G100UL - fuel leak

[exM20K]

15 hours ago, MikeOH said:

Depends on your definition of captive.

Lead has around a 1 month half-life in blood, 2 months in soft tissue, 2-3 years in the brain, and 20-30 years in bone.

Other interesting info:
1) OSHA PEL 8-hour shift atmospheric workplace limits are <50 ug/cubic meter.
2) SoCal AQMD ran a study at Whiteman airport (KWHP) with the following results (note these data are in nano-grams/m^3, 1000 less than micro-grams/m^3!):

 

 

 

“These levels were also within the typical range of
concentrations measured Basin-wide as part of MATES V (Figure 2)”

Q.E.D.  

-dan

 

[exM20K]

On 12/27/2024 at 11:11 AM, GeeBee said:

Yeah, it's being held captive in you liver and brain cells.

Don’t forget the kidney.  As discussed in another thread, physical lead is safe to handle with proper hygiene.  It cannot be absorbed transdermally.  Lead in solution as in 100LL can.

-dan

[ragedracer1977]

My confidence level decreases with every non-answer Braly gives.

[Marc_B]

3 hours ago, EricJ said:

I wound up down a bit of a rabbit hole yesterday and inadvertently discovered that o-ring swelling was researched quit a bit in the context of the Sustainable Aviation Fuel program

I'm not sure if I started to jump down your rabbit hole or was sucked down it @EricJ.  But both were interesting papers.  Some of the points I found interesting (for those TLDR) (from Faulhaber, Conor J., "Elastomer O-Ring Seal Swell Measurements for Sustainable Aviation Fuel Material Compatibility" (2022). Honors Theses. 384.  Comments in blue my own.)

The blend limit set to provide o-ring swelling was established partly to maintain aromatic content at approximately 8%v in any fuel blend containing SAF. Interesting that this is much lower aromatic content than either 100LL or G100UL

As mentioned, higher aromatic content, especially those with less and/or smaller alkyl branches, play a large role in the absorption of fuel [18], while nalkanes tend to contribute more to the extraction process [19].  There was a chart showing the various agents tested and seal swell at 8%v.  Aromatics used in G100UL in general showed increased swell percentage than aromatics used in 100LL, and the total aromatic content in G100UL is higher than 100LL, so it's no surprise that G100UL in general would result in higher percentage swell based on their testing.

The o-ring material has a significant influence on how the seal absorbs fuel. Aviation o-rings are typically composed of one of three materials: acrylonitrile-butadiene (nitrile rubber), fluorisilicone, and fluorocarbon. Of these materials, nitrile rubber seal swell is significantly more sensitive to compositional variance in jet fuel [19]–[21], [25], [26]. The higher swell consistency associated with fluorosilicone and fluorocarbon o-rings does not simply solve the material compatibility issue with SAF, however, because nitrile rubber offers considerable performance advantages in low-temperature scenarios [27].

Currently, there is no certified ASTM test method associated with measuring o-ring seal swell.

Material compatibility with elastomer o-rings in fuel systems is currently one of the main limiting factors keeping SAF from 100% drop-in compatibility with existing fuel systems.

This study also investigated the linear blending rule, albeit only at several concentrations up to 15%v in C-1. Two common elastomers used in aviation o-ring seals, fluorosilicone and nitrile rubber, were studied for blending and showed general adherence to the proposed rule, though fluorosilicone o-ring swell appeared more difficult to predict.

------------------------

Given a variation in swell, temperature range, and tear strength...I don't think that the various O-rings are simply interchangeable.  So I'm not sure one could just decide to switch out all your o-rings and expect all works out perfectly.  Not sure if there are service documents showing applicability of o-rings in Mooney applications?  i.e. what would one reference to see if approved/safe to change material used?

