.
Click to expand...

It's certainly possible, I was advised to not do it because it's not reliably metered between the tanks, and you can fill one more than the other. You have the SPRL?
 
Aircraft designers generally do not like homebuilders modifying the design. While some things are obviously not going to effect safety or airworthiness, nothing is usually more serious to "redesign" than the fuel system. While I know that some you builders posting in this thread are quite smart and capable people, I still urge caution changing the basic fuel system from what Bob designed - which has worked and proven safe. If you do, then you become the test pilot. Mark
 
Yes. SPRL 4. It is possible that it returns more to one side than the other when set to both. If so, it has not been an issue.
 
I'm with you, Mark. With 2 pick-ups per tank I really don't see the need to modify anything. Ok, with a FI system, you need to put in a secondary electric pump but the basic system is sound. I know it is called "Experimental" for a reason, but highly complex FI systems that require dual batteries and return lines etc don't really - in my mind- seem to have a place in what, is after all, a bush aeroplane........

Of course, in the end, it's your aeroplane so do whatever you want.
 
Any fuel system, carb, MFI, or EFI, needs to be "fed" fuel. Since Bob's design works, I will start with that. Downstream of that, fuel will enter the fuel pump to be pressurized. But any fuel system needs to be reliably "fed". No type of fuel injection changes that.

There will only be a short section of pressurized fuel line aft of the firewall. Maybe 18 inches, and 2 fittings. The rest of the pressurized fuel system will be ahead of the firewall.
 
Let's consider this: One of the areas where experimental amateur built aircraft fall significantly short of their certified counterparts is in the category of "Fuel Starvation" related incidents. That's where the aircraft had fuel available, but the engine quit operating because the fuel could not get to the engine. Some of these fall into the "stupid pilot tricks" category, where fuel tank selected by the pilot was empty when the engine quit. But a not-insignificant number of them occurred because even though there was fuel in the tanks, there was no way that fuel could possibly be delivered to the engine. These typically get classified as "pilot error", but should really be classified as "builder error" (or in rare cases, "designer error"). In the came of all three Bearhawk designs, Bob has designed a fuel delivery system that eliminates the "designer error" part of the equation, leaving it up to us as builders to either follow his design or go design our own system. If we opt to deviate from Bob's design, we're effectively designing our own system. And unless we're professional engineers competent to design our own fuel systems, we probably should tread cautiously in this area...

For a CERTIFIED airplane that uses a fuel pump to deliver the fuel to the engine, the manufacturer is REQUIRED by 14 CFR 23.995 to demonstrate that the fuel system can deliver fuel at a rate equal to 125% of the engine's maximum full-throttle fuel consumption. Gravity-only fuel systems (with neither an electric boost pump or an engine-driven fuel pump) would need to be able to flow 150% of the max full-throttle fuel consumption.

Both "pump" and "gravity" types are required to demonstrate they can meet the stated fuel flow capability while in the most critical flight attitude for that aircraft design, and the testing must be done with the tanks at very low "fill level" – only the "unusable" fuel plus whatever is needed to perform the test. My reference for these statements is 14 CFR 23.995, which can be found at https://www.law.cornell.edu/cfr/text/14/23.955.

While that requirement does NOT technically apply to Experimental Amateur Built aircraft, I think we would all agree that this fuel flow test is a really good idea. (And as a side note, my local DAR will NOT sign off an EAB aircraft that has not had this test performed.) You'll also note that the requirement to perform the test at the most critical aircraft attitude would generally mean that the airplane would be in a very nose-high attitude, since max-performance takeoffs are generally the most critical situations for fuel delivery.

But if you're leaving off the forward pickup point for the fuel tanks, I would suggest that in addition to the nose-high attitude test, you might want to consider that your actual "most-critical attitude" might well be a nose-down attitude approximating the final approach profile. That's because a go-around would be initiated from that attitude, and if you're been in a nose-low descent for a while, it is possible that the aft fuel pickup point has been "unported" for however long that nose-low flight has gone on. Translation: The fuel line from the aft pickup point to the fuel pump could be bone dry when your engine quits due to fuel starvation. You might have sufficient fuel on board to be able to restart, but if you're flying using "Both" tanks, it's entirely possible that both lines could be bone dry. How long would it take to refill those lines so the engine could be restarted? If you're on final approach when this happens, would you have enough altitude remaining to maintain a level (or better yet, nose-up) attitude so the aft pickup point would again be awash in fuel and begin to fill the line?

