Flightglobal's current lead story is about Pratt & Whitney developing a geared turbofan engine to power the next generation of regional and single-aisle aircraft.
This type of engine is fuel efficient and its low-pressure spool operates at high speeds for peak efficiency, while its fan operates at slower speeds to maximise efficiency and significantly reduce noise.
And EasyJet, with its "eco-friendly" aircraft design, are aiming for open-rotor engines by 2015.
But what news is there of the FAA's requirement for turbofan blade containment (which will mean less noise) to be certified?
While it was developing the UDF, GE claimed it could meet the blade retention requirement - let's not forget, the FAA happly certificates turboprops and helicopters. The issue is not losing blades, but where the bits go. The FAA requirements are mostly about protecting people inside the aircraft - and people outside from aeroplanes falling on them - so engines aft of the pressure bulkhead (which they already have to do) and making sure no critical systems can be sliced through by flying blades are the key design requirements. Redundant load paths attaching the blades to the rotor - which helicopters have to have - pretty much take care of the rest.
The odds on open rotors by 2015 are 5:1 and closing fast...
Am I right in assuming that turboprops such as the Dash 8 Q400 have a reinforced section of fuselage adjacent to the blades to prevent injury in the case of a blade coming off?
With regard to open rotor, it is also worth bearing in mind that the rules can be changed. GE, for example, managed to obtain a special dispensation to separate a blade outside of the root during the blade-off test for the GE90, reducing the amount of energy and therefore damage to the engine. GE argued that it was so unlikely that a blade would detach at the root that it was unnecessary to test it.
Maybe for open-rotor engines it could be argued that the risk of a blade separation is negligibly small?
I'm not aware of any special reinforcement, other than to reduce the vibration entering the fuselage. With the UDF, because the composite fan blades were relatively small and light, GE argued the energy of fa lying blade was much less than that of a propeller or even the blade from a high-bypass turbofan. But the key is to stop them coming off in the first place so I think it is an engineering issue and not one that would prevent open rotors becoming a reality.
Noise is the issue.