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Header tank or not
Installing a UL350is in a Cruzer and am pondering a header tank. There seems to be a lot of good reasons to have one a only a few not to. The possibility of voiding a fuel line during uncoordinated flight is not a worry with a header tank. A duplex fuel valve is not required. A header tank adds a bit to the expense and has a couple of gallons of fuel in the fuselage.
I would appreciate hearing from anybody with some experience and advice with this method.
Replies to This Discussion
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Permalink Reply by Jan Eggenfellner on
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There is a point about there being some weight shifted aft, the rest is not factual since a header tank installation will save 35lb on every flight.
Real life flying is like this:
- Without a header tank, we need a minimum of 4 gallons left in each main tank to feel somewhat confident that we are not being irresponsible / unsafe while carrying our passenger around.
- These 8 gallons equal 50 lb of fuel being carried around at all times.
- Since the lightweight aluminum header tank / fuel pump system weigh less than the old fashion external pump systems, no compensation has to be made here
- With the header tank, the unusable fuel does not exist, however the 30 min VFR reserve is built into the tank, so 15 lb of fuel stay with the airplane.
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Nice valves, thank you for sharing. I will try one
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Dick Booher now has the Viking dual in-tank pump system installed in his UL-350 powered CH-750 and has started testing. The pressure is perfect at 3 bar / 45 psi. More info and pictures to follow.
He has removed the earlier system.
Jan
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Permalink Reply by Ken Ryan on
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John Bell,
You're right. There are good reasons to have a header tank, especially in a Zenith. With only one outlet at the rear of each tank, there is a very real possibility that in a long descent with low fuel level the remaining fuel will not be sufficient to provide flow to the engine. What that means is that you will always carry more fuel than you need, just to feel safe. That means a reduced range and more weight. The weight of the extra fuel that you have to carry will more than likely offset the weight of the header system.
Ideally, the header tank would be about five gallons, with the ability to visually see the fuel level, and a light that comes on if it is not full. If you have a header tank that holds five gallons, and you can verify that five gallons absolutely, you are now free to run in your wing tanks only the amount of fuel necessary for a particular mission. A typical day's flight might be around the patch for an hour. If you burn 5 gallons an hour, just add 5 gallons to the wing tanks and off you go. If you have planned everything correctly, the header tank light will come on as you are taxiing back to your hangar or tie down. If the flight is extended, the light will come on as you are headed back and you will know that you still have an hours worth of fuel.
On long cross country flights, you will have every drop of your wing tanks available to you. You can confidently plan on burning all 30 gallons (or whatever) knowing that you still have that hour reserve in the header tank. You won't be biting your nails, wondering exactly how much is really left in those wing tanks.
And there will be no chance of ever taking off on the wrong tank, since both tanks feed the header tank, and you will never be sweating, wondering exactly how much fuel is left. A quick glance assures you that you still have at least an hour of fuel.
Contrary to Oliver's assertion, you don't need shutoff valves for each wing. You can put them in if you want, and if you do there are very light ones available so there is no significant weight penalty. One good reason to have shutoff valves is if you ever plan to park on a sloped surface with significant fuel in the tanks. In that scenario the fuel from the higher tank could bleed over to the lower tank, fill the tank and leak out through the vent. But because you have a header tank, chances are good that you wouldn't be carrying all that fuel and it wouldn't be an issue. And a lot of people never park on a tilted surface.
Oliver says that virtually no aircraft manufacturers use a header tank. I don't know how true that is, but I can tell you that Supercubs have header tanks, and they are not even fuel injected. They have header tanks to ensure flow to the engine, regardless of attitude. But I find Oliver's comment disingenuous for another reason, and that is fuel injection. Now that a lot of airplanes are being built with fuel injection in mind from the outset, you will start seeing a lot more header tanks. The plumbing is so much simpler than using a duplex valve and returning to each wing tank. The advantages are, as you noted in your original post, obvious.
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Permalink Reply by John Bell on
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Excellent points Ken and the exact kind of discussion I am looking for. The possibility of exposing the suction port would always be on my mind and take away a lot of the enjoyment around flying so I have pretty much decided on using a header tank. I have some time to decide on the most suitable one but won't put anything in without input from UL Power. They will say it's up to me as long as nothing on the engine is swapped out and I have done the fuel flow tests. With that in mind I am currently planning to use their feed components and only add a header tank, level indicator, supply valve etc. into the system. In the end, a header tank alone allows for reliable, maximum feed from the main tanks and provides a known reserve. As far as I know, the only Cruzer 750s flying with a UL350 use the direct supply/return method or have the Skytec header tank and I have not heard of any issues. That said, I am open to any tank or system that proves suitable and or is approved by the engine manufacturer.
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The UL engine dealer was at our airport when the engine was first introduced to the US. An engine manufacturer does not necessarily have the expertise regarding the aircraft fuel system.
