FAA To Approve Use Of 91UL Fuel In Two-Thirds Of Piston Fleet

I've wondered about this. I think you're likely correct, but I don't understand the regulatory mechanism.

My type certificate doesn't refer to the D910 (or any other) spec, and it doesn't say the fuel must contain TEL. It simply says "91/96 minimum grade aviation gasoline." At first glance, it would seem to me that any avgas which satisfied the octane requirement would be compliant with the type certificate. Why must the type certificate change?

The point is, it has to be a aviation gasoline. For now, for 100 grade, that means it has to meet D910. G100UL does not. The other products under development may do so, and would be useable without an STC. 91UL is a aviation gasoline, meeting a different ASTM spec.
 
It seems the long term thing to do is pull all 100 grade aviation fuels under D910.
It was my understanding that was the main focus for EAGLE. But people forget there has been a certified D910 unleaded avgas on the market and flying since the early 90s from an oil company in Sweden. However, while it enjoyed EASA and Lycoming approval it never got out of the EU as I remember. As I've stated when it comes to standards and specifications it gets a bit complex for reasons I've never fully understood.
 
Links to any info? I have not heard of a D910 compliant UL 100. But it might be hard, as D910 specifies a minimum lead content. :)
 
I have not heard of a D910 compliant UL 100.
Its technically a 91/96 UL but its compatible with and replaces 100LL per the available lists. They also have a 100 UL but while its meets D910 standards its short on something else so it hasn't made it to market yet as I recall. There's additional links within the link below and point to the D910 compliance on the 91/96 UL.
https://www.hjelmco.com/pages.asp?r_id=13395
 
91/96 is not 100. So, they really don't have a UL100 available.
 
91/96 is not 100. So, they really don't have a UL100 available.
Never said it was a 100 UL. Just that there was a D910 UL fuel flying for 20+ years. Regardless they have had a true 100UL since about 2006 however it causes increased fuel consumption and hasnt been released publically.
 
Its technically a 91/96 UL but its compatible with and replaces 100LL per the available lists. They also have a 100 UL but while its meets D910 standards its short on something else so it hasn't made it to market yet as I recall. There's additional links within the link below and point to the D910 compliance on the 91/96 UL.
https://www.hjelmco.com/pages.asp?r_id=13395
Is that the fuel (91UL) that is the topic of the original post in this thread? Or is there another 91UL?
 
Is that the fuel (91UL) that is the topic of the original post in this thread? Or is there another 91UL?
No. The 91/96UL I'm referring to has been available, approved, and flying in the EU since 1991 I believe. I think there is a 3rd 91UL (91/98) out there for the same length of time. Neither of which ever made it to the US and other markets.
 
Great, but the point is, it is MUCH harder to make higher octane without lead.

Not sure why 94UL is not D910 compliant, since it is 100LL without the lead.
 
If UL91 is the same price as 100LL I would use it every time.



The oil will stay cleaner longer and my O-200 exhaust valves really don't like the lead.



Please remind me did 100LL ever have any approval for the 0-200?
 
Not sure why 94UL is not D910 compliant, since it is 100LL without the lead.
From what I've read 94UL does meet D910 but they dont market that point and went with the ASTM standard for UL avgas D7xxx. But it is harder on the high octane side. As I recall Hjelmco went with an ethanol replacement additive route to meet D910 for their 100UL however it still had performance issues the last I followed it about 10 years ago. Maybe their closer now?
The oil will stay cleaner longer and my O-200 exhaust valves really don't like the lead.
FYI: if you use unleaded avgas Lycoming allows 100hr oil changes as the majority of contaminants is from the combustion bypass, ie, lead.
Please remind me did 100LL ever have any approval for the 0-200?
I believe 100LL was added for the later variants.
 
I believe D910 requires TEL to be used.

I thought so, but a quick look at the table only gives MAXIMUM amounts of lead. I would need to read the whole thing again, but I thought it did.
 
More than 2.
Motor / research are popular on the automotive side of things.
Avgas uses a "performance number" which doesn't end at 100.

That is because there is no such thing as "octane" above 100 technically.

