I guess we can forget open rotor technology for now:

Long-running plans to flight-test a Safran Aircraft Engines-developed counter-rotating open-rotor (CROR) engine demonstrator under the European Union’s Clean Sky technology initiative have been shelved. The decision, confirmed by Jean-Francois Brouckaert, project officer for the Clean Sky engine demonstrator programs, is a blow to proponents of the fuel-saving concept and could well delay by decades development of a viable commercial open rotor.

Article
http://m.aviationweek.com/technology/eu ... onstration

That just plain sucks. No excuse. The commercial aviation world is apparently united in its ignorance-based dismissal of all things open rotor/propeller driven.

A sad day and a giant step backwards for aviation.

I don't know what to believe anymore

viewtopic.php?f=5&t=1373295

Wasn't noise the killer in U.D.F. engines when they were previously explored ?

Shame.

For all we know, there just might be unsurmountable technical showstoppers with the technology that will prevent it from being a viable option in the near future.

Either that or it is believed that conventional jet engine technology will be able to catch up with any efficiency gains the open fan tech would give.
Bypass ratios keep increasing, so do temperatures, and the fans can now turn at whatever speed they want to, instead of being linked to a fast turbine...

It might just not be worth it anymore.

Francoflier wrote:

It might just not be worth it anymore.

What is not quite clear:
Did the Clean Sky research programme on Open Rotor terminate
or did Safran retreat ?

Well one problem with these is that they couldn't be mounted under the wing the way conventional engines are. In order to use this technology you would need a clean sheet T-tail or some other creative method.

Is it really bad news? Pardon my ignorance, but I would assume that an open rotor would generate tremendous noise and vibrations. Prop aircraft are unpopular with passengers after all. But much more importantly, wouldn't it be inherently unsafe? Jet engines are built to withstand a turbine breakdown, but what would happen if an open rotor blade breaks in flight? The consequence could be dramatic, all the way to severing electric or hydraulic lines, cabin depressurisation, extensive damage to the wing or stabilisers, etc.

rigo wrote:

Is it really bad news? Pardon my ignorance, but I would assume that an open rotor would generate tremendous noise and vibrations.

The programme take down tentatively indicates that there seems to be no perspective towards getting to grips with those issues in a reasonable timeframe. ( i.e. foreseeable future. )

More of a sad thing than a bad one. (bad would have come up if there is no competing tech path accessible).

Far out: could micro movable surfaces provide some solution in the future?

Francoflier wrote:

For all we know, there just might be unsurmountable technical showstoppers with the technology that will prevent it from being a viable option in the near future.

Either that or it is believed that conventional jet engine technology will be able to catch up with any efficiency gains the open fan tech would give.
Bypass ratios keep increasing, so do temperatures, and the fans can now turn at whatever speed they want to, instead of being linked to a fast turbine...

It might just not be worth it anymore.

Turbofans will NEVER equal open rotor efficiency for one simple reason: the fan cowling and its massive drag and weight which will only become more problematic as BPR's increase and fan diameter increases.

Is the 'open rotor system' the same as the Ultra High Bypass Jet Engine 'Propfan' or 'unducted fan [UDF]' https://www.youtube.com/watch?v=zxVAaIsfPIY [cheesy intro and ending]

A history lesson on GE engines... https://www.youtube.com/watch?v=4lip8lPWFLo

rigo wrote:

Is it really bad news? Pardon my ignorance, but I would assume that an open rotor would generate tremendous noise and vibrations.

More, yes. Tremendously more, no.
Propeller design has evolved quite a bit ; an A400M is fairly quiet next to a C130 (used to hear them both when I lived under Toulouse final approach a few years back). Obviously a CROR would spin much faster than those big turboprops, but I guess noise could be "managed" to a point.

rigo wrote:

But much more importantly, wouldn't it be inherently unsafe? Jet engines are built to withstand a turbine breakdown, but what would happen if an open rotor blade breaks in flight? The consequence could be dramatic, all the way to severing electric or hydraulic lines, cabin depressurisation, extensive damage to the wing or stabilisers, etc

Standard design requirement for any large aircraft, the airframe (structure and systems) shall retain minimum functionality in case of any external source of damage (engine burst, bird strike, wheel burst...). Electrical and hydraulic routes are doubled (or tripled) with paths that cannot be simultaneously hit by a fragment.

SCAT15F wrote:

Turbofans will NEVER equal open rotor efficiency for one simple reason: the fan cowling and its massive drag and weight which will only become more problematic as BPR's increase and fan diameter increases.

True for the propulsive efficency of the engine alone, not necessarily true for the propulsive efficency integrated {airframe + engine} system.
And the only efficency that matters is the efficency to carry X people of distance Y, which must account for speed, flight profile etc..., which may further compromise the CROR

Well, the aim of this program was, indeed, to further advance the tech, including tackling the noise issue. We've learned a "little bit" in fluid dynamics since this was last tested in the 80's, computing power enables much more complex CFD models, and advanced manufacturing has enabled much more complex aerodynamic blade shapes.

But sooner or later, if you want to advance the tech, you have to test it. Like NASA will do for the low sonic boom demonstrator.
This would have been a great chance, and is definitely a blow to open rotor technology. This is also quite a blow to Safran, which seems to have put significant effort into it.

Unfortunately the article doesn't state the reason, just pointing to a "recent decision". But the next stage was to be flight testing at Airbus, so it could very well be that Airbus didn't want to play along anymore, given their conservative, incremental improvement strategy.
As fuel is cheap, there is no hurry to develop something radically new, and Airbus still need to recover their invesment from NEO, which will take longer than expected due to PW's issues.

Ultimately, there are only two things that make aviation advance:
- wars between large powers
- expensive fuel

jupiter2 wrote:

Wasn't noise the killer in U.D.F. engines when they were previously explored ?

There were other problems too, namely greater vibration and stress on the airframe and the fact that UDFs generated a lot of low frequency noise that was extremely annoying to rampers and those around the engines a lot (e.g., they started to feel sick).