G100UL - fuel leak

[Fly Boomer]

A couple of data points.  According to an AVWEB article,

1. the gunk on the underside of the left wing of the AOPA Baron originated with a leaky patch in the 50-year-old bladder in that tank--no telling what was used to affix that patch

2. fuel then got between the leaking bladder and "chafe tape" that is applied to the wing to protect the bladder from wearing against the metal. The fuel dissolved the glue on the chafe tape, and that glue was the sticky residue on the underside of the wing

3. also, there were minor leaks from the other (100LL) tank (only 46 years old), and evidence of past leakage of 100LL from the left (G100UL) tank before the side-by-side test began.

https://www.avweb.com/aviation-news/aopa-baron-wing-stain-traced-to-leaking-bladder-patch/

These points don't constitute exoneration from all past, present, and future issues with the new fuel but, as usual, the conspiracy theorists that said the G100UL "ate right through that bladder" were hyperventilating.

[Jeff Uphoff]

On 12/12/2024 at 9:44 AM, AJ88V said:

(BTW, nice to see your name, Jeff.  I keep running across friends from the old Mooney mail list.  Glad you're still flying, and a much higher end plane!!)

AJ! Wow, long time!

I took some years off from flying--grad school for me and my (then) wife--but got back into it with a vengeance when I bought this Ovation.

You're around these parts, too, looks like--KCJR. Have to do a lunch run sometime!

--Up.

[George Braly]

Very much appreciate the discussion and the feedback, here.  

Please allow me to provide a response to some of the messages.

1)  I am a big Mooney fan.  Flew a 67 Mooney Super 21 for nearly 2,000 hours.  Commuted to and from law school in Norman, Ok. to the family Ranch (100miles each way) on a daily basis for 3 years. 

 2) Part I - - Some aviation fuel chemistry history: 

A- During WWII fuels with very large amounts of aromatics were adopted.  Arguably, the Air War would have been much more costly in terms of losses for the fighter aircraft without the introduction of aromatics to aviation gasoline. The fuel approved for D-Day was "100/150" - - and used a lot of different aromatic components;

B- In the ranking of the levels of "aggressiveness" as solvents,  the ranking starts (most severe) with benzene.  Then add a single CH3 group and you get toluene.  Yes.  Paint stripper you buy at the paint store. 

C- Add a second Ch3 group and you get xylenes (three isomers - ortho, meta, & para)  Xylenes are significantly less aggressive as a "paint stripper" than is toluene.  <== THAT is important.  Keep that in mind. 

D- Many fuel bladders were developed during WWII and are labeled "approved for aromatics" or something similar.  If you look closely at some of the P-51s and other planes at Oshkosh, you will see a placard that states "approved for aromatic fuels."

 Part II - - Post WWII.

A- We had "Green"  100/130 with LOTS and lots of lead.  And even purple 115/145 (with lots of aromatics) At the end of the piston airline and going into the late 1970s and 1980s, the ASTM folks decided to drop the lead content and created BLUE  100Low Lead.   Still lots of lead.  But much less than GREEN 100/130. 

B- Some of the refiners had very good "aviation alkylate" (~ 70% of some 100LL fuel formulations) with relatively high MON values for that aviation alkylate (a less than pure form of isoctane).  Those refineries could make 100LL with relatively low levels of aromatics (almost always "toluene" from the paint store).  Maybe 10-20%.  

C- Other refineries (P66 at Borger, Tx, for example) had lower MON quality "aviation alkylate" and the had to use a LOT of toluene.  I can show you detailed hydrocarbon analysis (GC-FID) test results for local (Ada, Ok. FBO) P66 Borger, Tx  100LL that has 29% toluene and another 4% of other aromatics for a total of about 33% aromatic content. 