NITRILE: Due to its excellent resistance to petroleum products, and its ability to be compounded for service over a temperature range of -35°C to +120°C (-30°F to +250°F), Nitrile /NBR is the most widely used elastomer in the seal industry today. Also, many military rubber specifications for fuel and oil-resistant O-rings require nitrile-based compounds.  Depending on the grade the working temperature range is considered to be -26°C to +205°/230°C (-15°F to +400°/440°F). But for short working periods it will take even higher temperatures. It should be mentioned that to obtain good resistance to low temperature, it is often necessary to sacrifice some high temperature resistance. Nitrile compounds are superior to most elastomers with regard to compression set, tear, and abrasion resistance. Nitrile compounds do not possess good resistance to ozone, sunlight, or weather. They should not be stored near electric motors or other ozone generating equipment. 

FVMQ (Fluorosilicone): combines the good high- and low-temperature properties of silicone with limited fuel and oil resistance.  Primary uses of fluorosilicone O-rings are in fuel systems at temperatures up to +177°C (+350°F) and in applications where the dry-heat resistance of silicone O-rings are required. Fluorosilicone O-rings may also be exposed to petroleum based oils and/or hydrocarbon fuels. In some fuels and oils; however, the high temperature limit in the fluid list is more conservative because fluid temperatures approaching 200°C (390°F) may degrade the fluid, producing acids which attack fluorosilicone O-rings. For low temperature applications, fluorosilicone O-rings seal at temperatures as low as -73°C (-100°F).  Due to relatively low tear strength, high friction and limited abrasion resistance of these materials, they are generally recommended for static applications only. Fluorosilicones with high tear strength are also available. Some of these compounds exhibit improved resistance to compression set. Many fluorosilicone compounds have a higher than normal shrinkage rate so production molds for fluorosilicone products are often different from molds for nitrile.

FPM, Viton: Due to its wide range of temperature range, chemical compatibility, low compression set, and excellent aging characteristics, fluorocarbonelastomers (FPM, Viton®) have grown to major importance in the seal industry.  Depending on the grade the working temperature range is considered to be -26°C to +205°/230°C (-15°F to +400°/440°F). But for short working periods it will take even higher temperatures.

[Marc_B]

@ragedracer1977 I had a hard time of reading between the lines of what Mr. Braly was trying to suggest on BT with his insinuation and open ended questions...I would have much rather had an explanation from him with clear and concise data points.  Really unsure what his post was supposed to imply??

[George Braly]

1 hour ago, Marc_B said:

@ragedracer1977 I had a hard time of reading between the lines of what Mr. Braly was trying to suggest on BT with his insinuation and open ended questions...I would have much rather had an explanation from him with clear and concise data points.  Really unsure what his post was supposed to imply??

Marc,

I apologize if my posts up on BT were unclear.   I will try to go back there and clear that up.   It has been a bit difficult as I have been out of the country for the last 10 days, and am just now getting back to a real desk where I can spend the time to read the numerous postings. 

The following are hard facts:

For the last forty-four years - - various OEMs have been recommending the replacement of nitrile / buna N  fuel system components with "modern"  fluorosilicone type O-rings, gaskets, seals and other fuel wetted components in our aircraft. 

There is a 1980 (yes,  44 years ago)  Allied Signal / Bendix service document that states exactly that.   It is not a mere coincidence that was happening in 1980.  The "timing" of that Bendix service document is consistent with the advent / roll-out of 100LL (which first began about 10 years earlier).  As mentioned elsewhere, that fuel often (nearly always) contained significant levels of toluene.   A whole new small maintenance business was created to reseal Mooney fuel tanks (example:  Weep No More, in Minn.) 

A C-421 owner on BT reported that when he recently ordered new seals and O-rings from Textron, they were Viton and fluorosilicone - -  not nitrile.   

When GAMI was first drafting the ICAs to go with the G100UL Avgas STC,  the Wichita Certification engineers forwarded that draft (as they are supposed to do) to the FAA  "AEG" group (now AED) for review.  The AEG group is a subdivision of Flight Standards that is responsible for maintenance instructions.  The AEG group actually asked GAMI to make the language in the ICAs related to the replacement of older style O-rings, hoses, and gaskets, "more explicit"  or "stronger" , as the AEG group had been trying to get the industry and the mechanics to stop using nitrile type O-rings and seals as replacements - - for decades.  

Again, if you have any specific questions, please post them up or send them to me directly.  I will try to provide data to support the answers.  