So, far from being a misunderstanding about differences between FI and Carbureted engine fuel delivery systems, my concerns are about whether or not your altered fuel system design can still safely meet the criteria of 14 CFR 23.995, regardless of the fact that it may not be required to do so... We kind of like having you around, Zane, and don't want to read about about you in an NTSB report!
 
Just to fan some air across the coals of this
thread.

There had been a comment about pumps and sucking a while back that needs some clarity.

Most positive displacement pumps are not
capable of operating successfully without a flooded or pressurized inlet. They do not suck well and basically quit pumping once they
cavitate or drop below vapor pressure at the inlet. If pumps sucked well every water well with a submersible at the bottom of the hole
would be unnecessary.
The typical engine driven diaphragm pump is designed to suck but the pressure capability
is minimal and the durability questionable.

With respect to feeding fuel from the tanks to
the engine. Half the conversation is unporting a line feeding the engine.
Liquids are funny things, they only go where you guide them. Many different factors determine how they get down the pipe.
one thing is sure. After unporting a feed line,
air has to come out for fuel to go in.
Hence the dual feeds from each tank.
The line with the highest static pressure becomes the feed, the other becomes the vent. No vent, fuel does not like to flow down where air is heading up.
 
JimParker256 said:
Let's consider this: One of the areas where experimental amateur built aircraft fall significantly short of their certified counterparts is in the category of "Fuel Starvation" related incidents. That's where the aircraft had fuel available, but the engine quit operating because the fuel could not get to the engine. Some of these fall into the "stupid pilot tricks" category, where fuel tank selected by the pilot was empty when the engine quit. But a not-insignificant number of them occurred because even though there was fuel in the tanks, there was no way that fuel could possibly be delivered to the engine. These typically get classified as "pilot error", but should really be classified as "builder error" (or in rare cases, "designer error"). In the came of all three Bearhawk designs, Bob has designed a fuel delivery system that eliminates the "designer error" part of the equation, leaving it up to us as builders to either follow his design or go design our own system. If we opt to deviate from Bob's design, we're effectively designing our own system. And unless we're professional engineers competent to design our own fuel systems, we probably should tread cautiously in this area...

For a CERTIFIED airplane that uses a fuel pump to deliver the fuel to the engine, the manufacturer is REQUIRED by 14 CFR 23.995 to demonstrate that the fuel system can deliver fuel at a rate equal to 125% of the engine's maximum full-throttle fuel consumption. Gravity-only fuel systems (with neither an electric boost pump or an engine-driven fuel pump) would need to be able to flow 150% of the max full-throttle fuel consumption.

Both "pump" and "gravity" types are required to demonstrate they can meet the stated fuel flow capability while in the most critical flight attitude for that aircraft design, and the testing must be done with the tanks at very low "fill level" – only the "unusable" fuel plus whatever is needed to perform the test. My reference for these statements is 14 CFR 23.995, which can be found at https://www.law.cornell.edu/cfr/text/14/23.955.

While that requirement does NOT technically apply to Experimental Amateur Built aircraft, I think we would all agree that this fuel flow test is a really good idea. (And as a side note, my local DAR will NOT sign off an EAB aircraft that has not had this test performed.) You'll also note that the requirement to perform the test at the most critical aircraft attitude would generally mean that the airplane would be in a very nose-high attitude, since max-performance takeoffs are generally the most critical situations for fuel delivery.

But if you're leaving off the forward pickup point for the fuel tanks, I would suggest that in addition to the nose-high attitude test, you might want to consider that your actual "most-critical attitude" might well be a nose-down attitude approximating the final approach profile. That's because a go-around would be initiated from that attitude, and if you're been in a nose-low descent for a while, it is possible that the aft fuel pickup point has been "unported" for however long that nose-low flight has gone on. Translation: The fuel line from the aft pickup point to the fuel pump could be bone dry when your engine quits due to fuel starvation. You might have sufficient fuel on board to be able to restart, but if you're flying using "Both" tanks, it's entirely possible that both lines could be bone dry. How long would it take to refill those lines so the engine could be restarted? If you're on final approach when this happens, would you have enough altitude remaining to maintain a level (or better yet, nose-up) attitude so the aft pickup point would again be awash in fuel and begin to fill the line?

