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PAFI. What killed Swift Fuel candidate

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Automotive engines are liquid cooled, therefore much tighter temperature control. Fuel and ignition is also closed loop computer controlled; knock sensors, the whole works. Those engines will destroy themselves if temperature, fuel mixture and ignition timing go places that airplane engines do.

Many auto engines, V6, V8, and V12's are flying in the same air that is occupied by certified engines. And these are not all running on 100LL.

Computer controlled, electronic ignition / fuel injection.
 
Absolutely automotive engines are used in airplanes. They being their engine operating requirements (pros and cons) with them. A Lycoming has a maximum cylinder head temperature of 500°. The Lycoming will continue to run safely at 500°. No detonation or pre-ignition. An automotive engine is liquid cooled, so cylinder head temperature doesn't get near that high, thus allowing for higher compression ratio before detonation or pre-ignition appears.
 
In addition to regulating out lead from 100LL, they should provide statutory liability relief, creating incentive for Lycoming and anyone else to create such engines.
Carl

If liability were the problem Lycoming wouldn't be making any engines today. The issue is certification costs. Not only do they have to certify the engine, but then someone has to get stc's for each make and model of aircraft. It's not like a radio that can be pencil whipped through with an AML STC. I've been involved in similar type OEM level STC's and the costs are measured in millions.

Keep in mind that Lycoming already has a full FADEC on the shelf that I suspect could run most of their engines on just about anything short of mule pee. They spent a lot of time of money developing it. There has to be a reason they aren't rolling it out onto lot's of airframes.
 
cylinder pressure sensor

If we can get a company like this one to make cylinder pressure sensors cheap enough, they would provide the information needed to safely burn lower octane fuel in higher compression engines.

https://www.imes.de/index.html

George Braly has been experimenting with CPS for a while.

https://www.airspacemag.com/flight-today/first-church-of-combustion-5992521/

I predict we'll have high enough capacity batteries before we have a drop in replacement for 100LL. Batteries only need to get about a thousand times better to match the energy density of 100LL!
 
We will have a battery powered B-777-300 with international range before we have a “drop in” fuel replacement for 100LL.
 
Not for everyone!

I see a lot of good suggestions and ideas but what everyone is always forgetting is that the replacement fuel will have to be working for all piston airplanes.
Knock sensors, automotive engines, FADEC etc. etc. all good but none of those things will work in a high compression certified production engine/airplane.
We are spoiled in our experimental category, we can make almost anything work without the burden of a heavy handed and expensive bureaucracy stalling our efforts.
My IO 540 runs just fine on 91 E10 and has done so for the last 10 years and 600 plus hours. I am a lead free veganore.
It has to work for everyone or else its a no go.
 
I see a lot of good suggestions and ideas but what everyone is always forgetting is that the replacement fuel will have to be working for all piston airplanes.

We are spoiled in our experimental category, we can make almost anything work without the burden of a heavy handed and expensive bureaucracy stalling our efforts.

It has to work for everyone or else its a no go.

This is why I think it will be going the STC route initially. It will be a gradual phase in as more planes get the paperwork. Swift is already selling their STC for $100 for lots of certified models that can use their present 94UL fuel. This also allows a slow ramp up of production and distribution.

The turbo certified engine operators will have to play the same game if UL avgas is mandated. A true drop in UL avgas for all engines with no changes to the POH, seems highly unlikely in the near term.
 
It is ironic that the company excluded from PAFI may be the one that solves the 100LL fuel replacement problem. The important part of the story is the deal with AVFuel for distribution. Finding MOGAS is next to impossible in the southeast if you want to use UL fuel, however there are a lot of AvFuel FBOs that could easily add the new product.

You may want to encourage your local airport to request a grant from the FAA to add 100UL/R tankage to speed the transition from 100LL. Might as well use some of that infrastructure money for something useful.

John Salak
RV-12 N896HS
 
At the wholesale level, 85 cents / gallon more than 100LL. So how much will the retailers tack on...another 50 cents? More?

And how many years will it be before this new UL fuel is available at every gas pump, at every airport?

Amazing as many of us can safely get by with 93UL. Not only greater oil change intervals, a cleaner engine, but also $3 to $4 less expensive.

Pardon me if I don't get a warm fuzzy feeling about this. At least not yet.
 
Fear not, Wrights Law will save the day. This rollout is no different from the introduction of electric vehicles. At the start with low volumes, electric vehicles were seen by many as being an unrealistically expensive proposition, and now that they are being made by the millions, their pricing is approaching internal combustion vehicles and will likely reach price parity by 2025.
Initially this fuel will be taken up by those who think it is important and are prepared to pay a premium, but as the production volumes increase you can be assured that this will be available at pricing equal or below that of leaded aviation fuel due to the savings associated with not having to handle the fuel in dedicated lead-only infrastructure.

Tom.
RV-7, that only drinks unleaded fuel.
 
At the wholesale level, 85 cents / gallon more than 100LL. So how much will the retailers tack on...another 50 cents? More?

And how many years will it be before this new UL fuel is available at every gas pump, at every airport?

Amazing as many of us can safely get by with 93UL. Not only greater oil change intervals, a cleaner engine, but also $3 to $4 less expensive.

Pardon me if I don't get a warm fuzzy feeling about this. At least not yet.

I think we in the EAB fleet can fill up with any type of high octane UL fuel we like. The certified world can only use the STC fuel if 100LL is no longer available. Every parallel valve engine from the Vans OEM is approved for UL fuel operation directly from Lycoming.
 
Hopefully a massive switch to unleaded will quickly happen across the entire GA fleet. This is good news for everyone who likes to fly, since it can't be good for us to be seen as spraying lead across the countryside when we fly - even if some of us are already running unleaded.

From what I've understood George Braly to say, there will be STCs for a few months, and then the FAA will approve it generally for all piston aircraft. Sure hope this happens!
 
