After avgas

Across Australia avgas is generally available, says AOPA Australia Managing Director Allan Bligh, and many pilots are worried about what they’ll be able to fill up with after the only approved option disappears. It’s already scarcely found at remote airports and especially in nearby countries.

“There are people who persevere in Asia hoping that it’s going to get better, but i think everyone here thooughout this region are hoping that we’ll see a development of the diesel which could then be a common fuel for all airports and all aircraft, but that’s been a huge disappointment to us,” he says.

It’s repeated extensions and exceptions from US environmental laws that pulled along global availability, but environmental harm from leaded additives is leading US courts to ban the fuel 30 years after it was banned from other fuels.

The fate of leaded avgas, or 100 LL (low-lead), has long been sealed, but new aircraft and new fuels have been caught in a game of the chicken and egg waiting each other out. Options are few, and it’s was only in Spring 2008 that airframe and engine manufacturers agreed to bite the bullet together. After years of eyeing competitors for a first move, they all agreed to take the leap in May 2008 in a board meeting of the General Aviation Manufacturers Association.

The status quo has got to go, states Walter Desrosier, vice president of engineering and maintenance for GAMA. “There have been different kinds of engines developed, but the greatest challenge in terms of an unleaded fuel is our existing fleet of aircraft. I do believe that there’s going to be a significant shift in emphasis from research to development and implementation.”

Turning that corner a year ago doesn’t mean the answer is clear. Teledyne Continental spokesperson Mac Little says a common direction has yet to emerge and no one can chart this flight plan alone. Until the industry decides to adopt the lead-free 94 UL or to use diesel and jet fuel for its high performance needs, he says the engine makers won’t know where to spend R&D dollars. “Once they’ve settled on it, then we’ll look at our engines being ready for it,” he says. Meanwhile, “We have 1800 types of specifications and we have to test each and every one of them.” As for kits that could prepare today’s engines for tomorrow’s fuel, “It’s a very active program,” he hints, adding, “We won’t get STCs. We will actually re-certify the engines.

A lot of pilots are eager for the Lycoming IO-360 and O-360 lines to be certified for automotive fuel in addition to avgas, mentions Bligh. “There’s a lot of attention on that because it’s such a popular engine,” he notes. Lycoming initated that engine approval program in June 2008 and first predicted completion by Fall, putting that effort a year behind schedule. The goal is Unleaded 93 AKI automotive gasoline conforming to either Euro Norm EN228 or ASTM D4814 as the basis of this Lycoming specified fuel. Aircraft certification would be needed separately to permit operation with this fuel.

Fuel availability is a consideration during aircraft purchase, says Bligh, right alongside performance and price. “At normal airports, those frequented by GA, avgas is available,” he says, “In certain remote areas, and even bigger areas, you can find strips out there with no fueling available, and having to rely on drums, in which case getting motorcar gas is more feasible.”

Depending on drums for refueling is “all very well for flying schools,” he points out, but extended travel by private pilots is rules out.
Diesel retrofits are problematic because of weight and size issues, as well as differences in the location of supporting systems. Plans for a new diesel Cessna 172 and Cirrus SR22 stalled when Thielert became insolvent. While battery-powered microlights are emerging, efficiency and duration of very heavy batteries doesn’t yet approach petroleum power. Hydrogen fuel cells are even farther off, and research into known fuels like methanol proves they aren’t right for aircraft.

Agreeing on the best option for new aircraft is a puzzle, but it’s not as harrowing as discovering which fuel can keep today’s fleet in the air. Additives and refining tricks have been tried for 30 years and they do work. They’re also extremely expensive, and the challenge is reaching the same performance at the same price. Between 70 and 80 percent of the global GA fleet doesn’t need the maximum octane performance of 100 LL and many were not even designed to use that extra power. They’re the low and mid compression engines designed for octanes up to 80 and 91 Motor Octane Number (MON). A Cub owner may not be too worried because aircraft with low and mid-range compression ratios can get by on the same fuel minus the lead, but it’s unclear if the oil sector wants to produce it. Aircraft barely rate as a customer group. Today’s avgas production and tanker infrastructure is antiquated and something of an annoyance to the oil sector, which would prefer everyone could just pump the same fuel.

Pilots would prefer that, too, especially as ethanol permeates the automobile fuel (mogas) supply and kills that option. There’s disagreement on how simple or impossible it will be to use ethanol in aircraft, but most agree that ethanol blends spell disaster without fuel system modifications to counter corrosive effects. While environmental concerns lead to chemistry and economic puzzles crushing from above, environmental motives behind ethanol are pulling the floor out below.