Also, see the recent / ongoing testing, reflected in the photograph, below. 

George

 

Please feel free to ask me any explicit questions you want for which you do not believe you have received satisfactory answers.   

 

 

 

 

 

[Marc_B]

@George Braly out of curiosity, do you have a link to the Allied Signal/Bendix service document you're referring to (I'm not familiar)?  I'm also curious if the G100UL fuel you show tested in the picture is from the same batch and composition that was sold in California?  If it was different batch, how did the Baton Rouge sample differ from KRHV sample (how did the overall aromatic percentage differ)?  Has GAMI tested this fuel to see if there were any contaminants or issues in the field?

The G100UL SDS is pretty broad; how much does one batch of G100UL composition vary from another?

Also what was the thought of "high toluene" vs 15% toluene and what was the amount of toluene in the "high" sample?

Thanks for your help to understand this all.

[Marc_B]

While jumping though the rabbit hole of trying to make sense of o-rings, I found this publication from Lockheed Martin that was a special issue on o-rings (from '96 FWIW).  Most GA aircraft owners are not in a position that they can make a determination of what hoses, seals, o-rings, sealant, etc are used and why.  If G100UL affects the equipment commonly found in aircraft and engines listed in the G100UL AML, then it is incumbent on GAMI to specify which equipment needs to be replaced, updated, or addressed prior to implementation of an alternative fuel.

@George Braly I don't think that it's prudent or acceptable to just say it's up to the owner, or its up to the A&P filling out the 337, or it's up to someone else to make that determination.  With a new fuel that you're marketing, I feel it's incumbent on GAMI to test and develop standards.  Where would I even start to find which composition and age of material is not compatible or potentially detrimental with an alternative fuel??  Its one thing to defer to standard aviation and manufacturer recommendations.  It's completely different for a fuel to have to have specific requirements outside of what may still be standard practice, if there is potential for detrimental effects (even if cosmetic and especially if safety of flight).

https://www.lockheedmartin.com/content/dam/lockheed-martin/aero/documents/sustainment/csc/service-news/sn-mag-v21-v30/V23N1.pdf

"This entire issue of Service News magazine is devoted to O-rings. It seems ironic that a simple, molded, doughnutshaped part made of a single material could warrant so much attention. The selection of a specific O-ring is based on a variety of factors, including fluid media resistance, temperature range, hardness, durability, gland size, static or dynamic application, etc. There have been some significant technological advances in materials in recent history, but sometimes the best solution is still the simplest. While the use of fluorosilicone and fluorocarbon materials has become more widespread, the best choice often continues to be a basic nitrile butadiene (or Buna N) elastomer. Unfortunately, the nitrile compounds require age control.
"Why is basic nitrile a better choice than a fluorosilicone or fluorocarbon compound which doesn’t require age control? The tradeoff for fluorocarbon is higher cost and decreased low-temperature resistance; for fluorosilicone it is high cost and decreased durability. The cost factor is influenced by raw materials costs, processing costs, shrinkage control, and other considerations."

[EricJ]

As previously mentioned, the primary materials used for o-rings are Buna-N (aka nitrile), fluourosilicone (the blue stuff we use on fuel caps), and fluorocarbon (aka viton).  They are all different, and each has strengths and weaknesses, and, as also previously mentioned, some OEM applications still specify nitrile because it has the overall qualities preferred by the manufacturer.   Also, many existing aircraft still have parts and materials that, while potential locations for update, are still populated with nitrile.   This is common in GA, and as previously stated by myself and others, many A&Ps use IPCs and other guidance that still specify nitrile due to a conservative regulatory approach and/or a conservative safety approach.   It's hard to argue with either, even if we have personal viewpoints that differ.   I still respect any A&P that takes a more conservative approach than I do on a position from a regulatory or safety perspective.   I have a more difficult time with a vendor insisting that accomodations be made for their product that have a reasonable probability of compromising safety.