It's an important first step to get the ball rolling. Now it may be a battle between Swift and GAMI formulations and who can produce and distribute enough of it.
 
As stated in the AOPA article, It seems GAMI already has many test cell hours running on a turbo Lycoming. If I read the article right, they are hoping with a bunch of real world experience with the fuel released to STC'd users, that the FAA may open things up more in the future.

Too soon to tell if that's the case. Maybe they need to get some Experimental turbocharged engine users to be filling up with this fuel for a couple years and reporting carefully documented results.

I'd be willing to test if they sent a few barrels up to me...:D
 
Reduced timing?

Ross, early in the thread (post #6) you mention mid-CR engines running mogas with reduced high MAP timing. As my engine, like many others, approaches 9:1 CR (I’ve got a stock longblock O-320H2 at 8.9:1) and is not in SI-1070 to run UL, I’m curious to get your opinion on what the reduction in advance is from baseline. Is it 5*? More? I’m running a CPI2. Thanks.
 
On 9 to 1 PV engines, you can reduce timing to around 20 deg at high MAP, say above 25 inches. This seems to be pretty safe on 91 mogas and will lower the CHTs in the climb with minimal loss of power, perhaps 5-7hp on a 360.
 
Sorry to disappoint, but the FAA will not authorize any fuel for the entire fleet outside of PAFI. Braly's STCs are for 3 non-turbocharged engines (Lycoming's O-320, O-360, and IO-360) and the aircraft flown by the Embry-Riddle flight school (like the Cessna 172). He claims he will expand the STCs to other aircraft and engines using the AML-STC (approved model list) system, but will this include turbocharged engines or aircraft?

I suspect Braly's fuel will get even less traction in the marketplace than Swift's 94UL. Until an unleaded fuel is authorized for turbocharged aircraft, which represent 70-80% of AVGAS demand, deployment will be a gamble for any airport. According to GAMI's 2019 patent, G100UL contains ~30% aromatics plus 10-12% of an aromatic amine octane booster. Octane is below 100 and closer to 98 MON, if that. His "spec" minimum calls for 96 MON, barely above 94UL. A recipe for detonation in large turbos and a gamble for materials compatibility.

Until Braly shares his data with the OEMs and Industry, skepticism will remain. The 60 cent to a dollar upcharge may also dampen the enthusiasm.

This ^^^^^^^
 
Thanks for the link. Also quote from article regarding turbo engine testing

"What was the compression ratio, manifold pressure and the highest horsepower achieved during detonation testing that successfully passed a formal FAA 14 CFR Part 33.47 detonation test?

At the conclusion of the two days of detonation testing, GAMI elected to complete an optional test item from the FAA-approved test matrix.

That test item was to determine the maximum Brake Horsepower (BHP) at which the 8.7:1 CR IO-550 turbocharged test engine could be operated and continue to pass a standard Part 33.47 FAA detonation test.

With redline cylinder and induction air temperatures, the engine operated at 41.4” MP, 380 actual BHP (414 BHP when corrected to standard day conditions). We were unable to determine how much more additional HP could be obtained because the pressure relief “pop-off” valve on the induction system was limiting further increases in manifold pressure.
 
ASTM Specification AvGas

Sorry to disappoint, but the FAA will not authorize any fuel for the entire fleet outside of PAFI. Braly's STCs are for 3 non-turbocharged engines (Lycoming's O-320, O-360, and IO-360) and the aircraft flown by the Embry-Riddle flight school (like the Cessna 172). He claims he will expand the STCs to other aircraft and engines using the AML-STC (approved model list) system, but will this include turbocharged engines or aircraft?

I suspect Braly's fuel will get even less traction in the marketplace than Swift's 94UL. Until an unleaded fuel is authorized for turbocharged aircraft, which represent 70-80% of AVGAS demand, deployment will be a gamble for any airport. According to GAMI's 2019 patent, G100UL contains ~30% aromatics plus 10-12% of an aromatic amine octane booster. Octane is below 100 and closer to 98 MON, if that. His "spec" minimum calls for 96 MON, barely above 94UL. A recipe for detonation in large turbos and a gamble for materials compatibility.

Until Braly shares his data with the OEMs and Industry, skepticism will remain. The 60 cent to a dollar upcharge may also dampen the enthusiasm.

Early on in the GAMI UL100 development, I recall that George Braly stated that they tested 100LL AvGas from various sources and it did not meet the ASTM specifications that it was supposed to meet. George held that the FAA should reduce some of the requirements for unleaded fuels because 100LL didn't even meet those specifications. I think this is key to the suitability of UL100 in spite of it falling a little short of some requirements.

Skylor
 
Early on in the GAMI UL100 development, I recall that George Braly stated that they tested 100LL AvGas from various sources and it did not meet the ASTM specifications that it was supposed to meet. George held that the FAA should reduce some of the requirements for unleaded fuels because 100LL didn't even meet those specifications. I think this is key to the suitability of UL100 in spite of it falling a little short of some requirements.

Skylor

I had read somewhere that most of the FAA concerns seemed to be about specific gravity and other factors about the Swift and GAMI fuels. Both had passed detonation testing on turbocharged engines at Purdue and GAMI's facility as far as I am aware.
 
The (L)TIO-540-J2BD has the manifold pressure redline at 49", so should be expected to operate there with no problems. Yes, 45" is normal, but 49" is allowed. Compression ratio is also quite low, can't recall the exact number. That certainly helps with detonation margin.
 
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I just watched the AOPA weekly broadcast and GAMI initial goal is to STC its fuel for all the GA training fleet, and that includes all the C172s and other smaller trainers. I guess the twins with turbos will have to wait a bit longer.
 
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Unleaded Avgas Update

I've been asked by a participant here to update and share this summary from late last year.

Avgas December 2020 Update – updated - Part 1

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It’s been a few years, what is going on with no lead aviation gas? I thought it was down to one or two. With the new administration on fossil fuel, the EPA will probably do more nudge to force a transition to an unleaded fuel.

