Manufacturers Making Progress With Diesel-Powered Airplane Engines
September 13, 2014
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  • When it comes to the next big thing for general aviation airplanes, aviation experts are looking toward diesel engines that run on jet fuel. Several major aircraft and engine makers have announced the development of diesel engines suited for aircraft, including Wichita’s Cessna Aircraft, in part because of a need for alternative fuel sources.

    “I make a prediction that as time goes by, the majority of models of today’s piston aircraft will at least have a diesel option,” said Brian Foley, an aviation consultant with Brian Foley Associates. “Eventually, I suspect the family of aircraft will move to diesel.”

    Cessna Aircraft, for example, recently reinforced its commitment to diesel. Related Stories

    Textron among local exhibitors at Oshkosh air show Last month at the AirVenture Oshkosh fly-in, Cessna launched the Turbo 172 Skyhawk JT-A, its popular single-engine airplane with a Continental diesel engine. It will be offered as a factory option next year.

    It’s Cessna’s second light plane to sport a diesel engine option. It joins the Turbo 182 Skylane JT-A, expected to be delivered to its first customer later this year.

    The Turbo 172 JT-A is expected to be on the market by the middle of next year.

    “We have a lot of demand that is just waiting for this kind of solution,” said Joe Hepburn, Cessna senior vice president of piston aircraft. “The majority of the turbo-diesel demand is global, not domestic (and) generally in places where they can’t get avgas.”

    In many places of the world, aviation gas is not available, but jet fuel is.

    In addition, “we’re finding the early adopter crowd is also made up of a fairly significant group of folks who want to move on to the next technology level,” Hepburn said. “There is a good demand here as well.” Cessna will likely offer diesel engine options on other models, he said.

    The first step is to get the 182 certified so the pathway is understood with the Federal Aviation Administration and with those in the field, Hepburn said.

    “We want to take our time and make sure we get this one done correctly with our local FAA,” Hepburn said. In addition, “we’re looking at what the market response is for the first two we’ve got out there.”

    At the same time, the aviation industry is working to find new alternate fuel sources as environmental regulations change and because of the difficulty of finding aviation gasoline in some areas of the world.

    The push is to find an alternate fuel source to replace 100 low-lead aviation gasoline, which comes from emerging regulations on leaded fuel and its associated engine emissions.

    Environmentalists are calling for a ban on leaded aviation gasoline, or avgas, which powers the majority of today’s light general aviation aircraft.

    The automotive industry long ago replaced leaded gasoline with unleaded fuel. Finding a suitable replacement for airplanes has been more difficult and has taken much longer.

    A suitable replacement is in the works, but it’s not yet available and there are other unknowns, Foley noted.

    As a result, airplane manufacturers are finding it increasingly difficult to attract buyers who are reluctant to buy an airplane when the future of the fuel that powers it is unclear, Foley said.

    In addition, in countries outside North America and Europe, avgas is often is unavailable, in short supply or prohibitively expensive.

    Diesel aircraft engines take Jet-A fuel, the same fuel used by airliners, commuter jets, business jets and military fighter aircraft.

    Whether leaded or unleaded, availability of aviation gasoline in some parts of the world is a big issue.

    “With the combination of Cessna and Beechcraft piston engine products, we have a significant amount of airplanes that are already produced and in the field,” Hepburn said. “We’re very supportive of alternative fuels to be available to those airplanes. as well as … a different type of power plant that runs on fuel already available.”

    Pilots also want to lower costs.

    When engines that used aviation gasoline were originally developed, avgas was only a fraction of the cost it is today, Foley said.

    Although planes with diesel engines cost more to buy, they use about 30 percent less fuel than the others, he said.

    “That investment will start paying back as the owner flies and pays less for the fuel they put in,” Foley said. “That engine could pay itself back in two, three or four years. There’s definitely a crossover point where the initial cost is offset by the fuel savings.”

    The natural industry response will be widespread adoption of the diesel engine, he said.

