rheinwaldner
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Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 7:48 am

Sorry, the source is again in German (closer sources are often written in one of the EADS languages but tend to catch more news):
http://www.ftd.de/unternehmen/indust...eues-flugzeugkonzept/70041830.html

Summary:
- Open Rotor trial flights on an A340 would be realistic in 2016

- The on-going A30X project would draw benefit from those tests

- An Open Rotor A320 replacement could be launched with EIS between 2020-2025.

- Rotor size: about 4.2 meters. So the configuration would require fuselage mounted engines.

- Time from launch to EIS: 7 years


Other interesting news:
- A new laminar flow wing mounted on an A340 testbed could fly in 2014 and bring 10% fuel reduction.

- There is a pressure to bring new technologies quicker on the market than today. Certification efforts have become too much of a burden.

- A reserach center in Bangalore will be established to catch the Asian spirit and ideas for future programs.
 
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ptrjong
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 8:09 am

Why are propfans suddenly called 'open rotors'?    Helicopters have open rotors.
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Btblue
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 8:22 am

I wonder if it will look anything like this...

http://www.youtube.com/watch?v=Yo0Rp6TQPXo
146/2/3 737/2/3/4/5/7/8/9 A320 1/2/18/19/21 DC9/40/50 DC10/30 A300/6 A330/2/3 A340/3/6 A380 757/2/3 747/4 767/3/4 787 77
 
BMI727
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 8:23 am

Quoting rheinwaldner (Thread starter):
Summary:
- Open Rotor trial flights on an A340 would be realistic in 2016

- The on-going A30X project would draw benefit from those tests

- An Open Rotor A320 replacement could be launched with EIS between 2020-2025.

- Rotor size: about 4.2 meters. So the configuration would require fuselage mounted engines.

- Time from launch to EIS: 7 years

Do the engine manufacturers have anything to say about this? Because that might be a little bit important at some point.

Furthermore, it is hard to read the partnership of Rolls-Royce with Pratt and Whitney on the GTF as anything other than a tacit admission that open rotor will not be ready in the near future.
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PM
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 9:15 am

Quoting rheinwaldner (Thread starter):
The on-going A30X project

Is this a new narrowbody or something else?

Quoting BMI727 (Reply 3):
Do the engine manufacturers have anything to say about this?

I'm guessing that RR, for one, will not be displeased.

Quoting rheinwaldner (Thread starter):
A reserach center in Bangalore will be established to catch the Asian spirit and ideas for future programs.

I'm moving to Bangalore in seven weeks. Looking forward to lots of aerospace activity!   
 
scouseflyer
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 9:24 am

Quoting PM (Reply 4):
Quoting rheinwaldner (Thread starter):
The on-going A30X project

Is this a new narrowbody or something else?

It's the new build NB plane, I think that they've also called it the NSR

http://www.flightglobal.com/blogs/fl...irbus-outlined-future-a30x-co.html
 
parapente
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 9:24 am

Here is another 2 examples of 'future aircraft'
http://www.youtube.com/watch?v=XKncIxPZIHQ&feature=endscreen&NR=1

http://www.youtube.com/watch?v=WGBLRNrZN1U&feature=related

There were examples of Boeing patent designs posted not long ago on this forum.Again they were very similar (an extra small tail on the fuse as I recall for blade out/noise reasons.
However all the designs have roughfully come to the same conclusion of 3 lifting surfaces,FSW and double (triple) tails with or.Lower cruising speeds with thicker laminar flow wings.BUT

The NEO and MAX have now been launched. They will want at least a 15 year production run,there is no real competitive pressure, so I don't see it happening in the time frame suggested.
 
justloveplanes
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 9:55 am

Sounds like a sonic cruiser type of lead in.
 
rheinwaldner
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 11:52 am

Quoting BMI727 (Reply 3):
Do the engine manufacturers have anything to say about this? Because that might be a little bit important at some point.

This is true of course (if flight tests should start in 2016). The article mentions ongoing discussion between RR, Safran and Airbus.

Quoting BMI727 (Reply 3):
Furthermore, it is hard to read the partnership of Rolls-Royce with Pratt and Whitney on the GTF as anything other than a tacit admission that open rotor will not be ready in the near future.

And the article is an open announcement that the open rotor could be ready for flight test in 4 years and ready for operation in 8 - 13 years. Possibly your interpretation (which was shared by me until yesterday) has to be revised.

