My opinion: old fibre-glass fuel tanks are a real hazard

[Kiriako]

In case this is useful to any Kitfox pilots out there:
Flying my recently purchased 18 year-old Kitfox III I experierienced sudden loss of RPMs (a thousand at a time) with the 582 engine actually spluttering as if it would stop; fortunately it did not and I was able to land safely quite a while later. I dismantled the carburetors and found both jet assemblies full of fibres that were clearly partially obstructing fuel-flow. I had a couple of eventless flights after that but on another flight just recently it happened again and once more the jets were found to be full of fibres! I have now put in an additional BMW fuel-filter in the fuel circuit above the gascolator (the paper-like membrane type) which should finally take care of these horrible fibre-shedding old tanks. I have had a long flight after this latest repair and the engine ran as smooth as silk, I hope the problem has now been definitively laid to rest. Have any of you faced similar problems?
All the best,
Kiriako

[szicree]

It has always been my understanding that paper element filters are a very bad idea on aircraft. Water in the fuel can quickly swell the paper shut and you know what happens next.

[Kiriako]

That is a very interesting point you are making Szicree and I am very grateful for it; I have been told that the paper membrane is folded in 'concertina' fashion in the filter-drum, so if I understand you right what you are saying is that with water the concertina-folds in the membrane swell-up and start binding together, am I right? If this is the case surely there must be some surface area on the membrane that remains unfolded and without overlap so that some fuel can go through (perhaps at the two ends of the 'concertina? Or am I being unrealistically optimistic?

[Kiriako]

I think you are right about the only definitive fix being to acquire some new tanks. Meanwhile I will attempt to flush the exisitng ones as you suggest. The fuel filters I use are the ones used by Rotax for the 912 engine (I replaced the original flimsy disk filters used normally for the 582 model. ) I also thought that the BMW paper membrane filters were also a good high quality solution and would definitely stop the fibers from getting through but the comment by Szicree as to the possibility of any water making them swell-up and obstruct the fuel flow has put the dampers on that idea...
In any case I am very grateful for the advise.
Thank you,
Kiriako

[szicree]

It is my understanding that the paper fibers swell and block the tiny holes in the paper. At this point it is no longer porous and that is not good!

[Kiriako]

Steve, thank you for the clarification .
Kiriako

[SkyPirate]

the fibers will also clog the filter, and this will shut your engine down quick..I had a phantom ultralight with 503 DCDI with a fiberglass 10 gallon tank,. after about the 5th dead stick landing ,..I installed the in line filters that you can take apart and clean,..they have the chrome ends with the glass center and a wire screen in the center and you can twist it apart with out tools,..every 10 hours on the meter I took the filters apart and cleaned them until I finally sloshed the tank ,..I used the slosh they use on motor cycle tanks because I could purchase it locally and the slosh for aircraft tanks hadn't yet made the market or it was so new I didn't hear about it,..but it worked well,..I sold the plane shortly after the fix,..and the purchaser never said anything about clogged filters so I assume the fix worked.

Chase

[avidflyer]

Here is another idea about filters. After a forced landing because of a plugged filter, I put a second filter in parallel to the first one with a small valve that I could shut the flow off to the second filter. Both filters are used for takeoffs, and then I close the backup filter valve off. If I ever have the first filter start to plug in flight, I can quickly open the valve and the second filter should still be clean and ready to get me home. Take care, Jim Chuk
Avid MK IV (flying)
Kitfox 4 (building0
Northern Mn

[Kiriako]

Jim and Chase, thank you for some very useful tips. Chase: would you be able to give me a model or part number for the filters that you can twist apart? Also the "slosh" you refer to, how would I refer to it when asking for it at my local general/sport aviation service center? Fuel-tank cleaner? Please forgive my total ignorance :(.
Kiriako

[SkyPirate]

I don't have the part number ,..but it's an easy part to purchase ,..just ask for a filter that can be cleaned ,.. I'm thinking my was a holley model ,..not positive , it's been 15 years since I used one ,.. I haven't used the "aircraft" tank slosh ,..I used the slosh for motor cycle tanks ,..it's a sealer for the most part,..the two might be the same in design ,..just different applications, maybe someone who has used the "aircraft" fuelk tank slosh will tune in and give you a location and name of the product to purchase it.

Chase

[Kiriako]

Thank you.
Kiriako

[cap01]

it may not help in spain but california power systems llc has the take apart filters .http://www.rotaxparts.net/scripts/prodView.asp?idproduct=1349 (http://www.rotaxparts.net/scripts/prodView.asp?idproduct=1349)

[Av8r_Sed]

The problem with paper filters is water. If you get water soaked into the paper it will block fuel flow. There are filters with fine stainless steel screens that should solve your immediate problem without causing another. I purchased some from LEAF at Oshkosh last summer.

