Fair use excerpts:
"Initial performance and noise studies conducted in the wind tunnel show that an open rotor engine with counter-rotating propellers in pusher configuration will have margin for Stage 4 operations and will likely meet and exceed the more stringent Stage 5 levels to be set by ICAO next year and implemented by 2020, General Electric (GE) says."
"Overall the results were outstanding," says Ron Klapproth, GE Aviation's director of commercial product strategy, of GE's wind tunnel tests. "In the 1980s, designers of the first unducted fan architectures had to compromise performance to achieve an acceptable acoustic signature. With what we tested in wind tunnels, we're confident we can design high performance blades [with acceptable] acoustic signatures."
"He says "tall poles" in the technology development path include blade-out impacts to the fuselage and icing."
Funny that we should hear of OR advances from GE when RR seemed to be the main proponent of the technology...