Any discussion of general aviation’s future must include piston engines and the fuel they burn. True, avionics get a lot of press, but it’s the engine technology that really determines how reliable, affordable and useful an airplane is. And trouble is brewing.
Unfortunately for pilots, advances in powerplants have lagged behind avionics and even airframes for some time now. While modern glass cockpits like the Garmin G1000 offer Cessna 172 pilots the latest in digital technology, airplane engines would look familiar to pilots of the 1940s. Almost no pilot flies with the features considered essential in the world of cars: electronic ignition, variable valve timing and instant starting with the twist of a key. This old technology is jarring for new student pilots, and it certainly doesn’t help general aviation appeal to outsiders.
An endangered species?
Besides being harder to operate than car engines (which are shockingly easy to use, it must be said), traditional piston airplane engines have seen far fewer advances in fuel efficiency. The Chevy you can buy in 2013 has anywhere from 60-100% better fuel economy per mile than a Chevy in 1975. But a 2013 Cessna will burn the same amount of fuel and travel almost exactly the same speed as one from 35 years ago. This lack of progress on fuel efficiency was easy to ignore when 100LL was $1/gallon, but it has become increasingly painful as prices rise above $6/gallon in most part of the US. Such price rises are unlikely to be reversed anytime soon.
And then there is the lead issue. From lawsuits by environmental groups to EPA rules, it’s clear that the decades-long war against leaded fuel is not going away–if anything, it’s heating up. Already, 100LL is nearly impossible to find in many countries outside the US.
In short, avgas is threatened on all sides: cost is rising, availability is declining and regulators are working to ban it. While it probably won’t disappear overnight, it’s clear that 100LL’s best days are behind it.
Plenty of options – any of them good?
But if 100LL’s decline is obvious, its replacement is anything but. Mogas is an appealing solution, but its lower octane simply won’t work in high performance engines like the IO-520 and TSIO-550 that power so many traveling machines. Plus, the recent introduction of ethanol into automotive gas has complicated matters for pilots, since almost every engine manufacturer advises against it.
Given these limitations, many companies are working on a “drop-in replacement” for avgas that would maintain a high octane rating, but without using lead. This approach would cause the least disruption for pilots, whose engines could be operated without expensive modifications. But while some of these efforts look promising (GAMI and Swift to name a couple), they face a number of practical problems beyond the chemistry. For one, a new fuel would need a well-developed distribution system to be available at enough airports–a major job. And most estimates of the price for such a replacement fuel are at least $1/gallon higher than avgas is today, so it hardly solves the cost problem. As Peter Garrison has exhaustively described, a true drop-in replacement just may be too good to be true.
All-electric airplanes are attractive, but won’t meet the demands of most pilots.
Some want to bypass the fuel issue entirely, with all-electric airplanes. This moonshot approach promises huge reductions in noise and emissions while offering nearly unlimited options for recharging. But the key enabling technology for electric airplanes–batteries–seems too immature right now to offer reasonable performance. To offer even modest endurance, an electric airplane would have to carry a lot of batteries. But that drives up weight, which means the engine would have to be bigger, and the vicious cycle begins. It’s hard to imagine an electric airplane being useful for anything other than local training flights until major advances in battery technology take hold.
That leaves diesel engines. While it’s hardly new technology, “compression engines” have a lot going for them. For one, they burn Jet A, which is already available at thousands of airports, is less expensive than avgas and is not threatened by the EPA. Diesel engines are also more efficient, burning 20-40% less fuel per hour than comparable avgas engines. Finally, they are often easier to operate, with single lever power controls and digital engine monitors.
Diesel engines are hardly perfect. They’re heavier than piston engines, they have lower TBOs and jet fuel isn’t available at many smaller airports. Still, they may be the best option among a variety of unattractive ones.
Who will lead the revolution?
Lots of companies seem to agree that diesel is the future, including big players like France’s SMA and Diamond Aircraft (its line of Austro engines is growing). There are also hard-charging startups, like Engineered Propulsion Systems and DeltaHawk. But the leader of the diesel transition isn’t some young startup–it’s the 100 year old giant named Continental Motors.
The Centurion line of diesel engines found early success on the Diamond DA-42 twin.
Continental is a familiar name for pilots, having delivered tens of thousands of O-470s and IO-550s throughout its long history, but today’s Continental Motors Group is hardly the same old company. AVIC, the huge Chinese investment firm (which also owns Cirrus among many other aviation businesses), purchased Continental in 2010, instantly adding deep pockets to a company accustomed to operating on tight margins. They’ve also set up a Chinese operation to service that growing market.
