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."

@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.

@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??

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.

I think this is one of the issues of pursuing an unleaded fuel independently outside of working with current airframe and engine manufacturers. It also highlights that in order to go alone, GAMI should really be freely sharing their data and test findings. The only stamp of approval for G100UL has been from the company selling it and the "court of public opinion" in terms of a fan base. So if detrimental things happen, fingers are pointed not based on fact but based on assumptions. The only people who know the data and what data was actually obtained, are the ones not openly sharing it. And since this is outside of a third party consortium there are no other airframe and engine groups to review, audit, and approve the testing data and results/conclusions. "If you want to go fast, go alone. If you want to go far, go together."

@GeeBee The other thing to note is that if there wasn’t a mandate to move away from 100LL, and G100UL wasn’t being used in California to attempt to escalate a ban on 100LL, I personally wouldn’t be commenting on these threads at all but rather just wouldn’t purchase the STC or fuel till it was proven reliable, safe, and any untoward effects were shown. Given the political mandate and currently no other UL option, I have a vested interest in a fully vetted and safe fuel.

I already reached out and he responded that he was out of the country for business over the holidays and wanted to have some owners on both side of the fence tour the facility. I am planning on taking him up on the offer if we can work out the details But I feel the benefit of discussing things on the forum is that we all can learn and discuss.

@GeeBee not arguing, I'm asking... It's one thing to have swelling that is part of the spec. It's another thing to have swelling where it's either not part of the spec or more swelling than spec. But we see of a lot of generalizations that "it's known" or "don't worry about it" as well as "holy crap unleaded affects this WAY different than 100LL." What we don't see a lot of are specific tests with specific airframes showing this is either within spec or outside of spec. So what we're left with is conjecture on either side and irrefutable for both sides. We need to see testing data from GAMI for more than just less detonation compared to UL94 on the test stand. As another aside, over on BT there was a previous military publication suggesting harmful effects from cycling high and low aromatics...we've yet to see if there are detrimental effects from patchy coverage of an unleaded fuel that's routinely cycled between 100LL and high aromatic UL fuel. I'm not aware of any such testing being done either...has this been tested by GAMI?

Is that how the Mooney fuel system works?

Continental's response to what fuels are safe for my engine: Does anyone know what the testing process was to approve the IO-360-AF with the FAA? i.e. what materials and elastomer testing was required by the FAA? Perhaps there already IS a benchmark for testing to approve equipment for alternative fuel use? Also, what was the testing process for Peterson with STC approval with the FAA? Was this at all similar to the process that GAMI has gone though or much different??

The main issue I have with this, is that there have been instances of damage to aircraft and potential damage to elastomers used in the aircraft. You'd think for an STC that the manufacturer would be responsible for proving that if modifications were or were not needed and be able to show open and clear data as such regarding what was tested and what wasn't. GAMI (or any potential fuel manufacturer) is the one that should be responsible for convincing me as the owner and operator that their product is safe. Continental and Lycoming have a list of authorized fuels by engine model (doesn't include high octane UL). I'm not sure which o-rings, hoses, and seals could potentially be at risk. It's not OUR job to be test pilots with our aircraft, paint, tank seals, and potentially our own lives and the public, solely because we care to remove lead from the environment. FACT: GA pollution is not only just lead. Just saying that "we know about that and we're okay with it" or "don't worry about your paint because that's cosmetic and doesn't matter to us" or "you have wet wings and they leak from time to time so it's not our fault if that's accelerated"...doesn't address the concern. FROM GAMI's G100UL ICA: "When replacing seals or O-rings in the fuel systems of aircraft or engines operating on G100UL Avgas replace Buna N or nitrile fuel system components with components made of silicone or fluoropolymer elastomers (such as Viton) where practical. When replacing flexible fuel hose assemblies utilize tetrafluoroethylene (Teflon) lined hose assemblies per TSO C53a or TSO C140 where practical." If my Airframe and my Engine is on your STC AML...you should be able to tell me exactly which parts that I need to replace to run your fuel safely. It is your job to prove safety, not mine. You are the STC holder that has shown your data to the FAA, and you haven't shown this to me. So if your product is ultimately unsafe or leads to unairworthy condition, the liability is yours. I cringe when I hear "we have to stop loving the problem" because the follow up is we need to start loving a new problem.