Sure, let’s summarize what’s been going on, and address some of the questions that have been posed over the last little while. First the disclaimer, I was an engineer at Chevron for 38 years. The last decade plus, I was involved in unleaded avgas development, until Chevron became so frustrated at the FAA’s ignoring science that Chevron walked away, as eventually did all of the major energy companies. I’ve provided some small consulting to Swift and GAMI since then, but am not privy to their confidential stuff, and am not representing either of them in expressing my observations on the passing scene.
While the FAA’s PAFI (Piston Aviation Fuels Initiative) is stuck, because ignoring science is a bad approach, there are four companies working the issue. In diminishing order of successful probability, IMHO: GAMI, Phillips/Afton, Lyondell/VP-Racing, and Swift. [Shell walked away in January 2021.] Let’s look at each approach.
GAMI has been working on this issue since 2010, and they do observe the science. Their formulation and additives have evolved impressively. The FAA has streamlined (!) the approval process, and GAMI was granded limited approval just before Oshkosh last month. That will probably result in fleet trials, maybe at a flight school or two. The FAA and GAMI have agreed on a final testing program, which will lead to fleet-wide approval by June next year, GAMI says.
Phillips came to this game late, announcing at Oshkosh 2019, and giving a technical seminar. They plan to replace the lead with Methylcyclopentadienyl Manganese Tricarbonyl (MMT). Manganese is much less toxic than lead, although when MMT was used in mogas, principally in Canada, there were issues with spark plug fouling. Phillips thinks they know how to devise a scavenger for the aviation application that will spare our expensive plugs… I’m guessing a molecule that was considered too expensive to be competitive in mogas, but avgas’ higher margins make it feasible. Phillips website says 2025 or 2026 completion.
Lyondell (the former ARCO Chemical) is working with VP-Racing on a conventional avgas without lead, achieving the necessary antiknock property via ETBE (ethyl tert butyl ether), MMT, and methanol. Each of those additives presents challenges, so there are many moving parts to making this work.
Swift seems to be struggling a bit, but the underlying science of their R100UL should be workable. I’m not sure they have the resources to get there. Swift is selling an interim 94UL fuel that they originally planned to discontinue when the 100UL is available. Swift nows says they might continue manufacturing both fuels, which is surprising. Folks are concerned that the supply logistics on the 94UL Swift fuel seem sketchy, and worry what that might imply about Swift’s viability. It may however only be a learning curve experience for Swift. I wish them well.
Shell was the primary contender in the FAA’s PAFI, and that effort was not successful, even after the FAA changed the rules to accommodate them, versus being left with no players after Swift withdrew from PAFI. It’s important to note that it’s NOT the Shell refining company that’s pushing this effort. Instead, it’s kind of a speculative effort by their Global Solutions company, which was spun off a few years back. They’re hoping to develop a salable solution, rather than developing a solution for the Shell corporation. After the problems with their fuel removing paint from wings and their engine endurance testing failing, Shell has said they’re sitting back, awaiting a stronger business case for their fuel to appear.
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It’s not the politics that has held up this change, it’s that pesky physics thing. It’s got to support the high compression engines which burn most of the 100LL

It’s a combination of factors… The FAA has to follow the scientific method, but as a federal agency, it is an inherently political animal. So it tends to be a combination of confounding factors.
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Maybe they need to reduce the compression in those engines. Not a big deal to change pistons. Then, unleaded mogas can offer a real solution.

The certification burden is enormous for the fleet… each engine/airframe combination would have to be recertified, with new performance tables compiled from flight testing. This is a very expensive effort… and not one popular with aircraft owners, as it will result in reduced gross weight and performance. No one is excited about spending the money to make that happen.
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It’s been 25 years since EPA ban on lead in fuel, just how long do you think Kerry and the new administration are going to wait.

You overlook that the EPA and FAA duked this one out in Federal Court during the W administration (the White House didn’t want to take the heat, I guess). The SCOTUS decided that the FAA is in charge of avgas regulation, so the EPA sits by waiting for the FAA to do their thing. The EPA could make a finding of endangerment, that might adversely motivate the current producers of leaded avgas. But, that didn’t happen under 44, and I think Biden et al might be more interested in observing Supreme Court rulings in letter and spirit than running roughshod over them.
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Will this lower the price for avgas?

It’s hard to say. The unleaded fuel will cost slightly more to make. On the optimistic side, since high-liability lead facilities aren’t required, any number of additional blenders might choose to enter the marketplace, introducing more competition than currently exists. My guess is avgas prices will eventually be roughly the same: at wholesale, avgas sells at 80 cents to $1/gallon more than premium unleaded.
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Mogas isn’t really a replacement. The vapor pressure is too high. A good chunk of the fleet would have to be retrofitted with in tank boost pumps to keep airframe fuel lines from forming vapors.

There’s a number of issues with mogas, although in the summertime mogas vapor pressure and avgas vapor pressure are nowadays about the same. Ethanol content and octane are the big show stoppers.
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The mogas you buy at the Texaco station doesn’t have the QC/QA that aviation fuels do.

That’s true.
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Probably would also need to go to electronic ignition with knock sensors and variable timing… more money.

There are technical problems with knock sensors in aviation engines; lots of the aerodynamic noise looks like knock to conventional sensors, which is why GAMI tried developing fiberoptic based sensors. But none of that is certified and ready for prime time. And you’re right about more money.
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Unleaded avgas can be made to equal the current 100LL… I do not know what the holdup is.

