Diesel engines bring a number of additional benefits beside that of simply not using 100LL. In terms of emissions, diesels emit fewer harmful emissions (for the most part) while being able to drive the prop at low rpm (for substantially lower noise levels). They have the huge additional advantage of being extremely fuel-efficient at the altitudes where small airplanes mostly operate. In theory, a well-designed, powerful diesel engine (or a pair of them?) would be a tough matchup for any other comparably powerful engine technology — piston, turbofan or turboprop — up through the low 20s.
SMA
SMA is not a brand-new company, and some of our readers might recall an SMA diesel aero engine from the recent past. Indeed, French company SMA, which began as a joint venture between Socata and Renault, launched a diesel engine, the SR305-230, in 1997. First flight was in 1998 in a Socata TB-20 Trinidad. That engine, which was not a big seller, was a purpose-built 230 hp engine with direct drive (no prop-reduction gear box), modest turbocharger capabilities and low rpm. It earned European certification in 2001 and FAA approval a year later. The engine was initially marketed toward the retrofit market, and an STC was awarded for the installation in some existing models of Cessna 182s.
Last year the company, which is today part of the Safran group, earned certification from the European Aviation Safety Agency and the FAA for a greatly enhanced model, the SR305-230E. A close variant of this engine, the SR305-230E-C1, is the model that Cessna will install in the Skylane.
The new engine is based on the original 305 design but features a few game-changing improvements. First, its turbocharger is bigger and more powerful, resulting in greatly enhanced performance and operating envelope. As installed via STC in existing Cessna 182s, the original engine had a ceiling of just 12,500 feet and a critical altitude of sea level. The critical altitude is the altitude at which the turbo will no longer bring the power up to a sea level value. Thus, even though the former engine was technically turbocharged, it behaved for all intents and purposes like a normally aspirated model.
The new version boasts a critical altitude of 10,000 feet and gives the Cessna 182 JT-A a ceiling of 20,000 feet. There is, not surprisingly, a new, larger intercooler too, to keep up with the hotter-running turbo. There’s also a feature that automatically adjusts the timing to allow for optimum performance at idle, at low power and for starting. Indeed, the new engine starts more easily when it’s cold, and it restarts more readily at altitude (in the case of a flameout). It also boasts improved temperature margins for better reliability, as well as a backup fuel pump for smoother operations at altitudes above 15,000 feet. Cessna is going to try to certify the JT-A for operation without anti-icing additives as well. TBO stands at 2,400 hours, and there are indications that it could climb even higher. All things considered, the E-model engine represents a quantum leap for SMA.
While the name SMA is not well known to most North American pilots, the company has solid roots. Its sister company Snecma is a global manufacturer of commercial aircraft engines, engines for military applications and rocket motors, among other products. It employs nearly 60,000 people, has 35 locations around the world and had sales of around $14.5 billion last year. Snecma manufactures the Silvercrest engine that Cessna announced would be on the new large-body Longitude jet it unveiled at EBACE (European Business Aviation Convention and Exhibition) earlier this year.
The missing ingredient in the relationship was service. While SMA has headquarters in France and its parent Safran has facilities in Grand Prairie, Texas, Cessna decided to make sure that there were adequate service options for future 182 JT-A operators, so it reached an agreement with sister Textron company and engine manufacturer Lycoming to provide service for the SMA engine at any one of the dozens of Lycoming service centers around the country. Lycoming, which has no production diesel product line of its own, will work with SMA to get up to speed by the time the engine enters service, a process that Cessna JT-A project manager Brian Cozine said was already under way by the time the new model launched at Oshkosh.