    Cessna’s turbocharged 172 and 182 with diesel engines cost about $60,000 more than those without the diesel, but they have 25 percent to 40 percent better fuel efficiency, Hepburn said.

    At the same time, “we still want to offer regular avgas solutions,” he said.

    And there is a big need for alternative fuels, Hepburn said.

    The challenge of alternative fuels

    Recently, the FAA selected four unleaded aviation fuels for initial testing to evaluate their use as an unleaded avgas that will meet the needs of the existing piston-engine aircraft fleet.

    Two of the fuels were developed by Swift Fuels and one fuel each was developed by Shell and Total.

    The fuels, submitted for consideration through the Piston Aviation Fuels Initiative, or PAFI, will undergo laboratory and rig testing this fall.

    A second phase, to be completed in 2018, will produce standardized data to support fleet-wide certification for one or more fuels.

    “We’re very, very encouraged that there are four candidate fuels that have been selected,” Hepburn said. “These four look like they are all good candidates for a drop-in replacement,” without modification to existing aircraft.

    Testing will evaluate how good of a replacement they will be for 100 low-lead avgas, said Walter Desrosier, vice president of engineering and maintenance with the General Aviation Manufacturers Association.

    GAMA is one of several organizations on the PAFI Steering Committee.

    “What we want the industry to do is make it seamless,” Desrosier said.

    “Hopefully … you can have the low-lead one day, and you could fill up on the replacement the next day. That’s part of the testing and analysis.”

    Fixed-base operators that service airplanes, such as Yingling Aviation at Wichita Mid-Continent Airport, are keeping a close eye on the issue.

    If the fuel that’s chosen is a simple replacement, the changeover at FBOs will be seamless, said Yingling president Lonnie Vaughan.

    But if high-performance airplanes will take a separate fuel, then that will complicate things, Vaughan said.

    “We’re going to have to carry a third product,” he said. Right now, the line personnel must have heightened awareness to make sure planes receive the correct fuel, although there are safety measures in place.

    A third fuel means another fuel tank and truck and another level of awareness, Vaughan said.

    The line personnel will also need extra awareness when small planes with diesel engines pull up for jet fuel.

    While there will be markings on the wings, “if a single-engine airplane like a Skyhawk pulls up on my ramp out there, the first thing a guy is going to do is get in the avgas truck and drive up in front of it,” Vaughan said. “You’ve got to make sure your line guys have a heightened awareness of what they’re doing.” Slow evolution

    Engine technology has remained relatively unchanged since the 1950s when engine makers used leaded gasoline to create lots of horsepower from a small, lightweight power plant.

    Those engines remained the mainstay of small, piston planes for decades because of high certification costs of new engines and a lack of anything better.

    In addition, engine makers were reluctant to offer even casual improvements because of a litigious environment that may view any changes as an admission that the original design was defective, Foley said.

    The automotive diesel engines of yesteryear were clunky and not geared toward aviation, particularly in weight, durability and future availability of parts, he said.

    “In some ways, putting a modified car engine in a plane is akin to putting a … boat motor in a Le Mans race car,” Foley said. “Yes, it will work, but why would you?”

    The diesel engines of today are “high-tech, computer-controlled, lightweight power plants designed specifically for the needs and rigors of aviation,” Foley said.

    Piston engine technology continues to evolve, said Cessna’s Hepburn.

    “This is a great pathway to follow as far as improvements or making airplanes easier or more economical and in some areas even safer to fly because of the kind of things these airplanes bring,” Hepburn said. Pilots can take advantage of airplanes that are simpler to operate, he said.

    “All the manufacturers that produce piston aviation engines are looking at diesel engine technologies, Desrosier said. “I think there’s definitely going to be a lot of markets in the world (where) that’s going to be of high interest to them because Jet-A (fuel) is readily available in many areas of the world.”

    And in the United States?

    “I think consumers will be able to choose what preference they might have,” Desrosier said.