There were subtleties when one starts looking at the entire fleet, and then there’s the certification process itself. The FAA has very limited experience in certifying fuels, and has made missteps.
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Environmental benefit? The amount of aviation fuel used is microscopic

Perhaps, but there’s no safe lead exposure… from molecule one, the best we understand it, children exposed to lead suffer from reduced IQ. Today, 1/3 of the lead entering the ecosystem is from our “microscopic” avgas use, so it needs to go away as a matter of social policy. There are studies implicating the one remaining tetra-ethyl lead plant in Liverpool, England in adverse impact on children down wind. How does one stand tall about that?
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leaded gas supposedly helps lubricates the valves, but I think that can be addressed in other ways.

Leaded gas is actually bad for the valves. There’s scholarship and industry papers explaining that the valve problems we saw when lead was phased out of mogas came from the drop in octane, not the lack of lead; and the FAA has done at least one validating study on aircraft.
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Ethanol contamination is a ridiculously easy check. Just add 10% water, shake, & see if the apparent water volume increases.

So, what do you do if your airport tank is full of mogas-derived avgas that flunks that test? It’s not pretty. It needs to be controlled for upstream, not remedied after the fact.
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High temperature and high humidity reduce horsepower now, yet we accept it. Maybe just reduce the max gross weight?

But the impact of temperature and humidity can be calculated in an FAA-approved manner, per the POH and the AIM. To reduce horsepower will require a similar certification effort with flight testing, and that’s expensive.
 
Unleaded Avgas Update

Avgas December 2020 Update – updated - Part 2

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Not interested in paying for expensive engine modifications to burn lower octane fuel and thereby getting less horsepower, less gross weight, less climb performance, less speed.

Don’t forget, less range too, as fuel efficiency declines when you reduce compression ratio. The lower compression turbo Cirrus burn a gallon an hour more than the more efficient turbonormalized Cirrus with higher compression ratio.
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Kwik Trip has 91, no ethanol.

Don’t forget the plethora of different octane scales. That Kwik Trip 91 is actually about 86 octane on the aviation octane scale…
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Many of the QuikTrip locations have pure-87.

OK, that’s about 82 octane on the aviation octane scale.
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You’re overestimating the impact of a reduction in compression ratio. It would likely result in less than 5% decrease in peak HP.

I don’t think that’s the issue as much as the certification and modification expense.
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There are more turbo-charged engines in autos today than ever before, and most are running 87 to 91 octane.

They’re accomplishing that today with scheduled direct injection which doesn’t seem to work well with very large diameter pistons, say like in aviation engines. And the certification burden would be significant.
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I have an IO360 Lycoming with the SureFly variable timing. 8.7 compression ratio. I am guessing that I could run on the 94UL, without a problem.

First, note that your SureFly is only advancing the timing from stock, not retarding it. There’s no detonation detection. The certification standards require you demonstrate 10% fuel flow detonation margin at red line CHT and oil temperature. Flying behind an angle valve IO360 myself, I’d be very surprised if you could make that work. So, you’ll need to lower the CHT and oil red line temperatures, then do climb cooling tests to prove to the FAA that you still have adequate margin for the 100 F day… none of that is cheap, even if it might work.
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All they know is ‘lead bad, must get rid of’. The unintended consequences are rarely a thought.

I guess IQ impaired children are a consequence that is being considered, and given that, the forbearance for us to get our act together is astonishing.
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Their ignorance is matched only by their zeal for quick solutions.

This is a quick solution? Lead was regulated out of mogas in the early '90’s, the industry unleaded avgas task force began work in 1991, and declared failure in 2011… this has been anything but a quick solution. Fortunately, it turns out the task force was trying to solve the wrong problem; the real problem was much more amenable to solution.
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It’s been decades since I first heard the trope that 20% of the sales base burn 80% of the 100LL. I just wonder if there’s been a more recent snapshot. That study is 20-30 years old.

As you know the FAA does an every-three-year survey of aircraft utilization. My recollection is that their more recent analysis is that 30% of the aircraft are burning 70% of the fuel… that’s a distinction that doesn’t make much of a difference. See the PAFI papers on their website.
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It seems like competent FADEC could take care of the knock issue.

It could, but not without reducing performance, which introduces the large-cost certification issue, and the very-large-cost engine modification issue… plus time to comply.
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Having computer control over our ignition and fuel would let us run a lower octane fuel without losing horsepower. Shouldn’t be hard to develop a system for our engines

Yikes, I don’t think the science supports your assertion, it’s been attempted in the engine test cell. Depends on your definition of hard… time, cost, installation details, recertification…
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I could understand the lack of an STC for older planes. But the new stuff coming out has done nothing.

Cessna attempted with the IO580 in the 206, and the IO360 in the 172. But the IO580 blew the heads on the cylinders, and the marketplace didn’t want the lower compression 172, folks converted them to higher compression to improve power and fuel efficiency. Cessna responded to the marketplace.
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The Diesels do have slightly less horsepower, however all of the ones I know of are turbo, at cruise altitude the diesels end up being far more efficient. The Diamond 62 will carry 7 adults on 12-14 gallons per hour.

Careful how you measure efficiency. From an engineering and aircraft performance perspective, it’s horsepower per pound of fuel. Diesels appear to be more efficient because the fuel is heavier, so in HP/gallon it looks better. But, airplanes aren’t inherently limited by volume, but by weight… and in horsepower per pound, diesels don’t have much or any of an advantage.
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My understanding is that that 7:1 is what you have when the turbo isn’t … turboing. The whole point of turbo is to boost more air and fuel into the cylinders - so you have actually higher compression when the turbo is working.

