What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Unleaded Avgas Update

There is a possible wrinkle here - the STC may not simply be a paperwork fee. I know that the SWIFT 100UL has a higher density than 100LL. (about 4%)

Swift didn't meet ASTM D910.

Purportedly, G100UL does.

As I recall, ASTM D910 includes a density specification; which implies that G100UL can't stray measurably from the "normal" 100LL density we all know and love.

I thought the entire point of the fleet-wide approval was that you'd be able to pump it into your tanks without caring about details like W&B, achievable horsepower, CHT/EGT changes, decomposition and erosion of components, etc because it met the same specification of that which it replaces.

There seems to be a lot of head-scratching around various forums in the last 12 hours based on the assumption that none of that happened -- that it was approved for fleet-wide application by the FAA even though it behaves differently.

That doesn't seem credible to me. I'm going to assume that it's a drop-in replacement for 100LL, just like it says on the tin, unless and until there's more detail that says otherwise.

(notwithstanding that nobody needs to care about what I assume, given that none of us can buy it yet anyway :) )

- mark
 
Swift didn't meet ASTM D910.

Purportedly, G100UL does.

As I recall, ASTM D910 includes a density specification; which implies that G100UL can't stray measurably from the "normal" 100LL density we all know and love.

I thought the entire point of the fleet-wide approval was that you'd be able to pump it into your tanks without caring about details like W&B, achievable horsepower, CHT/EGT changes, decomposition and erosion of components, etc because it met the same specification of that which it replaces.

There seems to be a lot of head-scratching around various forums in the last 12 hours based on the assumption that none of that happened -- that it was approved for fleet-wide application by the FAA even though it behaves differently.

That doesn't seem credible to me. I'm going to assume that it's a drop-in replacement for 100LL, just like it says on the tin, unless and until there's more detail that says otherwise.

(notwithstanding that nobody needs to care about what I assume, given that none of us can buy it yet anyway :) )

- mark

I don't think that is right. A drop-in replacement is what they were hoping for and never got. Neither fuel meets the full spec because the density is different. I think that was really the only sticking point, but it has implications for GTOW, range, W&B. Thus the STC, rather than just start pumping a new fuel that does fully meet the spec, and would require no paperwork.
 
Free

In the AOPA interview there was a very brief mention that the STC would be free. Guess they will make their money on the fuel (Which is fair enough, they need to make the money somewhere.)
 
In the AOPA interview there was a very brief mention that the STC would be free. Guess they will make their money on the fuel (Which is fair enough, they need to make the money somewhere.)

One interview seemed to indicate it would be $50 to $100, and they want it to be available with an app where you could buy it on the spot at the pump. They are pushing for FAA approval of this method.

On the video today I thought George Braly said that the STC cost would be in line with other similar STC costs, which are about $360, if my 2 mins of googling is correct.
 
Please pardon my ignorance, perhaps I’ve missed something in the prolific amount of information on this subject that has been generated , but if it’s gonna become the only option to be had in the new lead free aircraft fuel world then why and how can it be required to PURCHASE the STC if the new fuel is apparently approved for ALL piston engines. Being compelled to buy basically permission to utilize what’s destined to become the only option just rubs me the the wrong way. Or am I the only one who sees the STC requirement this way?

I am not aware of any requirement for an EXPERIMENTAL aircraft to purchase an STC for anything.
 
In the AOPA interview there was a very brief mention that the STC would be free. Guess they will make their money on the fuel (Which is fair enough, they need to make the money somewhere.)

I kind of hate to pay for an STC that I don’t need. I hope that it’s not free.
 
I emailed the contact link at the GAMI G100UL website and got a response back quickly that STC is N/A to EAB, and that is GAMIs stance on their fuel.
 
‘Supplemental Type Certificate’. If you have a 172, it has a type certificate - a lot of specifications, tests it passed, etc. That type certificate says, ‘must be operated on 100LL or 100/130 av gas meeting astm standard….’ So if your A&P/IA finds any other gas in your plane at annual, he can’t sign it off because it doesn’t conform to its type certificate. An STC is a license to use someone’s data (sort of like a software license) which the faa has blessed to modify the original type certificate, in this case, to use this new gas. EAB aircraft don’t have type certificates, so the notion of an STC for one is meaningless.
That was irony, no didactic response required 😉 but thanks nonetheless…..
 
G100 UL Fuel Density

I don't think that is right. A drop-in replacement is what they were hoping for and never got. Neither fuel meets the full spec because the density is different. I think that was really the only sticking point, but it has implications for GTOW, range, W&B. Thus the STC, rather than just start pumping a new fuel that does fully meet the spec, and would require no paperwork.

