Runways and tank leaks

[DonMuncy]

I keep reading about landing on unpaved surfaces and hard landings as contributing to fuel tank leaks. Does anyone have any statistical or other type indication that this is true, other than just a general idea that jarring of the plane must cause them. I am far from the smoothest landing pilot you know, and my 32 year old 231 has never had a leak. (Full disclosure, I did have a screw on the top of the wingwalk that seeped a little fuel when full, but stopped when the screw was removed, sealed and replaced.)

I know Mooney wings are stiff, but I assume they must flex a little in flight. Would that be worse/better than rough taxiing or hard landings. From what I can see or guess, just plain age, the state of the art of the sealing material used during a certain time span, or perhaps the skill of the person doing the original seal might be more important than the landing and taxiing.

[Alan Fox]

Don in the 70s mooney started sealing the wings during assembly , as opposed to after , these are far superior to the earlier mooneys , but they usually seep from the rear of the tank at the main spar next to the gear ...From you guessed it hard landings ,     soft landings and keeping the tanks full will make them last longer , also gear discs every ten years or so will increase longevity as far as tank sealing goes....

[Piloto]

The idea that rough landings or turbulence would cause leaks is a myth. The sealant has enough flexibility to overcome any structural deformation that may occur duriing these events. The sealant is a form of rubber and not glass. 

 

Major cause of sealant failure is long term heat exposure. The sealant like any rubber looses it elastic properties and bonding when exposed to extreme heat for a long time. Such as when is tied down outside in the sun instead of hangared. If the plane is to be out in the sun for a long time it is recommended that tanks be at least half full. The fuel helps in preventing extreme temperatures that can degrade sealant qualities. The same apply to bladder tanks.

 

Rough landings due increase wear on landing gear components just like in a car. It can also affect structural attachments of heavy components like oxygen tanks, battery, engine and others. Unlike Bonanzas Mooney landing gear has little shock absortion. Best way to cope with it is with soft landings and lower taxing speeds.

 

José 

[bonal]

I know keeping the tanks full is better to keep moisture from accumulating. I have O&N bladders and I was wondering if full tanks are better or not an issue to the life of the bladders. Also sadly our mooney has yet to find a hangar and the field is not secure so some times fuel is stolen so I prefer to keep them at a lower level

Comments.

[Dave Marten]

I keep reading about landing on unpaved surfaces and hard landings as contributing to fuel tank leaks.

Don,

 

Where are you reading about hard landings and unpaved surfaces contributing to fuel leaks?

 

I suppose if we tried substituting a Mooney into an Alaskan Bushplane operation you'd have an increase chance of fuel leaks (in addition to many other complications). I agree with Jose's post. Age and enviornmental factors are the two key ingredients to leaks.

 

If you did land hard enough to bend metal/pop rivets then yes, you will by default now have a tank leak in addition to your structural problems. There are many concerns/considerations with proper landing site selection and landing technique - fuel tank issues doesn't even make the top 50 on my list.

[DonMuncy]

Just a couple of examples: cliffy posted today on "shameless opinion..." on the vintage forum, and on September 24, 2013, on the modern Mooney forum, under leaking fuel tanks, jlunseth mentioned them. (Sorry, I don't know how to send you directly to the cites.) I'm not saying these guys made these assertions, just that they were mentioned. but over the years, I believe I have seen several people who stated that rough fields and hard landings were a large contributor to leaking tanks.

I'm not denying or agreeing, just trying to figure out if this is really true.

[carusoam]

Seeing Oscar's video from the wing. I can imagine that bumpy runways are not much different than bumpy air.

Best regards,

-a-

[jetdriven]

I know keeping the tanks full is better to keep moisture from accumulating. I have O&N bladders and I was wondering if full tanks are better or not an issue to the life of the bladders. Also sadly our mooney has yet to find a hangar and the field is not secure so some times fuel is stolen so I prefer to keep them at a lower level

Comments.

O&N only says to not let them sit empty for any length of time.

[BigTex]

 Also sadly our mooney has yet to find a hangar and the field is not secure so some times fuel is stolen so I prefer to keep them at a lower level

Comments.

Bonal - I'd recommend you find a common hangar at your airport.  I've found that at almost all airports, has space available in one of the larger hangars.  If not at your airport something close is available.  I'd do that before I'd ever leave my plane on the ramp.

[bonal]

So far I hadn't had any luck but I will keep searching

[N201MKTurbo]

I have no more or less data then anybody else on this site (none). But it is my opinion that hard landings do contribute to tank leaks. All the leaks that I've fixed we're caused by the sealant coming loose from the metal. I have a feeling that the stress of hard landings can cause the sealant to eventually delaminate.

[Hank]

The sealant comes loose from the metal because it deteriorates. When my tanks were redone, some of the sealant had the consistency of sand. It breaks down due to time and heat. Once it's in bad shape, heavy turbulence or thumping arrivals may increase the leak rate, but only because the sealant already needs to be replaced.

