TEL (tetraethyl lead) had and has other advantages over ethanol beyond patentability -
Unlike TEL, ethanol is hydrophilic, which makes gasoline blended with it more apt to be contaminated with water, and other water containing contaminants, this is particularly relevant for aviation uses and also reducing incidences of vapor lock.
TEL is also (more) rubber and seal friendly, other than the (very) high risk of lead toxicity, TEL blended gasoline is easier to work with and process than Ethanol blended gasoline.
TEL also acts as a natural lubricant of its own, the lead acting as lubricant, particularly on valve and other top end engine components.
This isn't really a defense of TEL - particularly not in road gas, while it was understood that exposure to large quantities of lead was toxic, toxicity of low dose exposure to environmental lead wasn't really fully understood until the 50's/60's, we also didn't really understood how long environmental lead lingered around until the 60's. Modern technologies have overcome much of the issues from ethanol in road gas, but there are reasons TEL is still used in AvGas.
TEL in AvGas was vital in reaching higher octane, and Ethanol is contraindicated in AvGas (at the last I looked into the topic) because of its hydrophilic nature - our ability (the allies) to produce high octane AvGas is one of the factors that won WW2, and use of TEL was a deciding factor in that.
Those problems were solved for cars, they can be solved for planes. We shouldn't use it. Bioaccumulation of heavy metals was understood very early. Everything has a cost, spraying lead everywhere should be higher than what we are willing to pay.
I am guessing it's still allowed because people who fly planes can afford to lobby.
I was astounded to find TEL was still allowed in aviation fuels. Rates of cancers etc are higher near military bases due to fuel handling incidents.
> Rates of cancers etc are higher near military bases due to fuel handling incidents.
Avgas is only used in piston engines, and the military mostly flies turbines, which use ordinary jet fuel (which does not contain lead). They have some, but I think if you told the military "jets and turboprops only" it wouldn't be a big problem. (Not sure how they would train new pilots, however.)
If you're looking for disease/damage from lead in avgas, you want to find a little airport in the middle of nowhere that has a really good restaurant on the field ;)
> I am guessing it's still allowed because people who fly planes can afford to lobby.
People that fly piston engines do not have any money to lobby.
To me it feels very similar to why software engineers pay so much tax -- we get paid just enough to be dinged by things like the AMT, but not enough to afford lobbyists.
Politically the rationale is likely that this constituency is small and so forcing them will have a relatively small benefit compared to the main policy goal; but they really care. If you fly a piston prop, you likely don't have $1M spare (you could use that to trade your piston plane for a small jet) for Washington lobbyists, but you do have a vote and you care about banning the only fuel you are authorised to use enough that you're going to use that vote and you're going to be loud about it.
A previous article about Leaded Petrol caused me to read how the UK exempted some very old cars which could not be effectively modified. There's actually a waiver so that, in theory, every fuel station in the country can do paperwork to get a small amount of leaded gasoline (a tiny fraction of their total fuel sales) and sell it for this purpose. The politicians were thus able to tell their constituents we did not screw you, just ask your local supplier to set aside fuel for you.
But economics does the rest, at first those retailers see sales of leaded fuel are very low. Those who love classics maybe decide to set aside the option for a year or two and see how it goes, everybody else stops selling leaded fuel. The wholesalers now see that sales of leaded fuel are tiny, so they don't bother making it, it becomes a special order, which then further increases the pressure not to bother stocking it. Today enthusiasts will just mail order the lead additive and pour it into their tank after a refill or they use a substitute additive which these days works well enough, the politicians didn't have to lift a finger.
It will be over, but it’s not over yet. Your link says that it will both take a while for it to come to market and also be more expensive to produce…an expense that will likely be balked at by the airlines until forced to use it at which point it will be the customers that pay.
Airlines (outside of bush planes) are not using AvGas in any substantive quantity, and have not been since the early 60's. The amount of AvGas used a year is dwarfed (several times over) by the amount of Jet Fuel (Jet A does not have TEL in it).
AvGas (which uses TEL) is used by general aviation exclusively.
I would guess one thing that confuses non-pilots is that while say an A320 or a 747 looks like it has jet engines, lots of small regional aircraft (e.g. a Dash-8) visibly have propellers, and so it's natural for lay people to assume that's basically the same idea as on a Cessna 172 or a Spitfire scaled up.
