The open rotor design from French aerospace manufacturer Snecma uses twin counter-rotating fans driven by a turbine using a conventional gas generator, but it gets rid of the traditional cowling and ducting that you'd find in a regular airliner jet engine. By letting the fans spin out in the open, Snecma says that the engine can draw in and eject much more air at slower speeds, increasing the efficiency by up to 30% over a standard turbofan. They also claim that the open engine is quieter and has lower CO2 emissions than today's engines, although they're still working to make them meet future standards.

Snecma is currently testing a 1/5th scale version, with plans to start flight tests in 2019 using a full scale version mounted on an Airbus A340. Regular passenger service is projected to take until 2030, mostly due to all of the regulatory approvals needed for this unconventional design. So while it may look to the uninitiated like we're going back to a weird looking version of the old school turboprop planes of the 1950s, in reality this open design may soon represent the cutting edge.