The University of North Dakota John D. Odegard School of Aerospace Sciences has released a two-page communication concluding that engines that had been operated on Swift Fuels 94UL unleaded fuel experienced more than 128 episodes of recessed valve seats or other valve problems. The report details the flight operation’s experience switching from 100LL avgas to Swift Fuels unleaded 94UL and then back to 100LL.
The paper, authored by Dean Robert Kraus and Director of Maintenance Dan Kasowski, relates the flight operation’s experience, with the school’s fleet of 76 Piper Archer singles, 14 Seminole twins, and five Robinson R44 piston helicopters. The reason for reinstating 100LL after about three months with 94UL as the exclusive fleet fuel supply was a cumulative total of 128 cylinders experiencing recessed valve seat events. Some of those events occurred after the switch back, but involved engines that had been run on 94UL for some time.
After the switch back to 100LL, the report says, “None of the replaced cylinders have shown exhaust valve seat recession while operating on 100LL Avgas.” UND is working with Swift Fuels and Lycoming to help assess the cause of the valve problems. The UND fleet logs a total of more than 100,000 hours of flight time annually “with some months seeing up to 13,000 hours.”
The first flight exclusively flown with 94UL was on June 22, 2023. The first sign of trouble was in late August, when a Seminole exhibited a 500-degree-low exhaust gas temperature reading. In the next two months, the report relates, 11 more valve seat recessions were discovered. It was then that, “a walkthrough of the entire fleet was performed and a quick check uncovered another 15 aircraft (17 cylinders) with possible compression issues.”
UND then initiated a triage plan with Lycoming, including an immediate compression check and borescope of all 114 Lycoming engines before further flight. “That check revealed nine more cylinders with recessed seats.” Logbook checks showed that most of the engines that experienced valve problems had flown more than 400 hours on Swift Fuels 94UL.
The report concludes: “We are continuing work with Lycoming and Swift Fuels to identify the specific causes of damage experienced here. Unleaded fuel is the future of general aviation and UND fully supports the industry moving towards further adoption in a safe and cost-effective manner.” A PDF of the full report follows.
Russ Niles co-reported on this story.
There is enough vested interest for all parties involved to diagnose a root cause. As a small guy flying 1 plane about 60 hours a year, I’m grateful larger organizations have the wherewithal to accelerate findings of fact. Lycoming-Swift-UND will get to the bottom of it and make the transition safer and cost effective for everyone.
Old car engines need valves hardened to run on unleaded — or a can of the poison in the tank every refill. Why are aircraft engines different?
Possibly because aircraft engines are stressed much, much harder than those in cars and as one of my A&P Instructors once said, “Do it right. You can’t pull over to a cloud.”
rekabr52, you are saying that the 8:1 compression ratios and 2,600 RPM must be murder on engines? Excuse me but it’s only murder on 1940’s tech that aero engines are based on. It’s laughable that people these days think such low performing and low stressed engines are “working harder”.
Totally agree with You, Mr. Arthur J Foyt!
It’s not (just) engine speed, it’s load. Aircraft engines spend most of their operational lives producing over (often well over) 50% of rated horsepower. Meanwhile, a typical street car is rarely asked to produce more than 50% of rated power, and when it is, it is pretty brief. (Seconds, not minutes to hours.). And, in fact, most are probably producing less than 25% of rated power in day-to-day driving. For instance, my car includes a display that continuously shows horsepower output in realtime. At typical interstate highway speeds (65 to 80mph), it’s producing at most about 10%.
Modern high power marine outboards will run most of their lives at 75-100% power. Modern motorcycles also produce incredible power without failures for decades. Hell, even modern car engines will run 700hp and have a better warranty than a 160hp Lycoming!
Too good not to read.
Arthur J Foyt February 23, 2024 At 9:09 pm
Modern high power marine outboards will run most of their lives at 75-100% power. Modern motorcycles also produce incredible power without failures for decades. Hell, even modern car engines will run 700hp and have a better warranty than a 160hp Lycoming!