B.t.w. Boeing killed the 7J7 in 1987 not because the prop-fan would not have been ready in the near future (at that time!), but because the pressure due to high fuel prices was gone.
 
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 12:03 pm

Quoting rheinwaldner (Reply 8):
the pressure due to high fuel prices was gone.


And the noise problem..
 
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 12:08 pm

Quoting BMI727 (Reply 3):
Furthermore, it is hard to read the partnership of Rolls-Royce with Pratt and Whitney on the GTF as anything other than a tacit admission that open rotor will not be ready in the near future.

Maybe you could look at it like that or maybe (this is my view) pratt realised that the GTF is only the short term solution and needs longer terma cash flow which they see getting from the open rotor while RR didn't want to lose narrow body revenue in the medium term.

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tdscanuck
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 12:41 pm

Quoting rheinwaldner (Thread starter):
- Rotor size: about 4.2 meters. So the configuration would require fuselage mounted engines.

Wow...that's gonna put the engine centerline about 8' away from the fuselage...that's a loooooong strut. This seems like a great application for the HondaJet over-wing style mounting.

Quoting rheinwaldner (Reply 8):
And the article is an open announcement that the open rotor could be ready for flight test in 4 years and ready for operation in 8 - 13 years.

The A350 and 787 didn't face nearly open rotor level configuration/engine issues and they still took more than 8 years to get to operation from conception...I don't see this one going faster, even if they commit today.

Tom.
 
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 12:53 pm

Quoting justloveplanes (Reply 7):
Sounds like a sonic cruiser type of lead in.

There aren't too many similarities.

SC was about burning fuel to go faster, OR is about saving fuel and going slower.

SC came out of nowhere, OR has decades of research behind it.

SC claimed to have launch customers lined up (IIRC it was AA, no?), OR is about using a testbed to prove out a technology.

Quoting 76er (Reply 9):
And the noise problem..

To me, the biggest problem is safety, in particular the blade failure scenarios.

Second is market acceptance: will the fuel burn savings be enough to make it so customers accept longer flights?

Third is community acceptance, i.e. the noise issue.

I'm also told a variable pitch mechanism is desired, and doing this is challenging.
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PlaneAdmirer
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 1:05 pm

How can this possibly make sense in light of the NEO? Airbus has over 1,000 orders for a plane that they will render outdated in under 10 years?
 
nasula
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 1:32 pm

To me this is the really interesing tidbit:

Quoting rheinwaldner (Thread starter):
- A new laminar flow wing mounted on an A340 testbed could fly in 2014 and bring 10% fuel reduction.

Any more information on this? A new wing for the A330/340 family? Or some other target just being flown on an A340?

If this happens for the A330 and gives a 10% reduction + the additional reductions from the engine optimisations being talked about for the A330 sound VERY interesting indeed. That would make the A330 a tough competitor for the 787 and sound like killing off the 350-800?

Or am I missing something?
 
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 2:23 pm

Quoting PlaneAdmirer (Reply 13):
How can this possibly make sense in light of the NEO? Airbus has over 1,000 orders for a plane that they will render outdated in under 10 years?

OR and A320 could live together very well for decades. OR means lower speed and that is optimized for distances below 1000 or 1500 miles, while the NEO we know to be targeted for a range extended compared to the current A320s - where OR slower speed would really start to make a difference.
 
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 2:24 pm

This sounds a lot like the 1980s GE-36-UDF, P&W/Allison-578-DX, Progress D-27, and the RR RB-3011 programs. The GE-36 actually flew demo flights at the FAS aboard an MD-81 demo aircraft, and flew flight testing in the US aboard a B-727.

The GE-36 was chosen to power both the B-7J7 and the MD-94X, both programs were canceled.

The Progress D-27 is available on the An-70.

The TP-400 and NK-12 are turboprops, not UDFs.
 
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 2:29 pm

Quoting nasula (Reply 14):
Any more information on this? A new wing for the A330/340 family? Or some other target just being flown on an A340?

Airbus use their A340 testbeds for all kinds of weird and wonderful stuff, and just because whatever it is they're testing is hanging off, or is bolted on to, a A340/330 family aircraft doesn't mean that's where it's going to end up. If Airbus are going to bring laminar-flow anything (wings sounds a tad ambitious) to the market, they'll probably do it on their newest and shiniest - why sink the money into the old dog, when there's a new one on the block with a hefty R&D bill in need of servicing?