So, far from being a misunderstanding about differences between FI and Carbureted engine fuel delivery systems, my concerns are about whether or not your altered fuel system design can still safely meet the criteria of 14 CFR 23.995, regardless of the fact that it may not be required to do so... We kind of like having you around, Zane, and don't want to read about about you in an NTSB report!
Click to expand...

Nobody wants to not die more than me, but a life lived with a boring carburetor and nothing to provoke old EAA guys is a slow death of sorts. If you guys think that making modifications automatically means eschewing FAR 23.955, or testing, that MUST be entertaining and get the cushion sweaty.

I'm not pushing the envelope of design. Several have come before me implementing similar designs, many RV guys. Even the beloved old 170 only has a single mid-tank pickup. I guess I've never flown one low enough on fuel to make it an issue.

My design of rear port only is predicated on avoiding unporting the front pickup. The fuel system will be circulating fuel at 35-45 GPH. What happens when either of the pickups, that are T-ed or Y-ed together downstream, is unported? Will it suck air? If you don't line the word "suck" to describe fuel or air filling the void behind the supply side of a high pressure fuel pump, please suggest another term. It does create a lower pressure region, compressible or incompressible, right?

So, a few scenarios:

1. For some reason my imagination has failed me for the better and an unported front(or rear) pickup doesn't actually "suck" air. Everything remains primed nicely, the pump never cavitates.

2. Air DOES get pulled into the supply line upon unporting or one of the fuel tank pickups. Fuel pump manages to push it through into the fuel rail and the engine dies or runs like crap long enough to vent the air through the injectors, if it even will. I've heard reports where it was a non-event.

3. The air is circulated back the tank quickly via the return lines, and is removed from the system. Or the fuel pressure regulator purges it through a bypass.

As for in-flight fuel starvation, yeah, it sucks to unport front or rear pickups in any pitch attitude. But climbing steeply and maybe slowly is when I'd least like it to happen. it would suck in a descent too but usually you're carrying an abundance of airspeed. And for approaches,I don't approach any runway or airstrip pitched down aggressively. But one shouldn't have to use any flying technique to compensate for engineering flaws.

Any situation where you have unusable fuel is undesirable, though, I agree. I have a few emails out to other high wing EFII builders to see if they've intelligently mitigated the risk of unporting. But as far as I know, you either go header tank or full return with single tank pickup.
 
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There is some pretty good discussion of this in Glastar service bulletin 43. Apparently they use only rear tank pickups and mandate two small header tanks to preclude air getting into fuel feeds.
 
Personally, I don't think anything I've said should (or even "could") be construed as arguing against Zzz's desire for an EFI engine versus a carbureted one. EFI is more efficient, burns less fuel, can often be run LOP for even more fuel efficiency – though sometimes requiring tuned injectors for LOP operation. I have personally experienced some issues with difficulty re-starting at hot Lycoming engine, due to vapor lock following a "quick-turnaround" fuel stop. But that was with the stock Lycoming fuel injection system – not the one Zzz is talking about using. Even the "stock" Continental fuel injection design uses a fuel return line (as do several aftermarket EFI vendors), and there is apparently far less likelihood of vapor-lock in those engines that circulate excess fuel back to the tank(s). Turning on the fuel boost pump for a few seconds pushes cooler fuel through the lines, displacing the "gas" bubbles (vaporized fuel) from those lines pretty quickly. It's a far more elegant and pilot-friendly design than Lycoming's...

But if I go the EFI route, with a goal of not pushing the design envelope while adding a fuel return line (or lines to both tanks with a duplexing fuel valve) would be to use both fuel pickup points as Bob designed them to deliver the fuel to the fuel pump(s), and then add a 3rd port to the tank for the return line, as someone else discussed earlier in this thread. That would seem to eliminate any possibility of unporting a fuel pickup in pretty much any "normal" attitude, while also providing a port for the returned fuel. Yeah, you're going to have to run a 3rd fuel line, but that seems like small potatoes to me...

But let's assume I really didn't want to run that 3rd line for return fuel... Again using information gathered at the OSH seminar on fuel system design, it would seem reasonable to use a header tank of sufficient size to support a full throttle run for a reasonable period. And if I do that, the return fuel could go to the header tank. It doesn't take a LOT of fuel to cool the returning fuel – even if it contained "vapor lock" bubbles... A few gallons would be plenty to cool it below vapor lock state. The sizing of the header tank is more about the fuel demands of the engine than solving the vapor lock issue...

