Leaking wing tanks.

[Docspenc]

Hi all.. I have a kitfox 3 with 6 gallon aluminum wing tanks.. yes and they both leak. I've read some of the posts on hear but I'm still not sure how to proceed.. or where to buy replacements. Any thoughts? Thanks in advance..

[atosrider]

the RV homebuilts have owner made alu tanks, it's not impossible to take that project on .. I don't know if they have a suspension system to allow for the wing twist that the KF building technique imparts on the tanks ...
given the warning of no ethanol in the 'plastic' tanks that are available for the KF models, like why go ahead with that option, I find it odd that the KF homebuilders have avoided solving the suspension problem for going with alu tanks ...
I was lucky, a local RV builder (and so much more) lead me through building a new alu header tank, easier because it is all flat surfaces ... why not make 4 x 5gal tanks in alu, should provide lots of room for suspension ...

[Av8r3400]

"Suspending" the tanks is not possible because the tanks are structural to the wing in the Kitfox design. The tanks act as the drag tubes in the first rib bay of the wing.

To the original poster, there are or were until recently, at least a couple of people making ethanol resistant, fiberglass tanks for Avid Flyers, which would be "close enough" to use in the early model Kitfoxes. Maybe Avidflyer will chime in, this is more of his area of expertise.

[Docspenc]

What's the best way to remove the tanks? That bay is covered with 1/8 inch plywood, and I think that's what gives the wing strength. The tank is held in with rivets on the rear spar and silicon on the front spar. At least that's what the build book shows.
Also does anyone know who might make them? I don't think I want to make one myself.

[avidflyer]

I did see on the Kitfox facebook site that someone in Europe had a set of early 6 gallon Kitfox fiberglass tanks for sale. His name is Georgi Georgiev (https://www.facebook.com/groups/907503245998540/user/100006458375411/?__cft__[0]=AZVbt-B8ztE26yIBFYVPmp6cp46bTYt00Bw0kzveS-CJY9q1voop3Rb9brBjLupMLZ6djDWVBo59ytY3vyR9x_7wNENY xGR1upDLVANsKvMbYxRLgudXbQXX_gxw8QJafMqtjWo-o2mWM6HsE9k3Mha_QO0dkZAAzy_zTD0axSspTmG7X8N7YUsT6m Y6-syzHa8&__tn__=-UC%2CP-R) and he posted on December 9. One has a small crack, $300 for the pair. Shipping would kill, but may not be that bad considering his asking price. I sloshed aluminum tanks on an Avid Flyer once and they held for a while, but started leaking later. JImChuk

PS I've wondered if one was to fiberglass over the aluminum, kind of use it for a left in place mold if that would work. It might....

[atosrider]

pity that the early KF / Avid models placed so much emphasis on keeping the weight down, then combined with wanting the wing fold feature, the result is too much flexing in the first two bays - question, did the 13gal tank option only come out for the model 4 wing? is the 4 wing structure built stronger in this section?

adding some sleeving to the wing spars past this section might replace the cross bracing, in combination with heavier cross bracing mid-span .. oh, best I shut up, I'm not a structures guy .. tip tanks? oops, nice CoG positioning but different loading on the wing ...

some day I expect to be needing to replace the original model 4 tanks, not looking forward to that task, and hoping there will be a new replacement tank manufacturer willing to ignore the liability issues of this industry that has constrained progress for decades

BTW, what is the current tank solution in the newest kits? can it be used in early model 4 wings?

[Av8r_Sed]

My Model III has factory 13 gal fiberglass tanks (not Ethanol safe). They're still holding fine since I've always used non-Ethanol gas (thanks Wisconsin!).

[DesertFox4]

My first Kitfox, a model 3, had one 13 gallon tank in the right wing and a 6 gallon tank in the left. Both fiberglass and neither ever leaked.

[avidflyer]

Kitfox service letter # 10 dealt with replacing aluminum tanks with fiberglass tanks. The first Kitfox 3 I considered buying had been built with aluminum tanks, and they had been replaced with fiberglass ones. One thing to consider is sometimes these planes were built many years after they were bought, and so sometimes the new and improved things show up in older models even though those improvements weren't available when the kit was first bought. My understanding is that all kitfoxes after the Kitfox 3 can use the same tanks, except for maybe the STI wing.

[FoxbuilderWill]

Haven't finished the repair yet but I have a model 1 with a 6 gallon aluminum tank in the right wing. I cut the bottom out of the tank and fabbed a new cover plate that will be riveted in place after smearing a lot of proseal around all the welded joints31427

The above pic shows how I cut the bottom out. I have a plate that I fabricated with countersunk holes for the same kind of pop rivets vans uses on their fuel tanks. I did clean out the sloshing compound that was flaking off. Obviously no data on how well it will work yet but that's the direction I'm going.

[jrevens]

Hi Will,

Just out of curiosity, what is the thickness of the aluminum used for the original tank? Also, do you have any idea what the alloy is?

Thanks!

[FoxbuilderWill]

No idea on the alloy although in my research for what to use for the bottom plate 5052 was what Toby Bingelis recommended in those EAA how to books. Easy to form and weld.

I'm out of town right now but I'll put my calipers on the tank when I get home and let you know how thick the material is.

[Shadowrider]

Curious do you have pictures with the bottom of tank in? Curious what it looked like and why it was leaking?

[FoxbuilderWill]

Curious do you have pictures with the bottom of tank in? Curious what it looked like and why it was leaking?

I'm assuming that question is directed to me and not the OP?

If that's the case I have attached a pic of the plate I made but not yet installed.

If I have my history correct when they figured out the tanks were prone to cracking welds they recommended a sloshing compound for the tanks. Problem was it was impossible to adequately scuff the interior of the tanks enough for it to stick and eventually it would flake off and clog things up. I'm not aware if my tank actually developed leaks as it only had 75 hrs on the airframe when I bought it but the wing tank had been disconnected due to the flaking issue. I cut the bottom of the tank out for 2 reasons: I wanted to make sure the sloshing compound was completely cleaned out. 2. I wanted access to all the interior joints so I could scuff them up and proseal them.

As to the question of how thick the tank walls are its .050" , which is also the thickness of the plate I fabricated. I still need to attach a spacer to the middle tank baffle/rib somehow.

For those not aware vans uses a pop type rivet that is closed on the end so fuel can't leak through it.

31432

[Shadowrider]

Thanks for posting! Looking good and very interesting.

Are you thinking because the tank flexes, the rivets will allow movement that is needed that the welds could not provide and cause to fail?

[FoxbuilderWill]

Yes. Although rv wings being skinned in aluminum and of a much lower aspect ratio are obviously much more rigid than kitfox wings I'm sure they still flex to some degree and this method of construction seems to be well proven. With the proseal remaining somewhat flexible after curing and the rivets, yes I think this repair will last a good long while and if it becomes necessary in the future the interior of the tank can be accessed by drilling out the rivets and using heat to remove the proseal.