Inside the Diesel Revolution

Spend even a few minutes comparing the operation of an avgas-powered engine to a diesel—also known as a compression-ignition engine or a jet-A power plant—and a number of diesel benefits jump right out. Diesel engines don’t have spark plugs, and demand no magnetos. Jet-A-burning piston engines are water-cooled too, meaning they’re less susceptible to overheating on the ground or during climb-out. Better efficiency translates into 30 to 35 percent better fuel economy with a jet-A power plant. Avgas availability isn’t much of an issue here in the United States, but we live in a fuel bubble because 100LL isn’t all that easy to come by in other parts of the world. In a Flying story five years ago, Stephen Pope summed up the jet-A power debate: “They’re more efficient, run on cheaper fuel, and the EPA isn’t threatening to regulate them out of existence. With so much going for them, are jet-fuel-burning diesels ready to take over?” Whether a jet-A-powered piston engine actually makes good sense depends quite a bit upon who you ask. It also hinges on the specific problems a jet-A power plant is being asked to solve: save on fuel costs, increase range, reduce maintenance expenses or some combination of all three. What we can say for certain is that today, the options to install jet-A piston engines in an avgas airplane are closer to becoming a reality than five years ago, although the movement is certainly not a groundswell ... at least not yet.

Piper Aircraft delivered its first jet-A-powered Archer DX in June 2015. Following considerable testing and evaluation, the company chose Continental’s CD-155 power plant. The switch from the original 180 hp Lycoming gasoline engine to the Continental diesel brought a number of changes, many of which are common when leaving the world of avgas-burning engines.

The power quadrant in the cockpit incorporates just a single power lever linked directly to a single- or dual-channel full-authority digital engine control (fadec) that actually adjusts engine power. The fadec also controls a constant-speed propeller, with power now measured in percent rather than revolutions per minute. Continental’s CD engines also add a gear box and a coolant-temperature gauge.

Piper says the looming pilot shortage has of late fueled significant interest in its jet-A-powered trainers. Because a cooler-running diesel is more efficient than an avgas engine, Piper says the range on the DX jumps to 848 nm from 522 nm in the avgas Archer. The DX will cruise at 114 ktas while sipping less than six gallons of jet-A per hour. So positive were Piper’s results with the DX that the company in April unveiled a new version of the popular Piper Seminole multi­engine trainer powered by a pair of Continental CD-170s. Piper claims orders for 15 Archer DX aircraft to be delivered this year and a large number of fleet orders that might be switched from avgas to the jet-A power plants before delivery.

Diamond Aircraft has been selling the DA62 powered by two turbocharged Austro Engine AE330s for years, as well as the diesel-powered DA42 twin and the DA40 NG powered by a single Austro. While Textron’s Cessna Aircraft division in June 2017 announced a jet-A version of the 172 powered by a Continental CD-155 jet-A engine installed in-house, Textron quietly bowed out of that market in May 2018 to focus resources on more important projects, as it also did for a diesel 182 that never made a dent in the market. Continental will still handle jet-A conversions of Skyhawks for interested customers.

Before sidelining the in-house conversions, Textron said jet-A power would add about $60,000 to the price of a new 172, while Piper said the Archer DX costs about $58,000 more than the avgas model.

Jet-A engines might sound too good to be true, even to some GA pilots known to fly half an hour from home in search of cheap fuel. That skepticism on the part of many U.S. pilots is being fueled by the availability of relatively inexpensive 100LL here in the States.

U.S. pilots need only to look across the Atlantic, where European aviators have already learned their lessons about avgas. In that region, diesel engines on GA aircraft have become a normal part of flying life, partially because avgas is difficult to find. More important, the price of avgas in Europe is often three times higher per gallon than similar fuel in the United States.

Emmanuel Davidson, global marketing and communications director for Continental Motors Group, says there are “regions of the world where you can’t even find 100LL at any price.” Using European Union member Greece as an example, he says, “That country probably has 60 to 70 airports. You’d be lucky to find 100LL at 10 of them.” In Europe, jet-A, however, is available everywhere, and at a fraction of the price of avgas. Davidson says Continental, a company that built its first aircraft engine in 1906, has already delivered more than 5,750 jet-A-powered engines around the world since 2002, mostly outside the United States, where he says the market is becoming quite strong. While his perspective might appear a bit biased, he adds that a diesel engine “is beginning to make sense to some operators in North America.”