If fuel flow or horsepower output changes so will performance and the aircraft handbooks. A different weight of the fuel would throw off airframe balance, as would a new and heavier engine.

The solution could be a selection of fuels for the different GA sectors, which would mean increased cost because diversity in the fuel supply cancels economies of scale. One drop-in seamless replacement would be ideal, and so far only one research lab has stepped up with a possibility. Regulators and manufacturers are careful to keep their hopes in check as Swiftfuel continues to clear every hurdle the FAA can throw its way.

Companies developing alternative jet fuels continue to appear with ideas to convert coal, natural gas, algae, jatropha, forestry scraps, and virtually anything organic. They could tweak those processes to make avgas like they do for diesel or make-up cream, but so far Swift Enterprises appears to be the only contender with a drop-in 100LL substitute.

“That’s what it’s looking like right now. the oil companies were trying to fix petroleum and they couldn’t do it, except with a 94 octane, which all planes can’t fly on,” says Mary Rusek, who co-founded Swift with husband and Purdue University chemical engineer John Rusek. After Swiftfuel first leapt into the public eye with predictions of a 15 percent range boost and 50 percent drop in manufacturing costs, the company has become more modest in cost predictions. “Basically, until we built the full plant we won’t know, Mary says, “Compared to regular aviation fuel, it’ll be an attractive price.”

The 200 gallon daily production rate of their pilot facility in Indiana is not yet using pure biomass as its raw material. Like all fuel conversion processes, the energy tucked into carbon-based feedstocks is first broken down into basic hydrocarbons. Swift’s magic is in the second stage to make a fuel chemically identical to 100LL but without its drawbacks and with some nice bonuses.

Adding just two chemicals in that conversion produces fuel with no sulfur emissions, a 30-degree lower freezing point and no need for stabilizers. Proving that it performs and is safe is arduous, Rusek confirms, but very important. She can’t say how long the process will take. “The main thing we need is to get more data. Prove what we’re saying.” Lycoming is lending the FAA an engine for 150 hours of testing, and Hawker Beechcraft pumped Swiftfuel into a Bonanza for a successful test flight.

A Swift team is working with ASTM International to satisfy requirements of D910, the current specification used for leaded aviation gasoline. Swift principal investigator Jon Ziulkowski says response from ASTM was remarkable. “They said that, in the past 13 years of looking at renewable fuels, they have never seen anyone even half of the specification. We meet 42 of the 44 specifications, so that’s why we’ve captured the interest of the FAA.”

Eventually, 20-50,000 gallon/day plants are planned with the financial support John Rusek is finding now. “We’re finding a lot of people with a significant amount of money who are very interested in doing the right thing,” he says. They’re looking at the same high-energy plants being broken down by ethanol researchers, but Rusek is careful to stress their fuel is nothing like ethanol. “You can’t use oxygenates as fuels. It just doesn’t work. The energy is not there,” he says. Swiftfuel production could easily be adapted from existing ethanol facilities, though. “America has already invested in the infrastructure why not use it?” asks Rusek.

As for the fight against ethanol blending into the Mogas supply, or protecting exemptions for aircraft fuel, aviation groups like the Experimental Aircraft Association based in Oshkosh are preparing to drop their guard. “That’s a losing battle,” says Doug MacNair, EAA vice president of government relations. “Frankly, it runs at cross purposes with the petroleum industry itself, who wants a product with universal distribution.” A short-term solution they propose is finding a rare supply of unblended Mogas and cooperating with other pilots to keep tanks filled at the airport.

Ethanol drastically changes the water separation and vapor pressure of the fuel. Besides corrosion potential from regular use, sitting unused in the tank leads to damaging condensation. Ethanol requires more fuel flow which leads to a 40 percent range reduction. Outside of the warm weather and abundant ethanol infrastructure of Brazil, mainstream groups like EAA and Cessna Aircraft Company say the fuel just won’t be viable for aircraft.