The way they test for octane is in a special single cylinder engine. They run the fuel to be tested and increase the compression ratio until they get a certain amount of knock. Then, without changing anything, the run on various mixes of n-heptane and iso-octane. 100% iso-octane is 100 octane. So you can't have an "octane" over 100. But performance numbers is just a way to extend the range of numbers, they mean the same resistance to detonation
 
There are two octane determination methods, MOR (motor octane number) and RON (research octane number). For mogas the "octane" rating is an average of the results of the two methods.

Which method is called out in the various standards. I think for aviation RON would be the more applicable method.

https://www.differencebetween.com/difference-between-ron-and-mon/
https://www.petro-online.com/news/a...reaking-news/what-does-ron-and-mon-mean/55661

Nope, there are a number of more ways to test. But the AVGAS lean number test method is very close to the automotive MON method. The rich is nothing like the automotive methods. So 91 MON auto fuel, which would be about a 96 AKI fuel (see next paragraph) would be similar to the Lean rating of 91/96 AVGAS. A mogas that would replace 100 AVGAS would be around a 105 AKI mogas. Sunoco has pumps at many race tracks with 98 AKI fuel. But it makes 100LL seem cheap.

The number on mogas pumps is not octane. It is AKI, Anti Knock Index. In the old days, and in many other countries, like all of Europe, the pumps did list octane based on RON. But there is a lot of data that RON alone is not sufficient. The Germans found that long, very high speed cruise operations caused detonation and engine failures when the RON was fine, but the MON was too low. So they called for fuels where the MON was no lower than 10 points below the MON. And most top tiers fuels are.

AVGAS is test with Rich and Lean ratings, since we actually control the mixture in flight. That is the 80/87 or 91/96. The first number is the Lean Rating, the second is the Rich rating. 100LL is a Low Lead Version of 100/130, but no one wanted to say 100/130LL three times quickly. :D
 
91UL is not actually mogas. It is a avgas, based on mogas formulations.

The places currently selling mogas, are selling the same ethanol free gas you buy at the gas stations. That is NOT 91UL. For instance, 91UL is blended to a specific vapor pressure year round.

Sure, they are different things. But they could run their ground equipment on 91UL and also sell it to airplanes, right? Thus being able to still kill two birds with one stone.
 
Why would an FBO want to sell 91UL instead of G100UL? 91UL might get approved for 2/3 of the fleet, but the 1/3 of the fleet that can't use it consumes more gas. I can't believe any airport is going to sell both 91UL and G100UL, so if their choice is to sell limited quantities (91UL) or to sell a fuel (G100UL) that all piston engine airplanes can use, the decision will be obvious.

The single-fuel solution is how we arrived at 100LL back in the day, as it has universal use for piston planes. The logic behind that decision has not changed.

I can see some fields that are really small (say, 2000 feet or less longest runway length) might decide they're not going to see a whole lot of the planes that require 100 octane, and choose 91UL instead. But it won't be a very popular option.

I just don't get it.
Does anyone here own a piston powered plane that that can't and use get the auto fuel STC?
High (94) octane with no ethanol is still cheaper than Avgas and WAY cheaper than GAMI.

Many of us do. My Mooney, with a normally aspirated IO-550-G (2500 RPM/280hp derated) doesn't qualify for Swift, Petersen, etc STCs. I'd imagine there's many 200hp on up that don't qualify for less than 100 octane based on what I've seen.
 
I just don't get it.
Does anyone here own a piston powered plane that that can't and use get the auto fuel STC?
High (94) octane with no ethanol is still cheaper than Avgas and WAY cheaper than GAMI.
My Lycoming IO-390 215 HP can only use 100LL or the G100UL STC...
 
I just don't get it.
Does anyone here own a piston powered plane that that can't and use get the auto fuel STC?
High (94) octane with no ethanol is still cheaper than Avgas and WAY cheaper than GAMI.

1) MANY aircraft cannot use autofuel.
2) Some of those can use 94UL. Which requires an STC. Some of those might be able to use 91UL, but not sure until the testing is complete.
3) 94UL at the pump is more expensive than 100LL, except for a couple of places where it is subsidized and the same price at 100LL.
4) "WAY cheaper than GAMI" So what price have you seen for G100UL???????? What airport is pumping it?????? FYI, GAMI estimates it will be less than $1 per gallon more than 100LL.
 
The FAA will issue a fleet authorization this year that will allow more than two-thirds of the gasoline piston fleet to operate on 91UL avgas.
Today is 12/31/2023.

