Unleaded Avgas Approved | Hacker News Reader

Unleaded Avgas Approved

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Some years ago I obtained a "barn find" vehicle that still had some 1970s leaded gasoline in the tank. After much work getting things ready to run, I decided the best thing to do with the old gasoline was to install a disposable fuel filter and just run it through the engine.

The scent of leaded gas is something entirely different from modern products. Sweet-smelling and rather pleasant, it triggered childhood memories I didn't know I had.

Of course knowing what leaded gasoline smells like could have contributed to other issues...

I have a fun trivia fact to share actually - here in UK, it's one of the only remaining places in the world where you can still legally buy leaded petrol for automotive use. Only a handful of garages around the country are certified to sell it, the prices are very high, but it's the ultimate fuel for people who want to preserve their old vehicles in original factory state, without modifying anything to run on unleaded fuel. Alternatively, the sale of leaded additive is still allowed(which literally just contains TEL - tetraethyl lead - effectively turning 95 unleaded into the old 4-star leaded).

This website used to list the garages still selling leaded petrol, but they have changed the whole site very recently - so you can only see the list on wayback machine:

http://web.archive.org/web/20210225112828/https://fbhvc.co.u...

TEL additive:

https://www.classic-oils.net/TetraBOOST-E-Guard-15

Is there a https://www.howmanyleft.co.uk for numbers of leaded petrol cars still on the road?

Not sure if that would be useful, as there's no way to confirm whether a vehicle that was designed for leaded fuel was converted for unleaded, or if it simply runs on non-leaded additives.

Either way, there is this website, which used to really push for leaded petrol, it disappeared in 2009, but it almost reads like comedy:

http://web.archive.org/web/20090101030343/http://www.leadedp...

" Don't forget, if your local filling station doesn't sell leaded petrol, ask them to start!"

"Bayford is campaigning to have the extra duty on Leaded Petrol removed. You can help by printing this letter and sending it to your Member of Parliament"

"If you run a classic or high performance car, now is the time to throw away that can of additive, and fill up with award winning genuine leaded petrol"

In London last summer I caught a whiff of a smell that I hadn't smelled in years - 30 seconds later a vintage Jag came around the corner and I realised it was the exhaust of a car running leaded petrol. I was struck by the fact that I could literally smell it coming.

That may have been from uncatalysed exhaust. My '66 Mustang also has a very distinctive smell, despite running an unleaded fuel.

Sweet smell can also be from running ethanol-rich fuels.

Which is kind of interesting in this regard. Brazil converted a large portion of its passenger car fleet to ethanol and it seemed a better overall fuel, to the point some sportier models had only ethanol versions.

Wouldn’t ethanol be an adequate substitute for avgas with property adapted engines?

Ethanol is a terrible substitute for gasoline. It has something like 70% the energy density of gas, it readily absorbs water from the air, which means it also corrosive.

The main reason it works in Brazil is because they can make it cheaply from sugar cane. In the U.S., ethanol is just a highly inefficient subsidy for corn farmers.

The moisture thing alone would be a deal-breaker for avgas. You really don't want to have engine trouble mid-flight and avgas has special anti corrosion compounds afaik.

We always topped up the aircraft tanks every time to minimise condensation.

> It has something like 70% the energy density of gas

That's true - when running on ethanol, range is shorter. OTOH, it allows higher compression than gasoline - which is why some cars came with ethanol-only engines. When disassembling engines, we also note there is much less, if any, deposits.

> also corrosive.

This was solved (in cars) in the late 1970's.

> In the U.S., ethanol is just a highly inefficient subsidy for corn farmers.

Maybe not worth it for cars (especially now that we have viable batteries for EVs) but these are different markets.

This video was crazy, making ethanol from Corn provides something like 1% of the power of the sun hitting the square meter of farm used for it. Meanwhile using tonnes of water, space, and other things. It's basically a terrible idea over-all given alternatives like electricity and solar power.

And it mostly only works because its government subsidised.

But watch the video for the full story: Real Engineering - Why Biofuels Are Terrible https://www.youtube.com/watch?v=OpEB6hCpIGM

Ag subsidies in the US are pretty wild.

One study said that 75% of the price of dairy was subsidized. The fact that I haven't heard of any other studies (or that you even need a study to determine such a number) is a bizarre red flag by itself.

Can someone who understands the political history around this explain why this is still legal in the UK?

It's my understanding that no level of lead exposure is safe.

corruption. its use in aviation - and use of other chemicals involved in their engines - is not safe at all either -

https://www.latimes.com/projects/toxic-chemicals-planes-covi...

https://www.bbc.com/news/stories-51633897

oil-in-cabin-air issues are solved by not using bleed air for cabin pressurization.

I think that has problems which prohibit it from being implemented. I think a better option to just pass the air through a filter to remove oil particles before the air is used in the cabin.

IIRC it's not particles, but combustion/decomposition products.

And no, it's not an issue with using non-engine air for cabin pressurization taking too much weight/power: even a large airplane needs only little actual airflow.

Lobbying from interested parties. In this case, the Classic Car enthusiasts. The government most likely judged that allowing a dispensation for commercial sale would not in fact result in widespread continued use of leaded fuel due to the commercial realities of selling such a niche product, but it was worth the effort to say they supported this niche - and that's exactly how it turned out.

The original 1999 UK legislation envisions retailers will be given a maximum quota on how much leaded they can sell, a permit holder could sell 0.5% of volume per month for example. But as anticipated ordinary motorists just put unleaded in the tank and carried on as before so the quota system was pointless. If your "quota" is 10 000 litres of leaded fuel per month and you sold a total of 45 litres to one bloke in that time, you not only don't need a bigger quota, you won't order any more of that fuel from your supplier. If perhaps, the next summer, a motorist in a Victorian outfit driving a 1926 Chevrolet enquires about the leaded fuel you tell them "Sorry mate, we're out of stock" and most likely they put unleaded in the tank, but either way they're not wasting your time and money with this weird "leaded" fuel nobody buys.

Which is why there was an archive.org link above -- the actual site for the FBHVC now tells you that you probably can't get leaded fuel, and even if you could you shouldn't bother, even though that's the organisation identified in the legislation itself as asking for this exception.

I assume it's still technically legal for whoever actually bothered to have a permit - but the actual emissions involved must be pretty tiny.