[jlunseth]

I had my tanks resealed by Weep-No-More in 2009.  A couple of years ago I participated in a program that involved landing at all the airports in MN, some were grass fields, and even if not grass fields, because of the variety some were just deceptive and there were some hard landings.  I have had no issue with the tanks.  My practice is to leave the tanks empty and fill at the beginning of the next flight, which reduces the load on the tanks/sealant, at least in theory.  I have not ever had a problem with water showing up in the tanks regardless of temp changes (and we get some big ones here) or how full or empty the tanks were left.  I fly often - between 150 and 250 hours a year, so the tanks get filled often, but not so much in the winter when you would think empty tanks would create a condensation problem, but I have just not seen any.  The Weep-No-More tanks have been flawless.

[Jeff_S]

To answer this from a different perspective, I would question the assumption that non-paved runways are actually harder and more stressful at all, whether or not this would contribute to leaky tanks. Every turf runway I've ever landed on absorbed more stress and shock through the grass and softer dirt that it made all my landings seem even smoother. Now, I suppose if you landed on a dirt washboard runway in the desert this might be different, but the average turf runway here in the Easter US is pretty darned inviting.

 

Unpaved runways have different hazards which I do think make them a bit more dicey, especially for long-body Mooneys. Namely, they can undulate which reduces ground clearance and could be a hazard for a prop strike. I think anything from a J or older (and not including the nose-heavy 231/252s) shouldn't really consider this a risk. Finally, there's the question of the inner gear doors snagging debris.  But we have at least one Forum member who treats his Mooney like an Aviat Husky. If only he could get the oversized tires into the wheel wells!

[N201MKTurbo]

Let me just clarify my statement:

 

it takes years of consistant landing gear abuse to negativly affect the sealant.

 

 

FWIW My old F never had any leaks and had the origonal sealant. I generally don't top my tanks after every flight and it spent most of its life in Arizona. It spent a good deal of its time outside. The temperature in the summer with the plane sitting outside would probably hit 150, in the hanger about 120. I don't think heat is that much of a problem. I did fly the plane almost daily and it would get topped about once a week.

 

I think, like a lot of things in the plane, the sealant likes to be used.

[Shadrach]

Actually, the latest Mooney SI from Mooney infers that rough landings or bad shock biscuits can "potentially" cause tank leaks.  I think that is complete BS, but mooney has been saying this for years, why change now just because all of their airframes are out of warranty.  Having worked with the sealant, I can tell you that it is very flexible and adheres with amazing tenacity.  If a rough landing or subpar shock biscuits cause your tank to leak, you either bent something, or your sealant was already deteriorated. Leaks caused by bumpy landings and bad discs were on their way to revealing themselves, a few bumps may just hastened the leak by a few tach hours or less... No way, No how, good sealant is going to leak from a grass strip landing...  

 

http://www.mooney.com/images/pdfs/si-pdf/m20_122.pdf

[N201MKTurbo]

BTW,

 

I landed my mooney on a grass strip in MN once. If you can call it grass. It consisted of these hard clumps of plant matter about 4 inches in diameter spaced abour 8 inches apart. landing on river rock would have been smother.

[Shadrach]

 we have at least one Forum member who treats his Mooney like an Aviat Husky. If only he could get the oversized tires into the wheel wells!

 

Exactly,

 

Piper painter, how often do you have to reseal after landing on some the rock covered game trails that you use for runways?

[N201MKTurbo]

 I can tell you that it is very flexible and adheres with amazing tenacity.

 

When it is new.

 

When cleaning a tank or a cover plate most of the sealant is nearly impossible to get off, but you ocasionally find an area where it peals right off. And the old sealant is definatly harder then freshly applied stuff. It is like the difference between a soft pencil eraser and tire rubber.

[John Pleisse]

My Mooney Service Center IA has strongly suggested tank leaks come from stress. He attributes this to many new aircraft over decades (they were a dealer at the time) being returned with tank leaks in short order. Leaks are usually in corners or joints, inspection-access plates,  and on flat rivets on the wing walk. My tanks are 35 years old, have never been resealed and have been patched 3 times in the last 15 years. I agree with him. Tank sealant age and degradation are significant, but I personally believe hard landings and torsion type taxi turns do the deed, more so than age.

[carusoam]

Rainman has posted some spectacular photos of what a tank leak looks like before it was stripped. And a photo of the tank fully stripped with all the glory of the sheet metal, rivets and over laps...

Essentially the sealant cracked along a seam in the tank.

Appears to indicate that the sealant became brittle over time and failed on the seam. It also had a history of being resealed along an access panel.

Maybe Rainman can repost those pics here?

PM sent to R.

Best regards,

-a-

[Hector]

Unfortunately polysulfide sealant does harden with age. when the sealant is new or relatively new I seriously doubt rough fields can cause a leak unless you permanently deform the tank structure. After many years and after the sealant begins to harden it is plausible the hard sealant can disbond with excessive strain resulting in leaks. I work at an overhaul facility and see a LOT of old hardened sealant.

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