Loose wing tanks

[Jerrytex]

I do have builders manual. This part of the wing was built when I got the kit but I ran a camera down it and checked everything out. The person who built this part noted the process in the builder's log and it appears they used the correct adhesive. However, you can see a silicone bead on the lip of the tank that is not touching anything. I remember reading somewhere on this forum about someone who replaced a tank and noted that the silicone on the old tank wasn't touching the spar. I kind of wonder if that is the case on mine. I think the cracked hysol is from the tank pulling on the #1 rib via the blocks glued between the tank and rib as the tank moved outward. Maybe I should sell a kidney and buy the new tanks and do this once and for all. A real shame though since the tanks I have are like new, only not ethanol proof. If anyone else has experienced this and was able to fix it, without tearing off the fabric, I'd love to hear about it.

Thanks

[Dave S]

Jerry,

I would say the aircraft is unairworthy considering what the video showed with the loose tank and broken bond at the spar/rib.

The only way to be sure of what is going on is to strip the fabric and thoroughly inspect the entire wing.

I realize the notion of doing this is a bit daunting; however, a person has to consider what their life and others who might be on board is worth.

A person can't know what gremlins are at work without a complete teardown.

A few theoretical questions to consider:

1) Is the loose tank a cause or effect? What else might be damaged due to the cause.

2) What kind of abrasion/scratching/damage may have occurred to the spar? Has the spar been structurally compromised?

3) What condition are the drag tubes/drag tube fasteners in?

4) How many more ribs have a broken bond at the spar?

5) What condition is the lift strut attach point in? (maybe not connected to a loose tank; but, if out of date adhesives were used {which we can't know for sure anyway}, what else might be happening that can't be seen?)

6) If there is a question about the tank adhesive used.....if it was not the right kind what about spar corrosion?. (Note: The reason for a specific adhesive spec for the tank adhesive is standard Silicon products have a certain amount of ammonia present which raises the PH and can cause two bad effects.....damaging protective coatings on aluminum and instigating corrosion of aluminum...both of which can result in breaking the bond.

7) Thinking about the hysol.....I believe there was a case back in time when the old kitfox company (Not the current company managed by John) discovered an issue with some mixup in the shipped kits between labeling the microballoons and cotton flox where the wrong stuff could have been used by a builder with the hysol on the spars due to the mixup.

Sidebar to TJ: The term "RTV" is in part synonymous with "Silicon", RTV (an acronym for "room temperature vulcanizing") is a type of silicon product. A person needs to use the correct adhesive as specified by Kitfox for the fuel tank adhesive; and, assure it is within its usable expiration.

I don't mean to be overly dramatic, but, neither should any of us get pressed into rationalizing accepting something in an airplane that leaves a doubt about its safety because of the cost or inconvenience of having to fix it correctly.

I agree...its a tough call and not a lot of fun having to put a lot of effort into it. Wish you luck in assessing this issue; and, please understand that I realize that I am not on site looking at the problem directly....ultimately it is pretty darn hard to assess something a person does not have their hands on.

Just some ideas to try and keep my pals safe

Best of luck,

Sincerely
Dave S
KF7 Trigear
612ULS Warp

[HighWing]

Jerry,
I tend to agree with Dave S especially about the possible damage to the spar. I sure hope you don't find that you have more than a bit of RTV to worry about. My first Kitfox had one tank jigged improperly when it was closed at the fabrication shop. It rocked on the spars. I wonder if that is part of the issue. I have never seen a bedded tank that didn't fit pretty close to the spar - close enough that that amount of RTV would not be spread pretty wide by the contact.
Lowell

[Jerrytex]

That's a good point about the corrosion/abrasion issue. I didn't even think about that. I believe the original builder used the right adhesive, so hopefully there is no corrosion. It does however squeak when I move the tank so your right, it might be sanding the spar. I guess it's pretty much confirmed that there should be no movement between the tanks and the spars. I think I'll ground the plane and tear off the fabric over the tanks. That's the only way to know for sure, and it's not worth the risk to keep flying in this condition.

