MOGAS/E85 etc.?

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Rhino

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One of the things I like about living in the south is that there's a lot of folks with race cars and boats, so there are stations that sell pure gasoline for these purposes.
 
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pfarber

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While possibly not relevant to the original post, it's worth noting that E10 and E15 are significantly more volatile than gasoline (or 100LL). Under some conditions (high altitudes, elevated fuel temperatures in the tank, lines, gascolator, etc) and some fuel system configurations, the resultant formation of vapor bubbles in the fuel system can cause trouble. Once we get more than about 50% ethanol, the volatility (as measured by Reid Vapor Pressure) is less than gasoline, so the likelihood of these problems decreases.
With modern EFI and in-tank pumps, vapor lock isn't a significant concern. But some planes use gravity feed to a carb that doesn't do well with bubbles.

View attachment 114543

Edited to add: The graph above was interesting to me. Has anybody got a simple explanation for the shape of that curve (i.e. why E10 would be more volatile than either pure gasoline or pure ethanol?) Thanks.
This is pure conjecture.

What part of 'the FAA fly a 172 for 10+ years with nothing but 100% ethanol and had ZERO problems' is confusing people?

Airplane fuel systems are brain dead simple compared to auto fuel systems. The FAA test plane only needed the carb rejetted and rubber changed to ethanol safe and it ran flawlessly for 10+ years.

No, I don't care about your boat/1980's car stories. They mean nothing. This issue is 100% solved and the only reason its coming back to life is from uninformed people regurgitating old wives tales or incidents from bad MX. Not the fuel.


The above study should prove enlightening.
 
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TFF

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The FAA takes the stance that fuel poured in should not take maintenance to correct issues to make it run good. Your only choice is pouring fuel in. Rejeting is not acceptable to the FAA. That changes the type certificate. That is recertification. Common sense can’t be in play either. What keeps someone from pouring 100LL in if converted. Lowest common denominator is the game the FAA plays. It does not play it for you, it plays it for your neighbors, that’s who they care about complainants from.
 

pjphilli

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The actual % is rarely that high here in the Midwest. It varies with time of year (due to the average temperature fluctuations). Typically, terminals offer high ethanol blends from 50 to 75%. It depends on where it's going to be sold. As to the octane, ethanol is an octane enhancer, and a 10% blend will give a 3 to 5 point increase. It takes 83 octane neat unleaded up to 87. It takes 91 octane neat premium up to 94. I think the highest octane we posted for a blend recipe was 104, but I don't remember the ethanol % (I'm retired, so the memory is going!). The thing about adding ethanol is that it effects the vapor pressure as well, so you see a drop in fuel economy due to increased evaporation (keep your tanks full to minimize that). Also, it has a strong affinity for water vapor, and entrained water in your fuel, so there's chances for phase change dropping water into your tank, or pulling water/sediment into your fuel line. Check those fuel filters!
Quick comment on “octane”… please remember for our international friends what we see in the USA posted on the pump sticker is not “Octane”, it’s anti-knock index. The “R+M/2” is pretty unique to US. Octane is measured in a variable compression single cylinder lab engine under 2 different conditions yielding a “research octane” and a “motor octane” value. That the R and the M. Most other geographies, E.G.: the EU, Australia, S. Africa, etc. around the world use the Research Octane value which is the higher of two. A 90 octane elsewhere is closer to 85 R+M/2 in USA… brevity is old guy on phone…
 

Bigshu

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This is pure conjecture.

What part of 'the FAA fly a 172 for 10+ years with nothing but 100% ethanol and had ZERO problems' is confusing people?

Airplane fuel systems are brain dead simple compared to auto fuel systems. The FAA test plane only needed the carb rejetted and rubber changed to ethanol safe and it ran flawlessly for 10+ years.

No, I don't care about your boat/1980's car stories. They mean nothing. This issue is 100% solved and the only reason its coming back to life is from uninformed people regurgitating old wives tales or incidents from bad MX. Not the fuel.


The above study should prove enlightening.
This is exactly why the whole STC thing for mogas drives me nuts. If an engine originally was certified for 80/87, it should be able to burn any blend of ethanol from 10% to 100% with no problem, and no need to pay someone for a sticker and logbook entry to do it. Just do it. Get the bureaucrats out of the way. Obviously, you need to prepare the engine for the ethanol, but you have to work on the engine periodically anyway, so take care of that issue the same time you're already getting something done to the engine. How many home builts are flying on mogas right now? How many auto conversions are out there burning plain Jane pump gas? Lots.
 

