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Open Rotor Engines - The Future?  
User currently offlineFlyingBattery26 From UK - Scotland, joined Mar 2013, 25 posts, RR: 0
Posted (1 year 5 months 3 weeks 2 days 8 hours ago) and read 8476 times:

I was just wondering, what is the probability that open rotor engines will replace jet turbofans in the future? I have been doing a lot of reading on the subject, and from my understanding they are more fuel efficient but also slower and noisier than conventional turbofan engines.. they're also quite hideous looking in design. I personally don't like them, and would hate to see them replacing the turbofan jet engine that we all know and love. Would anyone care to comment on this?

For those of you who don't know about these engine types, here's a link: http://www.sustainableaviation.co.uk...en-rotor-engine-briefing-paper.pdf

What they look like:



11 replies: All unread, jump to last
 
User currently offlinecornutt From United States of America, joined Jan 2013, 338 posts, RR: 1
Reply 1, posted (1 year 5 months 3 weeks 21 hours ago) and read 8208 times:

AFAIK, everyone has given up on those things. They seemed like a great idea in the late 1980s when they promised to be a lot more efficient than the turbofans that existed then. But I believe the ultra-high-bypass turbofans we have now have matched what the unducted fans were going to accomplish in efficiency. And no good solution for the noise of the UDFs was ever found.

User currently offlinewingscrubber From UK - England, joined Sep 2001, 848 posts, RR: 0
Reply 2, posted (1 year 5 months 1 week 15 hours ago) and read 7538 times:

The concept of bridging the gap between a traditional turbofan, and a contra-rotating twin-prop turbofan is a viable one, as it seeks to find the sweet-spot between max fuel efficiency and highest economical cruise speed. Combining technologies such as gear-reduction and variable pitch blades could achieve a very efficient engine that sits somewhere between a turboprop and a turbofan.

The problem with the UDF though is the noise! the open rotor engines would work if only they put a duct around it, something like Kuznetsov NK-93 is a good example of what could be done, but Russian aerospace companies just don't have the economical clout to bring a concept like this to fruition, and western aerospace companies are too risk averse to try anything so radical. It'll be a long time before any commercial aircraft are flying with turbine engines this advanced.


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User currently offlineTWA772LR From United States of America, joined Nov 2011, 2040 posts, RR: 1
Reply 3, posted (1 year 5 months 5 days 17 hours ago) and read 7315 times:

Quoting wingscrubber (Reply 2):

The concept of bridging the gap between a traditional turbofan, and a contra-rotating twin-prop turbofan is a viable one, as it seeks to find the sweet-spot between max fuel efficiency and highest economical cruise speed. Combining technologies such as gear-reduction and variable pitch blades could achieve a very efficient engine that sits somewhere between a turboprop and a turbofan.

Couldn't an engine manufacturer make a turbofan engine with two main fans before the core and make them variable pitch?

Side question, does any contra-rotating prop powered aircraft have variable pitch props?

[Edited 2013-04-14 00:12:19]

[Edited 2013-04-14 00:13:07]


Go coogs! \n//
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17038 posts, RR: 66
Reply 4, posted (1 year 5 months 5 days 17 hours ago) and read 7299 times:

Quoting TWA772LR (Reply 3):
Couldn't an engine manufacturer make a turbofan engine with two main fans before the core and make them variable pitch?

Sure. But it's not a simple solution and apparently current solutions are still better.

Quoting TWA772LR (Reply 3):
Side question, does any contra-rotating prop powered aircraft have variable pitch props?

I don't have the data but I would think all of them do. Only the simplest propeller planes have fixed props in my experience. It would seem a terrible waste to go to all the trouble to make contra-rotating props without implementing a hundred-year old technology like variable pitch.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinejetlife2 From United States of America, joined Jul 2006, 221 posts, RR: 25
Reply 5, posted (1 year 5 months 5 days 9 hours ago) and read 7205 times:

Open rotor solutions are being studied for next gen narrowbody aircraft, 2030+. The noise problem has been largely solved using current gen aero tools that were not around in the time of the UDF; and this has been validated by test. Remaining hurdles are mostly regulatory (not a turbofan; not a propeller; rules are very different). This technology is very likely the next generation; of course new airframes are needed, so given the current narrowbody space, there will be many years of study before the industry is ready for that investment.