Personally, I think the additional weight of a header tank would likely offset the additional weight of running a third fuel return line, so I probably would not use a header tank, due to the increased risk and maintenance requirements. But that is an admittedly personal bias against carrying fuel inside the fuselage – or at least any more than HAS to be there because of the fuel lines... (I've read way too many NTSB reports about post-accident fires caused by ruptured fuselage and/or header tanks. If I put one in my plane, it would have to be pretty stout!)

But even with a header tank, the flow from the wings to the header tank is likely to be gravity feed, with no intermediate pumps. The electric boost pump is used to supply sufficient pressure to keep the engine running in the event the "other" pump (which may be engine-driven or electric) quits, right? So that pump would be located downstream from the header tank, between the header and the engine. The fuel lines would still need to be able to supply sufficient volume of fuel to the header tanks to sustain an engine running at full power. If it cannot, you have to add a "boost pump" before the header tank (even more complexity and maintenance issues).

I like Bob's KISS fuel system design... But then, I'll probably wind up using a "boring" carburetor for cost and maintenance reasons... LOL
 
Schu;
I was thinking about something similar. Build mini header tanks into each gravity fed line. Still thinking about it. I have seen a few EFI installations where I think fuel heating is also much less of an issue. The fuel divider is mounted aft of the engine. Should transfer much less heat to the return fuel.
 
Interesting discussion... Hopefully no one is thinking anyone is mad at anyone – we're all just trying to learn together, right?

schu said:
It doesn’t eliminate the possibility of unporting, it increases it. If you have a fuel pump cycling fuel at 40GPH and gravity can only feed that pump at 30GPH, then you nose down with minimal fuel, the rear port can come unported, and instead of simply not providing fuel like in a carb system, the pump will draw air into the system.
Click to expand...
I don't understand that statement. If you're only using the aft pickup point, it will unport in a nose-down attitude anyway. That's kind of the entire reasoning behind having both front and rear pickup points... Yes, one of the other could unport, but not both. And with both front and rear points, when one of them unports, you've still got a column of fuel from the other one to the "y" in the fuel line, and all the way to the pump. Last time I took a fluid dynamics course (admittedly MANY years ago) I understood that the mass of the fuel being greater than the mass of air would result in the pump pulling "fuel" rather than air.

But you're absolutely right that if you have a pump drawing 40 GPH and a supply line that can only deliver 30 GPH, you're going to have an issue. That's why the fuel flow test is required for certified airplanes, and is a REALLY good idea for experimentals. (It's also why it might be a good idea to use 1/2" fuel lines if you really need that much fuel supplied...)

schu said:
I would way rather have the fuel system inside the fuselage than outside because if it’s outside, it’s WAY more prone to rupture in a crash. Consider builders that run fuel lines or pumps under the tubing in the tunnel. If the airplane has a crash that wipes the gear off, you will have a ruptured fuel system. I’m planning for my fuel pump to go under the pilot seat and nothing extending below the floor. I figure the same cage that is protecting me can protect my fuel system.
Click to expand...

I agree with your position on fuel lines below the "safety cage" and am still struggling with the idea of having the gascolator mounted where Bob's design suggests. It seems like the gascolator would be the first thing to break off, and that would unleash a flood of fuel from the lines (assuming they're still intact). My "gravity feed" Citabria has a fuel drain way back behind the baggage area (low point in the fuel supply while on the ground), as well as a gascolator at the bottom of the firewall (engine side), and all the lines run between the floorboards and the "cage"... Seems more "protected" from a gear failure that way.

But the fuel in the wings versus in the fuselage thing is something that reading NTSB reports might change your mind about... I know I changed my thinking on this topic after reading a bunch of them. I wish I still had the reference(s), but it was many years ago, and the link was lost in a hard drive crash... The thing is that fuel is only one third of the equation when it comes to fire. You also need oxygen (which will pretty much always be there) and something to ignite the fuel vapor... Outside the fuselage, there are very few things that can create the spark necessary to start the fire going. Within the fuselage, you have batteries, wires, switches, generators, and all sorts of other things that can spark the fire... The NTSB post-crash fire accident reports where the plane had gas tanks in the fuselage were sobering... Lots of examples of the fuel catching fire and – key point – fatally burning the occupants before they could safely evacuate from an otherwise survivable crash.

