G100UL paint testing by YouTuber mluvara

[T. Peterson]

11 minutes ago, A64Pilot said:

I’m assuming of course that the recent issues aren’t real.

If they are I’d assume the fuel will be voluntarily withdrawn, prior to the FAA taking action.

That’s a LOT of assuming, from admittedly a non expert, heck my total knowledge of the GAMI fuel is second hand, I’ve never even seen it.

Ahhh….. understand. Your point is that all things being equal, folks will not pay a premium for G100 if 100LL is available. I completely agree.

[McMooney]

you guys can be mad but honestly i hope 100ll Is gone in the next 3 years,   hate crap that drags  on forever.  if they had bit the bullet 50 years ago we wouldn't be worried about it now.  oh my paints falling off anwyay hehe

[T. Peterson]

17 minutes ago, McMooney said:

you guys can be mad but honestly i hope 100ll Is gone in the next 3 years,   hate crap that drags  on forever.  if they had bit the bullet 50 years ago we wouldn't be worried about it now.  oh my paints falling off anwyay hehe

I’m not one bit mad. I completely respect your opinion. I just hope 100LL is here until replaced by a fuel I want, meaning offered, not forced. I further expect it to be completely vetted by time and experience. In other words, let the market drive it, not dubious science and cowardly bureaucrats.

[Ryan ORL]

It’s hard to track all the various G100UL threads but it seems like they’re all full of complaining that we need 100LL to remain available until we get a perfect replacement and then for quite a long while after that.  Some of these are even seemingly directed at George Braly for reasons I can’t fathom… they’re probably better directed at your congressman, or maybe members of the incoming administration.  
 

GAMI isn’t taking away anyone’s 100LL, but it seems crystal clear to me that it’s only a matter of time before we (the GA community) lose the battle and governments (local, state, and federal) force the issue.  Whether it ought to be that way isn’t terribly important, because that’s how it is.  We can’t even keep our airports open and financially solvent, let alone simultaneously fight a never ending battle against the environmental authorities.

It also seems likely now there’s not any silver bullet forthcoming… G100UL has the big STC paperwork hurdle and these possible paint/elastomer issues, and reportedly the (only remaining) EAGLE candidate from VP/etc isn’t able to meet the full octane requirements.  So what do we do now?  Give up and hope something else emerges?  100LL extinction is coming whether we like it or not.

I have my own concerns about G100UL based on the o-ring test and reports of leaks.  But I think it would be useful to have a sober and objective look at how serious these problems are and whether they can be overcome.  It’s highly relevant to me whether, for example, G100UL attacks and compromises even freshly sealed tanks using the sealants in wide use today, versus only older tanks with various patches, etc.  Does it affect bladders similarly?  Is the o-ring issue causing actual problems in the field and can Viton o-rings be sourced if needed?  Does it affect all types of aircraft paint, including new paint, or does it primarily affect older oxidized paint?

Yes, it would suck have to do a full tank strip/reseal just to use G100UL, but as a Mooney owner I know that’s inevitable someday anyway.  It would just be good to understand whether newer sealants are more compatible or will it just leak again in short order, etc.  Basically, if G100UL ‘wins’, what does the world look like for us?

Also, if it really is true that the EAGLE alternative is lower octane than ‘100LL’, I don’t know that a slightly better materials compatibility situation outweighs the loss of detonation margin, especially after it seems likely that the UL94 valve seat issues were octane related.

[Pinecone]

12 hours ago, A64Pilot said:

I suspect that if it’s $1 more than 100LL that very few will buy it if they can buy 100LL.

Only way it will be a success is if 100 LL isn’t available.

I would hope that before 100 LL is banned overall, that ADI will become widespread in STC’s, I would also suspect that on a Mooney to burn car gas that it might take an electric fuel pump running continuously, possibly not our current boost pump, but if 94 UL becomes widely available that it wouldn’t.

Only the high compression or turbo motors need 100, the rest of the fleet doesn’t, pretty much anything with a Carburetor doesn’t need 100, not 100% but most.

There used to be three grades of Avgas, then two, then for some reason only one.

There used to be 4 grades.