Candidates for jet-A-powered aircraft here in the States are not likely to be individual owners with an engine in need of overhaul, however, due to the economics surrounding the cost of an engine retrofit, upward of $70,000. With a fleet of 32 training aircraft based at Hollywood, Florida’s North Perry Airport (KHWO) and Miami-Opa Locka (KOPF), however, Wayman Luy, of Wayman Aviation, reviewed the numbers and says he is already beginning to exit the avgas market where it makes sense. Having recently earned a Part 145 repair station certificate for its shop, Wayman Aviation flies its Part 141 aircraft about 2,000 hours each month, keeping 34 flight instructors busy. In order to dip its toe in the jet-A marketplace, the company recently purchased a pair of diesel-converted Cessna 172s.

When asked about the payback on jet-A engine conversions, Luy explains the capital cost for an engine replacement is not his first concern.

“At OPF, our FBO has just one avgas truck. We waste a lot of time just waiting for that truck to refuel our aircraft,” he says, time during which no one is making any money. With a more efficient jet-A power plant, Luy’s aircraft fly much longer without refueling, an important benefit with so many cross-country flying hours each week. Because jet-A power plants are water-cooled, rather than air-cooled, pilots need not worry about aircraft climb speeds, which pretty much eliminates the chance a new pilot might cook the cylinder under the scorching Florida sun as they often do on an avgas engine. “A single power lever and lack of a mixture control also means we’re not burning valves because pilots don’t understand how to lean properly,” he says, adding that single- lever control makes teaching pilots about engine operations simpler too.

Luy sees other benefits to the upgraded 172s, such as spending less time in the shop compared to a 100LL-fueled airplane. “Without lead in the fuel, we no longer need a 50-hour inspection to clean the spark plugs or change the oil. Now we only inspect at the 100-hour mark.” That’s a significant savings since Wayman Aviation currently consumes a 55-gallon barrel of oil each week for the fleet. The company expects to soon be ready for its own mechanics to begin complete engine conversions in house.

Despite Luy’s enthusiasm, acquisition cost of a GA aircraft with a diesel engine is no small hurdle for many fleet operators. Geoff Brown, president of Leading Edge Aircraft Co. in Calgary, Alberta, Canada, says he thinks leasing offers another option. While his company has been primarily focused in Canada, “the time is right to begin reaching out to U.S. operators,” he says. Brown is currently in negotiations with Wayman Aviation about potential aircraft acquisitions.

“Until now, a flight school either purchased an old Cessna 172 for $50,000 or spent $250,000 to completely retrofit an old airplane with a new avgas engine, avionics, and interior,” Brown says. “We offer a third choice. For perhaps $15,000 down, customers receive a newly converted jet-A-powered aircraft like a 172 that’s been refurbished with state-of-the-art avionics and a new interior. Operators guarantee us 50 hours each month at a dry-lease rate of about $75 an hour. These aircraft will arrive with full warranties, and of course, this new aircraft will burn four and a half to five gallons of jet-A per hour versus closer to eight in an avgas machine.”

Even five years ago, customers worried about diesel reliability whether on a conversion or a complete engine replacement. Those worries haven’t disappeared altogether, but as more engine companies point to the road ahead, a path with little or no avgas, entrepreneurial ventures are readying power plants to meet what they see as the coming jet-A revolution.

Continental Motors is one of the largest suppliers of jet-A engine conversions and replacement motors, offering three models in its CD line, the 100, 200 and 300 series, with power outputs of up to 300 hp, all while the propeller spins at no more than 2,300 rpm.

That means the loudest part of a Continental diesel might well be the propeller. Continental recently confirmed its commitment to jet-A engines by announcing a new 250,000-square-foot manufacturing facility near its current Mobile, Alabama, campus that Davidson says will significantly improve Continental’s manufacturing processes and “help the company keep its pricing stable.”