By the way, that whole "post-crash evacuation" thing is the key reason I'm building my Patrol with doors on both sides (seaplane version) even though I'll probably never put it on floats. Hopefully, with doors on both sides, I can evacuate away from the fire... Unless I REALLY have a bad day, and manage to rupture both wing tanks, after crashing into a field of flint...

(As total aside – I knew a pilot in Brazil who crashed three airplanes into the jungle, and sheared both wings off the plane each time. Once he even managed to shear both wings and the tail section, just aft of the cabin. All three times, he survived with only bruises and very minor cuts. No fires Amazing...)

schu said:
Bobs design is great for carbs and for lycoming injection which has no return. It’s probably not sufficient for return type fuel systems with continentals or EFI. Those systems demand much more fuel to be flowing. If I was building one, I’d probably use a duplex valve, return to tank, and build two 1.5”x10” round tubing header tanks with 1/2 on one side and 3/8 on the other, and put one on each line between the front and rear mains and the T under the door jam, then use 1/2” line between the mains and the small header tank. That would hold almost a gallon per side, be very well protected under the door jam, and would be very hard to unport, while maintaining Bob’s simple system.

The pump would have to suck enough fuel to empty two 1.5x10” columns of fuel, along with 3 ft of 1/2 tubing faster than the engine can use it before it sucks air. I think I like that way more than 3/8 lines when dealing with a fast pump and the engine at idle.
Click to expand...

Probably why someone else suggested upgrading Bob's design by using 1/2" tubing through the entire system for the non-Lycoming EFI solution. Doubtful that even an IO-540 could use more fuel than a 1/2" line can deliver... (But the fuel flow test would confirm that one way or the other...)

schu said:
That said, ill probably run lycombing injection, and know that mogas might not work in my airplane.
Schu
Click to expand...

So, will you still use the mini header tanks you described under the door jamb area? I'm trying to visualize that, but I'm building a Patrol and it's pretty crowded under there, with rudder cables, flap cables, and aileron cables, not to mention the throttle cable for the back seat, and the fuel lines themselves... Have to ponder that one a bit.

As I said earlier, interesting discussion...
 
Jim;
I totally agree with the threat of fire, and the gascolator being so vulnerable, but like someone said, light planes are designed to fly, not crash. If you use a true header tank then the normal fuel lines are more than adequate as they are not "feeding" 40 gph. Only what the engine is consuming.
 
There have been ground loops in Bearhawks where the gear collapsed. But I do not recall that anyone has ever sheared off the gascolator on the belly. Mark
 
This subject has spiked my interest in the last few weeks as I put our Rebel floatplane into the trees on a go-around. The only reason I'm alive is because God must have more for me to do! I walked away but the pastor who was with my broke his femur :( You can see more at :(http://thesteidingers.com/blog/2018/05/rebel-accident/). Climbing out from a low pass to check for wires, etc I was turning from cross-wind to downwind. Because the creek was narrow, I had to climb out over the trees. The motor didn't falter, it just stopped dead. What happened? why would a reliable Lycoming O-320 just quit dead? The fuel design in a murphy Rebel has just one port in each tank. Initially it was about in the middle and connected to the fuel sight gauges. A bulletin called for the exit to be separated from the sight gauge and moved farther back. Our Rebel had no header tank, just gravity and with the 150% flow test completed.

On this particular day we had taken off with a little more fuel in the right tank. After talking off, I closed the left tank and was burning fuel from the right to equalize. A storm came up so I descended fairly quickly, did a high pass and then a lower pass about 250 feet off the water to check for power lines running across the river. First mistake, waiting to do my landing checklist until i was in the pattern instead of when I approached my landing site. As soon as it quit I immediately remember the left tank but only had time to open the valve-- I'm guessing I had about 10 seconds to shove the stick forward and land in the forest. No time to try and re-start. I had 30 litters in the left tank and 25 in the right at the time of the accident (verified by sight and our fuel flow meter). I was using my right tank, I was in a left turn and if you are in a coordinated turn (see Mark's post in this thread) the fuel should not flow away from the port, but even if it would have, it would have flowed down to that port. I have flown and done hundreds of landings in this plane with the above fuel scenario. After some research, two things I see were different this time. ONE; I was not using both tanks. I can't remember ever approaching a landing site when I wasn't on BOTH. TWO: This was not a "planned" approach. The storm was coming so I descended steeper than normal. What do I think happened? The fuel tank is integral, so there are quite a few obstacles (ribs, etc) that keep the fuel from "quickly" un-porting the single exit. However, because of my longer, steeper descent, I think the fuel might have had time to flow around / through the obstacles to the front of the tank. I believe it became un-ported and when I powered up and climbed there was air in the line. If this had happened in my other approaches, because of an un-coordinated turn for example, it would not have happened to both tanks. Therefore the tank not un-ported would have pushed the air out of the other line (see Jim's last post). What we've learned. Either have two ports in each tank or a header tank. I'm still not sure how the Cessna 150's get by with only one port (if I remember correctly, the larger Cessna models have two, but I believe the smaller models only have one).
 