3) Fleet Experience during the transition to 100LL - - 

A-Starting shortly after the introduction of 100LL, with high levels of aggressive toluene, A LOT of Mooney, Piper, and other airplane owners that had aluminum integral fuel tanks (no bladders) began to leak fuel out of lots of rivet holes.  That started a whole new business for G.A. with companies initially specializing in re-sealing those tanks.  Later, companies developed retrofit fuel bladders for those problematic "integral fuel tanks".

B- A big part of the problem was the aircraft manufacturers did an "inconsistent" (careful choice of words)  job of applying the polysulfide sealant to the interior  (rivets and seams) of the aluminum integral wing tanks as they were manufactured.  [As we have learned during material compatibility testing, the devil is in the details when it comes to the proper application of sealants to fuel tanks. ]

C) Over the decades, the level of toluene from most refiners has decreased due to better quality aviation alkylate, but some refiners - - for at least some production runs - - still (from looking at their data sheets) still have a lot of toluene.

4) G100UL Avgas - -

A- Uses a very high quality aviation alkylate (2-4 MON numbers higher than the alkylate used for 100LL) and then uses xylenes rather than toluene in order to achieve the  100/150+ octane/supercharge rating for G100UL avgas.  The right choice of xylene isomers will have higher octane blending value than does toluene.  Using "xylenes" also has the advantage of being less chemically "aggressive" than is toluene.  But the high quality alkylate and the premium xylene isomers also "cost more" than the related components in 100LL.  BUT - - there ends up being no lead.  

B- We did extensive material compatibility testing, including a whole variety of older bladders and a whole range of tests for sealants applied to aluminum.  All of that supervised (in person) by multiple FAA engineers and managers and then later  approved by the FAA.

5) The 100LL we have at the airport in Ada (typically Phillips from Borger, Tx) still tends to have a lot of toluene in that fuel. 

A- Late October of 2023,  AOPA brought their 1965 demonstration Baron to Ada.  Two freshly overhauled IO-520s.  One fuel bladder was 46 years old and the other ~50 years old.  They were supposed to have been replaced with new, prior to the start of testing, but the bladders were on "back-order". 

B- G100UL avgas was exclusively kept in the LH bladder and  100LL was exclusively in the RH bladder. 

C-Within 30 days, we noticed fuel "spots" on the hangar floor.  Investigation - - we found fuel leakage and staining on the bottom of the RH wing - - which had ONLY ever had 100LL.  See photographs.  

6- Oshkosh, the leakage from the LH wing tank (G100UL Avgas) was ( based on Eagle Fuel evaluation) caused by pre-existing damage to the tanks and the gaskets associated with the access panels. (In addition, there were pin-hole leaks in both fuel bladders). 

7)-G100UL Avgas is NOT a threat to normal aircraft paint.   

A- Embry Riddle did extensive certification testing of G100UL avgas.  They used G100UL in their C-172s for over a year, at Daytona Beach.   They had no evidence of any fuel leaks and they had zero staining on the wings.  

B- As part of our due diligence, wee have deliberately spilled a LOT of G100UL Avgas onto various painted components from the many Bonanza aircraft that come through the TAT shop for turbo systems.  That includes LOTs of wing tips and the lower cowling access panels, both of which are removed and replaced (with tip tanks and newly louvered lower access panels.) 

C- Some of that has been allowed to dry on those painted surfaces and then the process was repeated.  NO SIGN OF ANY LOSS TO THE INTEGRITY OF THE ADHESION OF THE PAINT.

D- We have even soaked a couple of those side panels in G100UL for a week or more.  The paint was fine at the end of that.  

E- What does and will happen - - is if you do not properly clean up the spilled fuel, and allow it to dry, it can and will leave a light tan stain on the paint.  If you do properly clean it up,  it will not stain the paint - - even after repeated spills in the same location.  But, to date, we have never seen any evidence of any type of "paint striping" activity to any of the dozen or more aircraft parts that were removed from our customers Bonanzas and used as "test articles."   See  https://g100ul.com/dl/Refueling Hygiene G100UL Avgas.pdf

F- An aside - - some of the recent crystal and graphene coatings improve the resistance of aircraft paint to any damage from any variety of 100LL or G100UL - - but that is not a cure all.  See the link Refueling Hygiene! 

