Last month, Lycoming expanded its support for alternative fuels by announcing that it was seeking EASA approval for operation of many of its engines on the unleaded aviation fuel UL91. The company also announced it was planning to approve its new O-233 LSA engine for autogas, a clear response to engines from Rotax, Jabiru, ULPower, HKS, Hirth, AeroVee and others that have been approved for autogas for years.
Despite tens of thousands of Lycoming engines operating since 1982 under autogas STCs from the EAA and Petersen Aviation, Lycoming has long advocated for an aviation-specific, lower octane, lead-free fuel.
This news of UL91 however has caused more confusion than euphoria, largely as it is unknown and unavailable in the US. The fuel adheres to the obscure ASTM D7547 standard, rushed through the approval process when the US Department of Defense needed a reliable fuel for its Rotax-powered drones. By the time the standard was approved however, DoD had shifted its attention to its “heavy fuel” initiative, with the goal to power everything from Abrahms tanks to helicopters, jet aircraft and diesel engine-powered drones with JP-8, the military’s jet fuel.
News about UL91 reappeared in December 2010 when the ASTM was reported to be considering changing the fuel’s designation to NLA (Non-Leaded Avgas) to avoid confusion with the popular 91/96UL and 91/98UL fuels from Sweden’s Hjelmco Oil. The term NLA however has disappeared, so it appears that the ASTM is sticking with UL91, which should not be confused with 94UL, another ASTM-approved unleaded aviation fuel that is also not available in the US. Confused yet?
As an aside, remember that aviation fuels are usually denoted by their lean MON octane rating (MON = Motor Octane Number). Thus, 100LL = 100 MON and UL91 = 91 MON. Hjelmco still uses the lean/rich MON numbers to denote their fuel, thus Helmco’s 91/96UL would be the same as a 91 MON aviation fuel. To add to the confusion, most countries denote octane ratings for highway vehicles according to their RON (RON = Research Octane Number), except the US, which uses the Anti-Knock Index, AKI (AKI = (RON+MON)/2 ). A fairly accurate rule of thumb is AKI = RON X 0.95; thus European Premium Plus autogas of 98 RON is closely equivalent to 93 AKI in the U.S. There is no simple conversion factor between MON and AKI; RON and MON numbers are determined in laboratory settings under strict, repeatable procedures.
UL91 is an unleaded aviation fuel approved by EASA (the European equivalent of the FAA) and now in production by France’s TOTAL. It is available at a handful of airfields in France, Germany, and the U.K. Given however that Hjelmco’s own unleaded aviation fuel has been around for two decades in Europe, one wonders why anyone would bother going through the effort and expense of approving and producing UL91. Lars Hjelmberg, owner of Hjelmberg Oil, seems to share our confusion in a recent posting on his company’s website:
“The initiative from Lycoming Engines shall be seen in light of a recent launch in France and the UK of the grade UL 91 unleaded avgas by the French avgas producer TOTAL. The approval from EASA is expected within a few months. Hjelmco Oil has proprietary unleaded Aviation Gasolines grade 91/96 and grade 91/98. These fuels have been in constant production since 1991 and were approved by Lycoming already 17 years ago. The performance of the Hjelmco unleaded avgas exceeds the performance of the grade UL 91 unleaded avgas and is thus approved by Lycoming Engines for all their avgas 91/96, AVGAS 80/87 and Motorgasoline rated engines.”
This statement suggests that UL91 is a joint effort between Lycoming and TOTAL to create a new fuel that will directly compete with Hjelmco Oil’s products. That’s what free markets do, but in the end consumers will have the last say. Assuming pilots prefer an unleaded aviation fuel (or are forced to buy it due to environmental concerns over leaded avgas), one can only assume that UL91 is less expensive than the alternatives, which in Europe are 100LL and autogas. While 100LL is generally available in Europe, its use has been in decline for years, with many airports no longer selling it. Autogas availability varies widely, from rare in the U.K. to common in Germany, where one recent EASA report estimated that half of all fuel consumed in piston engine aircraft is lead-free, ethanol-free autogas. Last week I asked some friends in the U.K. and Germany about the cost of these various fuels, and this is what they told me:
From Thomas Stute, CFI in a large flying club based in Friedrichshafen, Germany, and owner of a vintage 1960 Klemm 107C powered by a Lycoming O-320:
“Unfortunately, our fuel costs continue to climb steadily. One liter of 100LL now costs 2.7-3.0 Euro [$13.40 – $14.90 per gallon], depending on the airfield. Lead-free, ethanol-free 96 RON [91 AKI] autogas costs 1.70 Euro/liter [$8.44 per gallon] at local gas stations. UL91 is just now being introduced in Germany, first at the Bonn-Hangelar airport. The price is supposed to be around 2 Euros/liter [$9.93 per gallon]. Whether this is the sensible alternative to 100LL has yet to be determined. We have used autogas in our Klemm for years and have had no problems with it. We’re now also converting our club’s PA-28 Cherokee over to autogas.”
From Paul Hendry-Smith, whose company, TLAC, sells the Sherwood Ranger kitplane in Fakenham, England:
“The UL91 is beginning to take off (pardon the pun); we might stock it here shortly. It is 20p per litre cheaper than 100ll selling at about £1.73 per, plus it is the right fuel for the Rotax engines, zero lead. Mogas has ethanol in it now over here and is variable in volume of ethanol. Rotax and others along with the authorities will not allow ethanol in aircraft because of the vapour lock issues. UL91 hits the sweet spot.”
Based on Paul’s information, the cost of these fuels in his area are as follows:
Avgas: $10.25 – $15.08
UL91: $10.50 – $12.00
Autogas (can be E0 or E10, price at gas stations, not airports): $8.38 – $8.92
Although UL91 is not yet approved by the FAA, and is not available in the U.S., we can make some conclusions from the information here. First, Lycoming appears to no longer expect a drop-in replacement for 100LL and is expanding the number of fuels its supports. Second, availability of UL91 varies widely in Europe. Third, the cost of UL91 is comparable to avgas in the UK. Fourth, autogas, used widely in Germany, costs about 40% less than 100LL, which is similar to the U.S. Fifth, the higher cost of avgas relative to autogas is similar in Europe to the U.S.
There remain many unanswered questions surrounding UL91, for instance:
1. With Hjelmco’s lead-free aviation fuels in production for two decades and approved in Lycoming and other engines, why bother with a new fuel that has no clear advantages?
2. With lead-free autogas widely available at European airports, and engine manufacturers approving most new engines for it, why bother with another expensive boutique aviation fuel that, like autogas and UL94, is not suitable for high compression engines needing an 100 octane fuel?
3. Will Lycoming seek FAA approval for UL91?
4. Will anyone import or produce UL91 in the U.S.?
5. What percentage of the legacy piston-engine fleet can be powered by UL91?
And perhaps the most obvious question — why call it UL91 when all other aviation fuels are denoted by their octane rating first, ie 91UL, 94UL, etc.?
More choices for consumers, however, is always a good idea. Now it’s up to free markets to determine if and where UL91 will find its niche.
The GAfuels Blog is written by two private pilots concerned about the future availability of fuels for piston-engine aircraft: Dean Billing, Sisters, Ore., a pilot, homebuilder and expert on autogas and ethanol, and Kent Misegades, Cary, N.C., an aerospace engineer, aviation sales rep for U-Fuel, and president of EAA1114.
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