But it isn't. Those planes aren't aren't fuelled by AvGas. Their engines use JetA (basically kerosene) because they've got a turbine inside like those turbofan engines which look so visibly different, however their turbine powers the propeller rather than a set of fans to drive more air through the engine and produce thrust that way.
For people not familiar with terminology, “general aviation” does not mean “regular airplanes”, but, to a first approximation, “small piston-engined airplanes”, operated by hobbyists or small charter operations.
I don't think most "small charter operations" would be General Aviation (unless I understand what's being chartered here?) and although most GA planes are pistons that's not part of the definition. What matters is why you're flying, not what you fly.
The categories (for non-military use) are generally Scheduled or Air Transport (any time you buy tickets for a flight, that's the category, you don't know or care who is flying, you paid for the journey between a specific origin and destination at a specific time; a FedEx plane is also Transport), then Commercial (not Transport but somebody is getting paid to fly aircraft, maybe it's crop spraying, TV news copter, police, or just another TV priest being flown around in his private jet), and only if nobody was getting paid is it General Aviation.
If your cosmetic dentist can afford a brand new Vision Jet so that he can live 100 miles away and fly in to do $5000 appointments without sitting in traffic, that's General Aviation. The authorities don't care that he's getting paid to be a dentist, he's not getting paid to fly his plane.
If your airline uses a relatively tiny PA-42 to get customers to an obscure but important airstrip with maybe 3-4 passengers per day that's still Air Transport.
On the other hand if some oil sheik owns their own A320 with their own custom decor and has a team of pilots to fly it wherever they want, that's still only Commercial, not Air Transport because nobody is buying tickets, it just goes wherever he wants.
GA is non-commercial, non-military, non-aerial-work (application, survey, etc). The pilots can be paid employees and have it still be GA. (Your sheik A320 example would be considered GA, not commercial, as would business operators, fractional operators, and of course private operations.)
Don’t confuse the commercial certificate[“license”](which is required to be paid for flying) with commercial operations (typically holding out to the public for air transport).
>AvGas (which uses TEL) is used by general aviation exclusively.
And by people who don't want to ever have to clean or rebuild a carburetor in their small motors. It's been an exceptional motor-life-extender to my chainsaws specifically.
For what it's worth, unleaded avgas is already available at some of the Bay Area airports as of recent, and it's currently priced cheaper than traditional leaded avgas.
It’s UL94, so lower octane (94 octane, as the name suggests). However, this is still fine for lower performance aircraft that make up the majority of the GA fleet.
There’s been a lot of interest in it, especially in light of the recent discussions to close RHV in San Jose. I know one of the flight schools here just switched all their aircraft over to UL94.
Higher performance aircraft will need UL100, which is still not available, but is expected soon. There’s been significant progress in getting it approved over the last year.
Swift Fuels sells the supplemental type certificate aircraft owners need to use UL94. They are offering a free upgrade to the UL100 STC once it’s offered, so aircraft owners don’t have to pay twice to start using UL94 today.
> It’s UL94, so lower octane (94 octane, as the name suggests). However, this is still fine for lower performance aircraft that make up the majority of the GA fleet.
The standard story seems to be that 20% of the planes burn 80% of the fuel, and need all the octane in 100LL. And GA is such a small market that airfields can't justify having multiple fuel grades available, so 100LL everywhere it is.
But yes, nice to hear that UL94 is nonetheless available in some places.
The amount of TEL used in AvGas is infinitesimally small, its only used in Aviation Gasoline, which is only used in older piston engined craft, the military flies none of these as far as I know.
We fill our cars every week and when you stand there thinking "damn I love this smell" yet when there's 1ppm of benzene in sun cream people scream "caaaancer"...
There are few technical reasons, to be sure, but there are plenty of economic and business reasons. The most popular engines in general aviation are Continental/Lycoming ones, and these are based on what, 50+ years old basic designs? Automotive industry have developed significantly better piston engines in last few decades, in terms of power to weight ratio, fuel efficiency, MTBF and service interval. However, the nature of the field, its relative niche quality, and regulatory framework make it difficult to adapt and adopt them in general aviation. There has been recent attempt to do it, with diesel engines from German automotive industry, but they are facing a lot of very real problems, for example, lack of maintenance infrastructure.