-- Paul S

[rogerh12]

Yes, these take appart filters are not without there own problems. I had one on my bike and it unscrewed itself and leaked fuel all over (with the vibration and all). Take a look at the link in the previous post, what really holds it together? What if the glass cracks? Perhaps a metal throw away version of this type filter would be best. Also, I suggest a fule pressure guage to monitor fuel flow heath, even on gravity feed systems.

Roger

[Av8r_Sed]

I'm planning to use disposable fuel filters with stainless mesh in each line from the wing tank to the header. These are manufactured by ITW-Fastex.
Here's a link to their datasheets: http://www.itw-fastex-cva.com/content/view/32/33/

file:///Users/Gunther/Library/Caches/TemporaryItems/moz-screenshot.png

-- Paul S

[Av8r3400]

[engineer hat = on]

I just need to restate my dislike of filters anywhere gravity is the only form of flow motivation. (between the wing tank and header/gascolator) It would take very little restriction to stop the flow in this location. Even with a metal screen filter.

One man's opinion.

[/engineer hat]

[Kiriako]

The filters I have used so far are the ones recommended by Rotax (atleast in Europe) for the 912 engine. They have a very fine metal mesh but it seems that because they are cilindrical and quite large the fibres are aided by the way fuel flows through the filters and little by little they get through. It seems quite amazing that they can get through such a fine mesh but believe me they do! The smaller disk-like or conical ones suggested by Paul are normally recommended for the 582 engine but I am concerned that their filtering surface area is much too small and even a small accumulation of fibres in a very short period of time could cause a blockage before you can realize and decide to take them apart to clean them (or change them).

The filter suggested by Cap01 looks high quality but I have been warned off glass-filters by a fellow flyer here locally (and ex-fighter pilot) who says that glass filters tend to break and thus cause all sorts of problems with pieces of glass flying all overt the place!

I have taken another look at the additional BMW filter that I have just installed between the header tank and gascolator, which has atleast temporarily resolved my problem and I feel that it might very well do the job even in the long term; I mistakenly said earlier that it was of a paper membrane type but I was wrong, it is of a very fine metallic mesh that is folded on itself several times so it should make it very difficult for the fibers to get through; that and the fact that I will be changing it every 25 hours makes me feel that I have a chance to crack this particular problem.

AV8r3400's concern of the gravity fuel feed being too fragile to tamper with by using multiple filters etc. seems valid to me. In my particular Kitfox there is a pitot like air-feed into the wing tanks that sit on the fuel tank caps which assume are there to force feed the tanks with air and thus ensure better fuel flow. Is this normal ?do all Kitfoxes have them and should these "pitots" be looking forward? My concern is that if you ever end up flying in rain their position will also cause water to be driven into the tanks! Any opinions?

Many thanks for all your much valued opinion, with every new reply I am becoming more knowledgeable of this beautiful little plane of mine and thus more able to enjoy my flying with it, I am much obliged.
Kind regards,
Kiriako

[moosepileit]

Autozone, $9.99 seems to be the same part as A/C Spruce and Rotax Parts.

Spectre Clearview Part Number 2369. Includes ends for 3/8, 5/16 and 1/4 inch.

Have to see one to make sure it's able to be disassembled for cleaning.

[Slyfox]

the fibers will also clog the filter, and this will shut your engine down quick..I had a phantom ultralight with 503 DCDI with a fiberglass 10 gallon tank,. after about the 5th dead stick landing ,..I installed the in line filters that you can take apart and clean,..they have the chrome ends with the glass center and a wire screen in the center and you can twist it apart with out tools,..every 10 hours on the meter I took the filters apart and cleaned them until I finally sloshed the tank ,..I used the slosh they use on motor cycle tanks because I could purchase it locally and the slosh for aircraft tanks hadn't yet made the market or it was so new I didn't hear about it,..but it worked well,..I sold the plane shortly after the fix,..and the purchaser never said anything about clogged filters so I assume the fix worked.

Chase

I used one of those filters once. I landed with fuel going all over the place. I went back to the paper filters. I have over 2000 hrs on paper filters in my kifox. Never an issue. I think the key is to fly the plane. Letting it sit for months on end is no good for any airplane. My cure is to fly fly fly. If your not flying than drain the tanks. simple as that.

[Jwayneball@aol.com]

I just bought a KF III which had sat for years w/o being flown. When I fueled the wing tank, it leaked like a sieve. Fortunately a drain hole had been built into the wing. Now, for a fix. Do I take the tank out and repair and replace it, do I buy an $500 tank from Kitfox or is there a solution to the problem like a pour-in coating that can be used without taking the tank out?
I would appreciate any suggestions.
Wayne

[HighWing]

Wayne,
For me personally, I would remove the wing and with a friend rinse the tanks with Acetone until clear, then slosh with Kreem. I have had the exact same problem and did the deed. My new Model IV has original Kreemed tanks from 1992 with no issues - Yet!. Other opinions are sure to vary.