It is true that many o-ring and hose applications have been updated to fluorosilicone (for static applications) and viton, but not all have.   Additionally, many hoses have been updated to teflon-core, but not all.   I don't personally think the GA fleet should become an experiment in finding out where they all are by latent failures due to fuel reformulation.   e.g., I don't think the hoses from the fuel pickup to the hardline in the wing root of most mooneys has a teflon core. 

FWIW, some of us learned some of this stuff from A&P school, e.g., what material generally goes where, differences in temperature and abrasion sensitivies, etc., but there are a lot of details that are left to the materials scientists and engineers.   It's been interesting to see additional information in other sources like the Parker manual, cited papers, etc.  When an OEM engineer specifies nitrile in a parts catalog, it's reasonable to be reluctant to change that without other guidance from the manufacturer.   If somebody orders o-rings from a manufacturer and gets nitrile (as mentioned), it's reasonable to be reluctant to put something else in, and it's also then reasonable to be reluctant to use fuel that may (or could be expected to) cause problems with those seals.

[Fly Boomer]

8 hours ago, EricJ said:

A&Ps use IPCs and other guidance that still specify nitrile due to a conservative regulatory approach and/or a conservative safety approach

More likely historical artifact.  The IPCs for my airplane have not been updated in the last 25 years and, absent some life-threatening error, won't be.  Regardless of new  developments in materials.

[tony]

2 hours ago, Fly Boomer said:

More likely historical artifact.  The IPCs for my airplane have not been updated in the last 25 years and, absent some life-threatening error, won't be.  Regardless of new  developments in materials.

That's why there are STCs.  To put something on your certified airplane, you need paper to say its OK.  

[takair]

@George Braly, with all this talk of sealants and orings, my mind jumps to the internal regulating diaphragms in our fuel injection systems.  I can’t find the material type in my limited reference material.  Was GAMI able to determine this or do testing to ensure no long term degradation of performance of these diaphragms?

[Fly Boomer]

3 hours ago, tony said:

That's why there are STCs.  To put something on your certified airplane, you need paper to say its OK.  

If you are concerned about putting phony parts on your certified airplane, you should stick to nitrile o-rings.

[gabez]

top of my wings...permanently stained by G100. Unfortunately my plane hasn't hit the shop yet, they have been super busy and they don't have space in the hanger yet. I hope this coming week. 

The pain peeling has gone a bit worst. The leak seems to be confined in the Copilot Aux, however a paint buy a rivet in the co-aux popped as well as the paint on a rivet in the pilot main. 

[PT20J]

2 hours ago, takair said:

@George Braly, with all this talk of sealants and orings, my mind jumps to the internal regulating diaphragms in our fuel injection systems.  I can’t find the material type in my limited reference material.  Was GAMI able to determine this or do testing to ensure no long term degradation of performance of these diaphragms?

Bendix changed RSA fuel injection rubber components to fluorosilicone in 1976.

https://precisionairmotive.com/wp-content/uploads/2019/06/RS-76-Rev1.pdf

[PT20J]

The only nitrile o-rings I could find specified for my fuel system in my 1994 M20J are the o-rings at the input and output boss fittings on the Lycoming and Weldon fuel pumps. Everything else is Viton (sump drains, fuel selector, gascolator) or fluorosilicone (fuel injection).  The design of a boss fitting should constrain the o-ring under compression more than other o-ring applications and expose it to less contact with the fuel and I doubt swelling is an issue.

[Pinecone]

16 hours ago, George Braly said:

Also, see the recent / ongoing testing, reflected in the photograph, below. 

George

 

Please feel free to ask me any explicit questions you want for which you do not believe you have received satisfactory answers.   

 

 

 

 

 

The "test" in the video, and seemingly the issue with the airplanes reported seems to be where the area is rewetted, but allowed to evaporate.  Like a minor fuel leak.

It seems that some component of G100UL has a lower evaporation rate and becomes concentrated and that causes the paint issues.

And, to me, it looks like it may be attacking the primer.