No level of car exposure is safe, but we still allow people with the right licenses to drive on the roads.

The UK has a long tradition of massive taxes rather than outright bans. E.g. absinthe was never illegal there, unlike many countries, it just had a punitive level of duty put on it.

Right, but we don't have any economically viable alternative to cars. If we outlaw cars, then what?

If you put actual effort into not having cars, you'd find a way to make it work. Plenty of people do. At the least you could have stricter driving tests and jail drivers who kill pedestrians.

Cynically, my guess is that the laws were passed by classic car owners. There have been similar looking dispensations on road tax for classic cars in the past.

All European gasoline used to smell like that not so long ago. It's one of the major memories of my first trip to European as a teen.

"Not so long" must be somewhere in early 90s. Most of Europe phased out leaded gasoline by 2000.

From my experience the thing that affects the exhaust smell more than leaded/unleaded is whether the engine has a catalytic converter. A car without the converter running on unleaded will have the same sweet smell the parent is talking about.

The gas stations themselves used to have a different smell.

I remember as a child (in Canada) somehow enjoying the smell when my parents filled up on gas. Which is kind of terrifying in retrospect.

I remember that. I also remember unleaded had the same smell. Though this was 40 years ago so who knows if my memory is right.

I faintly remember. I'd probably be interested in having the weirdest irl meet up over a car found with a spare jug of leaded gas. Reliving old smells does so much for creativity

I remember that as well. I remember talking about it with my parents relatively recently as well.

They had claimed they used to enjoy the smell of gasoline in their youth and that it became repugnant only after they reached a certain age.

I thought that was a reasonable explanation back then. Similar to developing a taste for certain food ingredients.

However in hindsight, the transition from leaded to unleaded gasoline actually explains this better.

>enjoying the smell when my parents filled up on gas

I have never heard about anyone not still liking the smell. Granted it isn't an everyday topic.

There are a lot of issues with the leaded replacement gasolines. Lead was at least heavy, and "fell" close to it's point of use. The BTEX components added to gasoline after removing the lead, are carcinogenic. They are also volatile. They go everywhere, and affect everyone. Overall, neither the biological or human ecology are better off. The politics behind the leaded gasoline change is fascinating, as most of the other environmental decisions are, when studied from the point of view of toxicology and environmental science.

Where can I read more about this?

Yes this seems like a very interesting, important and overlooked issue.

I also think the fellow stating that we are not better off for having unleaded fuel is overstating the matter. Lead in fuel was quite strongly correlated with crime rates, no?

Yeah, but also general societal changes.

Correlation is not causation.

Sure, but lead has multiple known mechanisms which would indeed cause individuals to be more likely to commit crime, and serious efforts to get lead out of fuel correlated pretty strongly with a maxima in crime rates that had been steadily increasing for decades. [0]

While it is clear to me that there were other legislative and possibly environmental changes that also contributed to this drop, I think that applying 'correlation is not causation' here while applying no scrutiny to the argument that "removing lead from fuel didn't do shit" is pretty facile.

[0]: https://en.wikipedia.org/wiki/Lead%E2%80%93crime_hypothesis

That is complicated. The USA EPA (Environmental Protection Agency) is an amazing source of information. The problem is, there is so much information, it is hard to learn anything simply. (I just tried a simple search, and it is overwhelming.) Of the four ingredients in BTEX, it may be easiest to start with Benzene. It is the 'heaviest', safest and perhaps simpler. (But do try to search for BTEX and EPA online, and you'll get to many interesting sites. Contaminated water, air, food, etc.) To simplify; Here is an example: https://wwwn.cdc.gov/TSP/ToxProfiles/ToxProfiles.aspx?id=40&... I advise you to study without too much concern. As with a medical journal, if one starts reading about all the things that are bad for you, and surround you everywhere, it can be alarming. It is a fascinating field. Soil, water, and air chemistry are complex and interdependent systems, and when you throw in human, animal and plant toxicology, it is even more confounding. Unfortunately, the simplifications required for political battles, invested industrial lobbying, result in poor science.

Wrt health effects of gasoline, it is bad for you full stop.

The chemistry should be improved or changed if needed, however leaded (pb) fuel should never return. We are definitely better off.

I wonder if other heavy metals can also make a higher octane fuel.

How about tetraethil uranium? That sounds like a very high-energy fuel. ;-)

https://pubchem.ncbi.nlm.nih.gov/compound/57417459

I wonder, hoping it doesn’t, if it works as a fuel additive. Someone must have thought of that in the 50’s and 60’s.

Lead accumulates in the body poisons you for far longer than the other chemicals you mention.

Even with relative to the particular effects on health, you really can't compare lead and those others. Lead was really the worse.

DNA damage bioaccumulates too...

But with lead you have both neurological/etc damages and DNA damages! These lead derivatives are classified as probably carcinogenous!

So, you see? The comparison ends up easy!

My old roommate, a NASA chemist (Max Bernstein, Ph.D.) once said to me, "I don't worry so much about chemicals; they break down. I worry about heavy metals because they never break down."

Interesting to note that unleaded gas also has lead about 0.05g per gallon which is a lot when you consider how much gas is burned in a typical big city everyday. Aviation gas has 2 grams per gallon, so if you live near an airport you're probably getting a pretty steady diet of lead.

The actual amount of gallons of gas burned in planes using AVGas is extremely small compared to the gallons of gas burned by cars or by planes using jet fuel. Unless you were on the tarmac with prop planes running, I doubt you'd smell the lead.

What about the ground water near popular general aviation airports? Granted, there aren't nearly as many airplanes as cars, but over years, contamination can accumulate.

I remember a small lake in San Francisco that had to be decontaminated due to lead pollution from cars:

https://www.sfgate.com/bayarea/article/Workers-pour-poison-i...

"Lead from car emissions seeped into the water for decades until leaded gasoline was phased out beginning in the 1970s. The lead combined with pesticides flowing in from the golf course to form a toxic stew."

The EPA limits unleaded gasoline to 0.5 g/gal, but that doesn't mean your gasoline actually contains that much. The regs are meant to forgive some amount of cross-contamination from facilities that also handle avgas. I don't have any information on what values are typically encountered.

You're right, 0.5 g/gal is a lot of lead.

