80-octane avgas becomes extinct

Accoring to the AOPA, Kern Oil, the last known refiner of 80-octane avgas, has stopped making all aviation gasoline. At the time the article was written, 22 airports still had 80-octane aviation fuel. Not many, considering the number of airports in this country! Owners of aircraft that run on 80-octane will have to obtain an STC to run on automotive gasoline (“mogas”), or an STC to convert their aircraft to an engine that is happier running on 100LL avgas.

Would a moderator please change “cotane” to “octane” in the thread title? Thanks. :o

Are aircraft engines that much different than automotive engines that they can’t just use higher octane gas without any ill effects?

I mean, my car calls for 87 octane, but can use 94 with no ill effects (no good effects either). I always thought that the octane rating was a basic indicator of the fuel’s resistance to detonation, and as long as you’re above the engine’s minimum, you’re ok, even if you are basically burning money by running higher octane gas.

On further reflection, I’m starting to think it’s one of those FAA regulation things, like the one where I used to work. A certain bearing manufacturer made a bearing that was good to use in both tractor engines and in helicopter gearboxes. The FAA only certified the part as resold by the helicopter manufacturer, so if the maintenance guys bought the same exact bearing directly from the bearing manufacturer instead of the helicopter manufacturer, they were doing something illegal.

Hate to see it go, I guess. (hell, I’m old enough to remember the purple stuff :slight_smile: )

Sorta on topic: My Cherokee was STC’d for auto gas, but the FBO didn’t sell it, and promised a stern response to anyone caught transporting it onto the field. (Safety concerns, mainly). Due to that, and my A&P’s warnings, I never used it. The plane thrived just fine on 100LL. To this day, I don’t understand why some mechanics are so deadset against automotive fuel.

Isn’t aviation gas still leaded? Depending on the valve seats in a particular engine, using automotive unleaded would screw the engine up badly if it didn’t have the lead compounds to prevent valve seat wear.

I don’t know about lead still being in the fuel, but running an engine on unleaded gas that’s originally designed to run on leaded isn’t an instant death sentence for the engine (at least as far as automobile engines go, I doubt that aircraft engines are that much different). With no modifications you can run the engine for years without trouble. Ideally, the valve seats should be replaced with hardened ones, but it’s not absolutely necessary.

I was always told that LL100 stood for Low Lead 100 Octane.

Was that just a bunch of hooey?

Since you have no choice but to user higher octane it’s time to start hotrodding those old J-3s, 65hp isn’t enough. High dome pistons to raise compression, heck stroke and bore at same time. Hot cam, roller rockers, port and polish job to the heads. Finish off with custom headers and lake pipes. Well maybe a big glasspack under the cabin door is the best you can do. Gotta think about where the rubber meets the road or in this case the airscrew meets the air. Can’t have a hotrod car with stock tires so have to get a surplus 11’ Hamilton Standard from a warbird and cut off enough that it still has ground clearance. Damn, now that a Cub! Just mind the airframe. You’ll have the only plane that you have to watch never exceed speed while going straight up.

Rico: Yes, 100LL is “100 octane Low Lead”. IIRC though, that’s a littel misleading. I think “low lead” avgas has more lead in it than regular leaded mogas. (At least, that’s what I remember hearing back in the '80s.)

I wonder how long it will be before 100LL is gone too. Even though it’s “Low Lead”, it still has a bunch in it. People are gonna get tired of us spraying down the countryside with that stuff.

Car gas is the way to go. Or even better, diesel or Jet-A.

That’s the story as I’ve heard it too. It’s “Low-Lead” compared to the ordinary 100/130 avgas. If my ground school instructor was right, it’s still got more lead than even 80/87.

I dunno. I think most of the public doesn’t know or realize that there’s still leaded gasoline in use in planes. Eventually, though, someone will probably get in a huff about it. (And lead is bad for you.)

Yeah, and I’m really surprised Diamond Aircraft decided to develop and market the Twin Star with 100LL engines despite the original certification being with the new diesels - a step backward if you ask me.

Hm. I hadn’t heard that, but for the past few months I haven’t been keeping up with Diamond like I used to. They make great airplanes. and I consider myself very lucky to get to fly a DA-40 to work.

The diesel might be a hard sell here in the US, though. There isn’t a huge price difference between Jet-A and avgas right now (at my airport, $2.89 for avgas, $2.61 for Jet-A), so you probably won’t be seeing a whole lot of people changing over for the fuel cost benefit, even though it burns less too. The Centurion engine can’t be field overhauled like your standard Lycoming or Continental, and parts aren’t as widely available. A lot of people also get hung up on the fact that it’s based on a car engine.