If you can mix it with 100LL wouldn’t that mean the density is the same ? If you look at the picture at the on AVWeb ( link post 39 ) with both fuels mixed there is no stratification. With 100LL Blue and G100 UL yellow you get a beautiful green !
Am I being over simplistic to think that means the densities are equal unlike the oil and water mix we’ve all seen.
 
Last edited:
If you can mix it with 100LL wouldn’t that mean the density is the same ? If you look at the picture at the on AVWeb ( link post 39 ) with both fuels mixed there is no stratification. With 100LL Blue and G100 UL yellow you get a beautiful green !
Am I being over simplistic to think that means the densities are equal unlike the oil and water mix we’ve all seen.

Yes, you are over simplifying.

Not a chemist, but I don't believe that density has anything to do with solubility, though the densities will dictate the stacking of layers of stratification in insoluble mixtures, like oil and water. Thought is was about molecular bonding; Think back to HS science - some molecules happily combine with others and some don't. Something about free neutrons at the atomic level, I think. Mix oil and gasoline and they combine perfectly eventhough they are very different densities, but very similar at the molecular level. Gasoline starts as oil and requires heat and evapoation to refine it out. It doesn't naturally create different layers. Oil is around 7.5 lbs/gall and gas is around 6 lbs/gallon. Salt water doesn't perfectly mix with fresh water due to being the same density; We know they are different densities, as we humans float on salt water and sink in fresh water. Salt and water are also different densities, but mix perfectly and don't separate, otherwise the oceans would be freshwater with a layer of salt at the bottom.

Larry
 
Last edited:
Seems that G100UL has basically the same density as regular car gas or the mogas many of us use.
 
Yes, you are over simplifying.

Not a chemist, but I don't believe that density has anything to do with solubility, though the densities will dictate the stacking of layers of stratification in insoluble mixtures, like oil and water. Thought is was about molecular bonding; Think back to HS science - some molecules happily combine with others and some don't. Something about free neutrons at the atomic level, I think. Mix oil and gasoline and they combine perfectly eventhough they are very different densities, but very similar at the molecular level. Gasoline starts as oil and requires heat and evapoation to refine it out. It doesn't naturally create different layers. Oil is around 7.5 lbs/gall and gas is around 6 lbs/gallon. Salt water doesn't perfectly mix with fresh water due to being the same density; We know they are different densities, as we humans float on salt water and sink in fresh water. Salt and water are also different densities, but mix perfectly and don't separate, otherwise the oceans would be freshwater with a layer of salt at the bottom.

Larry

Have you seen the brine pools at the bottom of the Gulf of Mexico?

Try alcohol and water - vodka - -two different densities, but completely miscible - that would describe compatibility of the two fuels.
 
Have you seen the brine pools at the bottom of the Gulf of Mexico?

Try alcohol and water - vodka - -two different densities, but completely miscible - that would describe compatibility of the two fuels.

according to the referenced link, that is salt tectonics due to large quantities of salt trapped under sediment and doesn't really prove that salt will not naturally separate from water. It only proves that different concentrations of salt water can exist in a common body of water. That is a pretty unique penomenon, though I get your point.

Larry
 
Yes, you are over simplifying.

Not a chemist, but I don't believe that density has anything to do with solubility, though the densities will dictate the stacking of layers of stratification in insoluble mixtures, like oil and water. Thought is was about molecular bonding; Think back to HS science - some molecules happily combine with others and some don't. Something about free neutrons at the atomic level, I think. Mix oil and gasoline and they combine perfectly eventhough they are very different densities, but very similar at the molecular level. Gasoline starts as oil and requires heat and evapoation to refine it out. It doesn't naturally create different layers. Oil is around 7.5 lbs/gall and gas is around 6 lbs/gallon. Salt water doesn't perfectly mix with fresh water due to being the same density; We know they are different densities, as we humans float on salt water and sink in fresh water. Salt and water are also different densities, but mix perfectly and don't separate, otherwise the oceans would be freshwater with a layer of salt at the bottom.

Larry


OK, I am a chemist, and have no problem with the gist of your post. However, solubility has nothing to do with free neutrons, thank god. Free neutrons are unstable and give rise to beta emissions (a form of radioactivity).


Now back to your regularly scheduled programming ...



Peter
 
newt and RV6 flyer:
I fully understand that we can run our experimental engines on moonshine laced with goat’s milk if we could get it to burn and not spoil in the unrefrigerated wing tanks :eek:

My comment was more intended for the GA fleet as a whole that our RV’s are a subset of. I suspect that a large percentage of us currently fly certified planes as well.
 
newt and RV6 flyer:
I fully understand that we can run our experimental engines on moonshine laced with goat’s milk if we could get it to burn and not spoil in the unrefrigerated wing tanks :eek:

My comment was more intended for the GA fleet as a whole that our RV’s are a subset of. I suspect that a large percentage of us currently fly certified planes as well.