> 2 grams per gallon

I’m from a fully metric land, is the above a common way to express a ratio? It certainly stuck out to me but it’s a pretty tidy measure.

Hey, it doesn't even have internal unit cancellation or convention ambiguity like "kilowatt hours per month". We can do worse!

Gas in the US (aviation or automotive) is always sold in gallons, but quantity of chemicals (outside of cooking) usually done in grams/kilograms. Thus, grams per gallon is fairly intuitive in context.

AvGas is only used by small, piston powered aircraft.

Jets fly on Jet-A which is basically high-grade kerosene and AFAIK, lead free.

The only airports that could be giving off lead would be very busy, general aviation airports like Van Nuys, not commercial airports like LAX or JFK. Even then, the effect is barely detectable.

And a lot of those are getting converted to turbodiesel now which means they can run on Jet-A1 too. Avgas is really expensive and hard to get these days.

In Europe yes, less so in the US.

As a child I grew up in a 200 year old house which had many coats of exterior lead paint ... evidently the lead paint chips are sweet tasting ... my parents have memories scolding us kids to stop eating the paint chips

It's quite telling how long did this gas last while still being capable of powering engine. Modern gas won't last a year with or without stabilizer

Approval of specific airframes and engines through STCs (Supplementary Type Certificates) is slightly misleading. In the same way, regular unleaded gasoline is also approved through STCs for many airframes and engines. This isn’t the silver 1:1 bullet that replaces 100LL tomorrow. Nevertheless, I’m all for the 100LL alternatives efforts. If I was buying an aircraft, however, I would be more interested in a Jet-A burning piston (basically diesel). Unfortunately that market is currently limited to Diamond aircraft, which are fantastic if not for their tight grip on their service network.

I looked into using a diesel engine in an experimental aircraft (US/FAA definition). Unleaded car engines are fairly common in these planes.

It turns out that Jet-A isn't necessarily good for a piston diesel engine, due to lubricity and cetane number. After enough reading, I decided to stick with unleaded/100LL until the day I can afford a proper turboprop.

https://generalaviationnews.com/2011/03/17/jet-a-versus-dies...

https://www.thedieselstop.com/threads/jet-a-vs-diesel.62296/

Having typed all this, when I was in Afghanistan with the US Army, the tactical trucks with diesel engines all ran on the same Jet-A that the aircraft used. I assume there was something different about that fuel, or the engines in those trucks.

Jet-A is Jet-A. It's the engines: the Army would like to avoid having to schlep around two kinds of fuel that can get confused to disastrous results.

Yes, obviously. Safer to drive a diesel truck on Jet-A than a Chinook on diesel.

The Army is almost surely using JP-8, which is similar but not identical to Jet-A.

>I assume there was something different about that fuel, or the engines in those trucks.

Nope, it's just that the operational lifespan of those trucks isn't long enough for the Jet-A to really matter. It's only a major issue for the fuel pump, anyway. Those can always be replaced.

Yep, most up armored Humvee or MRAPs will last less than 10k miles.

All diesel fuels are lower lubricity than they used to be (due to changes for modern low-emissions diesel engines).

If you have an older diesel engine, you can use additives to restore lubricity, but I don't know if they are approved for use in Jet/A for a piston diesel aircraft.

Diamond’s are fine unless you need an airplane equivalent to a Cessna T206 or a 421. Diamonds, are really competing with Cirrus or the Cessna 172.

As someone flying a 310 horsepower turbocharged 206, using an unleaded AvGas is a scary proposition. The only way to operate these turbo engines on current unleaded technology fuels would be to significantly reduce the boost pressure of the turbo and massively de-rate the engines. Flying heavy or out of hot or high airports would be significantly more dangerous. On normally aspirated 172s with a 160 or 180 horsepower engine, it would be less of a big deal. On a turbo-high performance engine, getting the performance out of the fuel is something not likely (hence the STC only for 172 lycomings.) Detonation would be the main risk or you’d have to use significantly less power which defeats the purpose. There are already mogas STCs. Until those fuels work in high performance engines, this isn’t really a groundbreaking thing.

And just a point of fact, just because lead is “scary,” the actual environmental impact of leaded AvGas is trivial — despite the flawed “studies” put forth by the anti-airport lobby. If we want to improve the environment, I am all for it, but targeting AvGas is like trying to swat a fly circling a dead elephant. One Chinese factory spits out enough toxins in a day than the entire AvGas fleet does in a year. That’s not to say we shouldn’t work for better and cleaner airplane fuels, but in terms of environmental impact, this isn’t doing much. Resources would probably be better spent on lead and asbestos remediation in old, low income housing — or in the water supply. Kids aren’t getting sick from AvGas exhaust.

>> The EPA's own studies have shown that to prevent a measurable decrease in IQ for children deemed most vulnerable, the standard needs to be set much lower, to 0.02 µg/m3. The EPA identified avgas as one of the most "significant sources of lead".

Atmospheric lead is pretty dangerous, more so than encapsulated lead paint inside a wall.

That’s an incredibly misleading quote - do you have anything that can correlate atmospheric lead concentrations at ground level with flight hours or take/offs and landings somewhere?

I was curious so here's some napkin math

Assumptions:

- moderately busy airport, three Cessna 172s concurrently in the pattern during the day @7gph

- no significant wind

- 7gph3cessnas2glead/gallon=42grams of lead/hr

- The lead sinks as the combustion products are far heavier than the atmosphere.

To reach 0.02ug/m^3 you'd need to dilute it in approximately 1000m x 1000m x 2000m of air which is well beyond the boundaries of a typical airport of this type.

Honestly this seems pretty plausible.

Hmm, thanks for doing the math!

I don’t think that is that far off the boundaries of typical GA airports, and for those that are smaller they are almost always in the middle of nowhere with no inhabitants around them.

One of the more concerning types of GA airports is something like Reid-Hillview, which is surrounded on all sides by residences - and even has an elementary school right on it’s border. It’s 750mx1200m - and a lot of it’s pattern is going to be over a much, much wider area. Altitude wise, it’s going to be between 1-4 thousand feet most of the time too.

So it’s almost certainly going to be diluted well below that level, even if there is zero air movement, which there always is? It will be spread over a wider area of course, but if concentration is the concern, you’d probably only have higher amounts somewhere like the flight line?