I’d love to have one, myself. I think an RV-9A with a Centurion diesel would be a nice combination. Around 180 KTAS at 18000 feet burning cheap farm diesel I bought at the local Co-op? Yes please!

Av Gas, will travel

Although I am not a mechanic, I do have a little experience in the sorts of airplanes/engines affected.

Yes, engines originally built for 80 octane can use 100LL, but when doing so you have to take precautions against fouling the spark plugs with lead. This isn’t rocket science, but it does involve using one’s brain - something people aren’t always reliable about. You want to avoid too much time at low temp/rpm operations, and the drill I was taught was to increase rpm’s to a set amount for a set time period prior to shut down to “burn off” deposits. Takes all of 10 seconds but you need to do it consistently and properly. Also, regular inspection of the spark plugs is must regardless of fuel burned. And definitely do a proper engine run-up and pay attention to any engine oddity you find - don’t just shrug it off and go fly, hoping for the best. (I’ve aborted more than one take-off halfway down the runway because something odd popped up)

100LL is a relative thing - it’s lower lead than straight 100/130, but yes, I believe it has more lead than leaded autogas did.

No, lead is not good for you - I avoid getting avgas on me, and when I do I scrupulously wash my hands thoroughly before eating or drinking anything. On the other hand, it’s not like being within 10 feet of a drop of the stuff will cause instant death. Back when I did stained glass work I came into contact with a LOT more lead than I do around airplanes. Heck, if you plant a garden next to a major roadway dating from the 1950’s or 60’s you’ll probably get lead contamination from the vegetables because that stuff stays in the soil for decades.

The amount of lead compounds put out by small airplanes is miniscule beside that lofted into the air by heavy industry, or by the car back when they ran on leaded gas.

Could you run autogas through an airplane engine? Yeah. But it shortens the life of the engine (or so my A&P buddies tell me) and makes it less reliable. Let’s see… minor lead contamination vs. an airplane falling out of the sky, which is worse…?

There are STC’s available for many small airplane engines to convert to autogas safely, but it costs money, and many airports won’t let you re-fuel with autogas on their premesis. Having dealt with getting autogas from a car gas station to an airplane that does take autogas I can also add that a lot of gas stations will not sell you autogas if they know you’ll be putting it into an airplane (liability issues). So… you can’t get autogas at the airport, and no one else will sell you gas, and folks wonder why more people haven’t converted their airplanes?

There are also issues with ethanol in autogas. It’s not the engine in these cases, but some of the hoses and seals which, I’m told, can be degraded by alcohol and other additives.

Oh, yes, those other additives - unleaded gas is far from non-toxic, and some of the compounds used may be even more toxic than lead

The loss of 80 octane is going to be a headache for some people, but nothing like what’s going to happen when we lose 100LL - which I think we will lose at some point in the not-to-distant future. The C172’s and Cherokees will convert, but the higher-powered engines used in high performance prop planes are going to be a real problem.

Short article
I’ve never flown a diamond but I’m pretty excited about the chance to checkout in a DA-20C1 later this week. The Diamond Star looks perfect, and I believe they will eventually certify it with the diesel. Avgas is reason number three why I don’t want to buy a plane yet (reason number one is money, number two is the grande kitchen pass I’ll need from my old lady). In the absence of affordable GA turbines, diesel burning Jet-A seems the more appealing choice.

This reads to me like they will offer both. I hope so.

I think you’re right, and I agree. I just got back from flying a couple hours in the DA20-C1 Evolution (Katana) for the first time and that is a sweet little airplane. Much better climb performance than I expected from 125 HP - very spacious too. This was my second experience with the IO-240 and it’s a pretty impressive little engine. I haven’t read anything about STCs for mogas in these little fuel-injected motors - there may be a good reason for it that I’m ignorant of. The Katana’s clean aerodynamics make it tough to slow down if you get much steeper than about 3 degrees final glideslope, even with flaps down. It really wants to fly. Took quite a bit of elevator force to rotate on takeoff, and a lot of right rudder with the power up except at cruise. The painted canopy ceiling is a bit annoying as it detracts from the otherwise awesome visibility. I might get to test fly the four-seat Diamond Star this week and I hope they eventually decide to market that in the US with diesel like the Twin Star. I’d really like to read your impressions of the DA-40 because that would the ultimate family airplane for us if I ever scrape together the dough.

Article on the Diesel Twin Star trans-Atlantic trip.


At 152 KT, that’s about 30.5 statute miles per gallon, not bad