Wet Wing Longevity

[Marc_B]

With the recent discussion of wet wings, and Mooney wet wings at that, I was curious what the real world experience has been with wet wings.  My aircraft had almost a quarter century on the wet wing sealant before I started to see leaks.  I wound up having the tanks stripped and resealed at the 25 year mark not because I had to, but rather I was planning on having the aircraft painted and wanted to get this squared away before repaint (and to "reset the clock" as it were).  There's still a part of me that knows that I did a reseal more prematurely than I could have, and I suspect that I could have gotten another 5 years as is, and with a quality patch job maybe even more...

Here is the worst of the seeps/leaks under wing at year 24...for life in a caustic environment, this is pretty solid performance in my mind!  I flew like this for 2 years, and when the tanks were resealed, the area was cleaned and today you can't even see where the leaks were...no damage to the underlying paint from the leak.

[EricJ]

Most airliners/jets/turboprops have wet wings, and wing maintenance is a constant issue for all types.   There are successful and busy companies that make a good living doing nothing but mobile tank repairs on airplanes.   All types of wet wings can and do develop leaks.   Even bladders can and do leak and age out.   GA airplanes seem to have it better than most, it seems.

"Tank diver" is an actual job description for maintenance of big airplanes.

I didn't know how to answer the poll since I'm not sure what constitutes a leak vs a seep or something simple like a leaky screw that is repairable.   I have had a regular leak near the top of one of my tanks, but it's not an issue if I leave it only about three gallons from full so I've never bothered to fix it...yet. 

[Larry]

You should rephrase options for question 1 to for those of us that have original sealant.  I have 35 year old sealant that is not leaking.  Only repair was of an inspection plate several years ago.  

[Marc_B]

7 minutes ago, Larry said:

You should rephrase options for question 1 to for those of us that have original sealant.  I have 35 year old sealant that is not leaking.

Modified the first question to include this...I added separate lines as I am most curious how many years do Mooney wings get before leaking.  I also didn't want to lump in a 10 year old wing that doesn't leak with a 10 year old that just started leaking.  Thanks for the suggestion!

[Marc_B]

17 minutes ago, EricJ said:

didn't know how to answer the poll since I'm not sure what constitutes a leak vs a seep or something simple like a leaky screw that is repairable.   I have had a regular leak near the top of one of my tanks,

The intent was to see how long on average does the Mooney wet wing last before needing sealant maintenance; and for standard tank maintenance (either reseal or patch) how long before seeing further issues that need to be addressed?  i.e. if Mooney wet wings are failing 3 years off the line vs 30.

Things like a leaking gasket from a fuel sender that's over-tightened aren't sealant related and don't reflect sealant compromise.  So I wouldn't count that as sealant failure, If that makes sense.

[A64Pilot]

I can give you an idea about Thrush Crop Dusters, which have been built since 1965 and I believe there are more of them than Mooney’s. All are wet wing, a great many were Radials so therefore Avgas mostly, newer ones are turbines so Jet-A mostly, but just about everything from home heating oil to Diesel has been burned in them, so lots of different fuels.

A difference between Thrush wet wings and Mooney’s is Thrush wings are sealed only with sealant that isn’t top coated with anything, if I had to put a number of years before significant leakage I’d guess 20, but honestly it’s all over the place, there seems to be a correlation between being under a shade and tied out in the Sun, majority of Thrushes are yellow and I think that color gets hotter than white. 

I’ve not seen any fuel that had any effect over long periods of time that degraded sealant, I think it’s mostly just time and maybe heat, but is it heat or metal expansion and contraction? I have no idea.

We used the same fuel tank sealant inside of the hopper sealing the interior stainless steel braces, in the hopper some of the chemicals used eat sealant up and it’s very common to have to replace the sealant every year or so. I do not know which ones eat sealant and which ones don’t, just know some do, so sealant isn’t impervious to all chemicals.

There is nothing that I know of that makes a Mooney wet wing novel, except maybe most wet wings are on larger aircraft? Small aircraft usually have metal tanks, maybe because their pedigree is from fabric covered wings? Many aircraft have bladders, bladders do seem to outlast wet wings.