It depends on the FAA. (and maybe the insurance underwriters plus manufacturers)

An example is that they (FAA) want to promote safety and up until recently it was acceptable to get flight training in an experimental airplane. Due to an experimental warbird taking advantage of that, the FAA went to court and won their case by throwing all training in experimental aircraft out the window. Now we require a LODA to get flight training in our experimental aircraft.

The FAA decided to go down one path for unleaded avgas and it may not be the smoothest path. We as the end user of "certificated" aircraft may have a few extra hoops to jump through.
 
Should be interesting to see how the self-service pumps handle G100UL. I did hear one comment that current UL self-serve pumps somehow check your tail number with an STC list and will not turn on if the AC is not on the list. I presume this is a SWIFT 94UL pump because you need their STC to use their fuel. While experimental AC do not need an STC, the distribution infrastructure may require you to buy one anyway. I am sure we will see a lawsuit from a crash that involves an FBO fueling a plane with G100UL that did not have an STC for it.

George mentioned the STC cost will be based on engine HP. I hope the FAA will eventually approve/declare G100UL as a 100LL equivalent with no STC required, otherwise you may end up needing multiple fuel STCs (MOGAS, SWIFT, GAMI, whoever is next) depending on where you stop for fuel.

John Salak
RV-12 N896HS
 
Surely STC compliance would fall on the PIC and not the fuel supplier? Sort of like operating an airplane at an STC placarded increased gross weight without the STC?
 
Try alcohol and water - vodka - -two different densities, but completely miscible - that would describe compatibility of the two fuels.

I appreciate Larry's comments as it brings back dusty, faint memories.

Bill, your example is COMPLETELY clear! :D

Cheers!
 
OK, I am a chemist, and have no problem with the gist of your post. However, solubility has nothing to do with free neutrons, thank god. Free neutrons are unstable and give rise to beta emissions (a form of radioactivity).

Peter

No surprise I got it wrong after 40 years. :D Was it free electrons. I have these vague memories of the molecular universe liking even numbers of something. things would happily join when the combined number was even. Maybe I just had a bad science teacher.

Apologize for taking the thread off course, but always looking to add knowledge.

Larry
 
Last edited:
How about a subsidy for G100UL?

The taxpayers support ethanol production and blending of auto fuels through tax credits, etc. to the tune of billions of dollars annually. Ethanol use in auto fuels has debatable positive impact on emissions/CO2 reduction when viewed in totality (production of corn through ethanol blending).

The taxpayers also support EV and alternative energy tax credits worth many more billions - also for a somewhat debatable benefit to clean air.

Elimination of the lead from avgas provides an immediate benefit to clean air.

Seems like the alphabet soup organizations ought to be pushing for subsidies/tax credits to encourage adoption of G100UL. Even a $1.00 per gallon subsidy for the 150 million gallons of avgas produced each year would be small change compared to ethanol and EV tax credits.
 
The taxpayers support ethanol production and blending of auto fuels through tax credits, etc. to the tune of billions of dollars annually. Ethanol use in auto fuels has debatable positive impact on emissions/CO2 reduction when viewed in totality (production of corn through ethanol blending).

I thought the goal was less dependence on foreign oil. Getting ethanol from corn requires a LOT of heat and was pretty sure that ounce per ounce, producing the ethanol created as much or more CO2 than the burning of gasoline it replaced, possibly more. A study showed that the BTUs required to produce a gallon of ethanol was greater than the BTUs that a gallon of gas produced in an engine. Pretty sure this is just an end around by the farm boards for greater subsidies. Remember, most farms today are corporate and they have strong lobbies to keep the subsidies that have been around since Roosevelt.

Larry
 
Last edited:
Back to G 100 UL Density

Taken from GAMI’s website:

“Are there any airspeed or range implications with the use of G100UL avgas?
Essentially “no.” At the same volumetric (GPH) fuel flow and a LOP mixture, the aircraft will be one or maybe two knots faster, due to the slightly higher volumetric energy density. Likewise, with full tanks, the range of the air- craft will be the same or possibly increase by ~ 1%. However, G100UL avgas weighs about 6.3 lbs./gallon, rather than ~ 6.0 lbs./gallon.”

I apologize if this has been discussed elsewhere on this site but it does appear the densities of UL and LL are close ( aprox 5% difference ). In my RV-4 with 32 gallon fuel capacity that would add 9.6 lbs to my takeoff weight. Not a deal breaker for me but not exactly insignificant either. The good news is that almost 10 lbs is forward of my CG which is helpful on 4’s that tend to be on the tail heavy side.
 
POH

Since my 9A is almost done, I guess I will wite the POH with G100UL in mind.

Now if only I can get 1000 gals for phase 1……
 
Agree with John S

When I was planning the painting of the plane, I looked to the future of the possibility/probability of unleaded fuel being available in my flying future. So, I only had 100 Octane painted around the filler.
No need for modifications when the 100UL becomes available.