The A330 will receive minor dusting offs from now on. No new engines, no new wings, no new primary structures. But a properly directed bit of polishing can gain those incremental 1.5 or 1.6% that'll keep the sun shining for a bit longer on the old girl.
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 2:32 pm

As they're off the A320neo and 737 MAX, Rolls-Royce has a seriously vested interest in making Open Rotor work for the Airbus NSR and Boeing NSA because it's their way back onto the most important part of the commercial aviation market (just as the GTF was Pratt's).

I think 2025 might be a bit ambitious, but we shall see.
 
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 2:46 pm

The A340 has the necessary ground clearance for testing such an engine, whereas the A320 would be too low.
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CM
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 2:55 pm

Quoting rheinwaldner (Thread starter):
Certification efforts have become too much of a burden.

OEM's spend too much time in the cert process helping the regulators along, educating them in order to avoid the inevitable conservatism which results from not understanding how a design works. Delegated authority was intended to help this, but when someone at the ACO overrides the DER because they have failed to grasp the underlying design, the OEM has little choice but to take their top talent away from designing and turn them into teachers. Worse yet, the education process is not always successful, causing redesign or unwarranted constraints on the design. The cumulative impact of this happening hundreds of times over the course of a program is absolutely crippling. I agree 100% with Airbus on this point - it is something they are undoubtedly struggling through with the A350 at this moment.
 
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 4:08 pm

Re the agreement PW and RR if I am not mistaken it is for "future geared engine technology" or something to that meaning. An open rotor really needs a good gear technology, me think PW and RR have covered both bases with this agreement, not just the shrouded fan case   .
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tdscanuck
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 4:31 pm

Quoting nasula (Reply 14):
If this happens for the A330 and gives a 10% reduction +

They're not going to fit a laminar flow wing to the A330 in production. Laminar flow would be relofting the wing. That would probably mean a new static test and would certainly mean new flutter and stability and control testing, as well as requiring all new wing tooling. There's no way that business case closes.

Quoting ferpe (Reply 21):
An open rotor really needs a good gear technology

Not necessarily; some of the prototype open rotors back in the 80's were direct drive off the turbines with no gearing.

Tom.
 
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 4:45 pm

Quoting tdscanuck (Reply 22):
some of the prototype open rotors back in the 80's were direct drive off the turbines with no gearing.

Would that type of open rotor also be the most promising type? Or are gearboxes to be expected?
 
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 5:17 pm

Quoting EPA001 (Reply 23):
Would that type of open rotor also be the most promising type? Or are gearboxes to be expected?

Assuming the noise from a open-rotor engine can be solved at all, gearing the fan seems almost certain. The direct drive UDF engines tested 20 years ago by GE/Boeing were exceedingly loud.

http://www.youtube.com/watch?v=zxVAa...IY&feature=player_detailpage#t=92s

The open-rotor engines tested by PW/McDonnell-Douglas used geared rotors which were quieter (but still very loud by today's standards) and much heavier.

http://www.youtube.com/watch?v=1BMNaXc1rL8

In either case, the forthcoming Stage 5 noise requirements are likely to represent a huge barrier to entry for using this technology versus current high bypass ratio engines which are many dB quieter, yet have little margin against the new Stage 5 noise requirements.
 
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 5:23 pm

The EU especially is going ape about the least bit of airline noise...the open rotor is DOA. The closest we'll see is perhaps a ducted contra rotating fan and/or a variable pitch fan but I'm willing to bet their ain't no way that a pair of open supersonic fans will ever be made quiet enough to meet noise standards...and that doesn't even touch the lost blade scenario.

If fans get any bigger, we may see some more high winged jets, instead of fuse mounted engines.

That being said, I'm all for experimentation...there's lots of stuff that isn't intuitive that just plain works.
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 5:39 pm

GE claims the GE36 UDF did meet Stage III noise limits, but it was still a fair bit louder than a turbofan both inside and outside the aircraft.

As such, I do believe that a UDF engine will need to use the fuselage and control surfaces as baffles, like in the Boeing "Fozzie" concept, EasyJet's EcoJet design or one of Airbus' A30X design.
 
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 5:54 pm

It looks like Airbus is continuing to do investment in new technology. That’s no surprise. I am glad to see propfans get more attention.

With fuel prices where they are, propfans and open rotor will be talked about. There are still problems with them such as noise, but investment is still warranted.