C’mon Lirio Liu! I had such high hopes after the G100UL approval.
 
I can see some fields that are really small (say, 2000 feet or less longest runway length) might decide they're not going to see a whole lot of the planes that require 100 octane, and choose 91UL instead. But it won't be a very popular option.



Many of us do. My Mooney, with a normally aspirated IO-550-G (2500 RPM/280hp derated) doesn't qualify for Swift, Petersen, etc STCs. I'd imagine there's many 200hp on up that don't qualify for less than 100 octane based on what I've seen.
It’s not that they can’t use mogas, it’s that their engines haven’t been tested and approved to use it. I believe Peterson wouldn’t test and approve engines that had such small numbers made because there was no way he would ever break even doing every engine in every plane. My Cherokee 235 with a O-540 has a Peterson STC which he must of thought he would sell enough STC to make money by testing and approving it…..
 
It’s not that they can’t use mogas, it’s that their engines haven’t been tested and approved to use it. I believe Peterson wouldn’t test and approve engines that had such small numbers made because there was no way he would ever break even doing every engine in every plane. My Cherokee 235 with a O-540 has a Peterson STC which he must of thought he would sell enough STC to make money by testing and approving it…..
My Cherokee Six wasn't approved....it got the vapor lock.
 
Can TEL be injected at the fuel pump like Prist? Can we ship 94UL everywhere, claim to have "Banned the sale of leaded aviation fuels", then let the plane owner inject it back in as an approved fuel additive?
 
I just don't get it.
Does anyone here own a piston powered plane that that can't and use get the auto fuel STC?
I do. No Navion is approved for autofuel, and the IO-550 in mine isn't approved on ANY airframe.
 
Can TEL be injected at the fuel pump like Prist? Can we ship 94UL everywhere, claim to have "Banned the sale of leaded aviation fuels", then let the plane owner inject it back in as an approved fuel additive?


Why on earth would I want to add TEL? Give me 94UL and I’ll burn 94UL.
 
My Cherokee Six wasn't approved....it got the vapor lock.
Octane and Vapor Pressure (which drives vapor lock) are not related issues. I'm sure (but don't *know*) that the folks behind 91UL are smart enough to blend it so the vapor pressure is up to 100LL standards.
 
Why on earth would I want to add TEL? Give me 94UL and I’ll burn 94UL.

You wouldn't. I am thinking about those of us who use the 2/3 of the 100LL currently and can't run lower octanes in our motors. I would expect this to create a "one tank, two fuels" scenario which gets lead out of the delivery infrastructure, makes the local Karens find something else to use to attempt to close airports with, and gets rid of the need for the current STC nonsense.
 
Can TEL be injected at the fuel pump like Prist? Can we ship 94UL everywhere, claim to have "Banned the sale of leaded aviation fuels", then let the plane owner inject it back in as an approved fuel additive?
No....but that wouldn't "fix" the perceived problem.....since 80% of the leaded fuel is consumed by high performance commercial aircraft.
 
Octane and Vapor Pressure (which drives vapor lock) are not related issues. I'm sure (but don't *know*) that the folks behind 91UL are smart enough to blend it so the vapor pressure is up to 100LL standards.
Sorry....I was referring to the Peterson STC for Unleaded fuel. The engine is fine....but the airframe is no bueno.
 
Sorry....I was referring to the Peterson STC for Unleaded fuel. The engine is fine....but the airframe is no bueno.
Gotcha. I assume your engine has an 8.5:1 compression ratio? If that's the case, 91 UL should work for you...
 
Sorry....I was referring to the Peterson STC for Unleaded fuel. The engine is fine....but the airframe is no bueno.

Similar problem with my Musketeer and mogas. The O-360 would be fine, but the airframe fuel system has issues.

94UL, if it ever becomes available around here, won't even require an STC. Textron has approved it for many Cessna and Beech planes via a service bulletin (SEB-28-04) that only requires new placards.
 
Gotcha. I assume your engine has an 8.5:1 compression ratio? If that's the case, 91 UL should work for you...
It has nothing to do with the octane rating but everything to do with the vaporization pressure of the fuel. The fuel works for the engine….but not the airframe. 91UL and the G100UL would probably work fine.
 
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