Those of you with dual wing tanks, lets talk plumbing to the header?

[SuberAvid 617]

I have shutoffs on both tanks and run on one tank at a time once airborne.  If I have my tanks pretty full, the slight difference in pressure from the vents can cause one or the other tank to overflow (leak around the cap gasket) so I just run one at a time.  It also lets you run one tank completely dry(beyond visible in the tank) when you are stretchinbg your range and then you can visually monitor what you have left in the remaining tank so you can land with known fuel.

 

Also, like others have said on here, I just run vent ram air tubes on the tank caps and no vent on the header tank; about 850+ hours that way between 3 planes and no issues.  When I started fying Jeff's plane last year it was plumbed with the header tank vent.  I probably dumped as much fuel overboard as I burned for the first 5 hours or so until I convinced him to replumb it to vent the caps only.  The cap ram vents push fuel into the header tank and right out the header tank vent, coating the whole tail of the plane in gas and trashing the lexan, not to mention the pretty fire bomb it could make.

 

One other suggestion; do not extend the cap vent beyong the bottom of the cap.  It will just limit how full you can fill your tanks.  If the vent tube sticks into the fuel in the tank, it will push fuel out the vent instead of air when the tank needs to vent (when it heats up or whatever).

Edited 28 Feb 2014 by SuberAvid

[Av8r3400 1178]

That's why Kitfox vents the header tank to the top of the right wing tank.

[EDMO 1078]

I agree - the header tank vent tube should go into another tank - makes no sense to leave it open to syphon gas into the wind.

We have a problem with our J3 - the STC for the wing tank makes no provision for a vent line from header to wing tank - when the gas in the wing tank is used up the feed tube is full of air, or has an air bubble in it - the wing tank is filled with gas at the next stop, but it cannot flow to the header tank until the gas in the header tank is below the tube inlet, which is near the bottom of the header tank,  and lets the air out of the tube - at this point we are in the position to wonder if the fan is going to quit turning - and with no starter, we better have some altitude, which we usually don't...If it was "Experimental" we could fix this problem, but not with a factory airplane and it is nearly impossible to get a field approval here for any reason.

EDMO

Well, I just got told, that since we put ram air vents on the caps of the J3, that it will feed fuel from the wing tanks while in flight, but not on the ground if the tube has air in it.  I guess, problem solved!

EDMO 

Edited 28 Feb 2014 by Ed In Missouri

[1avidflyer 1983]

Lot of guys that use a vent line on the Avid header tank have a valve in that line and close it when the air is out of the tank.  That worked quite well for me.  Vent will suck gas out in flight thought if vent valve is open.  I think that was exaggerated with the ram air tubes in the fuel tank caps.  Jim Chuk

[Deejayel 1]

Picture of my right install

[EDMO 1078]

Where did you get that neat little shutoff valve?  How much?  Can you get it for 3/8 ID lines?

Thanks,

EDMO

Edited 3 Mar 2014 by Ed In Missouri

[Deejayel 1]

Yes. These are for 3/8id lines. I think i got them off ebay. Lemme look.

Inline Fuel Valve • 3/8" • Vintage Honda Motorcycle Petco... (171035023192)

4into1motorcycleparts | 4437 | 99.9%

Quantity: 2

Sale date: 05/13/13

$13ea.

Edited 3 Mar 2014 by Deejayel

[EDMO 1078]

OK - Thanks - Looks lighter than the one I have.

EDMO

[herman pahls 9]

I am very interested in this discussion regarding whether to vent the header tank or  not because of the serious consequences.

A few months ago a friends Avid went down (passenger will never walk again) and he felt that he had fuel starvation because his behind the seat header was not vented.

Both of his  wing tanks fed the header tank with shut off valves and one line drained the header forward to the firewall gasculator.

A few years ago I had my one and only forced landing in 36 years ( which was fortunately a none event) and was likely due to venting or carb ice.

I have the 8 gallon cowl tank (header tank) which is fed by one wing tank.

The only vent at the time was the wing tank filler cap ram air tube.

My Kitfox gets hangered with the wings folded so possibly the fuel line/vent tube got pinched in the folding/unfolding process.

The only solution I could come up with was to vent the cowl tank fuel cap and now if I forget and overfill the cowl tank when transferring fuel I get reminded with fuel on the windscreen.

So here is my question.

How can venting the behind the seat header tank  be a negative?

I like the #11 post where DeeJayel uses the vent line as a sight gage.

It seems like all the highwing airplanes I have owned are gravity fed, do not have header tanks but they do have both fore and aft drains out of the tank.

So regardless of nose up or down attitude the available fuel will drain.

Most of our Avids and Foxs only have rear fuel drains.

So what happens if you are only feeding off one tank and it is getting low enough that air enters the drain line.