Not accurate. You might have greater fuel energy packed into the cylinder, but you recover less of it… the thermodynamic power output is definitely dependent on compression ratio, and turbo boost can’t compensate for that.
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The latest FAA update (8/20/2020) just says, “The FAA, fuel suppliers, and aerospace manufacturers continue to develop high octane, unleaded fuel formulations. The goal of these efforts is to identify fuel formulations that provide operationally safe alternatives to 100LL. The PAFI program continues to support the efforts of fuel producers as they bring forth alternative, unleaded fuels for testing and evaluation.” Kind of a kick-the-can-down-the-road update from the FAA: https://www.faa.gov/about/initiatives/avgas/

Yeah, the FAA isn’t leading any longer, which might be a good thing.
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Infiniti has a variable compression turbo engine that can get up to 14:1 on 91 octane. However, there is quite a bit of tech/complexity involved in achieving that, direct injection being a big part of that, as well as some very efficient combustion chamber mechanisms. Most of that isn’t too useful for marine or aviation applications, since wide power adjustments aren’t really common for most aircraft.
Notice the cylinder volume and RPM generated by those high compression engines (often motorcycle engines). The cylinder volumes are small, and when the engine is making “real” power, the RPM are way up there. In comparison, our engines make full power at relatively low RPM and have huge cylinder volumes.
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Why does this matter? Detonation. Cylinders with large volumes are far more prone to detonation than engines at the other end of the spectrum.

In small cylinders, the flame front burns through the small cylinder volume fast enough that the fuel burns before the pressure and temperature at the “corners” of the combustion chamber self-ignite the unburnt mixture. In larger cylinder volumes (where the flame front has to travel several times as far), the fuel in the corners (the farthest points from the spark plugs) gets heated and compressed a lot (that’s a technical term) before the flame front arrives and you need high octane to make sure the fuel in the corners burns before it detonates.
Here’s a 1962 paper on the effects of cylinder size on detonation and octane requirements if you don’t mind registering: https://www.jstor.org/stable/44469482?s ... b_contents 1

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The thermal efficiency of the engine is directly related to its compression ratio. The higher the compression ratio, the higher conversion of heat to mechanical energy. That means a lower mass flow of fuel/air for a given output compared to a lower compression ratio Otto cycle engine. Lowering the compression ratio is “going the wrong way” for aircraft applications.

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Instead of a 2-decade sunset period that the EAA was prepping us for, it will be a 2-5 year sunset period.

I see no evidence that the EPA had any sunset time period in mind; in any case, the Supreme Court handed this responsibility to the FAA. That said, once a viable unleaded fuel is identified, the FAA will move quickly to require its use; but perhaps not as quickly as local jurisdictions may.
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offer two grades of fuel at airports.

As avgas demand continues to decline, no one has an appetite to invest in a second set of facilities; the diminished demand for both types of avgas would doom them to early extinction. The industry considered this in the '90s and moved on… factors today even more strongly support that decision.
 
Unleaded Avgas Update

Avgas December 2020 Update – updated - Part 3

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ship one grade of unleaded fuel, and very small amounts of octane booster (lead or other) and mix it at the pump

Lead is too toxic to be distributed that way, and no one wants to spend money on lead containing “solutions” to the no-lead problem.
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you could buy real lead additive at auto parts stores

That was never available. People marketed lead substitutes, but they really weren’t that, from an octane nor chemistry perspective.
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The EPA requires mogas to be oxygenated

No, Congress required that to appease corn farmers. There’s no technical justification for oxygenates for pollution control any longer; in fact, some studies show that pollution is greater with the ethanol mandate.
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You still need lead for valve lubrication.

Lead erodes valves, it doesn’t lubricate them.
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If the valve’s guides and seats were constructed in accordance with the latest specifications…

The last change in Lycoming valve hardness specs was 1974, and there aren’t many engines running valve seats older than that.
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Continental says that they believe their engines can make rated power on any of the proposed 100LL replacement even at slightly lower octane.

Continental made that claim, and were flying a Bonanza around the country with their supposed lower octane engine. Unfortunately, the cylinders cracked.
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The horsepower difference from lower compression ratio is comparatively minor.

Still requires unworkable certification costs.
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Fuel injection and angle valves raised the O360 engine to 200 hp on 100LL just by these two items. I don’t think compression was raised between the 180 hp O360 and the 200 hp IO360.

The compression ratio was raised from 8.5:1 to 8.7:1, and the angle valves are larger, allowing more fuel/air mixture into the cylinder, hence more power out.
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How many engines are running in test cells to establish that difference between mogas and 100LL?

GAMI has done extensive test cell work with a variety of fuels; their work does not support a feasible mogas path forward.
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Refiners sample and test every single run of avgas to ensure it meets the specifications before anything gets loaded in a truck.

Just like they do with mogas.
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Where is the lead mixed into the avgas in the distribution chain? I imagine it isn’t at the refinery, it’s at the distributor. And I doubt they have a truck or two that are specialized to only delivers avgas.

No need to wonder or doubt, these things are quite known and knowable. The lead is blended at the refinery by circulating the avgas tank, with its four components already batched in, through an eductor that sucks the lead out of the ISO container it arrived in from Liverpool. This circulation also serves to mix the tank. The dye and antioxidant additive are added through this same technique.
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I don’t believe any pipelines will carry leaded fuel anymore either, it’s all being trucked.

Avgas stopped moving by pipeline in the 60’s as the volumes became too small to tolerate the transportation mixing (transmix) that occurs in pipelines.
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Lots of fuel crosses the US/Canada border both ways as these two Canadian refineries do not produce avgas continuously.

Avgas is a batch product, unlike mogas that is continuously blended. There’s no reason a refiner couldn’t make batches consecutively, though, to remain in inventory, though it may not be economic to do so.
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Don’t know if any of the west coast refineries in Washington State produce aviation gasoline anymore.

Chevron in Richmond, California is the only west coast avgas producer.
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I’ve always wondered how the quality of AVGAS (100LL) changes over time. Some of these storage tanks at airports are huge, and I can’t imagine most of them are filled more than once a year.

Avgas has a one-year stability spec, unlike mogas that has a few month stability expectation. There aren’t many huge tanks at airports with avgas in them… most are holding monthly quantities.
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I think the cross-contamination argument is a bit over blown. If the tanker is actually empty, and you put 500, 1000, or 5000 gallons of AVGAS in it, it won’t matter which petroleum was in it before, in practice operationally. Regulatory wise is another matter.