[cap01]

On the up side if the fabric is removed and no other damage is found , the tank can be removed , cleaned and sloshed with epoxy . Hopefully saving the price of the new tank . This is the good time of year to attack this problem since the weather gets crappy and not too good for flying , besides the airplane probably shouldn't be flown anyway . Good luck with whatever you decide

[Jerrytex]

I think I am going to bite the bullet and get the ethanol proof tanks. I have one tank that was sloshed with Kreem from the factory and the other is not. This way I can go back with two good ethanol proof tanks and be done. Then I can make someone a real good deal on two like new tanks if they were not worried about using ethanol fuel.

[Jerrytex]

Started work on fixing my loose wing tanks. I decided to reuse my tanks instead of replacing with the Ethanol resistant tanks. Way to many mixed reviews on using Ethanol laced gas. The left tank was totally loose with no silicone holding. The right tank was held in with maybe 3-4 inches total linear amount of silicone on the front and more on the rear. It is strange too because the silicone feels weird. It is not rubbery but almost "crystalized". It almost turns to powder when I squeeze it. Very easy to remove. Don't see any signs of corrosion, pitting or rub spots.

Now for some questions. It appears that the original builder used plenty of silicone. However, it just didn't touch the spars in most places. On one of the tanks it looks like the back side had good contact but the front not so much. Then what did touch just pulled off with no effort almost as if the silicone was bad. I checked the manual and it looks like he did as per the manual but I guess the tanks don't fit that snug between the spars. In fact one tank is narrower on on one end when compared to the other end causing an slightly eneven gap between the spars and the tanks. I guess that is a characteristic of fiberglass though. Has anyone any any similar experiences?

I bought the correct non-expired silicone and I was thinking about running a bead under both the front and back lips of the tank and setting the tank onto the spars and let it dry. Then flip the wing over and pump silicone directly between the tank and the spar from the bottom side. That way I don't have 2 feet of a sillicone bead that is not touching anything. Thoughts, suggestions?

[Dave S]

Hi Jerry,

Great to hear that no abrasion or scratch or additional damage occurred. Beginning to sound like you got as lucky as a person could hope to be with the situation.

I'd have to disagree about the quantity of adhesive shown from the original installation. There may be some issues with fit of the tank that may hold it away from the spars; however, in my opinion, the bead of adhesive should be much, much larger than what it appears to be...there should be plenty to squish out and fill in between the tank and spars. The zig/zag application pattern is very important to prevent air bubbles from blocking fill-in.

Photos can be a little deceptive with regard to color; however, the stuff from the original installation looks more like the garden variety clear silicon from Menard's than the correct adhesive; which, from my recollection, the correct stuff was a definite solid white color.

Sincerely,

Dave S
KF7 Trigear - Flying
912ULS Warp Drive
St Paul, MN

[t j]

Jerry, take a good look at the picture of the RTV beads in your builder's manual. They should be much,much thicker than what your builder did. My manual shows a very thick bead of RTV with humps/waves that span the length of the tank.

Heres a couple pictures of the bead on a tank after I removed it from a wing by cutting the RTV with "Firewire" fishing line. The bead wasn't near this wide before I set it against the front spar but as you can see it needs to be thick enough to squish out good and wide.

Don't try to squeeze the bead in after the tank is set between the spars. It needs to be a wavy pattern like this so air can flow in to cure the RTV.

[Jerrytex]

Wow. That is a thick bead. So there is no silicone between the sharp edge of the fiberglass tabs and the soft aluminum spar? Seems like there needs to be some type of a barrier to keep it from rubbing. Or, a small space to prevent contact?

In reference to the silicone. It does look like plain old clear silicone. The stuff I bought, Owens Corning 739 only came in white or black. I don't see any signs that it corroded the the aluminum, but I am definately going back with what Kitfox recommends.