8.  So "what happened" on the bottom of the Mooney wings ? 

A- In one case, the sump drain appears to be leaking.  Likely the fittings inside the wing are also leaking.  

B- In the other case, there appears to be some kind of leakage from inside the wing.  Not sure from the photographs.

C- Almost certain that old drain valve has a "nitrile" set of O-rings.  

D- The paint on the bottom of the wings has likely had many months of exposure to steady drips of 100LL.   In California, probably with only ~ 15% toluene in the 100LL . . . maybe.  

E- No information about the age of the paint on the bottom of the wings, but from its overall appearance and the multiple rivet holes that are bare and which have lost their paint - - it is likely a they are rather old paint jobs. The paint on my personal Bonanza, N11RT is about 35 years old and it is in much better condition than the appearance of the paint (away from the damaged paint).  

F- It would be good to know the age of the paint for each of those two aircraft.  

9.  What to do ? 

A-There is a long standing FAA / maintenance bulletin (20 + years old ???) that tells mechanics that when they find fuel leaks or deteriorated fuel lines or gaskets or O-rings, they should replace those components with parts that are made from chemically resistant materials  (viton, fluorosilicones,  etc.) Those types of materials are specifically stated to be for use with a wide variety of fuels, including aromatic based fluids.  A lot of mechanics have ignored that recommendation over the years.

Last . . . 

10.  I would like to have the chance to borescope an older Mooney fuel tank that has not been converted over to a bladder. 

A- If anyone on this forum would like to bring their plane to Ada we can do that here.  You might find it interesting.  If you have the STC you can probably leave with some G100UL in your tank, if you want.  

I hope this information helps to bring some clarity and understanding to these issues that will be the subject of conversations during the transition away from leaded avgas.

Regards,

George Braly  gwbraly@gami.com

Edited December 14 by George Braly

[Fly Boomer]

38 minutes ago, George Braly said:

Very much appreciate the discussion and the feedback, here.  

Welcome to MooneySpace.  We love it when vendors hang out with us.  You may take flak from some, but there is a larger number who will read and learn from your posts.

[Justin Schmidt]

1 hour ago, George Braly said:

Very much appreciate the discussion and the feedback, here.  

Very much appreciate your usual calm data driven talks and explanations. 

I look forward to G100UL being available in Ohio in, hopefully, the not to distant future!?

I had tanks (with aux tanks) resealed in 2019, no leaks, however, out of commission for a period.

[A64Pilot]

Last years Concorde I A renewal seminar, I only screen shot screens that are of a particular interest to me. The presenter worked, maybe owned Eagle fuel cells, and has it seems a long history with fuel cells, his point is that aeromatics are hard on fuel cells, and my take on that is it’s likely hard on sealants as well.

On edit, I think his point was that ALL fuels are relying more heavily on aeromatics than they used to.

He seemed to indicate that they are hard on fuel cells and I’d assume he would have an educated opinion.   

If you search aeromatics in auto fuel you will get some interesting reading. I would suspect you would get only a few hits on a search of it in aircraft fuels based on just how little piston aircraft fuel is manufactured.

Edited December 15 by A64Pilot

[Fly Boomer]

29 minutes ago, A64Pilot said:

On edit, I think his point was that ALL fuels are relying more heavily on aeromatics than they used to.

That's true and, as George points out above, it's not like G100UL has a ton of aromatics, while 100LL doesn't--he has seen 100LL at his local FBO with 33% aromatics.

[varlajo]

19 hours ago, George Braly said:

7)-G100UL Avgas is NOT a threat to normal aircraft paint.   

George, thank you for a thoughtful and detailed answer. If you really want to drive your point #7 home, you might want to show a long-term test with say three identical painted inspection panels submerged in 100LL, Mogas, or G100UL for a couple of weeks. Even better if there is a fresh, controlled depth scratch, a rivet, and a screw in each test panel.