> but they are facing a lot of very real problems, for example, lack of maintenance infrastructure.
Comprehensive government regulation would create such an infrastructure. When the government says "in 5 years we will disallow creation of new airframes that use leaded gas, and in 10 years there will be no more leaded gas sold, and in 15 years additives will be illegal", everyone knows what's on the horizon - and you can bet that there will be engine vendors selling modification kits and maintenance infrastructure, since now everyone knows that there will be a massive market coming up as everyone has to adapt to the new rules if they want to keep flying!
> Comprehensive government regulation would create such an infrastructure.
Or, it would destroy small engine general aviation.
> and you can bet that there will be engine vendors selling modification kits and maintenance infrastructure, since now everyone knows that there will be a massive market coming up as everyone has to adapt to the new rules if they want to keep flying!
What if, you know, people can't adapt? What if people can't afford to replace their 40 years old aircrafts with sparkling new ones, costing 5-10 times much? Sure, some of them will, but there are many hobbyists who can afford loan payments and insurance on a plane worth $100k, but couldn't do the same on one worth $500k.
Yes, this would stop emissions of TEL, sure, but at tremendous cost. Is that cost worth it? To our (and FAA, and EPA) best knowledge, probably not, as lead emissions from GA have much different characteristic than the ones from cars.
"The temperature for Lead deposits to form tend to be favourable around the spark plugs (as the whole mixture is quite cool before the flame starts to propagate) and on the exhaust valve stem (as the mixture cools after combustion). The problem is that the deposits are electrically conductive, which shorts out the spark plug - and corrosive, which can start to attack the metal of the valve stems."
It's the supposed benefits of the post-combustion lead oxide deposits that defenders of leaded gas cite. I have never heard anyone cite the lubricity of TEL itself.
The most popular theory is that the lead oxide fouling reduces the occurence or effects of micro-welds between valve and seat surfaces, which otherwise produce abrasive particles that contribute to valve seat recession. While this theory is plausible, it has not been shown to occur under normal operating conditions in automotive engines, nor in aviation engines as far as I know.
The final report from the EPA's Valve Seat Recession Working Group found no evidence that leaded gas reduces engine wear under any but the most extreme operating conditions:
"In real world conditions, virtually no evidence of excessive valve wear has been found in vehicle or engine operation in normal everyday use, and several studies that monitored vehicles in actual daily service in countries that eliminated lead found no excessive valve wear."
"Dry gas" which is used to correct moisture problems in cars' fuel systems is alcohol: Ethanol, methanol, etc. and it takes advantage of alcohol being hydrophilic.
Ethanol has requirements for hoses and seals that might otherwise be degraded by alcohol. But this is not an ongoing issue in modern vehicles.
The same property, increased ability to absorb water, both helps to remove excess of water and can cause a problem in the longer-term.
It's like using a towel to dry your shower tray: in the short run it's helpful but if you leave it there all the time you'll end up with a permanently soggy towel keeping everything damp.
Unlike TEL, ethanol is hydrophilic, which makes gasoline blended with it more apt to be contaminated with water, and other water containing contaminants, this is particularly relevant for aviation uses and also reducing incidences of vapor lock.
TEL is also (more) rubber and seal friendly, other than the (very) high risk of lead toxicity, TEL blended gasoline is easier to work with and process than Ethanol blended gasoline.
TEL also acts as a natural lubricant of its own, the lead acting as lubricant, particularly on valve and other top end engine components.
This isn't really a defense of TEL - particularly not in road gas, while it was understood that exposure to large quantities of lead was toxic, toxicity of low dose exposure to environmental lead wasn't really fully understood until the 50's/60's, we also didn't really understood how long environmental lead lingered around until the 60's. Modern technologies have overcome much of the issues from ethanol in road gas, but there are reasons TEL is still used in AvGas.
TEL in AvGas was vital in reaching higher octane, and Ethanol is contraindicated in AvGas (at the last I looked into the topic) because of its hydrophilic nature - our ability (the allies) to produce high octane AvGas is one of the factors that won WW2, and use of TEL was a deciding factor in that.