Bigshu

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Your only choice is pouring fuel in. Rejeting is not acceptable to the FAA. That changes the type certificate. That is recertification.
That is why the FAA is a dinosaur agency. That is why GA can't have nice new things, or solve old ICE issues that car makers moved beyond decades ago.
 

rv7charlie

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Back when I was a student pilot (and a lot younger and dumber), I bought a Dragonfly (the tandem wing; not the hang glider tug) with only a few hours on it. Trailered it home, and reassembled at the local airport. While getting it prepped for 1st local flight (by a licensed pilot), I fueled it up with mogas from the nearest discount gas station. Next time I went to the airport, the plane wouldn't start. Had spark, so I checked fuel delivery. Nothing coming out of the gascolator, so I pulled its bowl. The bowl's gasket had partially dissolved, and the black gummy remains had completely coated the gascolator screen. The cheap gas had ethanol in it. When I looked closely at the header tank, the fiberglass was already getting soft. Replacing the gasket and removing all the E-gas (I was too ignorant when I bought the gas to understand the danger) solved the problem. If I'd been a licensed pilot at the time, or if my test pilot had been available a bit sooner, the fuel stoppage could have happened in the air.

Point is, STCs for certified a/c do make some sense; the issuer has to make sure that there aren't any 'gotchas' waiting to bite an unsuspecting owner in the backside. In the case of 'clean' mogas, the STC issuer is making sure that there won't be any vapor lock issues, for instance. Think about it. Most pilots can't even change the oil in their car; they pretty much expect the FAA to protect them, whether they can articulate that or not. FAA's just trying to do the job they're charged by law to do; make flying as safe as reasonably possible.
 

tspear

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That is why the FAA is a dinosaur agency. That is why GA can't have nice new things, or solve old ICE issues that car makers moved beyond decades ago.
You will not like the answer. Auto companies were required to become E10 compatible roughly 15 years before it happened. Auto companies had two decades to prepare for unleaded. They had almost three decades to prepare for low sulfur diesel.
The FAA could go the same route, but owners will not like it; but GAMA would! Announce a new fuel requirement, give everyone fifteen years to comply by buying a new plane, or doing the requisite research to know no effects and get an STC....

Tim
 

dwalker

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[
You will not like the answer. Auto companies were required to become E10 compatible roughly 15 years before it happened. Auto companies had two decades to prepare for unleaded. They had almost three decades to prepare for low sulfur diesel.
The FAA could go the same route, but owners will not like it; but GAMA would! Announce a new fuel requirement, give everyone fifteen years to comply by buying a new plane, or doing the requisite research to know no effects and get an STC....

Tim
Pretty accurate. All cars imported into the US starting around 1987-88 were required to have alcohol compatible fuel systems, with domestic cars needing to be compliant in 1990. The rubber bits were the easy part. The harder and most important part was the aluminum parts needing to be internally anodized to prevent the ethanol from eroding the aluminum.
My personal experience is a lot of people had poor experiences that were attributed to the ethanol in the fuel and it was not the actual issues.
 

TFF

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The FAA might be a dinosaur organization, but it is their football. It will always be their football. You are trying to change physics. The only way the FAA changes something is with more restriction not less. You can wait, wish, and cry, but that also means you won’t fly.
 

pfarber

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The FAA might be a dinosaur organization, but it is their football. It will always be their football. You are trying to change physics. The only way the FAA changes something is with more restriction not less. You can wait, wish, and cry, but that also means you won’t fly.
E/AB. Build or buy.

The GA fleet of Piper PA28s and 152/172 is hot garbage.

Once the old guard of pilots who solo'd in Piper Cubs finally dies off, we'll have people who understand modern electronics and practices. I hate to make car to AC comparisons, but when they work: A modern car engine can go 100k miles/10 years without any maintenance except oil changes.

A certified engine can't go more than a few dozen hours without needing an afternoon's week of work. Yet one is considered 'reliable'.... and they don't blink an eye when they have to dump a grand or two into a low compression cylinder after a few hundred hours.

Ethanol is not an issue. We know the changes you need to make, but even though there is Cessna 150 certified to run off of ethanol, Cessna's official policy is that ethanol is bad and will do bad things. lol sure Cessna, sure.
 

tspear

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Ethanol is not an issue. We know the changes you need to make, but even though there is Cessna 150 certified to run off of ethanol, Cessna's official policy is that ethanol is bad and will do bad things. lol sure Cessna, sure.
I disagree with this one based on what I have read from Cessna. They stated it would require new performance charts, and some modifications to the engine/airframe, and some testing. And heavily implied is there is no money from the feds or the market to pay for it, so Texitron has no interest in it.

Tim
 

TFF

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A few dozen hours equates to about 3500 miles. Oil change in order. Cleaning plugs. Some engines need it more than others, but the biggest reason I have found if you don’t, the plugs will get stuck. Air cooled cylinders are hot. Lots of auto stuff is EPA driven. 10,000 mile oil changes and not changing spark plugs for 120,000 miles is two of them. My first boss drove a car 80,000 miles with no oil change, didn’t believe in them; his math, he saved money. My first car leaked oil so bad, I almost never changed the oil. Just dump more in it. I still got it. I change my oil in my cars and trucks at 3000 no matter what they say. Just about anything will beat the 100,000 mile warranty. I want the other 200,000.