Sounds like the birth of an AD.

I have a flapper on my filler neck and many times fuel has splashed off it onto the wing if the pressure of the pump is high. I’ve never had any damage to the paint and never had any staining from this even when I didn't have a rag available and just let air dry. The paint around my wing is decent but definitely not perfect and some paint chips. Prior to getting my tanks resealed in 2022 I had a few seeps and runs that had blue staining down the seam under the wing. I had them resealed at Weep No More and Paul was easily able to clean the stains off and now you can’t even tell where these used to be. This appears to be a MUCH different process

I think that the numbers that @Pinecone may be trying to quote is the often cited estimate that 80% of the piston fleet could run on a lower octane fuel, but the 20% that can't use 80% of the 100LL. For what it's worth, Swift's website reports 100R designed to replace 100% of the US and global piston aircraft fleet in their FAQ. But I do not have any knowledge if designed is synonymous with usable. Fuel is bad for health. I'd not recommend bathing in it, drinking it, or using it to wash your hands. Lead is also like radiation...impossible to have ZERO. The use of 100LL is tiny in comparison to the use of Jet A and is infintesimal compared to the use of mogas. But the fact of the matter is that use of the "lead argument" has been more effective for those who would like to close airports or stifle GA. It's also been used within our own industry to push environmental boards further towards eliminating 100LL. But this isn't a litigation about health, and there are a sizeable number of people in GA community who feel that just accepting unleaded "pulls the rug out" under the litigation to close airports. Unfortunately we'll find out soon enough that it wasn't only about the lead in the first place. Do you think that GAMI is weighing in on the argument that G100UL is "commercially available in California" and 100LL should be banned? How does GAMI feel that the "consent judgement" should be ruled? Is this the truly best move for GA? I'd wager that many of the airports looking to move to unleaded fuel are the ones under attack for closure... https://www.energy.gov/energysaver/transportation-fuels https://www.eia.gov/todayinenergy/detail.php?id=62443

Makes sense for use of FD with airlines. Even when hand flying there is usually a flight path that you’re likely wanting to follow. Big difference with GA is that there are more times where I’m on a flight, but not really a path.

Why did the fuel industry use toluene (for lots of different fuels) and why did GAMI feel it was better option for them to use xylene? Would be interesting to learn how the fuel was developed…did GAMI trial toluene and various combinations of xylene and toluene? From what I understand, toluene has higher octane rating and better performance as octane booster. It is more volatile/higher evaporation rate so better cold start. Plus it is commonly used in unleaded high octane race fuel. Xylene has a longer evaporation time/less volatile and is slightly less aggressive solvent but lower octane rating. But I think the difference is much higher concentration of xylene and I’m curious how composition of G100UL changes as certain components evaporate increasing concentration of solvents with longer evaporation time with xylene. Of course if you listen to Swift, their finger points at the meta-toluidine and aromatic amines as the reason for issues with paint and elastomers. When mixing 100LL depending on the quality of the lead refining they were limited in total amount of lead so they’d test octane in the knock lab and add more toluene to meet spec to prevent knocking. So there was potentially less toluene than the 29% noted by Mr. Braly, but it varied. What concentration of toluene would lead to damage to paint and elastomers that have been noted vs the concentration of xylene vs the composition of G100UL. Would love to just sit down with Mr. Braly and an industry chemical engineer specializing in fuel over beers for a master class. Seems like a matter of cons for each choice and some with lesser and some with greater problems. Of course these are the things you wish key players shared info and actually worked together. But oil and gas is such a giant industry and everyone has a vested self interest and the 100LL segment is tiny but with a good profit margin as far as fuels go. Industry doesn’t change quick as it’s not in their best interest so it’s politically motivated rather than self directed. Chess.

@William Munney check ebay and speak with your avionics shop for pricing/selling assistance. I sold my ESI500 on ebay for $2K, but my shop took my King servos and control head in trade.

