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Comment by Reason077 | Hacker News Reader

The problem isn't so much the fuel, it's the ancient piston aircraft (or at least, ancient engine designs) that are still kicking around.

There are modern piston aircraft engines that not only run fine on unleaded fuel [1], but are even certified to run on standard automotive fuel ("Mogas"). There are videos on YouTube of pilots landing on remote highways and pulling up to regular gas station pumps to refuel their aircraft!

[1] https://en.wikipedia.org/wiki/Rotax_912

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> The problem isn't so much the fuel, it's the ancient piston aircraft (or at least, ancient engine designs) that are still kicking around.

Yes, that's my understanding too. Aviation piston engines are stuck in 1950, largely because more stringent regulations have made it more expensive to develop new engines vs. keeping producing largely existing engine designs grandfathered in, and also because the market is pretty small.

> There are modern piston aircraft engines that not only run fine on unleaded fuel [1], but are even certified to run on standard automotive fuel ("Mogas"). There are videos on YouTube of pilots landing on remote highways and pulling up to regular gas station pumps to refuel their aircraft!

AFAIK the usefulness of this has been reduced, due to a lot of automotive gas containing ethanol. The engine itself might work fine with an ethanol blend, but the fuel system (bladders, lines, etc.) might not. There is apparently also a fear of vapor lock or other trouble if the ethanol and the rest of the fuel separate in the tank.

Right. Contaminants like ethanol are no bueno. Ethanol absorbs water from the air, and an ethanol-water mixture corrodes fuel lines, gaskets, and other parts. And thanks to the EPA and the corn lobby, it’s getting harder and harder to find uncontaminated gasoline.

I’m all for the transition to 100UL. I don’t want to breathe lead either. But they need to either come up with a replacement that won’t destroy airplane engines, or they must fund the replacement of everyone’s engine with ones that will work with (and can be certified for) the new fuel.

> There are modern piston aircraft engines that not only run fine on unleaded fuel [1], but are even certified to run on standard automotive fuel ("Mogas").

Note that mogas is not necessarily the same as what one gets at a car gas station, called pump gas by some:

> Automotive fuel from the pump is NOT the same everywhere you go. There are summer blends, winter blends, geographical blends within the seasonal changes, varying levels and types of oxygenates (not just ethanol) and when tanks are switched over a mixture of "in between". The pump labeling is accurate for octane, and in some parts of the world, the maximum percentage of ethanol. It doesn't tell you everything you need to know to make "pump gas" fit-for-purpose for aviation and it's not just about octane and ethanol. We need to control a wider range of fuel properties for aviation. Your equipment, your life and the lives of your passengers depend on it. Let's walk through exactly what Lycoming did in authorizing automotive gasoline - "mogas" - for our engines. It's also suggested that you read Section B of the latest revision to Lycoming Service Instruction 1070 - and read it carefully.

* https://www.lycoming.com/content/unleaded-fuels-part-2

My airplane has a 1950s era engine (Continental O-300), which is able to run on automotive fuel (“mogas”). However, mogas is not much available at the airports. If there was a way to obtain it, I would use it. But it’s almost never an option.

One of the local flight clubs where I live has a trailer full of gas canisters. Once a week, someone drives with the trailer to one of the few gas stations left with ethanol-free fuel and fills up the canisters. It’s a lot of work but it saves the club a lot of money since mogas is much cheaper than avgas.

Very few piston airplanes above the entry-level and trainer fleet are normally aspirated. The piston airplanes that fly a lot (mostly in commercial service) are overwhelmingly turbocharged.

Those are the ones that need the higher octane fuel (and the ones that burn the most of it). I could have bought paperwork (the Petersen STC) to allow my Cessna 182 to burn alcohol-free unleaded car gas. That is not available for the replacement engine I installed in that airplane nor for my current airplane (nor any turbo airplanes to my knowledge).

The turbocharged variant of the Rotax, the 914, is also certified to run on unleaded / automotive gas:

https://en.wikipedia.org/wiki/Rotax_914

Fun fact: This engine also powers the USAF's Predator drones!

Which is tiny; it has 115 horsepower for 5 minutes and 100 continuous. That’s still trainer and entry level or 2-seat Cessna 152 sized engine and about 1/3 the power of a modern single-engine Bonanza.

For what it's worth, some kit planes are now using the Rotax 915iS (Newer injected variant of the 914) for 4-seaters [1]. This engine puts out 135 continous up to 15,000 ft. For comparison, a given Lycoming 161HP non-turbo engine (requiring 100LL) shouldn't run above 75% continous (120HP), and can't put out more than this above 9,000 ft [2].

[1] https://en.wikipedia.org/wiki/Sling_Aircraft_Sling_TSi [2] https://encoreflight.com/wp-content/uploads/2017/06/Piper-Wa... Page 100

Not quite - there are turbocharged piston engines running on Jet A1 (and even Diesel): https://en.wikipedia.org/wiki/Austro_Engine_E4

There certainly seems to be some innovation here, in this case driven by Diamond in Austria. It may have "helped" that Avgas prices over here in Europe are really quite high.

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