Paul Bertorelli (AVweb) comments: “Fresh off the announcement that Cessna will offer a Skylane with an SMA diesel engine, SMA said Tuesday that Lycoming will support the engine in the field with parts and services. SMA's CEO Thierry Hurtes said in an interview with AVweb that the chief lesson SMA learned from marketing its original SR305 10 years ago is that a service and repair network is a must for any new engine entering the market. Although SMA doesn't have its own, Cessna and Lycoming -- both Textron units -- do and the companies have struck an agreement for SMA support parts to flow through the Lycoming parts chain. Lycoming apparently has chosen not to develop a diesel of its own so Cessna obviously searched elsewhere for a Jet A-burning piston engine for the 182. The SR305-230E -- the latest iteration of SMA's engine -- was certified by the FAA in April 2011 and Hurtes told AVweb that the company is tooled up and prepared for serial production. Although the engine/airplane combination isn't certified yet, Cessna has committed to deliveries of the 182 NXT by the second quarter of 2013. It will replace the turbocharged version of the Cessna 182, according to Cessna. The commitment by an OEM may have given SMA just the boost it needed to continue development of the SR305 into a higher output six-cylinder version. At a press briefing, Hurtes was noncommittal on the specifics of larger engines but indicated they're a likelihood. The SR305 will come out of the box with a 2400-hour TBO based on more than 9000 hours of testing. Further, the engine's operating envelope has been expanded to 20,000 feet from about 12,000, thanks to an improved turbocharger and fueling tweaks. It also appears that the engine will be field overhaulable, but we're not sure if that means Lycoming or competitive field shops or both.” For more on the SMA engine, click on this podcast with Thierry Hurtes.

You can read it anywhere on the web: This is the first time that a truly innovative internal combustion engine concept gets such a significant financing. But does innovative mean more efficient? More efficient than a gasoline engine for sure, since it is a diesel. But how does it compare with existing aero diesel engines or developments in progress?

The OPOC (for Opposed Pistons, Opposed Cylinders) engine, says the website, is 15 to 50% more efficient than a conventional gasoline engine. I assume it means: Depending on the power rating. At maximal cruise speed, therefore at close to maximal power, a diesel is only 15-20% more efficient than a gasoline engine of same power. At most optimal economy cruise, a diesel can be 50% more efficient: This was demonstrated when 2 Cessna 182s, one with the SMA diesel, one with the O-540 gasoline engine, flying in formation therefore at same speed, traveled from Europe to Oshkosh. The diesel consumed 48% of what the gasoline engine did.

So, as long as Ecomotors doesn’t publish clear figures on their SFC, I can only assume that they have a very good diesel engine, but that it is not a breakthrough.

In fact, reading their literature, it seems that they abandoned their initial plans to equip a helicopter; they never publicized plans for an airplane engine; they concentrate instead, with Navistar, on a heavy vehicle engine; and they are talking of adapting the OPOC design to… gasoline engines.

I shall wait for more information, and for the time being consider that the OPOC engine will not be an aircraft engine in the foreseeable future.