The elimination of lead from automotive fuel long has been hailed as a top environmental achievement, but finding a replacement for the leaded aviation fuel used in tens of thousands of piston engine aircraft has proven to be much more difficult, wrote The Wichita Eagle’s Molly McMillan on May 30.
Eventually, the Environmental Protection Agency will phase out its use but, in the meantime, economic factors could affect its cost and continued availability, McMillan reported.
Identifying the right fuel and putting in a plan to transition to it is vital, Walter Desrosier, vice president of engineering and maintenance at the General Aviation Manufacturers Association, told her. It is necessary to “ensure the viability and health of the general aviation industry,” he said. The industry cut the amount of lead additive in aviation fuel in half during the 1980s, resulting in the 100 octane low lead aviation gasoline in use today. That’s the minimum octane necessary to ensure safe flight of the existing fleet of general aviation aircraft, GAMA’s Desrosier said.
Finding an acceptable fuel without lead is taking time. “We did not find a fuel that can simply replace 100 low lead and…have the same level of performance and the same level of operation for the entire fleet of general aviation aircraft,” Desrosier said. A replacement must ensure the aircraft would operate safely, be environmentally friendly, economically feasible and have the ability to be widely distributed to airports and fixed-base operators, Desrosier said.
The world has moved away from lead additives in fuels, and demand has plummeted. With less demand, there’s only one main supplier of the tetraethyl lead additive in the world, McMillan reported, and that brings the risk of rising costs or interruption of supply. The supplier, Innospec, in the United Kingdom, has assured the industry it will continue to produce the avgas additive and make it available. Still, there’s risk, Desrosier said.
“If something happens in the transportation… suddenly there’s a stop in supply and 100LL may not be available,” he said. That would have a detrimental economic impact to the U.S. Piston-powered aircraft engines, the high-performance variety in particular, have been built for use of high-octane leaded fuel, which boosts the fuel’s octane rating and helps prevent destructive detonation. “If you don’t have 100 octane fuel — leaded or unleaded — those aircraft will be grounded without significant investment,” said Michael Kraft, vice president of research and development and engineering at Lycoming.
It’s a big issue for airplane manufacturers.
“We’re trying to find an alternative that will work with the planes that are out there in the fleet,” said Stan O’Brien, Hawker Beechcraft‘s project engineer for piston engine aircraft. “It makes it a difficult challenge.”
“Can you imagine if you just bought a new Bonanza last year and we say, ‘Oh, by the way, here are your new, lower performance levels?'” asked Hawker Beechcraft vice president of product development and engineering Ed Petkus. “You wouldn’t have happy customers.”
Two unleaded fuels are being evaluated for their potential.
One is petroleum based and similar to avgas without the lead. Most planes would be able to use it and have the ability to transition to it relatively easily, Desrosier said, but because the octane is lower, high-performance aircraft would need physical modifications. While only 30% of the fleet using avgas comprises high-performance planes, they consume 70% of the fuel. They’re the planes most likely to be used in commercial businesses and would feel the biggest impact. “We need to understand the affect to the fleet and what modifications would be available at what cost,” Desrosier said.
A second fuel undergoing testing is a synthetic, bio-based fuel produced by Swift Enterprises in Indiana. It is both high-octane and unleaded and, so far, has performed well and seems promising. A Hawker Beechcraft G36 Bonanza was the first to fly on Swift’s fuel, the company said. However, Swift fuel still must be tested and validated to ensure its compatibility with aircraft aluminum, hoses, seals, fuel bladders and fuel systems, Desrosier pointed out, and its distribution and the ability to produce it must be determined at the cost, quantity and quality needed. The fuel is denser than avgas and has higher energy content, Desrosier said.
Lycoming is not endorsing a particular company but sees promise in a synthesized high-octane fuel, Kraft said. Along with other engine builders testing unleaded fuel, Lycoming is making sure that any new engine is capable of running on lower octane unleaded fuel, Kraft said. Last year, Lycoming introduced an engine that can use whatever the fuel of the future will be. “You have to be very much in tune with the fuel to correctly design the engine,” Kraft said. “That’s really driving all of our research and development.”
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