The recent announcement by Rolls-Royce that their future engines will contain gearboxes has put GE and its CFM partner SAFRAN under considerable pressure.
GE/SAFRAN were together with Rolls-Royce proponents to go directly from Direct-Drive turbofans to Open Rotor designs for the next generation aircrafts. This left Pratt & Whitney as the only major engine manufacturer promoting high by-pass ratio geared turbofans as a better alternative for these aircrafts. With the Rolls-Royce announcement of Advance for 2020 (Carbon fanned tri-shaft) and Ultrafan (Geared big fan) for 2025, this has all changed. Suddenly Pratt & Whitney has strong support in their strategy and GE/SAFRAN stand out as loners.
By honing key technologies in their traditional two shaft turbofans GE, and GE/SAFRAN in CFM, have built a market leading position in all thrust classes, Regional (CF34), Single Aisle (CFM56) and Dual Aisle (CF6, GEnx, GE90). Their declared next step was Open Rotor for future Single Aisle while keeping Direct-Drive for larger engines.
Airbus and Snecma continue to research open rotor technology. Aviation Week has this story.
Now this solid position is threatened. The geared architecture has won the future regional market (CSeries, MRJ, E-Jet E2 goes PW GTF), market parity on the A320neo family and the 757 replacement studies by Boeing (dubbed NAS, New Airplane Study) will not go Open Rotor as Open Rotor only works up to M 0.75 and the 757 replacement will likely fly over 4,000nm, necessitating higher cruise speed. The NAS will thereby favor a geared turbofan instead of Open Rotor. Why not Direct-Drive? There are two major reasons:
- A geared design allows higher by-pass ratios and thereby higher propulsive efficiency without the engine being too heavy from its large low pressure turbine needed to drive a high BPR fan.
- A geared design can allow the big fan to rotate slowly and with a low pressure ratio. This creates a low noise engine, a very important feature for aircrafts operating out of noise troubled airports.
GE/SAFRAN has shown with their CFM LEAP project that they can match the efficiency levels of a geared engine like Pratt & Whitney’s GTF, using its superior hot section technology to achieve the high efficiency. It cannot achieve the low noise levels of a geared fan however; engine noise stands in direct relation to fan rotational speed and pressure ratio.
It will thereby be the environmental factors that will put the most stress on GE/SAFRAN’s present strategy. Having lost the regionals to the geared camp, will it also lose the next generation short/medium haul? It will be interesting to watch the GE/SAFRAN over the next 18 months: does it change strategy or not? If one goes by the recent words of GE Aviation President David Joyce (who spoke at last week’s opening of their Indiana LEAP factory), he thinks his present line-up is fine for a 757 replacement, and he sees no urgent need for new developments.
By Leeham Co EU