GE, Snecma and NASA in May plan to begin running a 1/5 scale unducted fan (UDF) rotor on a test rig at the NASA Glenn Research Center in Ohio, an experiment that is both forward looking and retrospective.
The work is retro in that the first runs of the rig will use newly built composite fan blades that are identical to blades GE built in the 1980s as part of its GE36 UDF programme, an engine the company later tested on a Boeing 727 and MD-81.
By measuring in the same test cell, the baseline acoustic and performance properties of a blade design for which GE already has flight data, officials say their new blade results, extrapolated into the flight regime, will have more credibility than competing designs. The new blades, designed with the latest tools, should offer lower noise and better propulsive efficiency (total fuel/payload kg).
The work is part of engine manufacturers' research into open rotor technologies that could propel the next-generation single-aisle airlines to be built by Airbus and Boeing. GE's earlier data showed the UDF provided almost a factor of two reduction in propulsive efficiency compared with a CFM56-powered A320.
GE and Snecma are 50/50 partners in the CFM engine venture.
Noise was a significant concern at the time, however. GE said the UDF would need to be wrapped in a duct to attenuate cabin and community noise to acceptable levels.
Given that fuel prices at the time were low - 17¢ per litre (65¢ per USgal) - the economic advantages of the UDF did not warrant additional research work.
With today's fuel prices, the lure of the UDF is back and researchers are attempting to see if advanced design tools for the blades can quieten the engine to within 10dB of Stage 4 levels while equalling or exceeding previous performance gains.
Once the baseline tests have been completed, the team will begin testing new blade designs, five sets developed by GE and two sets created by Snecma.
Each set is composed of 12 blades for the front rotor and 10 blades for the counter-rotating rear rotor.