[Jwayneball@aol.com]

Wayne,
For me personally, I would remove the wing and with a friend rinse the tanks with Acetone until clear, then slosh with Kreem. I have had the exact same problem and did the deed. My new Model IV has original Kreemed tanks from 1992 with no issues - Yet!. Other opinions are sure to vary.

Thanks a lot for the advice. Makes sense. Does this product, Kreem, enable the use of gasoline containing ethanol?

[Av8r3400]

Personally, if it were my plane, I'd be putting in a new tank.

If it's "leaking like a sieve", I wouldn't trust any type of slosh compound to fix that.

If it is "leaking like a sieve", I also wouldn't trust the structural integrity of the tank any more. The fuel tanks are integral to the stability of the wing. The last think you want is the wing to fail on you in flight because the tank collapsed.



Just my opinion.

[HighWing]

Wayne,
Lots of controversy over the years regarding Kreem. My original tanks were factory Kreemed. About five years into the flying part and I began seeing some very small bubbles appearing under the Aerothane between the filler neck and the outboard edge of the tank in top. I finally shaved off one of the bubbles and it was a blister of fuel. This was on a week long camping flight with friends and we were on Avgas. I did as I mentioned and the problem stopped. I flew nine years on the first airplane with avgas only on the annual camping trips. My new Model IV has factory Kreemed tanks and as I said in the first post - one year and so far good.

There have been some Kreem failures, most notably having it separate from the tank surfaces in sheets resulting in clogged finger strainers. Some have attributed this to release agents, but the tanks are made up from female molds and any release agent would be on the outside of the tanks. My personal theory is that the resin used on the tanks is oxygen inhibited and the surface resin won't cure thoroughly and if it softens under the Kreem it can result in the Kreem sloughing off. The new OH resistant tanks have to be rinsed prior to use to remove any uncured resin in the thanks to prevent buggering up the carburetors - same issue, I believe.

Kreem claims Ethanol resistance, but it cautions about certain fiberglass resins and recommends a spot test. Like I mentioned, I am comfortable with it based on my personal experience and the guys I have flown with, but - and I am surprised others haven't commented yet - others are very leery of it.

[Jwayneball@aol.com]

Thanks for taking the time to respond. I wonder if there are alternative products that might work better. In any case, it appears that cleaning the tank well before application is critical to success. Thanks again for the advice.
Wayne

[Jwayneball@aol.com]

Personally, if it were my plane, I'd be putting in a new tank.

If it's "leaking like a sieve", I wouldn't trust any type of slosh compound to fix that.

If it is "leaking like a sieve", I also wouldn't trust the structural integrity.........


Just my opinion.
Thanks for the advice. I think you make a very good point. Once I get the tank out, I will be able to see just what the condition of the tank is.

[Dutch]

Wayne Was the plane ever flown? If not maybe the Quick drain valves were never installed. Seems like there was another post a couple of months ago that had the same issue. No drain valves and the whole wing filled up with gas.
Dutch

[Jwayneball@aol.com]

Not flown much, Dutch. I was told when I bought it with 7.5 hours on the Hobbs that no gasoline had been put in the wing tank. There is the standard drain that you use to check for water but when I tried to get some fuel out of it, nothing would come out. Gas did come out the wing drain hole which is near the root of the wing on the trailing edge. If there is any other drain access, I don't know where it would be. Can you tell me more about Quick drains?
Thanks for your help,
Wayne

[Dutch]

There is a small sump in the bottom of the wing tank.With a small threaded hole in the center it is covered up in the covering process. after paint you burn a hole through the fabric and install the quick drain valve. It is where you check for water contamination. The line coming out of the root of the tank near the rear spar is the fuel supply line to the system. Feel the bottom of the tank you should be able to feel a small bump it will usually have a re-enforcement patch installed over it.
Dutch

[n85ae]

This is in the category of, super duper highly unlikely, unless a total alignment
of all the planets in the solar system occurs on a Friday the 13th ... Leaks on
the other hand, That could happen.

Regards,
Jeff



If it is "leaking like a sieve", I also wouldn't trust the structural integrity of the tank any more. The fuel tanks are integral to the stability of the wing. The last think you want is the wing to fail on you in flight because the tank collapsed.

[Dutch]

Not flown much, Dutch. I was told when I bought it with 7.5 hours on the Hobbs that no gasoline had been put in the wing tank...............
Thanks for your help,
Wayne

Wayne It is extremly unlikely that a tank that has never had fuel in it would have deteriated to the point of leaking. I would look to the fitting installations for the problem. Before you tear your wings apart unscrew all the fittings and reinstall using a good tread sealant and being carefull not to over tighten. Then do the leak test that is described on the other recent post.

Dutch