Robert Sailor

Original 1965 tanks haven't leaked yet

Recommended Posts

I've owned several Mooney's in the past but that was in the 70's and leaking tanks were not an issue. Now it obviously is...so my question to all you experienced folks is..I'm looking at another mid 60's Mooney and as far as i can tell it's very clean and well kept BUT the owner tells me that the tanks are original and have never leaked. From what I read on these forums it's nice to buy a clean Mooney that has had the tanks done recently..What are the odds that these tanks are going to start leaking sooner than later???

Share this post


Link to post
Share on other sites

*Members that donate $10 or more do not see advertisements*

He might be right. Over the years the EPA has tried to take cancer causing chemicals out of sealants, paints, solvents, etc. One example: Mooney that was painted in the early 90's has better paint than one painted in the early 2000's.

That being said though, nothing lasts forever. I'd say if you buy it, start putting money away for a re-seal. Whether they leak now or not, at some point they will. Even if they never leak, although highly unlikely, on a 53 year old airplane there will plenty of other places for that money to go.

Share this post


Link to post
Share on other sites

We do a fair number of tank reseals and patching, and I’ve learned that time is not a factor in leaking. Each tank from the factory or through the good shops that do aftermarket chemical striping and resealing know that there are inconsistencies in the process from tank to tank.

That plane may never leak. But the older the sealants gets the more brittle they become. (There are three types of sealants used) Since it has never leaked I’d say you’re now into the luck of landings stage. Your biggest enemy will be an exactly perfect hard landing. The flex moments may now be enough to cause the Buna N top coat to split which is likely the only thing at this point that is keeping the wing dry.

I will advise that if it does start leaking you are not a candidate for a patch. Plan on a full strip and reseal and add that to your cost calculation.


Sent from my iPhone using Tapatalk

Share this post


Link to post
Share on other sites

I have a '69 C with original sealant except for one panel.  The only leak was the unfortunately placed access panel right where you step out of the cockpit; a panel smartly removed from later model designs.  A major avionics upgrade/new interior/etc caused ten years worth traffic in a few weeks and subsequent leak. Also, the sealant used for removable panels isn't as tough to allow future panel removal without destroying them. The compounds are well proven. Application is everything. You may wish to put a little money away as at some point, you may need it. Don't let anyone talk you to reseal until condition dictates it. Keep the tanks full and stay off of rough runways and taxiways and avoid the unfortunately placed panel in the wing walk.  BTW. The same sealant family and techniques are utilized to seal fuselages for pressurization.  

I'm making tanks for a project and the materials engineer from PRC-DeSoto was kind enough to answer my question about dry layup limitations (before introduction of fuel) even though I'm just a GA guy. His very informative reply (at least to me)  is below.  Hope this helps

We make no claims as to service life, and there is nothing in the material specs to which we certify that would duplicate sealant that has been fuel immersed, then dried for a long period of time.

As you are aware, the preferred method of aircraft storage is to keep some fuel in the tanks. This keeps the sealant from drying out and shrinking. (this also goes for the other types of elastomers in the fuel system such as O-rings etc.)

From my experience in the Industry over many years, a lot of how well the sealant does in long term aircraft storage is predicated on the original seal design that was used. OEM’s that specified thicker fillets, and used a more redundant seal design in their tanks will be less prone to leaks upon refueling.

Wow – you have a Mooney that doesn’t leak? Incredible. I deal with all aircraft that use Pro-Seal and PRC sealant, Mil, Commercial, and GA. Other than the first series of B-1b bombers, the Mooney seems to be one of the most leak prone aircraft. (my edit here, Mooney's have very stiff landing gear. The tribal knowledge in that community is to keep the tanks full and stay off of rough fields)

The Mooney materials engineer had to have come from Lockheed Burbank, because your plane is sealed the same way as the Conni, Electra and P-3 …and for that matter the F-117.

There are some people out there that use Shell 1010 oil over the seals, but the USAF materials guys advise against this, and neither Boeing, or Airbus approve either.

FYI – B-52’s are all over 50 years old and 80% of the sealant is still original (and these planes have like 36 feet of wing deflection). (My edit here, deflection probably isn't the problem. Mooney gear are very stiff. Sharp accelerations like hard landings and taxiway bumps are the probable Mooney culprits.)
 

All that said, if I had newly fab'd tanks and knew it would be a while before they were put into service, I'd probably have some fuel sealed in the tanks; reference the B-52 comment. We can assume they're always fueled. Just because they don't leak immediately after a long dry time/wait doesn't mean you haven't affected the sealant life.

Probably won't help me in my hunt but if this saves anyone some rework, all good.

  • Like 1

Share this post


Link to post
Share on other sites

Newer Mooney’s have a reinforcing stiffener under the panel which is in the wing walk area.  It is distinguished by 4 countersunk screws outside of the access cover screws.

Clarence

  • Like 1

Share this post


Link to post
Share on other sites

From personal experience, when you put those countersunk screws back in, it helps to put a little Permatex Aviation #3 sealer on the threads and let them cure a day or two before putting the new wing walk back on. Otherwise in a few weeks you are taking the wing walk off again.

  • Like 1

Share this post


Link to post
Share on other sites

It also helps to keep Marauder’s friends off the waning walk.

Clarence

  • Like 1

Share this post


Link to post
Share on other sites

My opinion is that if they are not leaking now, it is a total guess. They may go a long time with no problem or they may start leaking tomorrow.

Share this post


Link to post
Share on other sites

A couple of hardware issues to review on a 60s original fuel tank...

my 65C got a few things updated...

The fuel cap seats (there is a name for that piece...?) were not stainless steel... rust bits and holes were a challenge...rainwater entering was a challenge...

The fuel sender seals were original cork... and allowed fuel to go where fuel doesn’t belong...

the connector hose between fuel lines was swollen and crunchy...

Its tanks didn’t leak for a long time after that...

All machines age differently. Depending how they are used and stored...

Good luck with the purchase... not a requirement but it helps...

Best regards,

-a-

Share this post


Link to post
Share on other sites

They’ve likely had a few minor patches but patches aren’t too big of a deal. Far cheaper and easier than the nuclear reseal. 

-Robert 

Share this post


Link to post
Share on other sites
57 minutes ago, Immelman said:

You can buy a lot of patches for the cost and donwtime of a reseal.... a LOT of patches.

 

And if you ask your A&P to show you how its done you can do it for about $100 in material and whatever he charges to review and sign.

-Robert

Share this post


Link to post
Share on other sites
And if you ask your A&P to show you how its done you can do it for about $100 in material and whatever he charges to review and sign.
-Robert


So ... Finding the actual leak area(s) is usually 75% of the work, discounting that effort can be an expensive mistake. I can assure you that 99% of the time the leak(s) is/are not in the area of the visual leak.




Sent from my iPhone using Tapatalk

Share this post


Link to post
Share on other sites
4 minutes ago, DVA said:

 


So ... Finding the actual leak area(s) is usually 75% of the work, discounting that effort can be an expensive mistake. I can assure you that 99% of the time the leak(s) is/are not in the area of the visual leak.




Sent from my iPhone using Tapatalk

 

http://donmaxwell.com/fuel-tank-repairs-how-we-fix-them/

-Robert

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now