Fuel Filters, Wing Tanks

[djmc4344]

I'm right in the middle of changing out all my fuel lines, getting rid of the orginal factory stuff. Is it over kill or a good idea to have fuel filters from the wing tanks to just before the header tank and one filter just before the carb inlet. Opinions and thoughts on this appreciated.

Thanks

[Av8r3400]

My opinion and its only one man's opinion:

I do not like the idea of a filter between the wing and header tanks. The only flow there is via gravity. A small amount of water contamination could block the flow through these filters. Personally, I only like a filter where a pump provides positive flow through it.

[Dave S]

Hi Dan,

I unequivocally second Larry's comments. There should be no filters, for that matter - no partial restrictions of any kind, in the line between the main tanks and the header tank.

I had to experiment with this to settle the issue for myself. During my fuel system testing BEFORE first flight I experimented with a filter on each side. I found that all you had to do to get the fuel flow to stop is get a slug of air into one of the filters - the combination of fuel wetted filter and air sealed against the rather small amount of head pressure (remember the header tank vents back to the right wing tank balancing off most of the potential head pressure). This caused the flow to stop - it could be restarted only by significantly pressurizing the wing tank to overcome the cavitated wet filter. THE FILTERS WERE REMOVED FROM BETWEEN THE HEADER TANK AND WING TANKS before the first flight and the whole assembly replaced with a single one piece hose on each side.

You might think I am overstating the situation a bit - if you saw it happen in front of your face - I don't think you would consider deviating from the design specification.

That's just my opinion - based on experimentation with the setup.

Sincerely,

Dave S
KF7 Trigear

[Dorsal]

I support the last two posts, keep in mind that the tanks only balance with the differential pressure between them, that may only be a few inches of head for significant asymmetric draw. It does not take much (as pointed out above) to cause this to occur.

[Mnflyer]

Count me in with the 3 previous posters I agree 100% no filters on the tank lines.

[djmc4344]

Thanks for the advice guys, I think I'll go with one good filter.


I currently have a clear filter on each down line and one just before the carb. I have been experiencing unequal flow especially from the left tank it seems to draw down much faster than the right take. I think it may have something to do with filters I'm using.

I'm changing the tank hose to header to 3/8 I.D, I have 5/16 aluminum tube to the firewall. Then I will install either 5/16 or 1/4 I.D line from the firewall to the carb. The carb inlet is 1/4" I think.

[DesertFox4]

Sorry guys, my model 4's been operating just fine for 750 hours with filters and valves in the fuel lines between wing tanks and header tank. My previous model 3 , same thing for 1400 plus hours. Several Kitfox in "the Valley" are set up the same way with thousands of trouble free hours. :confused:
I do use blue Tygon type fuel lines so I can always see my fuel flow on both tanks and see-through filters. So far so no feeding issues in any attitude possible including limited aerobatics.

[sdemeyer]

I also run filters between each tank and header tank. Never had a problem in 225+ hours. I change the filters twice per year.

[DesertFox6]

Very sound reasoning all along here, but what else would one expect in this forum? My experience matches Steve's; 11+ trouble-free years on my Model IV Speedster (including positive-G aerobatics) with separate valves and filters on both wing-roots. I built my bird with a lot of "maintainability" features following 30 years' experience with military aircraft, not all of which were "maintainer friendly," lemme tellya.

Initial use of see-through Volkswagen (gasp!) one-way fuel filters was for early detection of possible contaminants following construction; early fill-ups really cleaned out my tanks, so a couple early replacements were expected and "clearly" necessary. The filters plug into the Tygon tubing perfectly and since there's never been a problem, I've kept using them. Annual swap-outs take about four minutes per side, including fiddle-time with the securing clamps...and you can tell if/when something funny is going through the lines before it disappears into the header tank and engine feed line...I like to see what I'm getting for my gas-money!

Use of in-line shutoff valves allows cutting off fuel flow from, or the total de-fueling of one wing, if working on the other, without a total defueling of both wings, when the need for emptying one side only arises. I also use this feature while refueling so I know how much imbalance I may be incurring, but no problems have yet surfaced. Using the shutoff valves while refueling also precludes fuel back-flow through the header tank up into the other wing while refueling, giving me yet another indication of how evenly each side is actually feeding. So far, I haven't found an imbalance worth mentioning.