But the big news hit earlier this year, when Continental bought the remnants of Thielert. This pioneering German engine manufacturer practically invented the aviation diesel market with their Centurion 1.7 on the Diamond DA-42, but soon hit numerous speed bumps and went bankrupt. The finances were shady, but the engines were not. By adding Thielert’s 200 employees at their facility in St. Egidien, Germany, Continental has become the leading player in diesel engines overnight.
Indeed, this acquisition–much more than simply a bargain buy–represents a major strategic shift for Continental. President Rhett Ross says by acquiring the assets of Thielert, the company is “confirming our commitment to diesel engine technology…We now become a one-stop shop for all of your engine needs in general aviation.” That’s because, in addition to the traditional piston engines, Continental now offers a full line of diesel engines:
The Centurion 2.0. engine is the established leader, with more than 3,500 in operation on a variety of airplanes. These smaller engines range from 135-155hp, and have been fairly reliable so far. Continental is already working on increasing the short time between replacement (TBR) and repetitive gearbox inspection intervals, which have been the engine’s Achilles heel. The 2.0 is well-suited to the light single market, but simply isn’t powerful enough for high performance airplanes.
In addition to the newly-acquired Thielert engines (sold under the Centurion brand), Continental has its own diesel engine, the TD300. This 200-250hp engine, based on an SMA engine design, was actually certified earlier this year, although the company seems to have gone out of its way to avoid publicity on it. It’s unclear where this model fits into Continental’s plans, although it would seem to offer a mid-range power option.
The big prize is at the high end, supplying engines in the 285-350hp range to power Cirrus SR22s, Beech Bonanzas and other high performance airplanes. There simply isn’t a viable diesel option in this range yet, but Continental believes the Centurion 4.0 is the answer. This 300-350hp V8 engine earned EASA certification, but has not been shipped in any significant number. Bringing this engine to market is clearly one of Continental’s highest priorities.
In a segment of the industry famous for moving slow, these changes and additions are remarkable. Continental’s future is clearly built on diesel, which means many pilots’ future includes diesel engines. The latest evidence? Continental now calls their avgas engines “heritage products.”
Good for GA?
Any major transition like this is sure to be difficult for existing airplane owners. But in some strange way, the elimination of 100LL may actually be a good thing for general aviation. If such a shock wakes the industry from its slumber and encourages companies to develop new engine technologies that are more efficient, cleaner and easier to use, it could lay the foundation for the next generation of airplanes.
Continental, so far, seems to be embracing this moment. They have work to do to repair the damage done by Thielert’s implosion, and fixes are needed for the gearbox and TBR issues. But there are three reasons to be optimistic.
First, it’s hard to overestimate the impact of AVIC’s investment. Continental now has the money to fix any issues with the Centurion engines and to bring the 4.0 model to the market. This is not a startup or a dying company that will run out of money before it crosses the finish line (like Thielert did). The diesel factory in Germany can produce 2000 engines per year, so scaling up is not an issue either.
The Centurion 4.0 engine – key to Continental’s diesel future?
Secondly, Continental’s ability to offer a complete line of diesel engines makes it the first serious player for all pilots. Until now, diesel engine programs have focused on specific airframes, which limited interest and profit potential. If the 4.0 can succeed, diesel may finally break through on new airplane sales.
Finally, the distribution and support network is in place. Continental is really three companies in one, with significant operations in Europe, the United States and China. Their press conference at Oshkosh featured as much Mandarin as it did southern drawl, a sure sign of the company’s global aspirations. For diesel engines to be truly successful, pilots must feel confident they can be repaired in the field and supported with warranties from a real company. Continental should be able to offer that.
In the end, a move to diesel engines would at least remove the cloud of uncertainty that hangs over general aviation. Pilots are hesitant to spend $700,000 on a new airplane if they are unsure of the avgas engine’s long term prospects. Likewise, existing owners may be reluctant to sink money into an overhaul of dubious value. Changing to diesel may be expensive, but at least owners can plan and budget for it.
Saving money wouldn’t hurt, either. With cost at the top of many pilots’ list of complaints, diesel engines offer some relief. They may not cut the cost of flying in half, but general aviation needs some short term, achievable improvements in addition to the miracle cures.
It’s not hard to envision a world where two seat sport airplanes with Rotax engines use mogas and higher end transportation airplanes with diesel engines use Jet A. That means cheaper fuel and lower fuel burn for everyone. That’s progress.