Glad you're here to relate that episode to us! What you described is the real bugaboo about experimenting with fuel systems. When problems arise, they pop up FAST and at the worst possible times.
 
Scshu;
Your comment on SDS's individual fuel trim? Your thoughts about why you don't like it?

MFI and a couple of electronic ignitions is just as expensive, or more, than full EFI/EI. Rebuilt carb and 2 rebuilt magnetos are cheap to buy, but the mags would need to be rebuilt 3 times to get to TBO, and the carb probably at least once, unless you fly a BUNCH. Running LOP should save 3-4000 gallons between TBO's. Rebuilt carbs and magnetos are cheap to buy, but I think they are the most expensive over the course of the life of the engine. By far.

If you are building a complicated IFR airplane, the electrical system is the same for EFI or a carb. If you are building a simple VFR airplane (me), EFI increases the electrical cost/complexity. I have a hard time justifying it other than I simply prefer it. But I do prefer it.
 
Right now I am leaning towards a header tank under the front seats. Maybe just under the right seat, with the fuel pumps under the left. I get access to all fuel components, plus the elevator cable adjustment. It is contained within the fuselage, at the strongest place on the whole fuselage.
 
Matt you are lucky to be alive. Looking at the blog and photos the aircraft destroyed. God has other plans as you said. Peter b
4 place scratch build Australia
 
Schu;
I like to make rational decisions instead of what I want. Usually rational wins out. In the case of MFI vs EFI, I think MFI is good enough for me, but I am much more comfortable working with EFI. For me MFI is a box of parts I don't understand. The cost of MFI and dual EI's is similar to EFI/EI.

I think I could have been happy with either, but in the end I am more I EFI's box of parts more than MFI's. Electrically I don't mind a few extra wires as i am good at that part and I will make it reliable. I only don't like the extra plumbing. More precisely, I don't like plumbing!!!!!
 
svyolo said:
Schu;
I like to make rational decisions instead of what I want. Usually rational wins out. In the case of MFI vs EFI, I think MFI is good enough for me, but I am much more comfortable working with EFI. For me MFI is a box of parts I don't understand. The cost of MFI and dual EI's is similar to EFI/EI.

I think I could have been happy with either, but in the end I am more I EFI's box of parts more than MFI's. Electrically I don't mind a few extra wires as i am good at that part and I will make it reliable. I only don't like the extra plumbing. More precisely, I don't like plumbing!!!!!
Click to expand...

No problem, svyolo., I reference Post #55... Realize, that making rational decisions is resulting in a compromise....the header tank being placed under the seats.

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 would feel more comfortable if a +5 gallons header tank was placed aft of the bulkhead with a "Not full" sensor in it, gravity fed by only the aft fuel tank bungs. Highly unlikely that a 5 gallon header tank could be emptied during descent to landing with the aft tank bungs unported....plus it increases fuel capacity. It can have 1 return line running back to it and have a simple on-off fuel valve. it removes fuel lines, removes fittings, and connections. It becomes almost a C-150 fuel system from the operators point of view. Sucking air problem is eliminate, its in a safer location.

Doing pattern work on almost empty main tanks would be no worry. Every landing would fill the header back up in seconds. If one ran the main tanks dry, VFR fuel reserves are in the still in the header.

Note this popular maxim, from Saint-Exupery:

..perfection is finally attained not when there is no longer anything to add, but when there is no longer anything to take away...

I look up to you who go the EFI, but I am not there yet.
 