Edited December 15 by varlajo

[Jim F]

On 12/11/2024 at 12:58 PM, GeeBee said:

As to Cirrus. They have been running G100UL for 14 years in a Cirrus wing tank, with no issues.

 

Any idea what sealant Cirrus uses on their tanks?

[Fly Boomer]

50 minutes ago, Jim F said:

Any idea what sealant Cirrus uses on their tanks?

Same as Mooney (CS3204):

https://www.inetefb.com/Documentation/Cirrus/AMM/pdf/20-10.pdf

  TYPE     P/N or Spec.          Manufacture               Application
---------  ---------------  ------------------------  -----------------------
Extrusion  MIL-S-8802                                 Fillet, faying surface,
Gun        Type 2 Class B*                            and injection seal
Sealant    CS3204 C1.B      Chem Seal - Flame Master  in fuel tanks.
           GC408B           Goal                      Install and seal
           P/S 890B         PRC Aerospace Sealants    windows. Seal fuel
           PR1440B          PRC Aerospace Sealants    system enclosure
           EC1675B          3M                        in cabin.
           AC-240B          Dynamold Aerospace

[George Braly]

46 minutes ago, Fly Boomer said:

Same as Mooney (CS3204):

https://www.inetefb.com/Documentation/Cirrus/AMM/pdf/20-10.pdf

  TYPE     P/N or Spec.          Manufacture               Application
---------  ---------------  ------------------------  -----------------------
Extrusion  MIL-S-8802                                 Fillet, faying surface,
Gun        Type 2 Class B*                            and injection seal
Sealant    CS3204 C1.B      Chem Seal - Flame Master  in fuel tanks.
           GC408B           Goal                      Install and seal
           P/S 890B         PRC Aerospace Sealants    windows. Seal fuel
           PR1440B          PRC Aerospace Sealants    system enclosure
           EC1675B          3M                        in cabin.
           AC-240B          Dynamold Aerospace

WRT Cirrus Fuel Tank Sealants - - 

Up until ~ 2010-2011 they (primarily) used "polysulfide" (PSFD) sealant (i.e. MIL-S-8802) for their fuel tanks.  

From then until May of 2023, they used "polythioether" (PTE)  sealant ,  AMS-3277.  

Starting in May of 2023, immediately after their discovery of the PTE sealant issue in their SR22T, they switched back to only using the PSFD at the Cirrus factory. 

However, in the interim, prior to 2010,  they then also sometimes used the PTE sealant.  

Our 2007 TNSR22 Cirrus (N223TN) - - as it turns out - -  had the same PTE sealant as Cirrus used from 2010-2023.   

That was the same sealant (PTE) that was in the wing of the Cirrus SR22-T that was found to have some sealant debonding.  However, that was a Cirrus "in-house" R&D aircraft and nobody at Cirrus ever inspected the fuel tank before they started using G100UL Avgas.  That aircraft is the same make and model Cirrus factory owned aircraft that was used for earlier PAFI fuel testing, including the infamous  "Shell Fuel" - - ie the fuel that was withdrawn from PAFI by Shell because it was literally "melting" Piper fuel bladders and stripping the paint of the wings of C-172s at Embry Riddle where it was (briefly) "tested." 

GAMI's TNSR22 Cirrus has had G100UL Avgas in the RH wing tank for most of the last 14 years.  Borescope inspection reveals that (PTE) sealant is, literally, in "pristine" condition.  We have conducted soak testing on two other Cirrus wings (from salvage yards) with PTE sealant.  NONE of that sealant has, ever,  shown the slightest hint of any adhesion failure. 

Summary:  Polysulfide (PSFD) is a better sealant for our fuel tanks than PTE, as it appears to be more "fault tolerant" of improper application techniques.  But, properly applied, in accordance with the manufacturer's instructions, PTE also works.  