Note that the word most is not in the quote from the source.

Given the heavy handed way that lead was removed from fuel for passenger vehicles, I'm still perplexed that a tiny lobby has managed to keep it around basically indefinitely. If I were to build an aerial vehicle that sprayed a toxic substance everywhere it went, the environmental groups would basically go nuts. But somehow because it is in a plane, nothing ever really happens about it.

The logical thing to do with 100LL is to ban it, like was done with passenger fuels. Existing planes serving a public good (basically just bush planes at this point) can continue to operate on it indefinitely. No sales of new planes equipped with engines that operate on 100LL would be allowed either.

I'm willing to bet that the amount of lead that's put out by aircraft in a year pales in comparison to what was put out by cars, and as a result going after lead emissions from cars was deemed to be the best course of action by the EPA. Also, it's worth noting that leaded gasoline didn't go away overnight. It was still sold for awhile even after the EPA said that you couldn't make cars that ran on leaded gas.

Can you not see how passenger vehicles, which are overwhelmingly for personal use, is a different category with a different economic impact than an entire class of public transportation?

Gasoline-engined planes are overwhelmingly for personal use.

I've seen 172 conversions with diesel. In fact that young guy that flew around the world in this 172 last week used one.

Per https://www.avweb.com/aviation-news/gami-awarded-long-awaite..., this new unleaded fuel is currently only approved for Cessna 172s with Lycoming engines, with expansion to more aircraft types coming next year.

Makes sense - the 172 is one of the most common training planes, getting a TON of low-altitude hours in the pattern.

Also because of the low altitude flights 172s will probably run rich.

Granted, they aren't burning a ton of fuel per hour - around 8g - but considering the sheer number of 172s out there this will make a reasonable dent in the total fleet of pistons.

Though I expect the infra changes to actually support this will take a very long time to actually put in place, and many people will opt for 100LL for a long time because it is all that's available at their local airport or it is cheaper.

I own a 182 that has the STC for auto-gas, and barely anyone sells auto-gas on-field. The only other option is to maintain my own tank, but that can't go on trips with me.

Still good news in the long run.

8 gallons of 100LL contains about 4 grams of lead, enough to measurably lower the IQ of over 100000 children.

Would love to see the source and data on that, given that I use 1000s of gallons of leaded fuel a year.

"The study found that for each 5-microgram [per deciliter] increase in blood lead, a person lost about 1.5 IQ points."

https://jamanetwork.com/journals/jama/fullarticle/2613157

You're conflating chronic and acute exposure. Pop epidemiology 101.

The saving grace is that your exhaust doesn't go directly into the bloodstreams of children, likely most of the lead ends up at other places on earth.

Maybe stop?

That's the point of the GAMI fuel approval: it provides a practical path to stop using 100LL.

You can't just take the mass of the lead and then assume it all winds up in humans.

For a given amount of lead output into the atmosphere lead output over an airport is going to get into people's blood a lot less efficiently than lead output in an automotive context.

... so we're just going to slowly build up base-level contamination in the soil, water, and ecosystem? Let's not?

I'm not endorsing lead emissions, just pointing out that emitting them not into people is a lot better than emitting them fairly directly into people.

While obviously it would not be ideal to evenly distribute lead evenly throughout the surface of the earth lead is a fairly common element and exists in ground deposits more or less worldwide without poisoning people. It's not as common as iron but it was used for all sorts of thing historically specifically because of how common (and therefore cheap) it is/was.

Well, NO, lead tetraethyl is not naturally present. It's a human-made metallo-organic molecule.

Elemental lead is nearly completely insoluble and very difficult to absorb. If entrained in dirt, even more so. Breathing vapors or aerosolized fine powders isn’t great, but uptake even then isn’t high compared to many other toxic substances - that is usually the dominant form however. It usually requires some kind direct ingestion + acid exposure of a significant amount of lead, or breathing in a large quantity of lead vapor or fine dust to get notable exposure.

Which is exactly what you get when every car in a city was burning tetra ethyl lead in large quantities, and/or kids were eating sweet tasting lead paint chips.

Leaded AVgas is a concern, but dilution of the resulting lead from combustion gets diluted very widely very quickly resulting in actual low concentrations. And since it’s not ‘every car in the LA basin’, it just isn’t at the scope or scale of a problem you’re making it out to be. We’re probably having bigger issues from all the random new stuff companies put into tires (including carbon nanotubes now), which then gets ground up and dispersed as fine power at the million ton scale every day.

Lead is not mobile in typical soil or water environments, and as long as the water isn’t strongly acidic, it settles out and stays where it lands. There is naturally occurring trace lead in most soils - it’s a somewhat common element.

Lead tetraethyl is not elemental lead.

I think you are mixed up.

Lead tetraethyl (the component found in lewded gas) is easily absorbed, it even diffuses through skin to the blood!

Once combusted, the exhaust contains primarily lead oxide (PbO), not TEL (C8H20Pb)

Alright, but it's still not elemental lead.

I'll look up PbO, but I'm expecting to be horrified at its harmfulness, rather than be reassured.

And neither PbO is "naturally occuring", it's anthropogenous. Naturally occuring Pb species are lead sulfide, sulfate, and carbonate.

Did you find anything?

I can't find any evidence it is significantly more toxic (hard to quantify, and most sources didn't seem to try - it all seemed within an order of magnitude or so).

At least what I ran across seems to be that the organic lead compounds (aka tetra ethyl lead, among others) are super nasty. Similar to how mercury is not great (and has similar exposure routes), and the common compounds of mercury in soil, etc. are the same - but the organic mercury compounds that occur when mercury is in wetlands environments are super nasty (like 100000x)

The EPA mentions on their lead site (albeit backhanded) that runoff, water contamination, etc. is usually not an issue even at heavily contaminated sites. Where you see lead poisoning around drinking water, it is always due to very acidic water conditions which leach/dissolve the lead. This can be from lead pipes pulling water from acidic sources (big no no), or heavily acidic mine runoff going through heavily contaminated sites.

The only major concern ground contamination wise seemed to be at smelting sites, which is truly a unique situation - and well know and easy to test for.