It is absolutely mandatory to insure a constant "downhill" one-"G" fuel flow with no exceptions, in-line goodies or no. If you can insure a constant downhill slope without any changes in line slope, that's even mo-bedda! A bunch of us here in the desert southwest have not experienced the original problem in this thread, but since it was an excellent question concerning safety of flight, any amount of shared "cross-tell" has got to be helpful.

Do what your conscience (gut) tells you is right for YOU and please keep us posted: Take care and a Happy New Year!

"E.T."

[djmc4344]

Guys,

Thanks for all the responses on this subject. It's been a very informative discussion and I really appreciate your experience and expertise.
I think I will go with 3/8 ID hose from the wing tanks to the header. No filters, a large ID hose for the fuel to flow with no restrictions from the wing tanks to the header is what I want. I may put some clear plastic tubing so I can see the fuel. Also going to add shut off valves between the wing tanks and header.I already have 5/16 ID aluminum tubing from the header tank to the firewall. After that I'll use 1/4 ID hose with a good filter between the fuel pump and carb.

Regards,

[5770phil]

Hi, my name is Phil and I have a Kitfox 3 and installing a 2180 VW. Can you tell how you vented your header tank and to where as I am not sure as I have had a number of people with different ideas. Thanks.

[cap01]

phil , not sure how the III are arranged with the gas tanks but the model IV vents the header tank to the inbd side of the right wing tank .

[5770phil]

Thanks Chuck, how is it plumbed to to right wing tank

[cap01]

the header tank has a fitting high on the right side and the vent hose runs along side the fuel hose from the right tank up to the tank . the fitting is forward of the tank outlet and the fittings for the sight guage and high on the tank . sorry this is the only picture i have with the fittings location . ofcourse the tank is upside down in the picture and has plugs in the holes , the vent fitting goes in the far right hole .

[GDN]

I have been experiencing unequal flow especially from the left tank it seems to draw down much faster than the right take. I think it may have something to do with filters I'm using.

I have same problem, it's nothing to do with filter, as i have only one filter after the Y junction of the 2 wing tanks, i read a lot of of posts from kitfox and other ultralights owners having the same issue. What is appearing after a lot of test is that we aren't good pilots ...:rolleyes: it's because we don't fly with a perfect symmetrical piloting try one day to fly all the time with the slipball perfectly centered and you'll see that your wing tanks will have the same consumption.

[djmc4344]

Yea I've heard that as well and I think now maybe thats the case, I'll watch the ball a little closer. I also have a heavy left wing that I'm trying to fix, that may have something to do with it also.

[GDN]

Strange we have exactly the same problems i have to hold the stick strong and the plane wants to turn left. Some flaperons' setting i think.

[Marshawk]

Does anyone have a fix for the fuel flowing out of the header tank vent, we have a check valve vent on a kitfox 2 sticking up threw the lexan near the right wing but it seems to trickle out fuel especially when flying especially when tanks are full

Thanks Willis

[DesertFox6]

Marshawk -

Is the "vent" end of this header tank vent line directly exposed to the free-stream (boundary layer) airflow outside the aircraft?

I'm thinking some combination of thermal expansion (not much heat up B.C. way this time if year as I recall, though) or fuel weight with full(er) tanks (a hydraulic-type action exacerbated by wing dihedral) or boundary airflow siphoning action...just guessing here without knowing how you've got it plumbed.

"E.T."

[Marshawk]

Yes Dessert Fox 6 you are correct, the vent end is exposed to the boundary layer airflow on top of the cabin near right wing. Your right about the temps up here although today it was a bomby 4 celcious which is probably about 38 F.We do have some awesome ski flying conditions though :)I think it is the siphoning action you mention that's drawing out the fuel. We have a plastic check valve sticking threw the top of
the cabin and this is were it trickles out .Wondering if I put a 90 degrees plastic tube facing forward somehow on top to blow the fuel back down,would that create any problems?



Thanks Again

[DesertFox6]

Hmmm..in this case Marshawk, I'm going to refer you back a few entries on this thread, to read the conversation between 5770phil and cap01 on 12-13 January where cap01 directly addressed this issue for 5770phil's Model III, to include offering an excellent photo and a short explanation of how to vent the header tank to the right wing, as has been the factory setup since at least my Model IV came off the line back in '94.

