The average age of the U.S. General Aviation fleet is 30+ years. While there are aircraft STCed to use unleaded automotive gasoline (‘mogas’), aviation gasoline (‘avgas’) still containes tetraethyl lead (TEL). I understand that this causes a distribution problem, in that existing pipelines can’t be used to move it from one place to another. (The TEL would contaminate unleaded fuels transported through the same pipes.) I read a couple of decades ago that 100 octane ‘low lead’ avgas has more lead than regular mogas had at the time. I’ve heard rumblings over the years that the EPA might revoke the TEL exemption for avgas. There’s an (experimental) unleaded fuel that would work for 70% of the fleet, and there are efforts underway to develop lead-free avgas or another fuel. (Aviation ethanol, for example. It does provide 10% or 15% more power, but fuel flow is increased by about 40% to 50%.)
Aviation companies are notoriously conservative – especially in light of the massive lawsuits that virtually destroyed the industry in the '80s. But surely the writing could be seen on the wall? Why haven’t Lycoming and Contenintal come out with an engine designed to run on lead-free avgas? Is it because of their conservatism? (i.e., ‘We don’t want to risk changing our designs.’) Or is it because engines designed for unleaded fuel would not run on leaded fuel? New engines will not be practical for the vast majority of the fleet. But engines have to be overhauled periodically. Can’t the old engines be modified at TBO to run on unleaded? Given that a factory-rebuilt O-360 might cost $25,000 anyway (pulling a number out of the air, as it were), would the (hypothetical) modifications cost that much more? What modifications can be made to engines to reduce the consumption of aviation ethanol?
ISTR when leaded gas was phased out they determined that older cars would run on unleaded just fine. Why is this not the same for airplanes?
Have they not switched over for the simple reason that federal regs for cars don’t apply to aviation? In a worst case scenario, if the older engines would not run on unleaded avgas, surely a fuel additive could provide the missing lead.
I’m with you. I don’t see any reason to continue the status quo.
Airplane engines using 100LL need TEL to prevent detonation – never a good thing in an engine, and doubly so in an aircraft engine. As I said, there are some aircraft STC’d for unleaded mogas, but IIRC these are generally aircraft with engines designed to burn 80 octane avgas.
Extreme temperatures. External and internal. Aircraft engines run at a much higher average % of RPM and HP usage than the auto engine.
More extremes of altitude change on a frequent basis. ( biggie here ) Auto gas does not work well at altitude nor with any kind of long continuos over boosting as the average modern aircraft engines uses.
Autogas STC’s are not usually applied to engines that won’t run on 80/87. Who uses an normally less then 150 HP engine at altitudes over 10,000 feet?
Aircraft engines are normally much slower turning and normally carry much longer, high combustion pressures and are air cooled. All things that lead to denotation and vapor lock.
I thought that generally, pipelines are used to transport just crude oil, before it’s been refined into various grades & types. It goes thru the same pipeline until it reaches the local refineries. There it’s refined, and the various additives to convert it into various grades, blend in required ethanol, and make it leaded or unleaded, are added. From there, most of the end product does not go in pipelines any more, but is transported by the tank trucks that deliver to the gas stations.
Here in Minnesota, we have only 2 pipelines supplying all the oil, gasoline, kerosene, etc. in the state. The Wood River pipeline comes north from St. Louis, Mo, and the Minnesota or MinnCan one comes south from Alberta, Canada.
I’m skeptical. I work for the company that liscences the TEL technology to Octel (that UK plant mentioned), and as far as I know there’s no TEL being used in the US in any application. And if there’s enough being used in aviation gas that they need pipelines to pump it around the country, then I should be able to at least find a specification for the US on that.
I’ll try to remember to ask one of the lead guys next time I have to talk to them.
According to the article, avgas amounts to 0.5% of the yearly U.S. gasoline production. But yes, TEL is used in avgas.
In any case, on re-reading the article my questions about engines may have been answered. General Aviation Modifications Inc. is developing a pressure reactive intelligent spark management (PRISM) system that will produce rated power in a Lycoming TIO-540 engine using 95-octane unleaded fuel. Teledyne Continental Motors says its full authority digital engine control (FADEC) system will enable its engines (Continentals) to run on 91/96 UL.
Still, what’s taking them so long? Yes, digital control was not available 30 years ago. But one would think that but for Lycoming’s and Continental’s conservatism they could have come up with unleaded engines a long time ago.
You answered your own question. They stick with decades old proven technology in existing small plane engines because there hasn’t been a defining need to change. New aircraft engines are insanely expensive to design and build because the certification requirements are so high. Even after certification, a flaw that slipped by could cause a few crashes and the game would start all over again. They have perfectly good engines that people are willing to buy already so that the end. It isn’t like there is a massive market for new, state-of-the art small plane engines anyway.
Some companies have designed and built new small plane engines but most of the ones I have read about are diesel (and run off jet fuel conveniently enough). I am not sure if any of those have gotten certified yet. Homebuilders have used every type of engine under the sun including some car engines but they take responsibility for the results and don’t have to go through the same certification process as the manufacturers.