I did find some evidence that it is also a concern with fly ash, though apparently the other really nasty stuff (including radon, uranium, nasty active chemical species, etc.) overwhelms the lead concern. Places still have to do a ton of paperwork on it though. If you die from fly ash exposure, it isn't going to be due to lead poisoning.

Someone else just made a good point though. These planes run full rich a lot which means some of the fuel is not burnt but simply evaporated, cooling the engine.

I still think the amount is so minor as to not cause concern but it's a point.

Contaminated soils don't contain elemental lead. The dominant form is lead oxide, one of the two common additives in lead paint (along with the carbonate) and also the end point of the combustion of TEL in fuel. Lead from lead oxide is easily absorbed orally from soil, paint chips, and household dust, and it's also a serious inhalation hazard.

> sweet tasting lead paint chips

What makes you think lead paint tastes sweet?

> Lead is not mobile in typical soil or water environments

Which is exactly the reason lead-contaminated soils are such a long-lasting hazard. It's the reason little kids playing in the dirt around old houses can be poisoned decades after contamination was laid down. For example, here in Denver entire urban neighborhoods were built on the site of a smelter that was demolished a hundred years ago, and the contamination is still largely unchanged. Remediation requires completely replacing the top several feet of soil.

> There is naturally occurring trace lead in most soils - it’s a somewhat common element.

Significant deposits of lead in surface soil are rare, and are limited to sites with unique geology. The vast majority of distributed lead in surface soils is of human origin.

> What makes you think lead paint tastes sweet?

Lead acetate has a sweet taste. Lead paint flakes/dust contain lead acetate.

https://www.smithsonianmag.com/arts-culture/sugar-of-lead-a-...

What makes you think lead acetate was ever used in paint?

Research. https://healthyindoors.com/2018/11/lead-paint-sweet-aint

Let's stop entertaining the sealion

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

I asked a simple and genuine question in the midst of my longer comments. If you think that qualifies as sealioning, then I imagine no discussion forum is a safe place for you.

If you have anything to contribute, I'd actually like to hear it.

Did you not actually read that article? The title is "Lead Paint, Sweet It Ain't", and its entire purpose is to debunk the myth of sweet tasting paint.

Even there, the claims that lead paint sometimes contained small amounts of lead acetate are unsupported. It's true that heavy metal salts have a long history of use as siccatives in oil-based finishes, but the vast majority of lead-based driers were the oxides, because they could serve double duty as pigments. And even if lead acetate were to be used in paint, it wouldn't taste sweet, because it would be bound in the polymer matrix (as your article points out), and there wouldn't be enough of it anyway. Look at the SDS for any oil based finish, and you'll see that metallic diers are added in just tiny amounts.

Regardless, I have never seen historical or scientific evidence that suggests lead acetate was used in any significant amount in paint. If you know of such evidence, I would genuinely love to see it.

> Remediation requires completely replacing the top several feet of soil.

I think the normal recommendation for backyards is several inches, not feet, of soil.

But there's also an alternative: fish bones. They bind the lead so it can't be absorbed well even if ingested. You can buy them by the ton from PIMS NW, Inc: http://www.pimsnw.com/ But you need to spread quite alot of fish bones. As cheap as they are, it's still not very cost effective, especially considering that, excepting extreme industrial contamination, lead-contaminated soil usually goes to a non-hazardous dump site or used for backfill, and rarely to a much more expensive hazardous dump. It's cheaper to haul the dirt away than to haul in tons of fish bones.

The more common chemical abatement technique is amendment with lime. Maybe fish bones are cheaper in some coastal locations, I don't know, but it's interesting.

There's also some evidence that calcium supplements given concurrently with lead exposure could reduce the absorption into sensitive tissues (particularly brain and bones), but I don't know how strong the evidence is.

EDIT:

The depth of excavation is determined based on the expected use of the land, and how deep the contamination extends based on soil sampling. Anecdotally, I know that excavation of residential areas at the smelter superfund site in Pueblo (south of me) extended to two feet around the houses.

> What makes you think lead paint tastes sweet?

Every time lead paint is mentioned it seems to state the taste. It’s in the Wiki as well.

Lead acetate seems to be the sweet compound, and it even gets called sugar of lead.

https://en.m.wikipedia.org/wiki/Lead_paint

https://en.m.wikipedia.org/wiki/Lead(II)_acetate

That sentence in the wikipedia article doesn't cite any sources to support the claim that lead acetate was used in paint. It only links to the article for lead acetate. It's unfortunate but common on wikipedia, and in this case serves only to perpetuate the myth of "sweet paint chips".

> serves only to perpetuate the myth of "sweet paint chips".

I wasn’t aware of it being a myth and there are reference to sweet lead paint every time I read about lead.

I believe it was in the white paint and an older painter has assured me it gives an excellent finish that lasts well without yellowing.

It seems the Romans even used it as a sweetener.

Why do you think it isn’t sweet and lead acetate wasn’t in paint?

https://www.sciencedirect.com/topics/earth-and-planetary-sci...

https://www.ancient-origins.net/history-ancient-traditions/s...

See my earlier response to @sokoloff, who helpfully posted an article debunking the myth of sweet paint chips.

Lead acetate is sweet, no doubt, and it is possible that it was used in small quantities as a drier in old oil-based finishes, however I've seen no actual evidence of this, and even if it was, the quantities are unlikely to be sufficient to be detectable at all, especially years later.

When we talk about lead paint, the lead is in the form of pigments such as lead oxides, carbonate, or chromate. These pigments constituted a large propertion of the paint, and it's these pigments that present the lead poisoning hazard.

Lead acetate is not a pigment-- it was only ever used as a drier-- and it would make absolutely no sense to add it in any significant quantity to pigmented paint, because the pigments are themselves very effective driers. And indeed, I've never seen evidence that lead acetate was ever used in any significant quantities in paint.

The legend about the Romans using it to sweeten drinks and sauces is historically verifiable.

Correct - and lead oxide is not tetra ethyl lead, or the nasty lead salts. It isn’t great, but it is also not that much worse than elemental lead from a mobility or toxicity perspective.

And I noted the exact hazard for breathing dusts and vapors, so thanks for repeating it?

It’s also a bit disingenuous to use someone LITERALLY BURNING AND VAPORIZING MASSIVE AMOUNTS OF LEAD, at a huge and industrial scale for a very long time time, as a safety comparison. Of course that is going to make a giant mess. Whoever let them build houses there without it being remediated should be in jail.

