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Comment by martincmartin | Hacker News Reader

Wait, airplanes don't already use unleaded fuel?

Nope. Not piston engines anyway. Airplane engines have to be much more reliable than car engines in a much harsher environment, and until today leaded fuel was the only solution that produced the requisite level of reliability.

Thanks. This was the question I was looking to answer, "if we did it in cars seemingly easily, why not planes!)

Was it easy, though? We already knew it was a bad idea to start with, and yet it took almost a century to phase it out.

It was introduced into auto fuel in 1921 and phased out in autos in the US from 1976 to 1996 (with the phase out being heavily front-loaded).

I would count from the very introduction, because everyone knew from the start it was a bad idea but profits spoke louder.

When do you think TEL was introduced to auto fuel?

> It was introduced into auto fuel in 1921

OK, so maybe the question then is “how many years is ‘almost a century’?”

It's always been trivially easy to replace lead in car gas if you don't care about cost. There are a thousand chemicals that will increase octane levels and prevent knocking, and some of them can be bought at your local hardware store.

But none of them were as cheap as tetraethyl lead in the early 20th century, so TEL won.

(This argument doesn't apply to avgas, where TEL did/does more than just prevent knocking.)

I know that, and if monetary cost is the only thing you're measuring it's a perfectly good explanation and it's totally worth it to knowingly poison people for that.

What do they run 2-strokes on in the US then?

Oil/gasoline mixture. No requirement that there needs to be lead in the gas, as far as I've ever heard.

Well, I know it's got oil mixed in. Presumably the leaded fuel requirement is only for four-strokes though, since two-strokes can't run on leaded?

It's kind of an orthogonal issue. Oil is needed in the fuel for two-strokers with crankcase ventilation for lubrication. Lead is needed to boost octane. But your old outboard engine is most likely a very simple low compression engine that doesn't need particularly high octane, so can run just fine on regular car gasoline (preferably without ethanol, but again a slightly different issue) mixed with the two-stroke lubricating oil.

I know how they work, I'm just wondering if 2-stroke aero engines get a pass from using leaded fuel since they run for about ten minutes before the lead fouls the plug.

> 2-stroke aero engines

Which 2-stroke aero engines are you thinking of?

> get a pass from using leaded fuel since they run for about ten minutes before the lead fouls the plug

Huh? Before unleaded automotive gasoline became the norm, all kinds of 2-stroke engines ran on leaded gasoline just fine.

That was also the argument for putting lead in fuel for cars in the first place.

The answer just seems "not enough political pressure to phase it out".

Thats true, but aircraft engines also run harder, must be lighter, and more reliable. It has been discussed elsewhere, and is a technically harder problem.

On top of that, general aviation makes up a much smaller part of the population motoring around every day, so probably less of a priority to gain political traction (until now).

That being said, I’m very happy to see an unleaded standard. It was my understanding that 100LL was not able to be transported via pipeline, which was part of the contribution to its higher cost.

Jets do (as well as turboprops), but piston-engine planes (aka almost all general aviation aircraft) currently burn leaded gasoline.

Jets and turboprops do not use "unleaded fuel", they use jet fuel (which is basically kerosene).

"Unleaded fuel" doesn't mean any fuel without lead, it specifically means gasoline (petrol) without lead. Hydrogen gas (or liquid) can be used as a fuel, but no one would call it "unleaded fuel".

Reminds me of the xkcd comic--

https://xkcd.com/641/

Yeah, that one is exactly like all the "gluten free!" stuff being marketed, which never had gluten in the first place.

Yeah, my reaction to this isn't "oh hey about time" but more "WHAT THE ACTUAL FUCK HOW IS THIS STILL A THING"

https://www.faa.gov/newsroom/leaded-aviation-fuel-and-enviro...

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