It’s about time people started to realise the differences between running high aromatic hydrocarbon percentages in fuel used in engines that rely on air for cooling the cylinder heads vs running alkylate based fuels with very low percentages of aromatic hydrocarbons. Take a look at the flame front rates and the combustion temperatures and understand why the outcomes as they are. No amount of obsessive ‘green wishing’ is going to change the combustion outcomes that are ‘set in stone’ so to speak, once the hydrocarbon choice has been made. Folks, cooling an air-cooled engine is entirely different to cooling a water cooled engine, and whilst this might sound like a statement of the obvious, anybody reading who is bright enough, educated enough, experienced enough, will actually get exactly what I am getting at without me spelling it out with crayons ….. the rest of you folks will just start a random ‘vomit’ of worthless and meaningless piffle.
You sound knowledgeable, so educate us using references that we can read and media that we can access. Piffle doesn’t have references. –43 year A&P/IA
Arrogance, sophistry and pedantry are not helpful. I guess I’m one of the “rest of you folks”.
Go read hundreds of peer reviewed journals on combustion science. It’s all there, but you might need an engineer or scientist to help you to interpret, and i’m not being rude. it’s complex stuff that you the education of a PhD is useful for.
I would put a lot of stock in the thoughts of an experienced A&P/IA. I would put a response that relies on arrogance, sophistry and pedantry in the potentially meaningless piffle file.
With respect, an A&P/IA has not a clue about the combustion processes inside an engine. They only get basic training in engine operation and 100 years of experience does nothing, not one iota to education them on these things, at all.
Me too.
See above. It’s simply an absurd assumption. They are mechanics not combustion scientists/engineers or engine designers. These disciplines are as different as being a pilot and being an Aeronautical Engineer!
It’s equally HOW the engines are run. I would not apply data from a flight school for my plane any more that I would apply data from Formula 1 for my daily driven car. Just because these old (as you improperly state as air cooled) engines have certain tenancies does not mean that I’ve not already already addressed and avoided these issues for decades in MY plane.
It’s not the fuel so much as the current crop of flight school students, flight school mechanics, and them ignoring 70 years of knowledge. So yea, they need some Grumman guys to help them out.
Many thanks to UND for the efforts toward our unleaded future!!
Here’s what I see. People are focused on just one variable (lead vs no lead) but this paper ways they switched from a 100-octane fuel to a 94-octane fuel and made “no changes to performance calculations or operating procedures”.
They started using the new fuel in late-June, and by August they had wrecked an engine? In less than two months? (Put another way, they had problems in less than 400 hours, on an engine that should run for 2000 before overhaul.) Any problem big enough to reduce engine life by 80% should have been noticeable in testing of the fuel during certification. How was this problem not found prior to approval of the fuel?
The only explanation I can think of is that during certification, they “flew” the fuel like it was 94 octane, not 100 octane.
The key take away in this, is the fuel was used / tried for 100,000 hours. I’m extremely grateful this school / company participated. 100 hours in a Baron (AOPA) running G100UL quite candidly tells me next to nothing on whether it’s a viable option regardless of hype.
True BUT … ‘ol Mark and his folks will be able to make grandiose claims about how they’re contributing to the testing of new green fuels while they beg for still more money 🙁
Absolutely 100% correct. I’m glad that there is at least one intelligent person in this conversation.
I’m glad there’s extensive testing going on with UL. They’ll get the lead out eventually.
Exactly Dan. Perhaps some can refresh our recollections on 100UL testing. It seemed short like 150 hours operating between various extremes with an IO-550?
Glad to see actual flight testing like D Brock mentioned.
Ignorant ex-pilot here… Why didn’t the fuel company and engine manufacturers run example engines on test stands and see the results? They could have run the engines quickly and for standard flight conditions, then do a strip down to the valves and see. It almost seems they just did “book work”, and concluded there SHOULD be no wear, rather than actually testing the actual engines. Now, the customers are doing the test flying…
Many fuels have looked great in test cells but in real world, (less than ideal) conditions they have all failed. I’ll only take ANY NOTICE of ANY claims once many engine variants (and not under-stressed low hp ones) have gone to TBO without any adverse outcomes in real world conditions with multiple different operators. My personal belief is that none of the current fuels (UL’s) with pass this test as the bulk of the constituents is all wrong.
This whole fiasco is a classic case of a solution in search of a problem. While lead toxicity is a know problem, leaded Avgas isn’t, as AVweb reported recently (https://www.avweb.com/aviation-news/good-news-airport-lead-exposure-studies-kept-under-wraps/). The concerns over leaded avgas stem largely from theoretical models and one poorly controlled study done by Santa Clara County, CA that was politically committed to shutting down the airport and used the study as pretext for doing so. EPA even laughably claimed that lead levels around ORD were the result of avgas despite the fact that GA operations there are minimal and piston engine ops are rare.