And liability wise. Defend that decision in front of a jury…]
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There are a lot of neighborhoods around airports that have higher lead contamination levels. IIRC this is one of the arguments that the people trying to close Reid-Hillview are making.

That’s true, and the EPA has been supporting that by conducting new “ambient” lead testing around airports, with sensors located just a few feet from runup areas, for example. Since there’s no safe amount of lead ingestion, the EPA has also reduced the action level by two orders of magnitude.
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Seems to me those folks need to be more concerned with drunk drivers around Reid-Hillview.

What-aboutism is seldom effective argumentation in a regulatory discussion.
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It seems reasonable (to me anyway) to have two grades now: unleaded and leaded.

It doesn’t seem reasonable to anyone who has to pay for leak-detecting tanks, and segregated production facilities. No one in the industry is interested in that expense, including pilots once they find out how it might affect avgas pricing.
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In clean and green California unleaded is only available at San Carlos, and it is the new Swift stuff.

The Swift 94UL is the only unleaded avgas being produced, but there’s not enough of it; San Carlos runs out regularly. Reed-Hillview (RHV) just this week announced availability of 94UL there, to hopefully blunt community criticism of lead contamination of the neighborhood.
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Is there really not enough interest or is it willingness in adding unleaded as a fuel choice in the areas that have the volume of traffic to support it?

The economics don’t’ work to have multiple fuels.
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The quickest, easiest solution to this is to make flying our “religion.” The AIM is our “Bible.” A flight is a religious “service” during which we commune with Sky (god).

You’ve heard of the Church of the Lean of Peak, and their patron saint, Saint George of Ada?
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Big bore Lycomings and Continentals require 100 octane because they run higher compression ratios. But does that mean they won’t run just fine on 94UL? At what load/rpm do they start to suffer from detonation? If they start to detonate at max rpm, would planning a limitation of 100-150 rpm less make the aircraft useless or undesirable?

Combustion chamber size and compression ratio are the biggest drivers. Higher RPM actually helps avoid detonation. That’s why you see bikes with tiny cylinder volumes and 12:1 compression do OK at 10,000+ rpm on pump gas. To make the high compression (higher than roughly 8.5:1), big bore engines happy on 94 octane would mean reducing compression ratio, which hurts efficiency and power.
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Is more octane needed to operate an IO540, above the 94UL currently offered? Has there been definitive proof of that, or are we just speculating?

It depends on which IO540. One of the chosen test engines at GAMI in Ada is a 540, and it won’t meet certification standards on mogas or 94UL.
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The NA IO550 is a 8.5 CR though. No different than the O320D3G was in my Warrior II. No need for 100LL.

That’s an overbroad statement. Most 550’s breath much better than your O320, putting more fuel/air mixture into the cylinder per displacement cubic inch. That means more power, more heat, and more tendency to detonate.
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On FlightAware, I’m looking at the “airborne aircraft by type” page. First on the list, the most common type showing up there is the Cessna 172, with 565 airborne. The next most common GA type is the Piper Cherokee of the PA-28 persuasion, with 244 flying. Number 3 is the Skylane, with 146. Fourth is the SR-22, with 73. After that, it’s the C150 with 62, C152 with 46, M20 with 45, Bonanza 36 with 32, and the DA40 with 29. I believe there is an 80-20 or thereabouts split, but the 80 and 20 are reversed from what “everybody knows”.

Have you corrected your calculation for fuel flow? Is your sample statistically valid? The FAA’s relook a few years ago was not far from the 80/20, maybe 70/30.
 
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This ^^^^^^^

Was me that asked after reading it over on Beechtalk. A little dated since the latest GAMI releases but still the best summary I’ve seen. Great post and I’m very thankful Mr. Milner shared his knowledge with us. Hopefully it gets read over here.
 
Octane Scales

Hi Paul,

Thank you for posting that interesting read. I do have a question on the quote below:

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Kwik Trip has 91, no ethanol.

Don’t forget the plethora of different octane scales. That Kwik Trip 91 is actually about 86 octane on the aviation octane scale…
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Many of the QuikTrip locations have pure-87.

OK, that’s about 82 octane on the aviation octane scale.

I've read a couple of times here on VAF that mogas' and avgas' octane numbers don't mean the same thing which doesn't make much sense to me because my readings indicated that iso-octane and heptane are used as the high and low references. You mentioned 'octane scales' in your post. Could you, or anybody else, expand on this so that I can get it straight in my head?

Thank you,
 
Hi Paul,
I've read a couple of times here on VAF that mogas' and avgas' octane numbers don't mean the same thing which doesn't make much sense to me because my readings indicated that iso-octane and heptane are used as the high and low references. You mentioned 'octane scales' in your post. Could you, or anybody else, expand on this so that I can get it straight in my head?

The “measurement methods” section of the Wikipedia page on octane rating has a good, straightforward overview.

https://en.m.wikipedia.org/wiki/Octane_rating#Measurement_methods
 
MON to MON?

Hi Spacedoc,

From that Wikipedia article, it would seem that 100LL has a MON rating of 100 octane for "aviation lean". The Wikipedia citation points to this doc (which is also an interesting read):

http://www.txideafarm.com/unpublished_blend_paper.pdf

Using Wikipedia's data for USA/Canada:
Regular: MON of 82-83 octane
Mid Grade: MON of 84-85 octane
Premium: MON of 86-88

These numbers agree with Paul's. So, it appears that it's a matter of comparing MON (avgas) to MON (mogas) - correct?

Thanks,
 
Lots of folks here on VAF have been burning lousy Mogas in their Lycs for years with no apparent ill effect. Yes, you have to watch the timing at high MAP and the CHTs to do it successfully, but that's easy enough if you understand these things and are using a programmable ignition system so you can tailor the advance curve.

So the theory and conjecture is great here but let's look at the actual flying examples using the stuff too.