Now on to a philosophical question: If the STC covers ALL spark ignition Internal Combustion engines, why do we even need to purchase one? Seems to me the blanket coverage would suffice for anyone flying an airplane requiring 100LL fuel should be "good to go" for dumping 100UL in the tank.
 
I did hear one comment that current UL self-serve pumps somehow check your tail number with an STC list and will not turn on if the AC is not on the list.

Uhhhh...I'm going to call a party foul on this one. :) Sounds like a CT to me.
 
Should be interesting to see how the self-service pumps handle G100UL. I did hear one comment that current UL self-serve pumps somehow check your tail number with an STC list and will not turn on if the AC is not on the list. I presume this is a SWIFT 94UL pump because you need their STC to use their fuel. While experimental AC do not need an STC, the distribution infrastructure may require you to buy one anyway. I am sure we will see a lawsuit from a crash that involves an FBO fueling a plane with G100UL that did not have an STC for it.

George mentioned the STC cost will be based on engine HP. I hope the FAA will eventually approve/declare G100UL as a 100LL equivalent with no STC required, otherwise you may end up needing multiple fuel STCs (MOGAS, SWIFT, GAMI, whoever is next) depending on where you stop for fuel.

John Salak
RV-12 N896HS

In this part of the country, rural Minnesota, Aviation fuel self service pumps for the most part do not support that technology. However, I have run into a few that require, as part of the purchase process, that you enter your tail number. I guess would be a simple matter to then check that tail number against a database.

Frankly, I think that this is one of the more minor problems that is going to be associated without the broad base roll out of G100 UL gasoline.
 
I could perhaps see it as some sort of credit card anti-fraud mechanism, but I doubt it will ever have anything to do with FAA rules or STCs or anything like that.

Next time you run into one that wants a tail number, test it out...enter something like 12345 or maybe a Canadian or Mexican tail number. Dollars to donuts it pumps your gas, no questions asked.
 
Some fraud measure. I never use my real N number on those pumps, but I do enter some random 5-digit sequence. Never the same sequence. On those pumps that can, it'll show me the last sequence I used associated with my credit card, but I type in something else. I think I'll just use 12345 from now on.
 
Fuel contamination

They want your tail number in case there is a problem with the fuel. We had a problem near San Antonio several years ago and they notified everyone that entered a real N number for fuel contamination.
 
I could perhaps see it as some sort of credit card anti-fraud mechanism, but I doubt it will ever have anything to do with FAA rules or STCs or anything like that.

Next time you run into one that wants a tail number, test it out...enter something like 12345 or maybe a Canadian or Mexican tail number. Dollars to donuts it pumps your gas, no questions asked.

actually, you’re right…one wouldn’t have to enter their actual tail number. For what it’s worth however, even out here in the hinterlands, many or most of these self-service fuel stations in these rural airports do video surveillance. Not that that would have anything to do with whether or not one has bought an STC. I agree, and don’t see that level of enforcement action at point of sale as being a thing.

If these rural airports do ever get around to selling G100 UL ( likely to be quite a while), I don’t see how they’re ever going to enforce STC compliance.
 
Last edited:
They want your tail number in case there is a problem with the fuel. We had a problem near San Antonio several years ago and they notified everyone that entered a real N number for fuel contamination.

I think this is the real answer. And seems like a good reason to enter your correct tail number.
 
I think the tail number entry before pumping is also used by the airport manager to track usage by planes based there. Might be a factor, albeit small, in hangar lease renewal (as part of the case to boot inactive planes ?).
 
If the STC covers ALL spark ignition Internal Combustion engines, why do we even need to purchase one?

If you believe that unleaded fuel is a positive development in GA, then you can see the purchase of the STC as payment for the people who did this good work.

If you feel less positively about all this, then I can see how paying for an STC might not sound so great, of course.

(Personally I think that less lead in the air is probably a good thing, but I've heard some people say that the data are debatable and I have not had the time to look into it, so I don't want to stir up that hornet's nest, at least not until I work on being more informed. But regardless of that: I have a strong feeling that 100LL won't be around for ever, and that we should all prepare for this future if we can).

Also: In any case, experimentals should not need to purchase STCs.
 
Last edited:
G100UL and P-Mags

So just pissing into the wind here...

What about P-Mags advance curves, do they need to change given the G100UL differences? I heard on the Avweb video that it is really a 100/150 avgas, (100 lean, 150 rich). Will the P-Mag advance curves need to change now based on mixture setting?

When GAMI looked at all the certified engines, I bet they did not look at the experimental io540s with Pmags with the 32 degree maximum advance and 10:1 pistons, operating lean of peak... (you know who you are...)
 
Back
Top