[PT20J]

I suspect that the longevity is highly dependent on the quality of the original application. Personnel changes over the years, factory shutdowns and restarts, etc. might cause gaps in proficiency. The two women that did tank sealing that were interviewed in the Boots on the Ground video admitted that it was a challenging job and had a learning curve and that they weren’t very good at it when they started. Someone got the airplanes they learned on.

[Marc_B]

2 minutes ago, PT20J said:

I suspect that the longevity is highly dependent on the quality of the original application

I think there are several variables that may affect sealant life including original quality of application...hangar vs tie down, extreme temps vs stable temps, fuel in the tanks vs not flown and kept dry...  But I was curious in general for the population of Mooneys represented here on Mooney space if there are brackets and clumps.

BUT...if the quality was so bad with certain planes, when would you expect to see it??  1 year, 3 years...or does even this "low quality" application last 20+ years???

[Marc_B]

13 minutes ago, A64Pilot said:

There is nothing that I know of that makes a Mooney wet wing novel, except maybe most wet wings are on larger aircraft?

The allegation of difference here, I believe, is that some wet wings are fabricated with sealant between the ribs before they are riveted.  However, Mooney wings are riveted together, THEN sealant is used at the joints between rib and wing skin.

But I'm not convinced this is a detriment, and certainly makes the process of resealing the tanks probably higher quality.  I think it's a PROs and CONs on both sides and likely just a difference but not a "one is good and the other is bad" type discussion.

[toto]

Just FYI - you can't not answer these questions.  So even though it says "answer if you've...," you still have to pick the last one if it doesn't apply.

[MikeOH]

I didn't really know how to answer this.

Near as I can tell from the lack of log book entries, my tanks have the original sealant from 54 years ago.  I have no idea how many time the tanks may have been patched before I purchased my plane roughly 7 years ago (nothing I saw in the logs but, who knows).  I have had NO leaks in the left tank.  I started to get a small seep in the right tank after about 2 years of ownership.  I had it patched.  About three years ago the right tank developed another seep (different place) and I had it patched.  No problems since then.

At this rate, I have no issue with continuing to patch vs. a $15,000+ reseal.

[Marc_B]

26 minutes ago, toto said:

Just FYI - you can't not answer these questions.

I started out for just a question for those who patched or resealed, but wound up adding a line for those who hadn't.  So fixed it.  thanks!

[N201MKTurbo]

You didn’t ask the question “If you had your tanks resealed by one of the names above, how long before they started leaking?”

In my case it was 6 months. I have been fixing it ever since. Biggest waste of money in my long aviation life.

My M20F was 36 years old when I sold it. It didn’t leak at all.

[A64Pilot]

1 hour ago, Marc_B said:

The allegation of difference here, I believe, is that some wet wings are fabricated with sealant between the ribs before they are riveted.  However, Mooney wings are riveted together, THEN sealant is used at the joints between rib and wing skin.

But I'm not convinced this is a detriment, and certainly makes the process of resealing the tanks probably higher quality.  I think it's a PROs and CONs on both sides and likely just a difference but not a "one is good and the other is bad" type discussion.

We built our Spars with the layers wet, but didn’t shoot the skins etc wet, the Spars aren’t riveted but Huck bolted and the spars are about a foot wide. I don’t think you could shoot solids with wet sealant, so the Thrush is sealed after the wings are built too.

It’s a pain too, there are often leaks, we tested our wings with a big homemade manometer, 5 ft or so tall U of clear vinyl tubing filled with food colored water, once they get fuel the difficulty of fixing leaks got a lot worse.

[Marc_B]

24 minutes ago, N201MKTurbo said:

“how long before they started leaking?” In my case it was 6 months.

THIS...is what I'd expect with issues with sealant application/product curing/bad sealant batch...

My suspicion is that if you have issues with application, then you are likely to see them within the first 6 months of application...but I wouldn't put this in the same category as a wet wing that lasted 25 years without a leak.

@N201MKTurbo did you ever get this inspected and have a sense for what the issue was?  poor prep vs bad sealant vs bad application vs something else??

[N201MKTurbo]

13 minutes ago, Marc_B said:

THIS...is what I'd expect with issues with sealant application/product curing/bad sealant batch...

My suspicion is that if you have issues with application, then you are likely to see them within the first 6 months of application...