[MikeOH]

2 hours ago, PT20J said:

Bendix changed RSA fuel injection rubber components to fluorosilicone in 1976.

https://precisionairmotive.com/wp-content/uploads/2019/06/RS-76-Rev1.pdf

Interesting that, per this table, fluorosilicone is rated 'fair'; only Viton (and Kalrez) is 'satisfactory' for toluene:

 

[PT20J]

24 minutes ago, MikeOH said:

Interesting that, per this table, fluorosilicone is rated 'fair'; only Viton (and Kalrez) is 'satisfactory' for toluene:

 

I guess the 100LL should have destroyed my servo by now.

 

[MikeOH]

Just now, PT20J said:

I guess the 100LL should have destroyed my servo by now.

 

My point was: Viton would have been a better choice when they changed materials.  Maybe Viton wasn't available in 1976? IDK

[EricJ]

14 minutes ago, MikeOH said:

My point was: Viton would have been a better choice when they changed materials.  Maybe Viton wasn't available in 1976? IDK

Swelling isn't the only parameter that is of concern.   Abrasion resistance, thermal properties, etc.,  also matter as well as cost, so there is no one material that fits all applications.   Nitrile is still specified in many applications, so it's unlikely they'll be purged from use in GA any time soon.

We haven't even talked about hoses much, which can have similar issues and are often nitrile for fuel.

[Marc_B]

3 hours ago, PT20J said:

The only nitrile o-rings I could find specified for my fuel system in my 1994 M20J

Out of curiosity, would this be applicable to all Mooneys past a certain year?  Are you just referencing the IPC and looking at PN for o-rings?

[PT20J]

7 minutes ago, Marc_B said:

Out of curiosity, would this be applicable to all Mooneys past a certain year?  Are you just referencing the IPC and looking at PN for o-rings?

References:

Weldon pump: M20J IPC

Lycoming pump: Lycoming IO-360 IPC

Fuel drains: SAF-AIR website (I don't know what OEM parts used and Curtiss doesn't specify the internal o-ring because it is not field replaceable; the Curtiss static o-ring that seals against the wing is nitrile.,

Fuel valve and gascolator: manufacturer's drawings.

 

 

[PT20J]

42 minutes ago, EricJ said:

Swelling isn't the only parameter that is of concern.   Abrasion resistance, thermal properties, etc.,  also matter as well as cost, so there is no one material that fits all applications.   Nitrile is still specified in many applications, so it's unlikely they'll be purged from use in GA any time soon.

We haven't even talked about hoses much, which can have similar issues and are often nitrile for fuel.

See, this is the problem when a bunch of amateurs (me included) try to pretend to be materials engineers. Aviation fuels have always been pretty nasty stuff. At some point we have to assume that the engineers and the FAA know something about what they are doing. 

I looked into hoses a few days ago. It's hard to tell the exact composition because the Mil Specs don't specify the material except generically as "synthetic rubber compounded with the necessary ingredients to meet the requirements of this specification" Interestingly, the hoses used for the short connection between the fuel tank outlets and the aluminum fuel line that goes to the fuel selector are allowed by specification to swell 85% when exposed to "fuel." This hose is designed specifically to be terminated in beaded connections secured with hose clamps. 

The o-ring swelling comparison in the video may not be meaningful. According to @George Braly (and I have no reason to doubt him on this) 100LL can have varying amounts of aromatics depending on the aviation alkylate used. So, we don't know if the sample had a lot or a little toluene in it. Maybe a different 100LL sample from a different refinery would behave differently. Who knows? And, does it really matter? We get whatever comes out of the FBO's pump.

Attached are the files for MIL-DTL-6000D (hose Mooney uses to attach tanks to fuel lines) and MIL-H-8794D (hose material Mooney specified for flexible fuel hoses in the engine compartment). 

MIL-DTL-6000D.PDF

MIL-H-8794D.pdf

[EricJ]

50 minutes ago, PT20J said:

The o-ring swelling comparison in the video may not be meaningful.

And it may be, especially since it shows that it exceeds the limits discussed in the Parker manual you posted as well as the papers I posted, which all show similar limits.  A visual inspection of the swelling shown in the vid is comparable to the swelling measurement methodology described in both papers.

I still think I'll rely on the guidance from the established industry rather than a lawyer taking a first stab at being a fuel formulator, but that's just me.