[Edited 2013-04-14 08:55:39]

User currently offlineStitch From United States of America, joined Jul 2005, 30977 posts, RR: 86
Reply 6, posted (1 year 5 months 5 days 8 hours ago) and read 7191 times:
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I think UDFs might have a chance in the sub-150 seat market for regional work where distances are short enough that the slower cruise speed doesn't really matter. One issue with UDFs is that they have to be mounted in the rear so you're not going to see a UDF-powered plane larger than an MD-90.

User currently offlineJoeCanuck From Canada, joined Dec 2005, 5455 posts, RR: 30
Reply 7, posted (1 year 5 months 5 days 8 hours ago) and read 7181 times:

The new generation of jet engines, (especially the GTF), is already encroaching on the fuel efficiency estimates achievable by the Open Rotor engines.

I suspect that the Open Rotors will never be efficient enough to justify the cash to solve the speed and blade out problems. The GTF is such a simple design with a lot of room to improve still.



What the...?
User currently offlineUnited727 From United States of America, joined Nov 2010, 400 posts, RR: 1
Reply 8, posted (1 year 5 months 5 days 7 hours ago) and read 7153 times:

Quoting jetlife2 (Reply 5):
Open rotor solutions are being studied for next gen narrowbody aircraft, 2030+.

Thus one would expect...

Quoting Stitch (Reply 6):
that they have to be mounted in the rear so you're not going to see a UDF-powered plane larger than an MD-90.

I would expect up to Twin 757 "ish" size based on the 757 original model with the T Tail design. It's possible!



Looking for the impossible way to save those dying breeds!!!!
User currently offlineDocLightning From United States of America, joined Nov 2005, 19688 posts, RR: 58
Reply 9, posted (1 year 5 months 5 days 3 hours ago) and read 7091 times:

Quoting jetlife2 (Reply 5):
Remaining hurdles are mostly regulatory (not a turbofan; not a propeller; rules are very different). This technology is very likely the next generation; of course new airframes are needed, so given the current narrowbody space, there will be many years of study before the industry is ready for that investment.

Not just regulatory.

The development of a new airliner powered by such an engine will be astronomically expensive. No airframe manufacturer is going to just dive into this technology and risk bankrupting their company without seeing it in action on a smaller scale first. I predict we will start seeing UDF's in private aircraft first.

It is very rare that the industry wholesale adopts a new propulsion technology. Jet engines were available long before the 707. CFRP has been in use for major structural members for years now. Turbofans get better and better over time, too.

The OEM's and airlines are going to need a lot of convincing.


User currently offlinerwessel From United States of America, joined Jan 2007, 2351 posts, RR: 2
Reply 10, posted (1 year 5 months 4 days 20 hours ago) and read 7021 times:
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Quoting DocLightning (Reply 9):
Jet engines were available long before the 707. CFRP has been in use for major structural members for years now. Turbofans get better and better over time, too.

Boeing (not that they were actually first) started work on a jet transport, what was to become the 367-80 (and then the KC-135 and 707), in 1949. Barely a decade after the first jet took flight (the Heinkel He178, on 27-Aug-1939). And it's hard to credit turbojets as any sort of serious aircraft propulsion system before about 1943/44.


User currently offlineEaglePower83 From United States of America, joined Oct 2011, 231 posts, RR: 0
Reply 11, posted (1 year 3 months 1 week 4 days 4 hours ago) and read 5615 times:

Quoting DocLightning (Reply 9):
The development of a new airliner powered by such an engine will be astronomically expensive. No airframe manufacturer is going to just dive into this technology and risk bankrupting their company without seeing it in action on a smaller scale first.

Indeed.
The GTF wasn't even taken seriously by airframers until Pratt started building and flying them around ..... and only after hundreds of on-test bed hrs did anyone actually come to the table. Then once some small airframers started choosing it, did Airbus explore and offer the GTF for Neo.
Boeing is even more sceptical on the GTF.....plus they're in tucked in bed with CFM.


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