There is the engine, then the air-frame. This is also true with Cessna.
The first UL-260 that flew in a Zenith 750 used a Viking fuel pump system. Viking supplied all the parts and expertise since non were available. Viking already had 20 years of fuel injection / aircraft integration before UL was born and 25 years before Rotax started to use it.
The Skytec example is identical. The Rotax engine did not come with an air-frame fuel system. Just the requirement of how much fuel / pressure is needed to run the engine. So the Canadian dealer made a system they thought was good.
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Permalink Reply by Joe Hopwood on
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Hi ken, 172s have been fuel injected from factory since 1996. It is my understanding that Cessna has never offered a header tank even as an option. There have been 172s with belly tanks and tanks in baggage compartments but even those the fuel was pumped into wing tanks before supplying to the engine. I don't know why both sides can't just admit that there are advantages and drawbacks to a header tank. This a lot like the discussion on best way to land in a cross wind. You have the crabs and slips and never the twain shall meet! Also there is anther blog with title "Header Tank" in case anyone wants to see more opinions.
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A little more research and I find I am incorrect about Cessna's. It appears that some have what they call a header tank and may indeed have two, a left and a right. So not sure what that information adds or detracts from the discussion. My thoughts were that a header tank by definition was a single tank feeding the engine from two or more tanks. So if you have two feeding the engine I am even more confused than I was. Of course if you have a left/right selector you would still have one tank at a time feeding engine. This is too hard for me and purely academic as I have two planes with carbureted engines and do not intend to build any more planes. :-)
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Permalink Reply by Joe Spencer on
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I know you guys are talking/fussing about high pressure injected engines which I don't have any header tank design/fab experience with. I do have considerable design/construction/operation of header tanks in gravity flow systems and there are multiple complications with those. Whether they all apply to high pressure or not I don't know, if not please disregard..
There has been considerable discussion about operating with only an OFF BOTH valve. It's common knowledge that on the 701 the tanks don't feed evenly due to rigging and vent pressure variables and such. Did they maybe put a balance tube or otherwise fix that on the 750?
This from Mr Eggenfeller post
- A fuel injected engine MUST have a solid fuel pressure at all times, or the engine will stop
- Having reliable gravity feed, all the way from the wing tanks to the firewall mounted pumps, of 30-35 gallons / hour is much harder than the 2-12 GPH that the engine is actually using. When this system was used by cars, the pump was mounted right below the fuel tank.
- There is an illusion that these systems work because fuel usually come out of the pump when turned on. What is not so obvious is how small the margin is for the system to stop working.
- It is likely that even though the pump was never designed to pull fuel on the suction side, that in the airplane application it actually does this to keep up with demand. Since there is suction, any air leak prior to the pump has the potential for pump cavitation. An O-ring leak in a fuel drain, gascolator or selector valve would not be good.
This statement
What is not so obvious is how small the margin is for the system to stop working.
and the fourth paragraph is what my concern would be. Read that closely...it says that the pump actually sucks fuel from the source. Under Murphy's law which applies x10 with fuel systems I would have to assume that with the OFF BOTH valve that one of the tanks is gonna run dry and unport. Now maybe the header tank will take care of that but I'm not gonna rely on somehow it ignoring an open fuel line at a tee or whatever coming into a header tank. I'm gonna have to address that somehow and maybe it's been done in some of the discussion already and I missed it, if so disregard.
I've run my 701 with the plans ON OFF valve and also with the current L R OFF valve which gives us total control over fuel management. That's the only way I'll have it. The RVS are LR OFF and for good reason; IMO it's the only way to go. Total Control.
I didn't see any discussion about the HT vent. That has been a problem in the ones I've fooled with. I ended up with the HT normally vented by the tank selected and an added aux vent with OFF ON valve so we can fill the thing and also if it gets low inflight for some reason we can open the valve and it will refill. Maybe the hi pressure setup somehow takes care of that I dunno.
There are other considerations and we have to treat it like a rattlesnake in the bed, if we don't get it right it's just a matter of time before he gets you. In my experience a HT can be a major complication and fraught with problems, some unforseeable. Do what you want to but be careful and suspicious.
Personally on my 701, I go with the headerless system and total fuel control philosophy and accept the cons which in actual operation turn out to be much of a deal; it can all be taken care of with PIC adjustments, which is what he's there for all planes have compromises, we all know that.
KISS
Best
Spencer
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Permalink Reply by Loren Warner on
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Regarding header tanks, in our system a fuel supply and vent line from both wing tanks attaches to the top of the header tank. In the event that one wing tank does run dry before the other, the header tank will still remain full. Talk about the KIS principle. With this setup there is no need for a fuel tank selector valve, gascolator, or any fuel fittings in the cockpit.
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I think I got lost Loren. Just what is "our system"?
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