I care less about what turbo PA31s do for fuel in the future than what we can use in naturally aspirated Experimentals now. The universal drop in fuel for all is clearly a difficult nut to crack and that's why you see Swift selling their 94 UL for a bunch of years now to the lower hp folks now at multiple airports in the US. I say good on them for taking this step. At least they got the ball rolling and hopefully this leads to a higher octane UL avgas to suit the higher performance engine fleet out there.
 
I've read a couple of times here on VAF that mogas' and avgas' octane numbers don't mean the same thing which doesn't make much sense to me because my readings indicated that iso-octane and heptane are used as the high and low references. You mentioned 'octane scales' in your post. Could you, or anybody else, expand on this so that I can get it straight in my head?

Thank you,
Hi David,
Thanks for the acknowledgement.
Yes, 2,2,4 trimethyl pentane (a very specific isomer of iso-octane) is used as the 100 reference on ALL octane scales, and normal heptane is used as the zero reference on all octane scales. But of course, the fuel you BUY doesn't contain any normal heptane (hopefully) and not a lot of 224TMP either.

So the question becomes how does the blended fuel do under the engine conditions of your engine?

There are four commonly used octane scales today... F1, F2, F3, F4, aka research octane, motor octane (mogas), motor octane (avgas lean rating), and aviation rich.

The two motor octanes, F2 and F3, are very similar, but as became abundantly clear during the creation of unleaded avgas, there are important differences. Some of the industry STILL hasn't accepted that.

The excellent Wikipedia article summarizes the differences, but RPM, spark advance (varying as much as 45 BTDC to 13 BTDC), induction air temperature, cylinder head temperature, boost all vary between the tests... so very different numbers emerge for typical fuels... even if 224TMP measures 100 on all of them (by definition!)

Paul
 
The universal drop in fuel for all is clearly a difficult nut to crack and that's why you see Swift selling their 94 UL for a bunch of years now to the lower HP folks now at multiple airports in the US. I say good on them for taking this step. At least they got the ball rolling and hopefully this leads to a higher octane UL avgas to suit the higher performance engine fleet out there.

The fuel problem was a science project, successfully completed about a decade ago... getting the FAA on board took about another decade.

In any case, GAMI now has an STC for their 100UL for Lycoming powered Skyhawks... and they've completed almost all the testing for fleet-wide applicability. The FAA has requested two additional tests, which GAMI had already completed informally years ago, but now will repeat formally with FAA review. GAMI has said they expect full fleet approval from the FAA by 2Q22... and implementation work with AvFuel is underway.

It's great to use whatever fuel is available locally when you know how to make it work... but lots of us like to use our airplanes to go places, so it's real useful if a known usable fuel is available at airports we stop at along the way... if of course truck drivers are available to deliver it.

Paul
 
Swift has had a STC for their 94UL for quite a while now applying to about 2/3rds of the US GA fleet. 94UL could be used on most RVs since these have the same engines. The problem right now is lack of production and lack of wide distribution, which face all the contenders.

It would cost billions nationwide to install new tanks and you'd have to convince many hundreds of FBOs to carry your fuel along with 100LL. That's unlikely to happen.

Now if an UL fuel meeting all the specs of 100LL was available and the FAA/EPA banned 100LL, problem solved as the FBOs would have to come to you to fill their present tanks.

Presently, this really leaves Swift, GAMI and whoever else is in the game to offer their present fuels as boutique fuels to interested FBOs, flight schools, individuals etc.

STCs are of limited value if you travel with your plane and can't buy the fuel anywhere. More useful for flight schools and individuals who fly mostly locally.

It's a big Catch 22. If the FAA holds out for an UL fuel which meets every 100LL spec, including specific gravity, we may be in for long wait still for the universal drop in replacement.
 
Swift ... problem right now is lack of production and lack of wide distribution, which face all the contenders.
Swift seems to be resisting licensing others to blend their fuel for them... given the demand, it would seem to make sense to license a blender in California to meet the local demand. But apparently that doesn’t appeal to their business model.

this really leaves Swift, GAMI and whoever else is in the game to offer their present fuels as boutique fuels to interested FBOs, flight schools, individuals etc.
It’s a bit more pointed than that now in California, where certain jurisdictions have already directed their regulators to figure out how to outlaw leaded avgas. If they succeed, there are other jurisdictions that will jump on this bandwagon. Anti-avgas politicians get green attaboy points from some of their constituents, and they consider that the number of folks that care about avgas availability to be nominal.

STCs are of limited value if you travel with your plane and can't buy the fuel anywhere.
I don’t agree. If you’re traveling, and the available fuel at airport X is unleaded avgas, the STC is just what you want... it has tremendous value. If you then land at airport Y, and they have 100LL, you buy that. Having 100LL available at *some* airports doesn’t remove the value of the STC for when you land at an airport with ONLY 100UL.

If the FAA holds out for an UL fuel which meets every 100LL spec, including specific gravity, we may be in for long wait still for the universal drop-in replacement.
I concur. But... after all the participants withdrew from PAFI because of the no-win approach, the FAA realized they’d have a hard time declaring success to Congress for the $100 million spent so far on that boondoggle. So the FAA changed the rules, and are now reportedly [the FAA maintains it’s a secret] working with Phillips/Afton Chemical and Lyondell Chemical/VP-Racing on fuels that don’t meet every 100LL spec... which of course is where the FAA should have begun in 1991 when the Coordinating Research Council (CRC) Unleaded Avgas group launched. But that’s sad water under the bridge at this point.

Paul
 
So the FAA changed the rules, and are now reportedly [the FAA maintains it’s a secret] working with Phillips/Afton Chemical and Lyondell Chemical/VP-Racing on fuels that don’t meet every 100LL spec... which of course is where the FAA should have begun in 1991 when the Coordinating Research Council (CRC) Unleaded Avgas group launched. But that’s sad water under the bridge at this point.