80/87 - Red

91/96 - Brown.  This was the first one to go away, driving people to 100.  My AEIO-360-B2F (180 HP)is rated for 91/96

100/130 - Green, replaced by Blue 100LL.

115/145 - Purple.  Used by airlines and military.  Still made once a year for the National Air Races

ADI is a pretty major mod to keep flying.  And adds more maintenace and having the availability of the fluid everywhere.

[Pinecone]

12 hours ago, A64Pilot said:

I suspect that if it’s $1 more than 100LL that very few will buy it if they can buy 100LL.

Only way it will be a success is if 100 LL isn’t available.

I would hope that before 100 LL is banned overall, that ADI will become widespread in STC’s, I would also suspect that on a Mooney to burn car gas that it might take an electric fuel pump running continuously, possibly not our current boost pump, but if 94 UL becomes widely available that it wouldn’t.

Only the high compression or turbo motors need 100, the rest of the fleet doesn’t, pretty much anything with a Carburetor doesn’t need 100, not 100% but most.

There used to be three grades of Avgas, then two, then for some reason only one.

There used to be 4 grades.

80/87 - Red

91/96 - Brown.  This was the first one to go away, driving people to 100.  My AEIO-360-B2F (180 HP)is rated for 91/96

100/130 - Green, replaced by Blue 100LL.

115/145 - Purple.  Used by airlines and military.  Still made once a year for the National Air Races

ADI is a pretty major mod to keep flying.  And adds more maintenace and having the availability of the fluid everywhere.

And remember, while only a small part of the fleet requires 100, they burn the vast majority of the AVGAS.

[A64Pilot]

Any STC by definition is a Major mod.

ADI is way simpler than adding say an engine monitor. I believe I could do it in a half a day, maybe a full day depending on what’s required panel wise.

You wouldn’t need the fluid available every where as one tank of ADI fluid should last several tanks of fuel. Think like DEF for Diesels, if you think you would need it, carry some extra.

But honestly don’t believe me, I’m just some guy on the internet, read these four articles and pay attention to the date they were written.

Most pretty much say the same thing of course, I read somewhere some European manufacturer is building a twin with TSIO 540’s that will come from the factory with ADI, Tecnam maybe? Not sure.

https://www.avweb.com/features/the-return-of-anti-detonation-water-injection-adi/

https://generalaviationnews.com/2012/05/22/adi-bridging-the-octane-gap/

https://www.avweb.com/ownership/video-airplains-inpulse-anti-detonation-injection/

https://www.aviationconsumer.com/uncategorized/airplains-inpulse-adi-mogas-for-big-engines/

Edited January 3 by A64Pilot

[Ryan ORL]

Assuming a G100UL-compatible sealant exists or could be found, I think I would much rather deal with potential fuel tank leaks from my decades-old tanks but be using a fuel with the proper octane, versus be forced to retrofit some kind of ADI system.  Even more stuff to fail, and when it does, it would almost inevitably be discovered at the worst possible time (high power setting on low octane fuel).

[McMooney]

i wish i had more information, my understanding of the detonation issues, is that at the absolute worst conditions 500deg cht, worse mixture possible the engine detonates when producing max hp. why couldn't I just avoid operating in detonation possible conditions?  so ex  with my io-360-a1a, couldn't i just avoid running the thing above say 28in mp when its 110degs outside ?

[EricJ]

1 hour ago, McMooney said:

i wish i had more information, my understanding of the detonation issues, is that at the absolute worst conditions 500deg cht, worse mixture possible the engine detonates when producing max hp. why couldn't I just avoid operating in detonation possible conditions?  so ex  with my io-360-a1a, couldn't i just avoid running the thing above say 28in mp when its 110degs outside ?

Yes.    There's a fair amount of controversy around how practical it is to have to avoid detonation, especially with a naturally-aspirated engine.  I don't think it's anything to get paranoid over, myself.   If it were a huge problem there'd be a long history of many airplanes suffering detonation damage, but it appears to be rare and usually due to unexpected or extreme conditions, as you mention.   That said, it does and can happen, so it's worth paying attention.