Thanks for referencing my previous article. But, don’t forget the slender thread of relying on the continued participation of a single producer of tetraethyl lead (TEL). If for no other reason, that seems good motivation to advance lead-free aviation fuel.
This is untrue Mark. For some years now there is a Chinese producer of TEL and I’ve personally been involved with a hell of a lot of fuel produced using it, and its performance is easily the equal of that from the UK.
That may be true, but it only sidesteps Mark’s point: GA (for the non-jet set crowd) is still very much subject to the shifting political winds in not just this country, but also other countries. Given today’s geopolitical situation, I’ll freely admit that being utterly dependent on China as the only source (or even only other source) of anything important to me isn’t a position I find comforting.
China is in the business of making money. They sell no matter what, and you’re assuming a lot of long bows for both the UK plant to burn down AND the Chinese one to burn down or a trade ending war to break out etc, to cause a global issue. If that happens then we have bigger issues than some environmental NUTTERS trying to BS to everybody about Pb levels around airports that have been shown in recent weeks to be utter falsified and also non-reported, so as to force an industry (aviation) to make TOTALLY unnecessary changes that are a complete waste of time and money….. period.
Additionally, there is no point destroying GA engines (which is the real world experience) using any fuel that is inadequate for their safe and extended (to TBO) operation. Dream and hope all you like, but this doesn’t change the fundamental fact that the vast majority of the certified fleet (engine types/installations) has NOT been independently demonstrated of being able to be durably run in real world operation in ALL climatic conditions on any UL fuel currently on offer from the evidence presented publicly so far. I have seen no evidence for all engine types and in all installations (fixed AND rotary wing – and ROTARY BEING A KEY POINT HERE) that they have been shown to run to TBO in the real world rather than a few hundred hours in a test cell and another few hundred in the air. I’m not going to share proprietary information here, but I can tell you that there are many that will show issues. The comprehensive testing is up to the people/companies who hope to become a proper ‘drop-in’, certified by ASTM, accepted by ALL engine manufacturers, accepted without penalty by ALL insurers, accepted in all jurisdictions, supplier. Big oil, little companies ….. doesn’t matter… they all should be tested and treated the same IMO, and all meet the same rigorous standards that we have ALWAYS expected in aviation.
Skygypsy February 23, 2024 At 7:41 pm
China is in the business of making money. They sell no matter what, and you’re assuming a lot of long bows for both the UK plant to burn down AND the Chinese one to burn down or a trade ending war to break out etc, to cause a global issue. If that happens then we have bigger issues than some environmental NUTTERS trying to BS to everybody about Pb levels around airports that have been shown in recent weeks to be utter falsified and also non-reported, so as to force an industry (aviation) to make TOTALLY unnecessary changes that are a complete waste of time and money….. period.
Additionally, there is no point destroying GA engines (which is the real world experience) using any fuel that is inadequate for their safe and extended (to TBO) operation. Dream and hope all you like, but this doesn’t change the fundamental fact that the vast majority of the certified fleet (engine types/installations) has NOT been independently demonstrated of being able to be durably run in real world operation in ALL climatic conditions on any UL fuel currently on offer from the evidence presented publicly so far. I have seen no evidence for all engine types and in all installations (fixed AND rotary wing – and ROTARY BEING A KEY POINT HERE) that they have been shown to run to TBO in the real world rather than a few hundred hours in a test cell and another few hundred in the air. I’m not going to share proprietary information here, but I can tell you that there are many that will show issues. The comprehensive testing is up to the people/companies who hope to become a proper ‘drop-in’, certified by ASTM, accepted by ALL engine manufacturers, accepted without penalty by ALL insurers, accepted in all jurisdictions, supplier. Big oil, little companies ….. doesn’t matter… they all should be tested and treated the same IMO, and all meet the same rigorous standards that we have ALWAYS expected in aviation.
All good EXCEPT Skygypsy must have been born recently (so much of his assertions about TBO’s shows his lack of real world experience). Reality was that factory new Lycoming engines in the 70’s were much more likely to reach TBO than new ones in the fleet today. That included the widespread use of UL (MoGas) being used on many of these engines through the 80’s and 90’s.