Paul

so, like, what specs wont the new fuel meet?
cant be a paint remover
has to be less than a gazillion dollars a gallon???
 
I concur. But... after all the participants withdrew from PAFI because of the no-win approach, the FAA realized they’d have a hard time declaring success to Congress for the $100 million spent so far on that boondoggle. So the FAA changed the rules, and are now reportedly [the FAA maintains it’s a secret] working with Phillips/Afton Chemical and Lyondell Chemical/VP-Racing on fuels that don’t meet every 100LL spec... which of course is where the FAA should have begun in 1991 when the Coordinating Research Council (CRC) Unleaded Avgas group launched. But that’s sad water under the bridge at this point.

Paul

I had not heard this part though someone from Lyondell contacted me a couple years ago in search of an ignition system with programmable timing for a fuel research engine as part of their UL avgas development.

Maybe they will pull out the rug from under the original PAFI participants...

Will the others be allowed to participate again with the new, looser specs?
 
I had not heard this part though someone from Lyondell contacted me a couple years ago in search of an ignition system with programmable timing for a fuel research engine as part of their UL avgas development.

Maybe they will pull out the rug from under the original PAFI participants...

Will the others be allowed to participate again with the new, looser specs?

My guess is that anyone working through the official program with the FAA will have their hands so tied up in red tape that they will be hogtied from the beginning - and the private ventures that just ran out and DID it will be the ones succeeding.
 
so, like, what specs wont the new fuel meet?
Can't be a paint remover has to be less than a gazillion dollars a gallon???
Neither of those was in the 100LL spec. :eek:

GAMI's fuel is heavier (by 5%) than 100LL, and has a slightly higher end boiling point.

Swift's fuel is heavier, has a higher end boiling point, and has presented cold-start difficulties.

Shell's fuel (which removed paint) contains alcohols, and all oxygenates are forbidden by the existing 100LL spec.

Phillips and Lyondell both have manganese, not contemplated in the 100LL spec... Lyondell also has two different kinds of oxygenates, per their patent.

Gazillion has not been defined by the FAA.

Paul
 
Will the others be allowed to participate again with the new, looser specs?
We don't know, but historically the FAA hasn't allowed participants to join mid-program.
It's not clear that any of the others WANT to participate in PAFI... it's a burdensome process without much apparent advantage.

Paul
 
We don't know, but historically the FAA hasn't allowed participants to join mid-program.
It's not clear that any of the others WANT to participate in PAFI... it's a burdensome process without much apparent advantage.

Paul

FAA has invited any fuel offeror to participate in PAFI, including GAMI, regardless of timing. Yet, some still refuse to participate. The question is why? Are they afraid of the transparency required or the demands of the testing? Burdensome? You bet! Want to trust your life to "whatever"? Ask yourself this: why would a fuel supplier with nothing to hide refuse to submit his fuel to the FAA and OEMs for testing or scrutiny by the ASTM body for an industry specification? Why should you trust your life on anyone's claims without independent vetting? Why would an allegedly impartial reporter and industry expert question everyone's fuel but promote one without question? Important questions in these times.
 
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FAA has invited any fuel offeror to participate in PAFI, including GAMI, regardless of timing. Yet, some still refuse to participate. The question is why? Are they afraid of the transparency required or the demands of the testing? Burdensome? You bet! Want to trust your life to "whatever"? Ask yourself this: why would a fuel supplier with nothing to hide refuse to submit his fuel to the FAA and OEMs for testing or scrutiny by the ASTM body for an industry specification? Why should you trust your life on anyone's claims without independent vetting? Why would an allegedly impartial reporter and industry expert question everyone's fuel but promote one without question? Important questions in these times.

It sounds like they were getting tired of the whole thing when I emailed two of the participants and that the path forward was likely to continue to be slow.

It shouldn't take a decade plus to do this. Set the spec, invite participants who think they can meet it and then do the dyno, lab and flight testing.

Looks like nobody could meet the original spec so now the FAA has changed it. Everyone gets to start over again after flushing millions and years down the toilet. I could feel the frustration in the responses I got.

Now if a company didn't do enough lab testing to find out that their formulation removed the paint off the wing or dissolved the tank sealant, that's kind of elementary...
 
Ask yourself this: why would a fuel supplier with nothing to hide refuse to submit his fuel to the FAA and OEMs for testing or scrutiny by the ASTM body for an industry specification?

Why indeed?

Well here's one very good reason why - these are private companies looking to sell a product and make a profit on it. If the program, due to the very nature of the way it's set up and regulated, appears to be "dead on arrival" with no hope of success, why would anyone want to participate?

If it's not going to make money, they (the private companies) are not going to play the game. If it's capable of making money but not for 10 more years, they aren't likely to play the game. The nature of capitalism itself is such that people will put their money and effort where it will do the most good in the shortest period of time. If the program is run by buearacrats with no interest in following science, well, there just ain't NODODY got any time for that...

As I tell people regularly in my life - "Ya'll might get to make the rules, but I get to play the game."
 
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It shouldn't take a decade plus to do this. Set the spec, invite participants who think they can meet it and then do the dyno, lab and flight testing.

Looks like nobody could meet the original spec so now the FAA has changed it. Everyone gets to start over again after flushing millions and years down the toilet. I could feel the frustration in the responses I got..

It's not quite like that, Ross. The FAA has not changed the spec, first of all. The fuel standard is still ASTM D910 and the engine test plans developed during PAFI 1.0 are still used. What is different now is that both the FAA and fuel suppliers have learned from previous mistakes.

The PAFI entry standards are now stricter than ever and include more materials testing so that the previous mistakes aren't repeated. This will keep out fuels that just don't have what it takes to be a "drop in" for 100LL. Is it challenging to meet this high standard, absolutely. Is it impossible, absolutely not.

The real question is whether the regulators and pilots will have the patience to wait for a proven answer or throw caution to the wind. Time will tell.
 
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