In July 2012 at AirVenture, Cessna announced that it would be installing a SMA SR305-230E-C1 Jet A fuel piston engine in its Cessna Skylane airframe. The SMA engine is a turbocharged four-cylinder air and oil-cooled diesel-cycle engine that produces 227 take off horsepower at 12.2 gallons per hour. If you want an idea of the motive behind Cessna’s move, get this; it’s certified to burn Jet A, Jet A1, JP8, TS1 (Russian) and #3 (Chinese) fuels.
Cessna’s announcement cited the environmental advantages of this switch in this sentence, “The fuel technology used in this engine eliminates concerns about carbon monoxide emissions, fuel mixtures, propeller control, and exhaust gas.” It also cited zero lead emissions and zero CO emissions as well as 30 to 40 percent greater fuel efficiency over the avgas-fuel engine it replaces. It’s the Turbo Skylane JT-A.
The displacement of the four-cylinder SMA engine is 305 cubic inches (5 liters), the compression ratio is 15:1, the take-off manifold pressure is 90 inches Hg (3 bar), and the installed weight is 460 pounds (209 KG). The time between overhaul (TBO) is now rated at 2,400 hours and that TBO was determined at 90 percent power settings. Cessna warrantees the JT-A for three years or 1,200 hours, whichever comes first.
SMA is predicting that this simple compression-ignition engine will not be hard to maintain for a couple of reasons. According to SMA, there has never been a major mechanical failure with the “E” (for enhanced) version or the earlier version of the engine. No cylinder failures or no valve failures. Second, this SMA engine is simple and it was designed as an aero engine. There’s no propeller speed reduction unit (PSRU) or clutch nor does the 15:1 compression ratio put it at the cutting edge of compression-ignition engine development.
The checklist of required maintenance items is small and the maintenance intervals are long. The lack of a magneto-based ignition system — with its ongoing 500-hour magneto inspections and 100-hour spark plug cleaning and rotating chores — will save hundreds of maintenance man-hours over the TBO period of this powerplant.
SMA flew the first iteration of its SR 305-230 in 1998. That version was flown and tested extensively and was installed in nearly 50 Cessna 182s worldwide under a STC. Based on this operational data and requests from airframe OEMs, the engine was upgraded to the SR305-230E (enhanced) version in 2009. One upgrade was a larger turbo charger; the critical altitude is now 10,000 feet. 175 hp is available at the 20,000-foot certification ceiling.
SMA took a very long view of Jet-A fueled piston aircraft engine development and elected to keep these simplest of engines, the compression-ignition cycle engine, simple. This is shown in the use of a Bosch high-pressure direct-delivery fuel pump instead of electrically pulsed injectors and a common rail fuel manifold; it’s also shown in the direct-drive design. There’s no engine rpm reduction gearing installed between the engine and the prop. The propeller rpm is governed by a standard hydro-mechanical governor to 2,200 rpm — a speed that marries propeller efficiency with a relatively low noise signature.
Thierry Saint Loup is the vice president of SMA engines. SMA is a division of SAFRAN. According to Saint Loup, the SMA engine will require 50 percent less trips to the maintenance shop than an avgas engine. For example, recommended oil change intervals are 100 hours and the SMA maintenance manual (MM) requires compression checks every 600 hours. [Editor’s Note: FAR Part 43 Appendix D mandates that these checks be done at every 100-hour or annual inspection.]
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Oshkosh, WI, July 24, 2012 - Cessna Aircraft Company (Textron) announced on July 23, 2012 at EAA Airventure Oshkosh, that it has selected the SMA SR305-230E engine to power its Turbo Skylane NXT...
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