SMA Engines

SMA Engines (Société de Motorisations Aéronautiques) is a French manufacturer of diesel engines for light aircraft. It employs 60 people. Its production is currently limited to one model, the SMA SR 305-230-1 (rated at 227 horsepower), which has received a Supplemental Type Certificate for installation in the Cessna 182.

Engine installation in Cessna 182

The SMA SR 305-230-1 is a four-cylinder, horizontally-opposed turbocharged direct fuel injection diesel engine. It is controlled by an advanced electronic control system, which incorporates two control handles. The throttle is a T-handle, marked with "FULL THROTTLE", "IDLE" and "CUTOFF", and a white mark denoting the mechanical backup position. The mode selector is a T-handle marked with "NORMAL" and "MECHANICAL BACKUP" positions. In addition there is an independent prop cycling control, which is used only during runup to verify that the constant-speed propeller is capable of proper operation. This is the only other engine-operation control (other than the throttle) actuated during the pre-takeoff runup (no magneto or carburetor-heat or mixture-control settings or checks).

The engine installation includes an electronic central processing unit (CPU) which continually calculates the proper fuel/air mixture. If this unit fails completely during flight, the mechanical backup position is selected and the pilot can control the fuel/air mixture as required to complete the flight.

Full-throttle operation at sea level is at 90 inches of manifold pressure. Unlike most other aircraft engines (which recommend the maximum power setting be used only for five minutes during the initial takeoff stage), the SR 305 can be operated indefinitely at this setting, although normal cruise uses around 70 inches and economy cruise uses around 60 inches.

The STC conversion on the Cessna 182 includes a new cowl, both to accommodate the different engine dimensions and to provide the required cooling airflow. Belly-mounted cowl flaps are still used, but less cooling airflow is directed over the cylinder barrels and more cooling airflow is directed into side-mounted oil coolers. About one-third of the engine cooling is provided by airflow over the cylinders; the remainder is provided by engine oil. The engine's oil distribution system routes a large oil flow to hot zones in the cylinder heads and upper cylinder barrels, carrying the heat away to the oil coolers. [Cessna Skylane Joins the Jet Set, Flying Magazine, Vol. 135, No. 5, May 2008, p. 74]

tatus of Conversion Program

As of early 2008, SMA had provided over 50 conversion packages (the installation is usually performed by other companies, not SMA). Most of those conversions were performed in Europe, with less than a dozen having been performed in North America. The package costs around $75,000, and installation costs around $7,000.

The cost of conversion may be justified in areas where aviation gasoline costs significantly more than jet fuel. The justification is aided by the fact that the diesel fuel flow at cruise is about 10 gallons per hour, compared to about 13.5 gph with the original engine.

References

See also:
* [http://www.smaengines.com/ Company web site] .
*Thielert Centurion engines - a competing range of diesel aircraft engines.