So Brooks, I take it that you're planning on an electric pump at the rear header tank. That pump will run on low at all times, except high boost for starting - maybe takeoff/landing also.

A tank behind the baggage bulkhead will be well below the engine driven pump, on takeoff. You have to treat such an installation as one would view a low wing, injected aircraft.

Bill
 
Bcone1381 said:
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.
Click to expand...

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...
 
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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.
 
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.
 
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.
 
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.
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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.
 

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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..
 
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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.
 
I have been impressed with your answers on the forum describing the FI systems in the Bearhawks. so much so, that I decided to join (unlike me) and reach out with a few questions.

I am in Alaska and am in the final stages of completing my fuel injection system. I have a question regarding the header tank and specifically the return line plumbed to the header tank.

I have the factory IO-470 MFI system starting with 1/2 fuel lines feeding a fuel selector of L,R & both, then flowing to a 1L header hank (a small tank!) that we welded out of 1/8" aluminum (pretty heavy duty) and located on the cabin side of the firewall. From there we flow into a "Steve's gasgelator" and then to the CJ electric fuel boost pump and finally to the engine driven fuel pump (that is on the back of the motor and has scatt tube providing cooling. I have the Atlee vented fuel caps (It is a high wing aircraft).

My question is the fuel return line. Right now I am planning returning the fuel to the top of the header tank. My concerns are 3 fold:

1. Will I be pressurizing my fuel system by returning 20PSI fuel (assumption of the pressure of the return line) to a gravity system in a small header tank. Is this even an issue?
2. Do I really need to worry about the temperature of the fuel being returned? I feel like no, because the fuel never hits the hot part of the motor (front of baffling), but I am second guessing this slightly.
3. Do I need to vent this header tank? Or will the fact that the main tanks are adequately vented suffice? I would rather not have to weld another bung into the header tank and then plumb back up to the wing tanks.

Any input would be greatly appreciated!​
 
I am not flying yet, about to do FF testing and weighing the thing.

I originally thought return fuel should be plumbed into the top of the tank. Turns out it is preferable to return it low in the tank, away from in fitting feeding the pumps. This keeps bubbles and foaming down.

1. It shouldn't pressurize the tank if everything is done correctly, which includes venting the header to the main(s).
2. I can't answer that for MFI. If there is significant heating of the fuel, this could be a problem. Cessna 180 series used TCM MFI, and as they used header tanks to return fuel to. One of the solutions to this is a large header tank. I have zero experience with these Cessna's, so I don't know how big their header tanks are. Short answer - I don't know for your system.
3. Yeah the header needs to be vented. I vented mine to one main tank. I will hopefully change this at some point to both tanks, which will then be vented together.

Hope this helps, but keep in mind, Mine is not successful yet!!!
 
Kevin D,

Are you able to take a call from me regarding your information on this post? It appears you have the information that I am after as I complete my system. I'd love to ask you a few questions. As a side note, I wrote a post last night to the general group regarding my 3 remaining issues. Your advice is incredibly appreciated.
 
svylo, why does the header tank need to be vented? Wouldn't the vents from the main tanks supply the appropriate venting to the entire system?
 
Seth Kroenke said:
1. Will I be pressurizing my fuel system by returning 20PSI fuel (assumption of the pressure of the return line) to a gravity system in a small header tank. Is this even an issue?
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There will be a pressure regulator that drops the pressure to near zero before it is returned.

2. Do I really need to worry about the temperature of the fuel being returned? I feel like no, because the fuel never hits the hot part of the motor (front of baffling), but I am second guessing this slightly.
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I can't be certain for the Conti system, but I've heard that on some FI systems a lot of the heat comes from the fuel pumps pressuring the fuel? If this is the case, you will need to worry about heat. EFII asks for a minimum of 5 gallons in the header to support cooling.

3. Do I need to vent this header tank? Or will the fact that the main tanks are adequately vented suffice? I would rather not have to weld another bung into the header tank and then plumb back up to the wing tanks.
​
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Yes! It must be vented! The header tank can't fill if the air can't get out.
 
Cessna always vented theirs, and there are a bunch of commercially available "surge tanks" which are used to convert carbed cars/boats to EFI. That is what I am using. 100% of them have vents.
 
Regarding your question "why venting"... Have you seen the post by Whee, literally two posts above?
Because venting tanks together keeps you alive :)
"Airspaces of tanks with interconnected outlets must be interconnected"
 
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