6 ms·

The issues are totally unrelated. Jet turbines have always been capable of running on almost any fuel. I would hazard a guess that what Airbus did here was mo

by Merad 4y ago

The issues are totally unrelated. Jet turbines have always been capable of running on almost any fuel. I would hazard a guess that what Airbus did here was mostly certifying that the alternative fuel wouldn't cause any major problems, maybe also things like tweaking the engine management systems to ensure consistent power output and throttle responsiveness with the new fuel. The problem with avgas is that there are a huge number of aviation piston engines still in use that were built with 1930s-1960s era technology (in some cases the engines themselves are literally that old) that were designed to use leaded gasoline. Getting those engines to run on unleaded gas would at best require extensive modifications to the engine and at worst just isn't possible. In the cases where it's possible, someone has to foot the bill to figure out how to modify the engines and get the changes certified with the FAA, both incredibly expensive propositions. Once that's done all of the owners will have to drop the money to upgrade their engines. The death of avgas is inevitable but unfortunately it's probably going to take some sectors of general aviation with it. Those older planes are still flying in large part because newer planes have gotten so incredibly expensive. Also from what I've read the warbird community is working on the problem but many of them aren't very optimistic about being able to get those big WW2 era engines to run unleaded.

jabl 4y ago
There is G100UL which seems to be promising as a 1:1 replacement for the current 100LL. Though regulatory inertia seems to be delaying a large scale rollout: https://www.avweb.com/insider/faa-continues-to-stall-on-g100ul/ https://www.avweb.com/insider/faa-continues-to-stall-on-g100... I'm not aware of any experiences of G100UL with warbird engines.
krastanov 4y ago
I am not a chemist so maybe I am naive here. My understanding is that lead additives were necessary to "fake" higher octane content (and the 0.1% lead additive is much cheaper than the 99% octane). Why can't we just go back to expensive high-octane fuels instead of adding lead (or just use the various alternative additives used in other high-performance engines)? Edit: an internet search tells me that avgas has an octane rating of 100... So why can't we just use actual pure octane in these engines?
- HPsquared 4y ago
  Knock resistance isn't the only factor in leaded vs. unleaded. From Wikipedia, valve wear is also a factor (the lead deposits apparently act as a kind of lubricant): "Meanwhile, Teledyne Continental Motors indicates (in document X30548R3 most recently revised in 2008) that leaded avgas is required in their engines: "Current aircraft engines feature valve gear components which are designed for compatibility with the leaded ASTM D910 fuels. In such fuels, the lead acts as a lubricant, coating the contact areas between the valve, guide, and seat. The use of unleaded auto fuels with engines designed for leaded fuels can result in excessive exhaust valve seat wear due to the lack of lead with cylinder performance deteriorating to unacceptable levels in under 10 hours."[8]" https://en.wikipedia.org/wiki/Avgas#Properties https://en.wikipedia.org/wiki/Avgas#Properties
  - bdefore 4y ago
    Presumably 'valve gear components' could be designed to function without reliance on a toxic lubricant. Ultimately this comes down to being cheap.
    - tonyarkles 4y ago
      Absolutely for new equipment that would be the case. Safely retrofitting existing equipment is quite a bit more challenging, and my suspicion (without having actual numbers) is that the vast majority of the fleet that would require those retrofits is quite old. Some of the manufacturers don’t exist anymore, so having them sign off on “this retrofit kit will safely transport you in the air for thousands of hours” wouldn’t be possible. It’s not an unsolvable problem, but it’s thorny for sure both from a safety perspective and a cost perspective. You call it “being cheap” but my gut feeling is that retrofitting existing 40-year-old kit to handle unleaded Avgas safely would be capital-E Expensive.
      - bdefore 4y ago
        General aviation is expensive certainly and for a select few very wealthy individuals. I call it cheap because there is a way to solve it, but owners of small planes are choosing not to do so (and they're not compelled to do so despite the known externalities of their outdated machinery). Maintaining a beautiful car from the days of the Cold War is also not cheap, but it can be retrofitted to pass emissions tests. If you don't, you can't legally drive it. I don't see why the same doesn't apply to aircraft.
kelseyfrog 4y ago
For sure, Thank you. I meant it 100% with a not toward the regulatory/economic constraints at stake and have zero interest in the physical workings of engines.

by Merad 4y ago

jabl 4y ago

There is G100UL which seems to be promising as a 1:1 replacement for the current 100LL. Though regulatory inertia seems to be delaying a large scale rollout: https://www.avweb.com/insider/faa-continues-to-stall-on-g100ul/ https://www.avweb.com/insider/faa-continues-to-stall-on-g100... I'm not aware of any experiences of G100UL with warbird engines.

krastanov 4y ago

I am not a chemist so maybe I am naive here. My understanding is that lead additives were necessary to "fake" higher octane content (and the 0.1% lead additive is much cheaper than the 99% octane). Why can't we just go back to expensive high-octane fuels instead of adding lead (or just use the various alternative additives used in other high-performance engines)? Edit: an internet search tells me that avgas has an octane rating of 100... So why can't we just use actual pure octane in these engines?

HPsquared 4y ago
Knock resistance isn't the only factor in leaded vs. unleaded. From Wikipedia, valve wear is also a factor (the lead deposits apparently act as a kind of lubricant): "Meanwhile, Teledyne Continental Motors indicates (in document X30548R3 most recently revised in 2008) that leaded avgas is required in their engines: "Current aircraft engines feature valve gear components which are designed for compatibility with the leaded ASTM D910 fuels. In such fuels, the lead acts as a lubricant, coating the contact areas between the valve, guide, and seat. The use of unleaded auto fuels with engines designed for leaded fuels can result in excessive exhaust valve seat wear due to the lack of lead with cylinder performance deteriorating to unacceptable levels in under 10 hours."[8]" https://en.wikipedia.org/wiki/Avgas#Properties https://en.wikipedia.org/wiki/Avgas#Properties
- bdefore 4y ago
  Presumably 'valve gear components' could be designed to function without reliance on a toxic lubricant. Ultimately this comes down to being cheap.
  - tonyarkles 4y ago
    Absolutely for new equipment that would be the case. Safely retrofitting existing equipment is quite a bit more challenging, and my suspicion (without having actual numbers) is that the vast majority of the fleet that would require those retrofits is quite old. Some of the manufacturers don’t exist anymore, so having them sign off on “this retrofit kit will safely transport you in the air for thousands of hours” wouldn’t be possible. It’s not an unsolvable problem, but it’s thorny for sure both from a safety perspective and a cost perspective. You call it “being cheap” but my gut feeling is that retrofitting existing 40-year-old kit to handle unleaded Avgas safely would be capital-E Expensive.
    - bdefore 4y ago
      General aviation is expensive certainly and for a select few very wealthy individuals. I call it cheap because there is a way to solve it, but owners of small planes are choosing not to do so (and they're not compelled to do so despite the known externalities of their outdated machinery). Maintaining a beautiful car from the days of the Cold War is also not cheap, but it can be retrofitted to pass emissions tests. If you don't, you can't legally drive it. I don't see why the same doesn't apply to aircraft.

kelseyfrog 4y ago

For sure, Thank you. I meant it 100% with a not toward the regulatory/economic constraints at stake and have zero interest in the physical workings of engines.