The fuel is NOT destroying engines; the build quality and leaning techniques will.
I do not think lead in the context of GA harms the population, at all. That’s a political ploy by the environmentalists, politicians, and developers. It does harm our engines however. As far as valve recession goes I don’t know what to make of the UND situation yet.
I’d be willing to use UL fuel as long as it is safe for my O-360. I’d even say it would be worth a little more because of the lack of buildup in our engines and oil. May a dollar a gallon more, max. Otherwise I’d stick to LL or Mogas.
Wouldn’t it be nice if UND would do a similar trial with the GAMI G100UL fuel?
Don’t forget the statistics of the game. At one time 99.9 % of fuel was leaded auto fuel (aka the good old days of 96 octane regular and 101 octane high test). Since that was done away with, the remaining avgas (the 0.1%) now has become 100% of leaded fuels but it is treated like the a really huge amount of lead in the air, which it really isn’t.
Ok, the UND report is indeed ‘substantive’. It caught unpredicted wear. So what is the root cause of that wear, and are there any other TANSTAAFL gotchas (besides accelerated valve guide wear) that will show up with time operating our GA piston fleet in real world conditions?
Frankly, de-rating our engines to operate on lower octane fuel is a loser idea. Speaking from experience and the validating NTSB takeoff accident data, I have a stong desire to climb out of the takeoff & initial climb coffin of low elevation, high power, and slow air speed (i.e. LOW ENERGY) where a dead engine event offers me (and my passengers) very few options for a happy outcome.
You know, maybe the failure has to do with the 94 octane and not the lack of lead?
Like some lese mentioned, operating on 94UL like it was a 100LL fuel may be the culprit. I think the 100UL needs to be tested the same way to separate if it was leaded or octane causing the problem.
Well, these engines at the flight school never originally needed 100 octane fuel.
These same engine types have run for decades on UL MoGas until ethanol was introduced.
In chemistry we used to have a funny saying when reporting findings: “Only one datapoint can define a sphere, two datapoints can define a universe!” Let’s not define an entire sphere based on one UND datapoint. The data is not wrong, but let’s not get ahead on what it actually means.
Skygypsy, the educational comments is what draws me to AVweb. Thanks for your input and assertiveness.
He underscores the difference between the denotations of smart and wise.
Smart and assertive yes; but for educational purposes I’d rather have conversions with Bill Scott, Todd Petersen or Mike Busch when I need real world decision making for “my” engines.
Agree without minimizing anyone else.
Skygypsy is correct when he says flame front travel and combustion chamber temperatures are complicated. He’s also correct about the troublesome quirks found in burning aromatics. Indeed, it can be problematic. But to say well-experienced A&P/IAs know nothing about these complex matters is a bit much. In fact, Charles Fayette Taylor explained it all in his 1960 copyright edition of The Internal Combustion Engine in Theory and Practice, Volume 1 & 2. It’s a deep dive.
But complicated or not, it’s not beyond anyone with a red knob in the panel. A pilot adjusts the flame front burn rate and combustion chamber temperature with every turn. Hardly PhD material and it’s a great way to learn about combustion chamber dynamics.
The chemists and cylinder metallurgists will have an answer.
Unfortunately is might take years and $$$ for the owners of piston GA aircraft.
From what I’ve read, hardened valve seats and valves are what solved the problem in the automotive world, so when are cylinder manufacturers going to start producing a product with that? Instead of just the fuel fix, why not also work it from the other side in parallel?
What’s the cost delta per cylinder for new builds, and as a retrofit for one currently in service (if possible). Is it that prohibitive?
Extrapolating this a bit, what if all new cylinders had the tougher parts? Eventually all engines would be able to handle the new fuels. Sure there would be laggard owners flying 50 hours a year that would eventually have recession and be forced to move to replace cylinders or the seats, rings, and maybe valves……. but the highest fuel consumers at the average airport are flight schools, and they go through cylinders at a much faster rate. Personally I own more than one aircraft and would not like the expense in any way, but would be open to it if it helps the greater good and I could do it over a period of time, and ideally have my current cylinders retrofitted instead of purchasing all new cylinders.
And lastly, yes the Santa Clara County ‘study’ in CA was a scam, pushed by a political/developer agenda to justify airport closure before the study even started.