Snecma is building a prototype open-rotor engine which is to be flight-tested on an Airbus A340 in 2019.
The experimental powerplant with two unducted, contra-rotating fans will utilise the core of Snecma’s M88 engine for the Dassault Rafale fighter and is to undergo ground tests in 2016.
The production of the full-size demonstrator engine follows windtunnel tests with a 1:5 scale open-rotor model, which Snecma – an equal partner with General Electric in narrowbody engine joint venture CFM International – has been conducting at the ONERA research facility in Modane in the French Alps.
The tests initially focused on noise emissions from the novel engine architecture. Open rotors promise significant fuel savings, but have in the past showed much higher noise levels than conventional, ducted turbofans.
GE flight-tested experimental open rotors on a Boeing 727 and a McDonnell Douglas MD-80 during the 1980s. That programme was discontinued, however, and noise has remained a major challenge.
Low noise was thus the main focus during windtunnel tests in July 2013, and Snecma is confident that the issue can be solved. The open rotor’s noise level "should be similar" to that of the CFM International Leap powerplant for the re-engined 737 Max and A320neo as well as China’s clean-sheet Comac C919, says Snecma research and technology director Pierre Guillaume. This will be 10dB below the noise level of current-generation turbofans, he adds.
A second windtunnel test campaign focused on the open rotor's aerodynamic performance. Snecma promises it will save around 30% fuel over comparable turbofans for narrowbodies.
"After the tests at the end of 2013, we will be focusing on building a full-size prototype. That prototype should be ready for the [test] bench by the end of 2015," says Guillaume.
The production stage will be particularly challenging due to the complexity of the engine’s rear assembly, he says. While the core’s compressor section will be fairly conventional, the turbine will drive a rotating fan assembly, comprising a reduction gearbox and pitch-control system for the fan blades.
Flight tests on an A340 are due to begin in 2019, while entry into service for a production narrowbody engine is planned for 2030.
GE and Snecma have designed the core of the Leap engine – which is succeeding the current CFM56 series from 2015 – to be employed on a potential future open-rotor powerplant.
"We need to move fast, because certifying this new engine generation will take time," says Guillaume. He expects "extensive discussions" with the relevant authorities as current engine-approval standards – for example regarding fan-blade failure – will have to be changed for the open-rotor architecture.