@N201MKTurbo did you ever get this inspected and have a sense for what the issue was?  poor prep vs bad sealant vs bad application vs something else??

All of the above. After talking to a coworker at the time, the real cause was the technician who did my tanks was going through a bad divorce and hated the world at the time. The coworker currently owns the business. He didn’t at the time, he was only an employee.

The new owner of the shop has said he would do a complete reseal, only if I wait 8 months for a slot. So, no real warrantee. Plus I would have to get the plane to the shop and back, so the free repair would be a couple of grand.

[Marc_B]

@N201MKTurbo I think I would have been inclined to take them up on the offer and asked for them to include full tanks of fuel when I picked up.  I wouldn't have liked it but sounded like a bad situation for you all around.  I would have hoped and expected that they got everything right the second time around.  Hopefully your experience was a horrible one off!  Sorry, that stinks.

[Shiroyuki]

i've had my plane for just under a year now, and from what i can tell in the techlog, the tank has never been patched or resealed. There is a bit of stain under the wing but I don't think it is time for reseal yet.

[N201MKTurbo]

There is another Mooney owner who is in the same boat. His issue was caused by them  not completely cleaning out the stripper. It is blowing bubbles along all the seams and causing leaks. I have been mentoring him on tank repairs. He has gotten quite good at it.

[DCarlton]

I’ve owned my plane for about 20 years and the tanks have always been an issue; it’s just a matter of degree.  I had them patched about 15 years ago but the problem wasn’t completely resolved.  We tried again a few years later.  It’s been getting progressively worse with the last 3-4 years exceeding tolerable limits.  They’ve never dripped, only seeped with a build up of running residue that’s very difficult to remove.  My tanks have been a less than perfect evolving entity the last 20 years so I can’t answer either.  I opened my bladder STC kit today and inventoried the parts.  Install starts in a couple of weeks.  

[Marc_B]

29 minutes ago, DCarlton said:

I’ve owned my plane for about 20 years and the tanks have always been an issue; it’s just a matter of degree.  I had them patched about 15 years ago but the problem wasn’t completely resolved

Did you ever have the tanks stripped and resealed?  Are you still on original base sealant?  Seems like part of the issue that's uncovered with wet wings is that at a certain point you can just patch and kick the can down the road, but sealant surely has a finite life span.  At a certain point it seems that the solution is a strip and reseal rather than patching, I think.  Perhaps that time frame is 30 years?  More?

Good luck with the bladders; I hope the install goes smoothly!

[DCarlton]

5 minutes ago, Marc_B said:

Did you ever have the tanks stripped and resealed?  Are you still on original base sealant?  Seems like part of the issue that's uncovered with wet wings is that at a certain point you can just patch and kick the can down the road, but sealant surely has a finite life span.  At a certain point it seems that the solution is a strip and reseal rather than patching, I think.  Perhaps that time frame is 30 years?  More?

Good luck with the bladders; I hope the install goes smoothly!

Nope.  Never found anyone in SOCAL willing to do the work.  Was lucky to have my first mechanic patch them.  I had an appointment with weep no more last Oct but missed it due to a mechanical issue enroute to MN.  Plane ended up stuck in AZ for a month waiting on parts.  

[Marc_B]

@DCarlton That's a pretty good run.  '67 F on original sealant!  Just shows that with some occasional sealant maintenance you're at 58 years!  Of course that may also be the reason you've had issues intermittently for 20 years.  I'm guessing your bladders will need less overall TLC, but may not last that long!

[DCarlton]

3 minutes ago, Marc_B said:

@DCarlton That's a pretty good run.  '67 F on original sealant!  Just shows that with some occasional sealant maintenance you're at 58 years!  Of course that may also be the reason you've had issues intermittently for 20 years.  I'm guessing your bladders will need less overall TLC, but may not last that long!

I don’t recall there being a complete reseal in the logs but also don’t remember going through the logs looking for one.  Likely they’ve only been patched.  

[Pinecone]

I cannot vote, as I cannot answer several of the questions.  There is no option for Do Not Know or Not Applicable.

You also did not have options for people who resealed before they had leaks.

I don't know of any patching on my plane, so NA.  I don't know if the reseal was due to leaks, or just figured it was time.  The original went 23 years.