In the Midwest, two separate companies are planning new diesel engines. One, EPS in New Richmond, Wisconsin, is closing in on certification of its V43 turbocharged jet-A power plant. The privately held company has been actively designing various iterations of the engine since 2010. A functional prototype was completed and flight-tested by famed aviator Dick Rutan early in the program, using a borrowed Cirrus SR22.

EPS vice president and chief technology officer Steven Weinzierl speaks of the industry’s tardiness to the jet-A party. Because diesel engines operate under higher compression ratios than avgas power plants, they tend to be heavier by as much as 50 pounds.

“Until recently, no company has been able to create a diesel engine that was weight-competitive, often because these motors were created from old automobile engine blocks.” The EPS engine is a clean-sheet design. “Many of the early engines were also not propeller-friendly,” he says, a problem since most jet-A conversions demand a constant-speed propeller. Many other companies are using composite propellers with their jet-A engines, but Weinzierl says, “EPS’s engine will run any propeller.”

EPS, funded by dozens of angel investors who have already sunk more than $20 million into the engine, hopes to certify the V43 by the end of this year. Weinzierl says the complete “STC process will add another 18 to 24 months.”

In Racine, Wisconsin, DeltaHawk is also creating a clean-sheet diesel engine. While the DeltaHawk engine has for years been a work in progress, Dennis Webb, the company’s director of marketing and certification, says, “We recently got seriously funded and expanded our workforce to 35 people.” DeltaHawk is working toward certification of a 180 hp jet-A power plant by year’s end. Webb says the recent spate of downtime at the company didn’t go to waste. “We’ve now gone to a different bolt-on head structure, added glow plugs and improved the liquid cooling system.” In a world filled with fadec-controlled power plants, DeltaHawk chose a mechanical fuel injection system. The company continues testing the DeltaHawk on a Velocity V-Twin and is working on an STC to convert Cessna 172s when the engine is certified.

Other diesel power-plant manufacturers include Austro Engine, which powers Diamond’s DA62, DA42 VI and DA40 NG airplanes, and owns STCs to install its power plants in more than a dozen countries; and French builder Safran, with its SMA engines, which in 2012 announced a partnership with Cessna to power the Turbo Skylane NXT with an SMA SR305-230E. Cessna had “too many issues” with the SMA engine, however, and the diesel 182 never entered production. The last update on SMA’s website about its engine was a July 24, 2012, release announcing the deal with Cessna.

Despite a host of advantages, many pilots still have nagging diesel doubts. “But these engines are inherently more reliable than gas engines,” EPS’s Weinzierl says. “That’s why they’re used everywhere in the world on trucks. While I think the rest of the world recognizes the value of a diesel, some of the halfhearted efforts of other engine builders haven’t helped the cause here in the United States. Many people still think all diesels are the same and that they just won’t work.”

Experts believe that even with the price of oil still rising from a record-low $30 a barrel a few years ago to $94 a barrel in May, there still isn’t enough motivation for people to change. Whether an alternative fuel can be created before the Environmental Protection Agency takes action is anyone’s guess, but the recent halt to testing of the 100LL alternatives could be signaling the beginning of a significant industry change.

Continental’s Davidson says he believes it’s time for smart industry people like those who already understand the value of a diesel to begin convincing others that jet-A piston engines for GA are here to stay.

“There are many people who continue making the same decisions [about diesels] because what they’ve been doing has all worked, until now,” he says. The reduction in maintenance expenses alone creates “more billable hours to fly a working jet-A-powered aircraft.”

Realistically, Americans love a good crisis. That means the move to diesels will likely continue moving at a glacial pace until some outside event steps in to alter Americans’ cozy relationship with avgas, perhaps the EPA finally deciding on a sunset date for leaded fuel.

The chances of that happening, of course, depend upon the current EPA administration and its willingness or ability to make such a move. Should such a change to fuel policy begin, it’s unlikely the feds would simply drop a single deadline on the industry.

The more likely scenario would be a phasing out of 100LL over a period of years, a move that would likely spark shortages and price spikes for avgas like those that exist in other parts of the world.