It doesn’t change the fact that you essentially have to play every day in a literal superfund site with probably 1000x or more the worrisome levels before it really becomes a serious problem?

Lead isn’t a thing you want to eat or play in. It will mess you up. But let’s not pretend that a little piston plane is going to poison LA in any measurable way because it is flying over it while burning leaded gas.

And thanks for the lead paint chips not being sweet! I personally never tried, so good to know it’s not true

> Correct - and lead oxide is not tetra ethyl lead, or the nasty lead salts. It isn’t great, but it is also not that much worse than elemental lead from a mobility or toxicity perspective.

No, the dominant lead compounds found in soils are much more hazardous than elemental lead. They are much more easily absorbed orally, and elemental lead isn't a realistic inhalation hazard unless you work in an actual smelter.

> It’s also a bit disingenuous to use someone LITERALLY BURNING AND VAPORIZING MASSIVE AMOUNTS OF LEAD, at a huge and industrial scale for a very long time time, as a safety comparison. Of course that is going to make a giant mess. Whoever let them build houses there without it being remediated should be in jail.

The neighborhood is around a hundred years old. The smelter operated in the late 1800's. Who do you propose should be jailed?

> you essentially have to play every day in a literal superfund site with probably 1000x or more the worrisome levels before it really becomes a serious problem?

No, the vast majority of lead poisoning in kids happens in ordinary households. The most common sources of lead in thee poisoning cases are paint dust and chips, dust from vinyl miniblinds, leaded glazes in dishes, stuff like that.

Talk about moving the goal posts!

So we agree that leaded gasoline in common use for aviation is not a significant contributor to lead poisoning in the population?

And perhaps that whoever hasn’t red tagged the houses sitting on a well know multi hundred year old superfund site should do so, or is being negligent? And that said site is not representative of literally any other type of situation?

And that eating paint chips is indeed bad for kids - even if they aren’t sweet?

> Talk about moving the goal posts!

Nope. My original response addressed your bizarre and irrelevant comparison with "elemental lead". You wrote a whole paragraph downplaying the risks of elemental lead. When it was pointed out to you that environment contamination doesn't involve elemental lead, but rather compounds that are much more dangerous, you pretended to know that, but then kept on saying that they're "not that much worse than elemental lead from a mobility or toxicity perspective." If you would just do a bit of reading about this stuff, it would be clear to you that you've been talking a lot of nonsense.

> So we agree that leaded gasoline in common use for aviation is not a significant contributor to lead poisoning in the population?

I have no idea. I never mentioned avgas in this discussion, and I'm not informed enough about it to have an opinion.

> And perhaps that whoever hasn’t red tagged the houses sitting on a well know multi hundred year old superfund site should do so, or is being negligent?

Um, yes... these are superfund sites. By definition, dwellings at risk have been identified and remediation has been ongoing since the 80's. That's like, the whole point. So again, who exactly do you think should be going to prison for this?

> And that said site is not representative of literally any other type of situation?

No, a lot of non-industrial contamination is even more hazardous. As I said before, the vast majority of lead poisoning is due to lead paint and PVC miniblinds. Again, you could easily educate yourself about this if you wanted to.

> And that eating paint chips is indeed bad for kids - even if they aren’t sweet?

Nobody here would argue with that.

OTOH, if your lead gets dispersed on a field of lettuces or a pasture, it’s safe to assume a lot of it will end up inside humans.

True we'd always run full rich during most of the pattern. Good point.

It’s crazy to me that we’ve allowed leaded gasoline in general aviation for this long. The price of rebuilding all general aviation engines to take lower octane fuel (or possibly ethanol, which has very high octane but a few caveats) has got to be FAR less than the public/mental health burden of allowing leaded avgas.

It's not that simple. If there was a way to "rebuild" the engine (which happens around every 1500-2500 hours of operation naturally) and maintain the current performance on an unleaded fuel, it probably would have been mandated already*. (As someone who would bear that cost, I'd absolutely have supported the action and happily paid the money.)

The problem is that turbocharged airplane engines (the ones powering heavy, fast, working airplanes that buy/burn a lot of fuel) are already working close to the ragged edge of safe detonation limits on 100 octane fuel. Switching to a 95 or 96 octane fuel that contains no lead would not provide the same level of detonation margin, meaning that the engines could not produce the same level of power as originally certified, meaning that the approved performance data in the flight manuals would no longer be correct, meaning that the FAA would ground them.

The exciting thing about this week's announcement is that G100UL represents a credible path to certifying an unleaded fuel that's compatible and miscible with 100LL [for the transition period] and preserves the detonation margin and performance that the airplanes were originally certified with.

* This is not a matter of "install hardened valve seats and motor on" like we did with classic cars.

Ethanol and other such fuels have even higher octane.

And yes, it WOULD suck in the interim, would have been more disruptive to general aviation, range would have been impacted (in the case of alcohols), but this is such a MASSIVE public health issue, it would clearly have been worth it IMHO. Pilots would’ve absolutely hated it, but the wrath of pilots is not a good enough reason to justify lead emissions over the last several decades which may have depressed intelligence and increased crime rate.

I am NOT saying this wouldn’t have had negative, perhaps even massive, temporary disruptions in general aviation, including grounding some planes. I am saying it would be worth it.

Ethanol-inclusion fuels would require both airframe and engine modification and re-certification, which would probably be more difficult (read: slower) to accomplish than what GAMI just got over the finish line.

The industry and FAA have been working on this a very long time. I’m not happy with the pace of progress and not demanding “nothing changes”, but I give them credit that they’ve thought and worked 100x longer and harder on the topic than everyone in this HN comment page combined.

I think this is the best technical solution of the ones proposed and publicly tested. I’ve visited the GAMI test stand and gotten a demo of their operation and followed their progress over the last decade. I hope that this now goes quickly from “only Lycoming 172s” to include my and all other avgas-burning airplanes.

Oh, I’m glad with what GAMI has done and at this point it would be better than alcohols, but this whole thing shows the status-quo bias of the FAA IMHO where anything existing and established gets a pass (no matter how bad the environmental/societal consequence, no matter how many people the trolley runs over) because of the possibility of a temporary increase in risk for general aviation. Anyway, yeah, good on GAMI for developing this.