 

[George Braly]

With respect the discussion about the high levels of toluene and aromatics sometimes found in 100LL,  see the attachment, which is a "DHA"  (Detailed Hydrocarbon Analysis)  using a standard ASTM test method, that was run at the reference fuel laboratory (Dixie Services, Deer Park, Tx) from a sample pulled from our local FBO 100LL, supplied by rail from the Phillips refinery in Borger Texas.

[larryb]

My aircraft, which I posted in #49 is a 1997 encore with factory paint. The paint missing around the rivets bubbled up and rubbed off 1 week after my first tank of GU100. The paint there was fine before but is is possible or likely the rivets seeped a bit of fuel before.

Regarding the drain port it is actually only a few years old. It was replaced under my ownership when the previous one leaked. Not sure why the current one is leaking, perhaps a bit of debris bought in the valve.

[wombat]

Between @larryband the OP @gabez we have two people that claim that within a week of adding G100UL to their tank they've had paint peeling.

A couple of ideas on what could be happening:

1. Coincidence that these things just happened to occur shortly after a fuel switch but are unrelated.
2. The fuel as designed has a problem.
3. The fuel has been contaminated either inadvertently or intentionally.
4. The reporters are not being truthful about the situation. (I'm not saying it's likely or intentional but the list is incomplete if we don't include it)

The ones I think we can maybe test for are #2 and #3.

Could we get @George Braly some samples of the fuel from both the aircraft tanks as well as the fuel station, some of the 'stripped' paint, and maybe some paint chips or chunks that have not yet been softened?

[gabez]

9 minutes ago, wombat said:

Between @larryband the OP @gabez we have two people that claim that within a week of adding G100UL to their tank they've had paint peeling.

A couple of ideas on what could be happening:

1. Coincidence that these things just happened to occur shortly after a fuel switch but are unrelated.
2. The fuel as designed has a problem.
3. The fuel has been contaminated either inadvertently or intentionally.
4. The reporters are not being truthful about the situation. (I'm not saying it's likely or intentional but the list is incomplete if we don't include it)

The ones I think we can maybe test for are #2 and #3.

Could we get @George Braly some samples of the fuel from both the aircraft tanks as well as the fuel station, some of the 'stripped' paint, and maybe some paint chips or chunks that have not yet been softened?

the mechanic hasn't had the chance to pull my plane in. I will see what I can do. 

Edited Monday at 01:24 PM by gabez

[GeeBee]

Still have not heard how old is the tank sealant in these aircraft.

 

[Shiroyuki]

3 hours ago, wombat said:

Between @larryband the OP @gabez we have two people that claim that within a week of adding G100UL to their tank they've had paint peeling.

A couple of ideas on what could be happening:

1. Coincidence that these things just happened to occur shortly after a fuel switch but are unrelated.
2. The fuel as designed has a problem.
3. The fuel has been contaminated either inadvertently or intentionally.
4. The reporters are not being truthful about the situation. (I'm not saying it's likely or intentional but the list is incomplete if we don't include it)

The ones I think we can maybe test for are #2 and #3.

Could we get @George Braly some samples of the fuel from both the aircraft tanks as well as the fuel station, some of the 'stripped' paint, and maybe some paint chips or chunks that have not yet been softened?

As G100UL becomes more readily avalible, more report of such incident will occur if this fuel indeed strip paints and cause damage to tank sealant.

Honestly even if it does, that's fine. If G100UL is indeed damaging to old tank sealent or paint, it could be mitigated in the future with compatible paint and sealant. Eventually lead need to go away.

What's not good is claiming the fuel is 100% compatible with current aircraft and no effect or damage on exist fleet, when the fuel actually is. There should be a warning in the STC or at fuel distributor alerting owners such fuel MIGHT cause paint issue and tank leak. Then the owners can decide for their own good if they want to risk it or not.