[Ryan ORL]

It isn't particularly common with 100LL but if we're talking about a much lower octane fuel (UL94 or Mogas, for example), it obviously becomes a much bigger concern at a much wider range of power settings.  That is why the ADI stuff... it would effectively be required for some phases of flight if we were forced to operate on UL94 or something.

edit: And I believe the consensus on the UND valve recession issues w/ UL94 come down to it being lower octane.

[MikeOH]

2 hours ago, Ryan ORL said:

edit: And I believe the consensus on the UND valve recession issues w/ UL94 come down to it being lower octane.

Can you please provide a cite for that?

History of valve recession in automobile engines was directly traceable to the lack of lead in the fuel when UL came on the market. I'd like to understand why the situation is any different for our 'stone age' engines.

[Ryan ORL]

7 hours ago, MikeOH said:

Can you please provide a cite for that?

History of valve recession in automobile engines was directly traceable to the lack of lead in the fuel when UL came on the market. I'd like to understand why the situation is any different for our 'stone age' engines.

There is a whole Savvy webinar about it with data from GAMI, but I am guessing that’s not the kind of citation you’re looking for.  The short version is their engines were timed aggressively (25 BTDC), they operated at peak EGT by school SOP, and the observed recession is believed to have been caused by micro-welding due to continuous mild detonation.  (Which GAMI replicated in an engine test cell)

As to why it’s different than cars in the 70s, one important difference is that many/most aircraft now have hardened valve seats.  Especially the Lycoming powered stuff, I guess Continental started doing that much later.

[MikeOH]

2 hours ago, Ryan ORL said:

There is a whole Savvy webinar about it with data from GAMI, but I am guessing that’s not the kind of citation you’re looking for.  The short version is their engines were timed aggressively (25 BTDC), they operated at peak EGT by school SOP, and the observed recession is believed to have been caused by micro-welding due to continuous mild detonation.  (Which GAMI replicated in an engine test cell)

As to why it’s different than cars in the 70s, one important difference is that many/most aircraft now have hardened valve seats.  Especially the Lycoming powered stuff, I guess Continental started doing that much later.

True, data from GAMI are not exactly independent verification. 25 BTDC is standard for my IO-360A1A; never considered that to be 'aggressive'.

I didn't realize that Lycoming and Continental cylinders had hardened seats.  When did that change enter production?  Do cylinder overhauls check for/install hardened seats?  I just had a cylinder overhauled and that question never came up.  I would have assumed such a change would be well documented and discussed...but I've never heard hardened seats mentioned.

[PT20J]

8 hours ago, MikeOH said:

True, data from GAMI are not exactly independent verification. 25 BTDC is standard for my IO-360A1A; never considered that to be 'aggressive'.

I didn't realize that Lycoming and Continental cylinders had hardened seats.  When did that change enter production?  Do cylinder overhauls check for/install hardened seats?  I just had a cylinder overhauled and that question never came up.  I would have assumed such a change would be well documented and discussed...but I've never heard hardened seats mentioned.

I believe Lycoming switched to hardened seats sometime in the ‘90s in preparation for future unleaded fuels. It was mentioned when I took the Lycoming factory class but I don’t have any documentation on it. If you want the details, you could call tech support and see if there is a service publication. Lycoming only puts the most commonly requested service literature on its website, so there may be something that you cannot find by searching the site. 

[MikeOH]

29 minutes ago, PT20J said:

I believe Lycoming switched to hardened seats sometime in the ‘90s in preparation for future unleaded fuels. It was mentioned when I took the Lycoming factory class but I don’t have any documentation on it. If you want the details, you could call tech support and see if there is a service publication. Lycoming only puts the most commonly requested service literature on its website, so there may be something that you cannot find by searching the site. 

Good to know, thanks.

No idea what are in my cylinders...they've all been replaced over the years.  But do overhauled cylinders routinely have their valve seat replaced?

I wonder if the UND planes had hardened valve seats, or not.

[PT20J]

1 hour ago, MikeOH said:

I wonder if the UND planes had hardened valve seats, or not.

UND replaced its entire fleet with new Archers and Seminoles in 2016, so yes.