You really need to get your vapor vent line connected to one of your wing fuel tanks so your fuel stays withing the fuel system instead of de-icing your tailplane! :D I know there's plenty of folks on this august forum who can offer more specific advise for your Model II, but this internal-vent-loop hookup is the best solution for your situation; the 90 degree "L" bend won't do anything positive for you at all.

"E.T."

[mr bill]

KF4--- Aug 01 wing instructions show a fuel tank vent line protruding out of the bottom of the right wing (presumably for the header tank). May 02 wing tank instructions show the header vent going to the right wing tank vent. What I have seen in the forum says header vent to right tank vent. What is the vent line out the bottom of the right wing for?
Thanks in advance.

[t j]

Bill, the vent coming out the bottom of the wing is used when there is a panel tank ony and no wing tank. It is a 1/4" OD aluminum tube a little over 4 feet long with a couple 90 degree bends on the outboard end.

[Kiriako]

I share most of the experiences you have all mentioned on this thread and some more. Let me give you a quick list of my travails over the last 6 months of owning a KF3 built in 1992:

-In my first few flights I quickly realised that my left-wing tank drained fuel much quicker than the right one. I have put this down to my Rotax 582 torque causing the right wing to want to push up and this resulting in the greater fuel-flow (does anyone agree with this idea?)

-Soon after, I suffered my first serious problem when my engine spluttered about in-flight causing me certain angst only to finally track the problem down to fibres from the fiberglass-tanks obstructing the carburetor jets.

The plane already had two large Rotax plastic filters between the wing tanks and the header tank. I proceeded to add a further BMW membrane filter after the header tank and before the gascolator, thinking that the fine membrane filter would take care of the fibres; well it did just that...unofrtunately it also took care of reducing the fuel flow to the engine to the point where I suffered an engine failure inflight! I dead-sticked it to the nearest ploughed field and felt a better pilot for it!

After the BMW filter fiasco I proceeded to put a very fine glass-filter to replace it while initiating a jets inspecting regime after every ten hours of flying. This seems to have put paid to the fibres-in-the-jets issue for the time being.

I then proceeded to suffer another two engine failures in-flight with equally anxious but perfectly competent dead-stick landings out in the boonies!

It took me a long time to figure it out but to cut a long story short I finally found the problem in the metal tubing between the right wing tank and the header tank, which had accumulated raisin muck from the tank and was obstructing the fuel flow enough to cause an engine failure if I had the left tank shut-off and was working the engine at fairly high RPMs.

I have now run a vent/bleed-line from the vent-valve at the top of my header tank to the boundary air-flow layer below the right wing tank just adjacent to the top of the lexan of the copilot's door. If left open at all times this vent-line overflows and the fuel splashes horribly onto the lexan and even into the cockpit if the tanks are full. So I have put a little fawcet to it so that I can vent it if I suspect that air has entered the header tank or any other part of the system while keeping it shut-off the rest of the time.

The added value of this set-up is that it acts as a primitive but perfectly good fuel flow indicator. If the fuel circuit is full of gas I can see the fuel running up the transparent vent-line all the way to the fawcet; if however the fuel circuit becomes clogged up again with raisin-debris from the ever decomposing tanks (due to the high level of ethanol content in our local fuel) I am immediately alerted to it by seeing the vent-line filled with air bubbles moving up towards the fawcet; if the fuel blockage is major than all fuel is drained from the vent-line and all I see is air! I can thus take immediate emergency action such as to look for the nearest landing field before the remaining fuel in the header tank is gone!

As I am sure you more senior Kitfox flyers have realised by now I am just a dimwitted Kitfox novice with no technical acumen to speak of plodding along from one half-baked solution to another because I cannot drum-up the energy or the money to go for a new wing-tank installation and be done with all this nonsense!

It would be great to continue hearing from others with similar experiences and the solutions they have found.

My kindest regards to all of you...this is one hell of a great community of flyers that I am truly proud to be now a member of!
Kiriako

[rogerh12]

Kiriako
If you are having issues with the high alcohol content of your fuel, perhaps you should remove the orignal fuel tanks and install some alcohol friendly ones. Kitfox sells glass versions, and I ahave heard of other tanks made from blown molded plastic that can take the alcohol too.

Hope this helps

Roger

[Kiriako]

Roger,
Thank you for the advice, this is clearly the definitive solution to my problems but it is a major effort and I am trying to postpone it as much as possible. Although when my tanks are finally perforated by the alcohol and fuel is dripping off my wings I will be left with no choice!
All the best,
Kiriako