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.
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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.
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…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!
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.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.
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.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.
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....
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.
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.
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