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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

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.

sokoloff 5y ago
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.
- Robotbeat 5y ago
  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.
  - sokoloff 5y ago
    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.
    - Robotbeat 5y ago
      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.
  - VLM 5y ago
    > a MASSIVE public health issue Its not. Its the kind of topic made for karma farming on social media.
  - GekkePrutser 5y ago
    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.
outworlder 5y ago
> . 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.
- Robotbeat 5y ago
  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.
alethiophile 5y ago
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.

sokoloff 5y ago

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.

Robotbeat 5y ago
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.
- sokoloff 5y ago
  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.
  - Robotbeat 5y ago
    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.
- VLM 5y ago
  > a MASSIVE public health issue Its not. Its the kind of topic made for karma farming on social media.
- GekkePrutser 5y ago
  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.

outworlder 5y ago

> . 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.

Robotbeat 5y ago
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.

alethiophile 5y ago

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.