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July 30, 2014
By Thomas A. Horne
SMA isn’t standing still. Now that the first of its turbodiesel engines—the four-cylinder, 230-horsepower SR305-230E—has been chosen to power Cessna’s new Jet A-powered Skylane JT-A, the company announced a project to develop two new, more powerful variants.
Worldwide, there are a total of 45 airplanes flying with the SR305-230E, and SMA has run these engines to TBO on test stands. After the tests were complete, a disassembly and inspection of these engines showed no anomalies. On the other hand, a Skylane JT-A suffered an engine failure during its flight test phase. The problem was traced to burrs on the SR305’s crankshaft—burrs caused by manufacturing defects that have since been corrected at the factory.
The first follow-on engine is being designed to put out between 260 hp and 285 hp. Under the SR305-XX project name, SMA plans to use the same technology of its predecessor and adapt it for higher takeoff and cruise power. Currently several prototype demonstrators are undergoing endurance tests.
The other engine is the SR460, designed to develop between 330 hp and 400 hp. This six-cylinder turbodiesel has dual turbochargers and is being pitched to original equipment manufacturers of both single- and multiengine piston airplanes, as well as helicopters. Like the SR305 engine, an electronic control unit (ECU) optimizes engine starts, provides maximum power according to ambient conditions, and controls engine speed at low power levels. At high power levels, the diesel engine’s compression-ignition characteristics sustain combustion. There will also be a mechanical backup to the ECU.
The SR460 will maintain full power up to its critical altitude of 10,000 feet msl, SMA said, and will have a TBO greater than 2,000 hours. So far, two to three airframe manufacturers have expressed interest in the SR460, SMA said.
AOPA Pilot Editor at Large Tom Horne has worked at AOPA since the early 1980s. He began flying in 1975 and has an airline transport pilot and flight instructor certificates. He’s flown everything from ultralights to Gulfstreams and ferried numerous piston airplanes across the Atlantic.
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