G100UL Approved

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Dana

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The FAA finally approved a fleetwide STC for GAMI's 100UL avgas. Now we'll see how long it takes to implement...

 

Bigshu

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addaon

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Anyone have any insight as to whether this is a true performance equivalent for 100LL, or if it’s just “close enough” for most purposes? Especially on an engine that runs on 42” manifold… I’d probably advocate that my airport start stocking if, but not if it’s going to increase maintenance down the line.
 

Vigilant1

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Also, as G100UL starts becoming available, any thoughts on running auto conversions on it? Any concerns, or reasonably option?
It won't be cheaper than auto pump gas but if it comes without the ethanol issues it might be popular with folks flying auto conversions. If folks running auto conversions will be buying it anyway, is it practical to go to higher CRs to use the higher available octane?
 
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addaon

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Yeah, I’m not hoping for cheaper, just available at airports. I can’t think of any reason it would cause problems, but I’m not a fuel guy. The increased density (half way between 100LL and jet fuel) is a nice bonus, but would have to keep in mind 20 lb lower max-fuel payload for my bird.
 

rv6ejguy

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Anyone have any insight as to whether this is a true performance equivalent for 100LL, or if it’s just “close enough” for most purposes? Especially on an engine that runs on 42” manifold… I’d probably advocate that my airport start stocking if, but not if it’s going to increase maintenance down the line.
It was approved months ago for R2800s which run derated at around 52 inches. It completed testing on turbo Lyc. 540s and Conti 550s as well.
 
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Max Trescott interviewed George Braly back in February on Aviation NewsTalk Podcast. He explains a lot of the testing. It’s a great podcast, and I would have no problem running G100UL in any high performance engine. They even tested it in a Curtiss Wright 3350 supercharged radial.

 

rv7charlie

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I understand that you can blend up a 10,000 gallon batch right on the ramp with common ingredients. You will need a license to do so.
Now that is an interesting item, if correct. Of course if I was flying a couple of those $80,000 turbo'd hand grenades in a cabin class twin, I'm not sure I'd want to trust some random line boy to play chemist at the airport.
 
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I understand that you can blend up a 10,000 gallon batch right on the ramp with common ingredients. You will need a license to do so.
Might be kind of impractical unles you have a source of aromatic hydrocarbons?

"wherein R1, R2, R3 and R4 are hydrogen or a C1-C3 alkyl group, said one or more aromatic amines comprising from more than zero % (0%) to about two point seven percent (2.7%) by weight of said unleaded avgas fuel blend;

(d) about sixty percent (60%) to about forty percent (40%) by weight of one or more dialkylated and/or trialkylated benzenes effective to increase the detonation performance"


and some of this for the 2%:
1662327405095.png

It is no wonder this stuff is higher density.............
 
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Does the higher physical density come with an associated increase in energy density?
No. Looks like actually less:


Aromatics are pretty low energy configurations of HCs. The alkyl substitutions (Rs) help with the energy density but it doesn't appear to be that significant unless they in themselves are longer chain.
 

addaon

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Although the energy density of the additives is lower per unit mass than the base hydrocarbons, densities of solutions are not that simple (think of ethanol in water, for example). G100UL is about 5% denser, and has about 1.5% more energy per unit volume, so it’s volumetric energy density is a bit higher and it’s mass energy density is a bit lower. In general, if you’re running at a constant power and filling tanks with 100LL vs G100UL, you’ll have a bit more range; but if you’re flying partial tanks to a given MTOW you’ll have a bit less.
 

Vigilant1

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In general, if you’re running at a constant power and filling tanks with 100LL vs G100UL, you’ll have a bit more range; but if you’re flying partial tanks to a given MTOW you’ll have a bit less.
I had heard that this energy density issue was one thing causing the FAA to delay approval, on the grounds that any true "drop in replacement" must have substantially identical energy density to 100LL so that existing carburetors and fuel injection systems (volumetric metering) would work perfectly, and acft range etc from automated systems would read right. I'm guessing that they are calling this new fuel "close enough".
 
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