I think proposing timelines is a bit premature with the level of maturity of the technology. I am surprised Airbus would float numbers about such technology when it is just in the R&D phase and no one knows where it would go.
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 6:09 pm

One thing I wonder is: I hear talks about those OR designs using counter-rotating propellers for efficiency purposes - but aren't they by laws of physics a lot louder than 'one-spool' propellers?
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tdscanuck
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 6:42 pm

Quoting EPA001 (Reply 23):
Quoting tdscanuck (Reply 22):
some of the prototype open rotors back in the 80's were direct drive off the turbines with no gearing.

Would that type of open rotor also be the most promising type? Or are gearboxes to be expected?

Personally, I expect a gearbox. The big advantage of the gearbox-less designs was...the lack of gearbox. But now that P&W has proven you can do a gearbox with acceptable weight, power density, and reliability, I don't really see why you wouldn't do it. Otherwise you're seriously underrunning the turbine (or overrunning the prop).

Quoting JoeCanuck (Reply 25):
The EU especially is going ape about the least bit of airline noise...

The EU is also going ape about carbon emissions and fuel consumption...they're going to have to give somewhere.

Quoting Semaex (Reply 28):
I hear talks about those OR designs using counter-rotating propellers for efficiency purposes - but aren't they by laws of physics a lot louder than 'one-spool' propellers?

Basically, yes, since the second fan is running in the wake of the first. There are lots of tips and tricks to try to minimize this but it doesn't work against you from a noise standpoint. On the up side, with counter-rotating fans you don't need as large a diameter for the same thrust so you can keep the tip speeds down, which helps with noise.

Tom .
 
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lightsaber
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 6:51 pm

Everyone should remember an unshrouded fan has a lower optimal cruise mach number than a shrouded fan. Just to be clear, the openrotor is an unshrouded fan and a GTF is a shrouded fan. So the best engine will be mission dependent. The cruise mach number penalty is on the order of 0.1. In other words, cruise at Mach 0.7 vs. 0.8 of a turbofan/GTF.

Open rotors are for Quoting Roseflyer (Reply 27):
With fuel prices where they are, propfans and open rotor will be talked about. There are still problems with them such as noise, but investment is still warranted.

   But I want to be clear, the speed penalty is going to keep them in the 70 to 150 (maybe 180) seat range.

Quoting ptrjong (Reply 1):
Why are propfans suddenly called 'open rotors'?

Company based terminology. NASA and Douglas liked the propfan name. Not many others did...
Whatever sells better. Heck, it might go to market as 'GreenFan' or 'GreenRotor.'  
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 6:57 pm

Quoting Revelation (Reply 12):
To me, the biggest problem is safety, in particular the blade failure scenarios.

Which makes me want to ask . . .

Ever since GE introduced the composite fan blade in the GE90 for the 777, have there ever been an incident of blade failure for that engine? If yes, what was the result? Were there any major blade failure due to bird strike?

I was told by GE (way back when) that the failure of the composite blade is different from a metal blade and any failure would result in smaller pieces flying off instead of large chunks. Were they proven right after all these time?

If the failure mode for a composite blade is different than a metal blade, then maybe we can re-think open rotor failure scenarios.


bt
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rampart
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 7:06 pm

Quoting tdscanuck (Reply 11):
This seems like a great application for the HondaJet over-wing style mounting.
Quoting JoeCanuck (Reply 25):
If fans get any bigger, we may see some more high winged jets, instead of fuse mounted engines.

What advantage or disadvantage is there with 8 ft of strut above a wing (a scaled up Hondajet) or 8 ft of strut out the side of the aft fuselage (I'm envisioning a wider MD80 strut, right?). Or if it does happen, is it likely to fit between twin vertical stabilizers as has been illustrated frequently (which some have said has a maintenance access issue, but something will have to fall back in priority)?

And a high wing/low slung engine configuration would not help with shielding noise or controling uncontained failures, correct?

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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 7:29 pm

Airbus has long been interested in OR for the A30X, however a while ago they deemed the techonology immature today, while at the same time being impressed by the GTF demonstrator that they got to test one of their famous A340 testbeds, so they launched the NEO. But precisely because of that, they now need a return on investment on the NEO, so I don't expect OR before 2027, even if from a technological standpoint I consider it feasible earlier (assuming no NEO and full R&T resources dedication, which is not the case). I'm sure Airbus wants to give OR a second chance sometime though.

Quoting tdscanuck (Reply 29):
Quoting JoeCanuck (Reply 25):
The EU especially is going ape about the least bit of airline noise...

The EU is also going ape about carbon emissions and fuel consumption...they're going to have to give somewhere.

