The last couple of years development in aircraft engines has been more or less concentrating on diesels. We have seen one off installations to fully developed production lines. A number of companies are active on this market primarily due to major concern of long term availability and the relative high price of AVgas (Europe).
Diesel engines are able to use JET fuel (AVtur). This fuel is available worldwide and can also be made of renewable sources (algae) which should contribute to a cleaner environment.
In 1997, a joint venture between Socata and Renault Sport F1 led to the creation of SMA. A couple of years later Safran became 100% shareholder and subsidiary of Snecma.
From the first get go they developed a dedicated aircraft diesel engine for the small aircraft market, not being ultralights. This has led to an engine with remarkable achievements like the first transatlantic flight and a flight across the Andes by a single engine aircraft powered by a SMA diesel.
French Diesel Technology
Their company statement is: "SMA develops and manufactures piston engines burning Jet fuels, purposely-designed for the general aviation market, for single and multi-engine aircraft". And as far as we can see today, they have fully succeeded in their goal.
Their first engine has been under development since 1998 and has proven to be a dependable power house. EASA and FAA certification has been achieved at the end of 2010.
At the moment of writing (2014) SMA has one model in full production and a derivative model with six cylinders and more power under development.
Some advantages of these engines are:
The Single-lever control decreases the pilot’s workload as he / she does not has to fiddle with three controls during the heavy workload on take-off.
The turbocharger developed by SMA, supported by Safran’s expertise in turbines, to fully meet the required engine performance targets. The turbocharger maintains takeoff power up to an altitude of 10,000 ft, and retains its performance independently of outside temperature.
The electronic control unit (ECU) optimizes engine start, provides maximum power according to outside conditions (altitude, pressure, temperature), and controls the engine at low speed and power levels.
Below we will discus the properties of both engines as far as they are available.
The first development is the SR305-230 engine. It is a 230 hp air cooled, 4 cylinder, certified two stroke diesel engine and STC's are available for retrofit to existing aircraft. This engine has a certified ceiling of 20000 ft with a critical altitude of 10000 ft.
The engine has a one lever power control, the pilot sets the power he/she wants (90% - 55%) and the engine management system takes care of fuel injection and the setting of the constant speed of propeller. The engine / propeller runs at cruise at a constant 2200 rpm. A mechanical backup lever is available in case of any system failure.
Cessna Aircraft sells their venerable C-182 with this diesel engine named: Turbo Skylane JT-A. As a result that aircraft can no longer be bought with a ordinary gas turbo-charged engine. Fuel savings are expected to be substantial. Especially so if the aircraft is used in a flight training environment. For more details visit the Cessna Aircraft Company web site.
For more detailed information we direct you to this pdf file: SR305 specifications.
SMA SR-460 Diesel Engine
The latest development came to light in 2012. The SR460 is an air cooled, six cylinder, two stroke diesel delivering about 330 to 400 hp weighing 595 lbs, maximum ceiling 25000 ft and sea level power up to 10000 ft with two turbo chargers!.
The fuel system is also different: where the SR305 uses a single Bosch high pressure fuel pump, the SR460 uses six camshaft driven pumps, one for each cylinder. This is a simpler system with less parts and enables to precisely inject fuel per cylinder. The fuel system is operated by the ECU in normal mode, or by the pilot in manual backup mode.
The engine’s air and oil cooling system offers simplified engine integration and the absence of risks inherent in liquid cooling systems. This type of injection system has been proven on other applications, including under extreme temperature conditions.
The propeller is a variable speed propeller and installed on the engine without a reduction gearbox. The propeller is fully automatically maintained at a constant speed (2200 RPM) by its hydro-mechanical control system.