It's like a medicine, when you get the med pharmacy will tell you all the possible side effect the drug will cause, and you accepts such risk when taking the med. It only become problematic when some drugs claim they have no effect on health then people get sick or die because of it.

It's also similar to the cancerogenic group published by IARC. Group 2 is probably and possibly cancerogenic, but they are still listed their even though more reserach is needed. It would be a good warning.

I'm not saying G100UL actually caused these issue, obviously more investigation is needed, but it would be a good start telling mooney owners this fuel could potentially cause issue. After all a 10k strip and reseal and 30k for a paint job is a lot of money comparing the value of some short body mooneys.

[Immelman]

1 hour ago, GeeBee said:

Still have not heard how old is the tank sealant in these aircraft.

 

My sealant is still original 1966 and has held up remarkably well. Every few years I'll get a seep and patch it, and that's worked okay. Does the age of the sealant have anything to do with G100UL? I'm not well versed on what changes have been made to sealant since then.

[Fly Boomer]

4 minutes ago, Shiroyuki said:

There should be a warning in the STC or at fuel distributor alerting owners such fuel MIGHT cause paint issue and tank leak.

 

Also, I heard it can make your hair fall out, and causes flat feet.

[Shiroyuki]

13 minutes ago, Fly Boomer said:

 

Also, I heard it can make your hair fall out, and causes flat feet.

Yes, I love drinking fuel.

[EricJ]

3 hours ago, wombat said:

Could we get @George Braly some samples of the fuel from both the aircraft tanks as well as the fuel station, some of the 'stripped' paint, and maybe some paint chips or chunks that have not yet been softened?

The tests should be done by somebody else, not the fuel vendor.   You won't be able to rely on the results when there is conflict of interest.

[Marc_B]

@George Braly out of curiosity, what is the percentage of xylene and toluene in G100UL for comparison. The Kb value (solvent “aggressiveness”) for xylene is lower (98 vs 105) compared to toluene, but the evaporation time is over three times longer. Curious if this makes a difference in paint staining or issues…dwell time vs solvent “strength” vs concentration?

edit: according to the G100UL SDS there’s up to 40% Xylene. 

Certainly understand fuel containing solvents, but many use 100LL to clean painted areas (i.e. soot/lead/oil on belly). Trying to understand the refueling hygiene required with G100UL vs typical practice with 100LL; especially wrt not wiping or smearing spilled G100UL. 

Edited Tuesday at 08:27 PM by Marc_B
Added G100UL SDS info

[IvanP]

1 hour ago, Shiroyuki said:

As G100UL becomes more readily avalible, more report of such incident will occur if this fuel indeed strip paints and cause damage to tank sealant.

Honestly even if it does, that's fine. If G100UL is indeed damaging to old tank sealent or paint, it could be mitigated in the future with compatible paint and sealant. Eventually lead need to go away.

I would beg to differ. It is most definitely not fine if fuel that is billed as a safe drop-in replacement of the existing fuel would cause damage to tanks and paint, potentially forcing unsuspecting owwners to pay tens of thousands of dollars for repairs.

While we arguably do not have enough data to reach any definitive conclusions on this issue, the concern I have is that we may not have a choice if the govt will force the switch to G100UL before these issues can be conclusively resolved. Yes, the damage can arguably be mitigated if you throw enough money at it, but I would prefer it not to be my money, i.e, having to pay for resealing of tanks and repainting of plane because I am forced to use a fuel that is too aggressive on sealant and paint. 

[MikeOH]

@IvanP

You nailed it!

I'm going to be beyond pissed off if I'm forced to use G100UL and then end up having to spend $10K or more to strip and reseal my tanks!  Being told "well, they were going to need it anyway" in no way will ameliorate my anger.

[Pinecone]

On 12/16/2024 at 12:09 PM, EricJ said:

The tests should be done by somebody else, not the fuel vendor.   You won't be able to rely on the results when there is conflict of interest.

And who is going to contract and pay for this testing?