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.
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?
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]"
This seems like such a cop-out excuse. We'd rather harm potentially millions of people with toxic materials rather than inconvenience a few dozen aviation enthusiasts. Progress moves forward, if these old engines can't function in this new world they should be scrapped and replaced with something that can do the job.
And BTW, general aviation has been asking for leaded avgas to be dropped for decades now. The holdup is not the pilots or plane owners but the goddamn FAA [0].
This is really good thank you. Worthy of a follow-up submission on HN of its own since we're pretty deep into comments here.
Note that this study is specifically focused on North Carolina. I'm curious if similar research has been done in the Western US. California in particular is very popular for GA. Here's the top 10: https://generalaviationnews.com/2020/02/03/top-10-busiest-ge...
To save people the full read, here is the most relevant sentence:
> children living within 500 m, 1,000 m, or 1,500 m of an airport had average blood lead levels that were 4.4, 3.8, or 2.1% higher, respectively, than other children.
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.
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.
The trick is that there’s two tiers of expensive for GA:
- People buying, say, a new SR22 for $779,000
- People buying, say, a 1976 Cessna 172 for $72,000 and splitting it with 3 friends
Having Cirrus work on, say, regular Mogas by contracting Continental to develop a new engine would be expensive but the buyers aren’t particularly price sensitive and amortized across the typical lifetime of an aviation engine design (the IO-550 in the SR22 was first delivered in 1983) likely wouldn’t hurt much.
Trying to come up with an engine swap for the O-320 in that ‘76 172 is a whole other can of worms. Who’s going to even sign off on it? The whole aircraft is 50 years old and designed and certificated for that specific engine. There’s no financial incentive for Cessna to do it, and even if they did, the cost to do the swap would likely significantly exceed the financial capacity of many owners.
I absolutely would love to see a financially viable way to get past this! The use of LL fuel in 2022 is tragic. On the other hand, killing off a big chunk of the GA industry and leaving it solely in the purview of the Wealthy and not just dedicated hobbyists… that sucks.
For context, my family has an old Piper J3 sitting in a hangar on a farm. It definitely needs an overhaul, but to get it back in the air would likely be a low 5-figure bill; retrofitting a Mogas engine onto it in such a way that it doesn’t need to be categorized as “experimental” would be… prohibitive.
Thanks for this context. I'm not a pilot but I can absolutely relate to the joy such a machine could give.
I'd like to ask one thing further: Do you think the existence of these older cheaper planes is holding back the development of upstart companies aiming for a price point that's closer to the Cessna 172 than the SR22? If leaded fuel engines were banned by the FAA today, would that create an opportunity for new entries, maybe with EV/hybrid engines? Or are there fundamentally different manufacturing economics to safely put something like that up in the air at that price point today?
There are already alternative engines in wide use (particularly on ultralights and light-sport aircraft) that can run on regular, unleaded gasoline, like the Rotax 912[0]. The issue, as others have pointed out, is getting these newer engines certified for use on existing, older planes. This would require extensive testing to get a Supplemental Type Certificate (“STC”) to allow the engine to be installed on a certified aircraft (think anything manufactured, like a Cessna 172 or Piper Cub.)
> Do you think the existence of these older cheaper planes is holding back the development of upstart companies aiming for a price point that's closer to the Cessna 172 than the SR22?
Things in aviation are incredibly expensive because of how much it costs to have things certified by the FAA for safety and reliability. I'm no legal expert but I don't think an upstart company has much wiggle room to get around that if they want to legally sell their aircraft in the US. As an example Cessna 172s are still made and AFAIK the modern ones haven't required leaded fuel for some time. A 172 is just about the most basic small airplane you can get but today a new one costs as much as a house, about $400k.
I mean, there's being cheap and then there's getting a new aviation engine FAA certified. Those aren't exactly the same thing and Bob the dentist who likes to take his Cessna 172 up on weekends can't simply approve a new engine.
This is why buying a new spec Cessna 172 from the factory floor today will still come with the good old Lycoming O-360 engine, introduced in 1955.
Cessna sells ~250 172s per year, nowhere near enough to justify new engine approval.
I'm no expert, but I'll express a wish: that modern supply constraints mean Lycoming O-360 engines may be noncompetitive to an engine design conceived today. Perhaps these old engines are suppressing the investment into an invention that turns a 250 person market into a 25,000 one?
Whenever I see comments like this I always remember the airplane owner (Cessna 152) I used to know who drove a beat up old Toyota Corolla with the bumper sticker "My Other Car is an Airplane."
> 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."
Aviation moves very slowly because of the safety and reliability requirements. This is a blessing and a curse as far as things like that go. Generally speaking, equipment gets certificated under very specific conditions and deviating from those conditions is strongly discouraged (if nothing else, by your insurer). If the POH (Pilot Operating Handbook) says that your 1967 Cessna 172 has to run on 100LL, you run 100LL and not some unleaded 100-octane equivalent.
I don’t have the exact numbers, but outside of doctors and nouveau-riche tech folks, I would suspect that most of the North American GA (general aviation) fleet is 30-40 years old. There’s new GA aircraft coming to market, but they’re eye-wateringly expensive compared to perfectly serviceable older aircraft that can get an electronics upgrade.
Jet fuel is a fuel oil more like kerosene. High octane aviation fuel is for piston engine aircraft like a Cessna or a p-51.
There are actually very strict regulations on the maximum amount of biodiesel (fatty acid methyl esters) allowed in jet fuel. They are much more prone to microbial blooms than petroleum based fuel oils and the fungal films can clog filters, starving an engine.
Lead also has lubricant properties for things like mechanical fuel pumps and injection, valve seats and stems, so it's not just for octane boosting you need to replace the lubricant too.
Are there unique design constraints for engines used in general aviation that these components couldn't have a lubrication strategy akin to engines that work with unleaded fuel?
Nope it's just all the old planes flying around that require it. As the engine in a plane could be considered to be fairly safety critical people are extremely resistant to trying new things on it.
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.
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.