There is potential, though. On 18 December 2006 the Federal Aviation Administration in the US released the findings of its first extensive test of ethanol in an aviation engine. The study confirmed both a horsepower boost and the need for increased fuel flow. “The engine produced an average increase in peak horsepower of 4.3 (2.3%) when operating on the AGE-85 (aviation grade ethanol) than it did when operating on ISO. However, peak power required 39.7 lb/r (56%) more fuel mass flow with the AGE-85 than with ISO” reads the report by David Atwood and Anatoliy Ivanov. “Using AGE-85 (Aviation Grade Ethanol, 85/15 blend) would increase fuel weight by 9% above that of 100LL (Low Lead) for an equivalent volume of fuel and would reduce operating range by 35% from 100LL.

The FAA has also funded research at Baylor University in Texas, where, after 28 years of testing, Dr Max Shauck proclaims ethanol as “the best fuel there is.” As director of the Institute for Air Science at Baylor University in Waco, Texas, Shauck earned Supplemental Type Certification (STC) for 100% ethanol to power a Cessna 152. In 2000 he obtained STC for a series of crop dusting Piper Pawnee to fly on both Avgas and ethanol. That was the first dual fuel certification granted by the FAA.

Embraer’s Ipanema crop-duster first flew in Brazil in 1970 and its most recent version was introduced in 2004 with approval for 100 percent ethanol use. More than 60 are burning 100 percent ethanol today, with the Lycoming IO-540-K1J5 engines delivered with a special fuel-system designed by Embraer. More than 100 kits to convert earlier Ipanemas to run on ethanol have been sold. In Brazil sugar cane-based ethanol is widely available at airports and costs three to four times less than AvGas. Range is 40 percent lower than with AvGas, though, and the engines come set for a 40 percent richer fuel feed.

Shauck adds, “There is one drawback of ethanol, and that is that you reduce range, and it depends on the type of application, how much range you reduce. From a low of 7 percent to a high of about 30 percent.” Design considerations negate those drawbacks in a piston craft, Shauck says. “The fact is, ethanol has a higher octane. A very high octane. What I do in my air shows, is I fly an airplane that’s been modified to take advantage of the higher octane. I fly at a 10.5 to 1 compression ratio and I get much better performance.”

A bonus is the doubling of time between engine overhaul. “There is less vibration when you use ethanol as a fuel. That’s a function of the larger range of flammability. All of the fuel is consumed in the initial spark,” Shauck says. Embraer says its Ipanema can operate up to 80 percent longer than usual without an engine overhaul.

Michael Wagner has tested low percent ethanol blends for Rotax as head of the engine-maker’s aircraft centre, and says he plans to test higher content mixes. “In the European community there is a three-year mandate to increase alcohol in fuels, and of course we have to follow that,” he says, adding that ethanol is easy to work with and it’s good on the engines. “Combustion is stable. It burns nicely. It’s clean. Performance is good. If you tune it right, the fuel/air mixture, you will not easily kill an engine with it. For the engine, it’s much better than avgas.”

Cessna was thinking ahead in 1997 when they restarted piston production. With few exceptions, their compression ratios stayed in the mid range to ensure their aircraft would be compatible with future unleaded and lower octane fuels. A manufacturer could reduce the maximum cylinder head temperature via an AD or a type certificate revision. Others depend on the detonation protection of 100 LL and can’t easily compensate for a lower octane. If the fuel/air mixture inside a piston engine combusts at the wrong time it would create holes in the pistons and cause the engine to tear itself apart.

Technology does offer hope. FADEC and other electronic timing controls are capable of pinpoint monitoring and adjustments not normally possible. Lycoming’s iE2 Integrated Electronic Engine was designed to power the leading high-performance pistons of today with multiple fuels.

“By moving to an adaptive, closed loop, cylinder-by-cylinder control system you can compensate for some loss of octane,” states Michael J Kraft, Lycoming vice president of research, development and engineering. “Going further up the ‘trick’ line, you could include the go-fast gizmos that we’ve placed on Jon Sharp’s Nemesis NXT engine.”

Kraft believes a 100 octane unleaded fuel, or 100 UL, may come to market. “What would happen if we were faced with very low octane ratings…say 91Ul or lower? Possibly a change in engine technology. Remember, today’s high performance aviation engines were designed around the fuel. If the fuel changes – the engine will need to change either in controls methods or mechanical configuration,” he says.

“There are limits as to how far down you can go without impacting the power rating – in the end Mother Nature is not easily fooled.”
Mother Nature is on the minds of Friends of the Earth, the environmental group forcing the issue in the US through a lawsuit. Their pressure on the Environmental Protection Agency has restarted the final clock on 100 LL, hinders brain functions of those who touch or breathe enough of the poison.