[PT20J]

13 hours ago, Ryan ORL said:

here is a whole Savvy webinar about it with data from GAMI, but I am guessing that’s not the kind of citation you’re looking for.  The short version is their engines were timed aggressively (25 BTDC), they operated at peak EGT by school SOP, and the observed recession is believed to have been caused by micro-welding due to continuous mild detonation.  (Which GAMI replicated in an engine test cell)

But, George’s “replication” was reported to be using 94UL in a Continental IO-550. The UND issues occurred in Lycoming O-360s. 
https://www.aero-news.net/index.cfm?do=main.textpost&id=39119893-8D1D-43AE-9323-CA08523C6439

[McMooney]

I understand 94ul in an io-550 timed at 22 btdc detonates when run at peak egt and 73% power, but, isn't this the place we are explicitly instructed to not run the engines ? 

[Ryan ORL]

I would say 25 BTDC is at least moderately aggressive in the sense that Lycoming saw fit to issue a service instruction telling (asking) owners to re-time and re-mark their engines to 20 BTDC for, among other reasons, high CHTs and better detonation margins.

It really isn’t rocket science though… more spark timing obviously reduces detonation margin, and so does lower octane fuel.  This is true of basically any spark ignition engine out there, whether it’s in an airplane or not.

I screw around with the spark tables on my project Trans Am all the time… but I have knock sensors and an EFI system that’s capable of adding and removing advance as needed.  You can push the timing hard right up until you get knock (detonation), and dial it back a bit.  If you want more spark advance, the only way would be higher octane fuel… you can just dump cans of toluene in your tank if you’re so inclined.  In our primitive fixed advance system the only feedback we have is CHT.

25 degrees isn’t a ton of timing for most situations, but there are certainly going to be *some* manifold pressure/RPM/fuel flow combinations where it’s a bit too aggressive, and the evidence is that the CHTs get a bit high.  However even if you’re fine with your temps, the situation is obviously not improved by lowering the octane several full points.

It is basically definitional that your detonation margins are worse all around with lower octane fuel.  It is also obvious that it is possible to cause mild detonation at high power settings by manipulating the mixture control (I assume we’re all aware of ‘the red box’).  It follows then that the red box is larger with lower octane fuel, and importantly, may encompass more operationally useful MP/RPM/FF combinations!

Anyway this is all a sidebar… my original point stands.  Whatever leaking/sealant problems G100UL has would need to be quite severe to make running much lower octane Mogas in most of our engines the safer option, especially with timing at 25!  I would be willing to pay for more than one tank strip/reseal before I just gave up the ability to get book performance numbers without cooking my engine.

[Pinecone]

On 1/4/2025 at 10:30 AM, Ryan ORL said:

Assuming a G100UL-compatible sealant exists or could be found, 

The standard sealant used by Mooney and others seems to be fine with G100UL.  The question is about the application initially and if any patches were done and what was used.

[Pinecone]

We detonated and destroyed a cylinder in an O-470 powered C-182.  And it was running 100LL.

Less than 5 minutes after take off, running full rich.

 

[Ryan ORL]

16 minutes ago, Pinecone said:

We detonated and destroyed a cylinder in an O-470 powered C-182.  And it was running 100LL.

Less than 5 minutes after take off, running full rich.

 

What's the story there?  That shouldn't be possible without a badly mis-timed mag, a cracked plug insulator (pre-ignition) or some fuel flow blockage?

[EricJ]

1 hour ago, Pinecone said:

The standard sealant used by Mooney and others seems to be fine with G100UL.  The question is about the application initially and if any patches were done and what was used.

We don't know that.   We don't know how G100UL affects the integrity or longevity of tank sealant, but we have reason to believe it may affect it adversely.   According to the Textron letters there are multiple OEMs who have indicated tank sealing issues sufficient for Textron to be concerned enough to write the letters.

[Pinecone]

2 hours ago, Ryan ORL said:

What's the story there?  That shouldn't be possible without a badly mis-timed mag, a cracked plug insulator (pre-ignition) or some fuel flow blockage?

No idea.  Engine was fairly low time since OH.  It had an issue with glazed cylinders, most likely from improper breakin.  Rehoned the cylinders and did a new break in.

All was good.  Then took off, climbing through about 2500 feet, maybe 5 miles from airport, rough running and reduced power.  They returned and landed.

Engine was overhauled again.  No idea what happened. And only the one cylinder.