Even it you are feeding off 2 tanks.

How does that air get out of the header tank without a vent?

If you have huge fuel lines I can see the air burping back up the fuel line but it would not burp as easily with the 1/4 or 5/16 ID fuel lines that many AvidFoxs use.

I road race Formula cars that corner at 2-2.5 G's.

At less than 1/2 fuel the G forces will allow air into the fuel pick up, just like banking the wing on a less than full tank.

In race cars we all use some sort of internal or external surge/header tank to prevent air from getting to the high pressure fuel pump and to be able to use the last quart of fuel.

Those surge/header tanks are all vented back to the top of the main tank because that is the only consistent way for air to escape.

It sure seems like without a header tank vent we are playing "Air Bubble Roulette" when ever air gets between the fuel and header tank.

Please let me know what you think.

Herman

Edited 3 Mar 2014 by herman pahls

[EDMO 1078]

Herman,

       Kitfox was the first to put out the letter on adding the fuel vent line after some of the KF drivers had fuel starvation problems.  Without the extra port in the wingtank, you can put a "T" in the upper part of your sight gage on the tank.  I think in your situation, with only one wing tank, you could put a fitting near the top of your header tank and run that to the wing sight gage as a vent line.

      I am guessing that you have a fuel pump, you don't need the ram air vent in your header for flow pressure.  If you seal the header tank cap, then you could run with ram air pressure from the wing tank if you leave it turned on, which evidently, you cannot do now.

      I don't like the idea of an open vent line in my cockpit - looks like a good way to get doused with gas if you have an accident.  Maybe one with a shutoff valve might not be bad - but why not just run it on up to the wing tank and forget it?

      Everyone has their own ideas on this - I will have a vent line from header to wing tank, even tho some say that if you turn both wing tanks on, that the full tank will push the air back to the empty tank - but if you only have one tank on, and bank and get a bubble, well, what then?

EDMO

just my 2 cents worth.

[ChrisBolkan 130]

It was possible on my Magnum to route the fuel lines from each header tank up to the respective wing tank with a continuous upward sweep so air could escape the header tank into the fuel tank and not stay in the system for long. Eventually air trapped in a header would burp up hill into the fuel tank. That precluded the need for vent lines. I had to re-route the lines through notches I cut in the turtle deck to achieve the continuous sweep, but the peace of mind ws well worth it.

There is a long and scary (for me) engine out story and discussion on the yahoo board on the subject. I don't want to write it all over again here.

Bottom line if you cannot get a continuous upward sweep from header to fuel tank so air in header can escape, IMHO you need vent lines.

It is my opinion after a great deal of thought that if you are going to run vent lines they should vent into the fuel tank if possible. If not possible, I guess you have to do what you have to do to allow air to escape the header tank(s). Any siphon (uphill then downhill bump in the fuel line) between the header tank and fuel tank will make it possible for air to accumulate in the header tank(s)

Chris

[EDMO 1078]

Chris,

      The whole secret to using two wing tanks without vent lines is in fuel management - If you get an empty wing tank and the other is not turned on, then you can get air in the header and that line - If you leave that tank on and turn on the other tank, the fuel should push the air back up and try to equalize in the empty tank, and then you can shut the empty tank off - but if you shut off that tank before opening the full tank, then you block the air from escaping the header.  This is where the clear lines can let you know what is happening in the system.

I would rather have the vent line and not have to worry about it.

 Does this make sense?

EDMO

Edited 4 Mar 2014 by Ed In Missouri

[Bandit 286]

Mine is vented just like Chris's and has always worked good.

[allonsye 85]

I shut mine off when I park it. I got a flat once in the hangar and all the fuel transferred to one side and overflowed the other tank and made a heck of a mess in the hangar. I also shut mine off if I am fueling from a pump so I know exactly what went into each tank so I can pour the right amount of oil in. I only have a shutoff on the left tank.

Joey - Your 1st post wasn't clear to me. Are you operating with just a left tank valve or left and right?

 

I got mine w/o tank valves or header vent. The PO had operated it that way for 320 hrs. I will be installiing at least one tank valve.

 

On mine the only way to determine fuel qty/level is visually through the translucence of the visible side of the L/H fuel tank. Interestingly he painted the right tank completely so there's no way to tell what it has in it visually. unless both valves are left open I suppose and read from the R/tank.  Likely I'll strip some paint away from that right one so I can see it's level.

Edited 6 Mar 2014 by allonsye

[allonsye 85]

Fuel Vent Bulletin. 

 

http://www.kitfoxaircraft.com/support/service_letters/sl22.htm

 

Exactly how then to vent the header. A tee at one of the fuel tank inputs at the top of the header and a T at the outlet of on of fuel tanks?

