Zenith Aircraft Builders and Flyers
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Fuel Design: Risk of sucking air from one tank while in a steep turn
There are several solutions to prevent a fuel system from sucking air from a fuel tank while in a steep turn when the fuel level is low. This has been a hot debate on other forums.
I am curious to hear from folks who are actually flying their planes on which design you use to address this risk.
1) Header tanks?
2) Check valves?
3) Limit fuel selector valve to only use R or L tank but not both?
4) None, I use "both" on my selector valve and do not have a header tank and have not had any issues.
Could you you please comment which model you are flying and what engine, and if it is F.I. or carburated and if you have fuel return lines.
Thank you !!!!!
Charlie
Replies to This Discussion
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Permalink Reply by John Austin on
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(4) - Selector valve "Both," no header tank, no crossfeed prior to selector valve, zero issues in 600+ hrs!
(750 STOL, Jabiru 3300, AeroInjector TBI carb - no float bowl, no fuel pump, gravity fed, no return lines.)
KISS! ;>)
John
N750A
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Permalink Reply by charlie rosenzweig on
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John,
Thanks, good to know. Hope several others comment as well.
Charlie
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Permalink Reply by Robert Riat on
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I have the stol 750 with UL engine, fuel injected, return lines, 15 gallon tanks and no header tank. Also have a 12 volt selector valve ( Zenith supplied) which is only one tank at a time. Roger says they have never had issues with
that valve, but it does make me a little nervous that it will fail and not switch tanks so I change tanks every 30 minutes, or so, making sure I don’t run one tank too low. Also, I have never trusted fuel gauges much and, at my
older age, don’t like flying more than 3 hours at a time so I make it a point to stop, take a break and refuel. The stol
plane is not exactly a cross country machine anyway. Not to say that I couldn’t get fuel starvation from a steep turn,
but I don’t worry about it.
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Permalink Reply by Loren Warner on
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With Viking 130's gas direct injected engine, since there is not fuel return line, there is no reason to have a fuel selector valve. Our wing tanks drain into a 2.5 gal header tank, and we have found both tanks flow pretty equal so long as the wing tank vents are not obstructed. In any event, it does not matter to us if one tank runs dry before the other since both tanks drain into the header tank.
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Loren,
I still think a selector valve - or at least a fuel shut-off valve on each tank between the tank and header - is a good idea. You were lucky to have even flow from both tanks, but some are not so lucky and need the ability to draw a tank down when they are unbalanced. I also like being able to isolate/shut-off a tank if it is suspect for contaminated fuel such as water. If the engine runs rough due to water, etc., the selector helps you determine if its one tank or both. If it turns out to be just one tank, then it could be shut-off for the remainder of the flight until you're on the ground and it can be sumped, etc.
John
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John,
the way our fuel system is designed, we're confidant that contaminates cannot effect our engine during flight, but we do have wing tank isolation valves installed for ground maintenance purposes such as fixing leaks or changing filters.
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Permalink Reply by François Balaux on
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Hi
I don't understand why you anticipate a problem in a steep turn. If the turn is coordinated the fuel will stay level with the fuel tank. If it's far enough from coordinated you probably will have to manage a spin recovery before using all the fuel in the lines..
Anyway my plane is a CH-701 with one tank in each wing. One tank has a 2 liters tanks in the line for steep descent with low fuel. Both tank connect at the gascolator, then one valve and direct to the 912 fuel pump. The only problem I had was that one of the original gas cap had air intake problem. I installed snorkel on both caps and I have 400+ hours since.
Regards,
Francois
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Robert,
Rest easy. I have no concerns. But the topic has been hotely discussed in many forums (one being Vans Airforce). with various people having a wide variety of opinions and some very creative solutions.
Yes, the dilemma is only likely, even if minimal, if a person conducts an uncooridinated turn with a relatively low level of fuel. Ever done a slip on final?
This is a worthy discussion and potentially valuable as real world pilots share their information.
Thank you (and the others) for being willing to post. We can all learn from each other.
Charlie
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Permalink Reply by Ralph Powell on
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Francois,
Thanks for pointing out the facts about fuel level in a steep turn.
Concerning the need for a header tank, folks like to say that the header tank acts as a reserve. That may be correct only if you have a fuel sensor installed in the header tank. I decided that setting my EFIS to warn me when I drop below 5 gallons made more sense and saved me the expense and headache of installing a header tank. Five gallons gives me about one hundred miles of options, waiting until I only have one or two gallons in the header tank gives me about 15 minutes and that is just not enough time here in the Idaho mountains.
Ralph
N750RP
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Ralph,
although our 2.5 gal header tank does give us more fuel capacity (about 1 hours worth), we do not consider it a reserve. Our Grand Rapids EIS monitors the fuel level of both wing tanks and the header tank. The EIS is also a fuel flow monitor/totalizer and has alarm set points for everything.
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Charlie, I smiled at your response “have you ever done a slip on final”? I live in Kansas and any CFI out here will tell you - if you can’t land your airplane in crosswinds, you shouldn’t be flying! And, any pilot who would tell me that they have never been uncoordinated in a turn might be as windy as a typical day in Kansas. :-)
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Robert. Yes, I would hope most who fly realize that uncoordinated flight does happen. As far as the risks to sucking air, or as some call it "unporting" a fuel line, it is a worthy discussion.
There are folks on both ends of this discussion/debate. On one side of this discussion there are those that would say that no one should ever have a system where "both" tanks supply fuel at the same time, and that doing so presents a recipe for disaster. The other end are folks that say that it is a non issue. Depending on how the fuel system is set up, I think both can be correct.
There are certainly things we should do when contemplating our systems, and probably the most important is to test your systems in all (fuel selector) settings, and in all attitudes before flight. Both with full fuel tanks and with minimal fuel in the tanks.
Charlie
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