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