It would be helpful if we knew: 1) what materials were tested by GAMI and how; what was test protocol and what was fuel/aromatic spec for testing 2) what materials were shown to have swelling, deterioration or deformity with testing; which sealants have been tested and how; are there certain airframes or sealing processes that are more susceptible to G100UL 3) what is the fuel/hydrocarbon spec for the California G100UL 4) have any tests been run on fuel with aircraft damage to test for contamination of fuel 5) how does GAMI explain the cases seen with obvious paint damage that appears to be escalated by use of G100UL 6) are changes planned for the Instructions for Continued Airworthiness 7) has testing been done with ceramic coating, wax, varying ages of paint, etc to say what might be protective/preventative of staining/damage and to what degree It seems that Mr Braly is somewhat open to engaging with answers and explanations. Let’s hope it stays that way vs the idea that if you don’t like it then don’t buy it…until you HAVE to because there’s no longer an option. Also keep in mind that we don’t know what the exact composition of G100UL is, and there may be some variation in fuel tested in the lab years ago and fuel sold at the pump recently. The SDS shows 20-40% xylene and that’s a pretty big variation. Were the extremes of the conforming “recipe” tested or perhaps maybe a less “aggressive” mix? It will be interesting to see what the “best” future mix is for octane…oxygenates, aromatics, metallics, or a combination?? Certainly use of lead allowed lower amounts of aromatics to meet 100/130 spec and I believe Mr. Braly has said that G100UL supercharge octane rating is much higher, 145+? That’s from aromatics that are known to cause issues with elastomers. But if I’m going to either choose to use, or have to use, I want to do this in the safest most appropriate way. Instructions to change these specific o-rings for my particular airframe and reseal a tank prior to safe use is one thing. Finding out after the fact with damage is completely another.

Happy holidays! ps. Do you know where I can get the STC to run coal in my, er a Mooney? (Asking for a friend)

Don, do you have a rough idea of how many gallons of 100LL vs how many gallons of G100UL in each side? curious the same for @gabez and @larryb

There are comments about o-rings and hoses in the G100UL ICA, but it comments when replacing as practical, rather than ensure your equipment does not have.... HANDLING, SERVICE AND MAINTENANCE OF AIRCRAFT AND ENGINES WITH G100UL Avgas Storage and handling G100UL Avgas is the same as for other aviation grade fuels. All precautions and warnings that apply to 100LL also apply to G100UL. When replacing seals or O-rings in the fuel systems of aircraft or engines operating on G100UL Avgas replace Buna N or nitrile fuel system components with components made of silicone or fluoropolymer elastomers (such as Viton) where practical. When replacing flexible fuel hose assemblies utilize tetrafluoroethylene (Teflon) lined hose assemblies per TSO C53a or TSO C140 where practical. https://www.g100ul.com/dl/GAMI G100UL ICA Rev C.pdf

Out of curiosity, does anyone know how the underside of the AOPA Baron wings are fairing? I know the original issue was reported as fuel bladder leaks but asking if since then have noted any damage to the paint under the wing? Seems like there would be a case control there as well as both bladders were leaking…one 100LL and the other G100UL.

@PT20J thanks for the page. I know they describe the mode but was trying to find if Garmin ever described a flow or stepwise. Makes sense when using FD show a wings level 7 deg climb. Honestly I don’t think I usually pay much attention to the FD right off the deck. Of course I’m not usually taking off in LIFR and that’s probably where it’s most helpful…if it’s remembered/used as pointed out.

Have not heard line up and hold. Typically I’ve heard “Hold Short Runway…” Could see why confusing. I think it would warrant a call to the tower in question to discuss phraseology with supervisor. Taxi into position and hold = line up and wait.

The issue from my perspective is the potential for damage to components has not been publicized and the exact components that don’t play nice with G100UL aren’t listed. Yet airframes with these components are included in the AML. Makes it hard to say who should be concerned and who shouldn’t. I understand that the fuel works in engines. But don’t understand how the AML included every airframe that has components not compatible but yet no STC instructions for ICA and preparation for use??