> a MASSIVE public health issue

Its not. Its the kind of topic made for karma farming on social media.

I think you're massively overestimating the amount of avgas used in aviation. It is used by the fringes of aviation only. All jets and turboprops run on Jet-A1 which is unleaded. All that remains is flying much less hours and using much less fuel per flight hour as well.

When cars switched away from lead the impact was huge because there were so many of them using so much fuel. Avgas is really a minor thing and some airports don't even want to stock it anymore. Refineries don't like making it and as a result it's so expensive that complete engine refits with turbodiesel have become viable.

> . The price of rebuilding all general aviation engines to take lower octane fuel (or possibly ethanol, which has very high octane but a few caveats) has got to be FAR less than the public/mental health burden of allowing leaded avgas.

Engines are _already_ rebuilt based on number of hours flown. If it was this easy, the cost would be simply absorbed into normal maintenance.

I wasn’t implying it’d be easy. I think it’d be really hard and may even increase general aviation risk in the short term, but every flight using leaded avgas causes harm and I think the status quo bias of regulation is causing us to not weigh that risk appropriately. EDIT: I’m glad that GAMI developed this.

Piston-engine planes are a remarkably small market. Automotive dominates the fuel market in total, and jet fuel (which is a lead-free kerosene derivative) dominates the aviation market.

As far as I can tell, no one has demonstrated any tangible cost from the (very small) amount of leaded fuel still burned in piston-engine planes. Even imputed cost from environmental lead levels is iffy -- the only places you can find detectable lead are the immediate environs of long-used GA airports.

It's been a long time coming - manufacturer's been working on this for at least about a decade.

What's important about this fuel is that it should work in _any_ application that requires leaded gas. The most demanding applications are a small % of the engines overall, but get the most hours and burn the most fuel. So we've been waiting for a drop-in replacement that can supplant leaded gas entirely (market is too small for multiple aviation gasolines to be effectively distributed).

Of course, this is going to continue to take way longer to roll out than it should, but this first approval is a very big deal.

I can't realistically imagine the FBOs (fuel providers) at many airports providing a type of fuel only approved for C172s with Lycoming engines.

I fly out of Boeing Field (KBFI). Often the FBOs have issues with their fuel trucks or simply don't provide service. You have to taxi to their ramp. The wait can be significant - and that's with just one type of 100LL fuel.

Sometimes it's better to fly over to KPWT (Bremerton National), an uncontrolled airport, and use their self service Avgas station with a credit card.

I think the C172-only limitation is clearly interim. GAMI's been burning this in testing for a decade or so. Now, put it into a lot of low-powered trainers. Based on that experience, expand it to other engines and airframes.

The end game is an all-models STC; this is an interim step (and a massive one to get the FAA to go from zero-to-one approved models).

my personal guess is that this is going to lead to STCs that allow the installation of diesel engines as replacements for avgas engines. They're saying it's going to raise fuel by 40 to 80 cents (USD), so it'll probably be more than that. One of the pluses of AVGAS engines is that they can be overhauled repeatedly which saves on engine replacement costs over the life time of the plane. But the increase in fuel price is likely to bring it level with the replacement cost of a new diesel engine. Since diesels can run JET-A fuel, which is a global fuel source and much cheaper than AVGAS.. I just don't see how AVGAS engines survive in the long term.

(older planes can't just adopt an electric engine. batteries are too heavy and the airframe won't be able to carry batteries that provide 600-800nm of range)

404'd for me but I found this: https://www.aviationpros.com/gse/fueling-equipment-accessori...

And this: https://www.avweb.com/insider/gami-crosses-the-finish-line/

I hope we can get it, or even 94UL (which is 100LL minus the lead) at airports soon. Many of us can run 94UL just fine, but there's nowhere it's available.

Though many airplanes can, the working airplanes (that burn a lot of fuel) mostly cannot and if the FBO is faced with being able to sell fuel to all airplanes or just some with a tank and dispenser, it's a pretty easy call.

The promise of G100UL is that that FBO can (eventually) sell this fuel to all gasoline-fueled airplanes.

I know what the promise is. My point is I'd like any unleaded fuel at all to be available at the pump. Regardless of whether it needs to support the world's shittiest ancient engines or not.

Being able to support turbocharged engines is critical to being economically viable for FBOs which is critical to being actually available for sale. (Estimates were that 70% of the airplanes could use a 94UL-type gasoline, but that the 30% of remaining airplanes burned [and bought] 70% of the fuel sold, so a 94UL solution is, as you've experienced, not economically viable.)

Apologies, I’m not very familiar with aircraft engines, why can’t we simply use high octane unleaded gasoline, like most turbocharged car engines? Are the cylinder pressures significantly higher in airplane engines?

Airplane engines are overwhelmingly air-cooled, fixed timing (after starting), pilot-controlled fueling, and expected to produce 100% of rated power for 5 minutes and then 65-75% of rated power for hours on end.

Automotive engines are overwhelmingly water-cooled [providing a far more stable and lower cylinder head temperature], variable/computer-controlled timing often with knock sensing [providing the means to adjust timing dynamically when anything beyond light pinging is detected], closed-loop fuel control, and rarely producing more than 20% of their rated power.

Aircraft engines need to stay together with a cylinder head temperature of 460ºF, fixed timing, and fuel mixtures that are set by the pilot. It's a far more demanding (and less controlled) environment.

Some additional refs that might be interesting:

https://www.avweb.com/features/pelicans-perch-43detonation-m...

https://www.avweb.com/features/pelicans-perch-55lead-in-the-...

https://www.avweb.com/features_old/pelicans-perch-31those-fi...

Small nitpick but while aircraft engines cannot catastrophically fail at 460F, no one should be flying them that hot. Its basically guaranteed to shorten the TBO on the engine that way.

When I was flying a turbocharged cirrus (notoriously hot running engine) we always kept the cylinder heads to 380F. It limited our climb performance but was so much better for the engine.

I agree. I use 380°F as my soft limit for a TNIO550B and take more aggressive action at 395°F.

Nevertheless, it’s a certification requirement that the engine have appropriate detonation margin at the manufacturer’s declared CHT redline and TCM/CMI has chosen to put their redline around 75°F higher than I’m comfortable in normal operations.