What is wrong when Lycomings and Continentals need a lot of maintenance? It probably because they have been sitting around. Most manufacturers have a 10-12 year wipe their hands from it. I love the YouTube videos of people pulling junk out of the woods and trying to make it run. You wouldn’t make your wife drive it though. You might have an engine that has 500 hours on it, but it’s thirty years old. It’s been sitting and rusting more than being used. An auto engine will fair no better. I’m all for running used engines in homebuilts, but there is no magic. You will have to fix any of it. Either all up front or as you use it up.
 

tspear

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@TFF

I am curious what EPA stuff you are referencing that reduces MX. I have heard the claim but never found or seen to an actual reference.
With synthetic oils, many cars are now getting much more than 3K miles per oil change;. My older Subaru uses smei-synthetic and has a 7.5K interval, that is only 150 hours at 50 MPH average, if you go with all the city drivening I have done in the past couple years instead of the national average, it would be much higher than 150 hours.
I compare that to the 35 hours I have now on my current Cirrus. Over 35 hours, I add an average of 4 quarts; and do an 8 qt oil change. That is 12 qts times five for a total of 60qts compared to the 4qt I would have replaced in my Subaru (plus four extra oil filters).
.
The reality is the engine in my Cirrus is reasonably efficient in cruise which is likely 2/3 of the time the engine is running. But it is very dirty, uses a very dirty fuel, is a maintance headache, requires many processes/procedures to reduce/prevent critical failures, and in theory could be replaced with a much cleaner/easier power plant. The problem is the cost to develop such a power plant....

Tim
 

TFF

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Yes the synthetic makes longer oil changes possible, but the dirt and carbon is still there. Auto manufacturers are required to have the elevated maintenance schedules. Less oil changes means less used oil to deal with environmentally. Taking the spark plugs out counts towards gas vapor loses to the atmosphere. These are promises made to the government. The non service transmissions on my Tundras are not because you shouldn’t change the oil, but because most never do, they sucker you into another less old oil in the environment. They can easily make warranty , but if you change it after warranty, the new detergent will kill it.
 

skydawg

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I can share recent experience in using ethanol car fuel, 85 octane, fuel in a C172 (it has a GM V8 aluminum engine). first off, I have a background in marine industry as well as aviation engineering. Ethanol caused huge issues in boats for many reasons- melted fiberglass tanks, destroyed fuel fittings, carb gaskets, absorbed moisture and rusted out carbs, and it acted as a solvent which broke up hardened contamination in systems that had been there for decades.

for Our c172 project, we replaced all but one seal (o rings and gaskets) with ethanol rated seals. We intently left the right wing sump drain (a spring loaded push open valve for inspecting fuel and draining water) original. Because of knowing ethanols solvent property, we routinely inspected each seal and monitored fuel gascolator filter element. Just as expected, the 1969 airframe seemed to produce contaminates on a constant basis for the first 2 months….ethanol cleaned the system of all contaminates and flushed them down stream. 16 months later, the original seal on drain began to leak (upon inspection, was deformed, hard and brittle….. but it was in there for over a decade prior as far we could tell from logbooks). So lesson being really monitor the system after switching to ethanol fuels, even if you think your system is perfectly clean.

ethanol has a lot of advantages, and some disadvantages as we all know. For our C172, challenges we’re far out weighed by benefits. We didn't need to burn spark plugs clean before takeoff so didn’t have to stop for a runup ( we do if using AVGAS), gas was about half the cost and even got off highway use tax rebate, and a few others. When flight testing with AVGAS, oil lab analysis indicated we needed to change oil every 60-80 hrs, wherein with car gas recommended oil change intervals is 200 hrs (synthetic car oil). Also, spark Plugs stayed clean with little need to inspect on a regular basis (the system also has a OBD display which alerts if there is an issue in a specific cylinder).

As far as lower vapor temperatures, it’s really not an issue with modern EFI systems as it’s under pressure and most systems cycle majority of fuel feeding hot engine bay, so fuel stays cool in feed lines. But it is an issue with carb and mechanical FI systems, such as in aviation systems that already have an issue with vapor lock.

this is likely a moot point as MOGAS STCs are for ethanol free gas only. But, many experimentals are switching to auto engines from legacy and may experience these same issues.

as far as octane numbers, we started with higher octanes in the 90’s and been flying with lowest octane available, 85. On hot days, we did see some timing adjustment by the ECM, but it was minimal and well within specs. its important to note the engine is rated at over 400 HP in marine application, but is flat rated to 200 HP for airframe limits. So this obviously reduces cylinder pressures and temps and need for higher octane fuel.

I did video comparison of engine oil from running with AVGAS vs MOGAS, and there was a visible difference. I will post it on our YouTube page link (corsairV8.com) if I still have it.
 

TFF

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Depends on oil change schedule. 25 hours or 50. We both are on the same page. I find that if you change oil at the 50, it was toast at 40. I would rather have clean oil than force it. I would only change oil at 50 on a commercial operation where maintenance is scheduled shop time.
 
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