Edited 7 Mar 2014 by allonsye

[SuberAvid 617]

One thing I have always done as a practice but not with any knowledgeable intent is to open both tank valves when I start my walk around preflight.  I can usually see a couple of bubbles come up through one or the other lines to the tank.  Without thinking about it I have been venting myheader tank before I fly.  Once it is vented, you would have to run out of fuel and run the header tank down until the engine quit or close.  If you did that, better keep both tank valves open when you turn the other tank on to allow the header to vent. 

 

Still not quite sure I understand if they are just tying the header vent into one of the tank fuel lines up closer to the tank; since there is only one port in our tanks?  Not sure that is much different than just opening both tank line valves.

Edited 7 Mar 2014 by SuberAvid

[allonsye 85]

Thebriman has started a hugely important topic. So important that Kitfox/Skystar has written at least 2 SB's addressing it and recommending vent line out of the header. I don't recall a bulletin from Avid however.

 

I've not operated my Mdl C yet (still completing my FWF). The PO operated it for 320 hrs w/out fuel valves (from ea tank). There's no vent lines either.

 

My concern is what happens in decent, slips or banks when either fuel tank outlet becomes uncovered (or I believe referred to as unported). That will definitely create an air bubble. With out a dedicated header vent line, where does that air go? Does it somehow burp through the fuel lines? There must have been occasion NOT which created the SB's addressing it.  As Randy points out above, closed valves could create a problem I'm guessing. In my case, it wasn't an issue because valves are not in the system to become a factor from being closed. Still, I wonder how airbubbles escape from the system w/out a vent??????????????

[akflyer 1427]

My Avid came with the wing spar header tank (a short piece of the spar material was capped and ported for fuel in and out) but it was probly less than a quart in size.  I put the poly header tank from kitfox behind my seat.  1 I like to see the fuel level and 2 it gives me an extra gallon of fuel.  It will run me about 15 minutes if the fuel ceased to flow from the wings.  in normal flight I only run one tank, but for take off and landing I always have both tanks on.  I cant recall a time that I was so low on fuel that I was worried about the tank unporting even on a long decent from 6000 to sea level.  I try to not plan my trip so that land on fumes.  With both valves open, the header will vent to the lowest tank, but I only see air in the lines when I completely drain the fuel system for maintenance.  When its totally dry, I open both valves and put gas in one tank and watch the header fill up and burp to the empty tank.  Once the header is full and the air is out of the line to the empty tank, I will close the valve and then top off both tanks.

 

If your in a hard slip with both tanks on, I dont see how the high wing tank could come unported.  I slip to most landings and ahve never had an issue with it.

 

[allonsye 85]

Thanks Lenny, good feedback. Yeah, I have the 'lil-o-piece of spar header tank in mine So you essentially have complied with the Kitfox Bulletin.

So, you're saying, the header will self-vent. To the lowest tank makes complete sense. So, it still vents out to the tank feeding if one is closed as well?

[akflyer 1427]

if one is closed, it does not need to vent, it should be a closed system at that point.  I flew a buddies MK IV and he had put a small valve coming off the top of the "spar" header tank and used clear tube to just loop around and out the belly.  if in doubt open the valve and vent the header overboard then close it if there is not air in the line.

 

[Bandit 286]

This is how I plumbed my single tank. No vent from the header tank.

[lostman 198]

I never realized that my header tank was a short piece of spar before. Now that it's been mentioned I see that, but just never figured out where it came from. I thought maybe mine was something John had made up but evidently someone built a few of these and they are out there.

 

I still don't get why there is an issue with a dual tank system not venting as long as the tank itself has a vented cap. I've flown quite a few planes that are only a single tank and they don't have a problem with the system when vented properly. Just me not understanding the issue I suppose.

[Boat 10]

I have two 14 gal wing tanks which I always assumed would equalize through the header tank when everything was turned ON.  I made my final landing today and noticed one tank empty and own half full - why didn't they equalize?  They go through a header tank which does not have a vent.

[IFMT 36]

Maybe one fuel cap is not allowing air to enter as easily as the other. Do you fly one wing low? Fuel will flow to the low wing tank in flight.

[akflyer 1427]

I have a buddy that likes to fly one wing low.. he can never figure out why one tank if empty and the other tank if overflowing after a long flight...  Make sure your caps have the ram air tubing installed in them and once airborne shut off one tank and periodically swap tanks.  It would really suck to ride a glider in cause you ran one tank dry and the you wad the plane up with one full tank that you could have been feeding from.  Fuel valves do sometimes fail, so dont run a tank dry THEN decide to swap top the other tank, only to have the valve handle come off in your hand.  This has happened to many pilots before and it is the absolute shits to have a full tank of gas and not be able to use it when your only 10 miles out from the airport.