I just went under contract for my first turboprop.. the numbers there are nutty.

The engine can sustain 840C, it can go to 870 for less than 20 seconds and it can even sustain 1000C for up to 5 seconds without triggering any kind of exceedance.

We can and do, if the engines are upgraded with goodies like electronic ignition (yeah, all those old aircraft engines are using fixed timing magnetos). But a lot of aircraft engines just aren't. And if you're in a certified plane instead of an experimental plane, good luck ever getting it.

Basically any engine made by a European engine manufacturer takes "mogas" without incident, and prefers it because lead causes issues. But to the sibling comment's point, those engines also have goodies like single lever power (so no direct mixture or rpm control). That changes the parameters a lot.

Edit: to add on, if you're in an experimental plane, you can do all sorts of things to your engine. You can buy aftermarket electronic fuel injection and ignition kits with variable timing, and reclaim a good deal of fuel economy in the process. Most engines that these kits support will then quite happily run along with a fuel like 94UL. Some people have even converted automobile fuel ignition controllers for the purpose (I hear the Ford V8 ECU is pretty popular for this).

Yeah, don't diamond note you CAN use leaded, but recommends AGAINST it?

Thanks for the rundown! So with unmodified engines, the lead mainly just helps make extra sure there’s no knocking, which is very important because the engine won’t compensate (any issue midair would be very bad)?

Aviation gasoline is much higher octane than the "premium" (or however it's branded) high octane gasoline at your local gas station. Typically premium gasoline is about 98 RON / 88 MON, whereas 100LL aviation gasoline is 100 MON. The big news here is that GAMI has come up with a formula that provides the required octane without lead, and also otherwise fulfills the various requirements for aviation gasoline.

At least one airport I know of - KAWO - used to have it, but no longer does. Wonder what the story is there.

“Avgas” in Swedish means “exhaust”, as in what you get from the tail pipe of a car. But I can’t tell if their use of the name “Avgas” for the product here is intentionally connected to the Swedish meaning of that word or not.

It is a contraction of "aviation gasoline"

It's referring to avgas, a shortened name for aviation gasoline. I don't believe there's a relationship to the swedish. Historically there was also a corresponding mogas (motor gasoline), but the specifier got dropped in general usage.

GAMI is a super interesting and innovative company. They also pioneered the practice of using precision-balanced fuel injectors to help plane engines run more smoothly. Factory engines come with radically unbalanced fuel injection, one cylinder might get 10-20% more fuel than others. GAMI developed a procedure for you to test the imbalance in your engine and then sell you a set of balanced injector. That saves fuel, wear on the engine, and even lets you run lean of peak more safely if you want.

It’s a shame Light Sport Aircraft (LSAs) never really caught on. Most of them use Rotax engines which take regular unleaded gasoline. They’re much more fuel efficient too!

Huh? LSA is doing fine. It does considerably better in basically every other jurisdiction where the licencing is typically easier and the payloads higher.

“Comparing charts I see 506 registrations of LSA-type aircraft in 2020 and 358 registrations of GA aircraft in 2020,” Steve notes. “Thus, registrations of LSA-type aircraft account for more than half of the single-engine piston aircraft registered in 2020, 59% from data analyzed for this report.”

https://generalaviationnews.com/2020/11/02/up-or-down-how-fl...

I think the problem with LSAs was the industry adopted them too fast. There were so many manufacturers none of them could the volume needed for lower prices. Even Cessna canceled the C162. This has been improving over time of course.

And there's scuttlebutt that the LSA rules might be revised to be based off a load factor formula rather than a fixed upper gross weight limit, as well as the creation of PSAs (larger aircraft certified via ASTM standards rather than FAA part 31(? I can't remember the CFR part right now), which would allow for much faster and easier certification of PSAs (as opposed to standard category aircraft).

Here's hoping for a full revision to the LSA rules that allows 152/72/82 and Piper Cherokees into the category; that would open up Sport pilots to thousands of new aircraft they were unable to fly for essentially no reason. It's painfully obvious that the FAA's artificial limitation of 1320 lbs was completely arbitrary and is overall a detriment to the safety of pilots operating under the sport rules. Frankly, I think/hope that recertifying the majority of standard category aircraft as PSAs will help drive down costs and spur some new innovation in GA.

I guess it's just based on my observations in the US. I'm a Sport Pilot; I don't see many others in the Bay Area.

Often I'm the only one that rents the Skycatcher at KPAO in a given month, and there's basically only two LSAs that are accessible to rent nearby (that Skycatcher at KPAO and a SportStar at KRHV).

I think that the dream was that you were going to see $50k new aircraft due to the easier regulation, but it didn't pan out, and new LSAs are more like $150k. When you can get a used 172 for the same money and have a far more capable aircraft, that's the direction most people end up going.

I could see some resurgence in the market with the large number of late-70s light aircraft starting to become unmaintainable though. It's hard to say with the opposing force of the shrinking pilot population though.

Is the link wrong? I'm getting a 404.

Will this work in the old piston aircraft? I’m thinking about buffalo airways.

only if the engine doesn't need lead for lubrication of the valves/anything else

There are other additives that can provide that, the question would be do they have FAA approval.

Lead does not lubricate the valves, though that's a common misconception.

https://www.avweb.com/features/pelicans-perch-55lead-in-the-... (The fine author of this article sadly passed away earlier today.)

> The fine author of this article sadly passed away earlier today.

Aw! :( I hadn't heard that yet.

I'll have to read through Pelican's Perch again. So much knowledge, so densely collected.

Aviation gasoline or "avgas" is _only_ used for piston aircraft.

Fuel for turbines is closer in makeup to Kerosene than it is gasoline, whether it's a traditional turbofan or a turboprop like you'd see on a Dash-8.

Buffalo is famous for flying old DC-3s and some other small "bush" planes that are piston-engined.

Are they really using the old rotary engines? The only DC3s I've seen still flying were turboprop conversions with noticeably different engine nacelles of course.

Never seen them for passengers but there was a geo survey company operating in the area that used them. Really cool aircraft to see.

Can someone tell me why liquid fuel is called gas in the US?

"Gas" is short for "gasoline", just like "petrol" is short for "petroleum".

https://en.wikipedia.org/wiki/Gasoline#Etymology

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