The EU does not know the word trade-off. For example, with existing tech, you could decrease CO2 emissions tomorrow morning by simply tweaking the combustion, but at the expense of emitting more NOx, which is also emissions-restricted. But you can also consider it a great technological challenge - to reduce noise, CO2 and NOx, all by considerable quantities and despite

Quoting rheinwaldner (Thread starter):
- A new laminar flow wing mounted on an A340 testbed could fly in 2014 and bring 10% fuel reduction.

As others have said, they will not be rewinging the A340 (or A330); being a testbed I would assume that one or several sections of the A340 wing would be substituted by laminar flow sections to evaluate the technology, which could also feed into the A30X.
 
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 7:53 pm

Quoting rheinwaldner (Reply 8):
And the article is an open announcement that the open rotor could be ready for flight test in 4 years and ready for operation in 8 - 13 years.

You'd have a pretty hard time getting a new airframe with today's state of the art flying in 8 years, let alone with a change as big as open rotor engines. Plus with the pressure of continuing A350 development, I think we're talking at least 10 years, before you consider engine development.

Quoting rheinwaldner (Reply 8):
but because the pressure due to high fuel prices was gone.

There are also some nagging technical issues.

Quoting tdscanuck (Reply 11):
This seems like a great application for the HondaJet over-wing style mounting.

...until it sheds a blade anyway.

Quoting PlaneAdmirer (Reply 13):
How can this possibly make sense in light of the NEO?

For that matter, if you really thought that you could have this open rotor narrow body flying in 2020-2022, you probably wouldn't have launched the NEO at all.
Why do Aerospace Engineering students have to turn things in on time?
 
XT6Wagon
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 8:17 pm

Quoting lightsaber (Reply 30):

Company based terminology. NASA and Douglas liked the propfan name. Not many others did...
Whatever sells better. Heck, it might go to market as 'GreenFan' or 'GreenRotor

I honestly think its only hope to get past regulators is to approch it from "advanced turboprop" direction instead of "green turbofan". Blade out and noise are going to be thier own circles of hell, and that much worse when compared to something that is nice and shrouded in comfy kevlar wraps. I just don't see it happening unless the bribe money flows like a river if they keep pushing it for the 737/A320 market. Smaller market, but so much easier if they pushed for a model slightly bigger than the Q400 for the small, then move up into the 73G size in the "future" stretch if the "market" demands with a baseline in the middle. The smallest model is there mostly to help keep everyone on the idea that this is the 21st centrury turboprop of the future with more speed, and less noise.
 
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 8:36 pm

Quoting XT6Wagon (Reply 35):
...until it sheds a blade anyway.

Why is the risk of that different to a Dash 8 or ATR today?


Another problem with this proposal is passenger resistance to props, as they are seen as less safe than jets.
 
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 8:51 pm

Quoting fcogafa (Reply 36):
Why is the risk of that different to a Dash 8 or ATR today?

Well thats why I think its a total mistake to only mention the 737/A320 or that market in everything you say about the planes for these open rotor engines. It *should* lead the regulators to compare the safety to the current turbofans on the current narrowbodies.
 
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 8:58 pm

Quoting BMI727 (Reply 34):
For that matter, if you really thought that you could have this open rotor narrow body flying in 2020-2022, you probably wouldn't have launched the NEO at all.

   They will in effect be different markets just as the Q400 compliments the CR7/9. The slower cruise speed of the open rotor won't matter on the 1 hour mission, but for any mission over 2.5 hours... We're talking adding significant time.

Quoting r2rho (Reply 33):
For example, with existing tech, you could decrease CO2 emissions tomorrow morning by simply tweaking the combustion, but at the expense of emitting more NOx, which is also emissions-restricted. But you can also consider it a great technological challenge - to reduce noise, CO2 and NOx, all by considerable quantities and despite

It is quite a challenge. A higher pressure ratio will cut CO2, but it will be with higher NOx. But it often isn't done as the maintenance costs will exceed the fuel savings. At least on shorter missions. There is a reason widebody engines are so different than narrowbody engines. They average fligth time is longer and thus the tolerated compromises are different.

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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 9:15 pm

Quoting bikerthai (Reply 31):
Ever since GE introduced the composite fan blade in the GE90 for the 777, have there ever been an incident of blade failure for that engine?

No failure due to any blade/engine issues. Blades have been replaced due to FOD damage (bird strikes and so on) but I don't believe one has ever actually failed (i.e. come off or come apart). GE likes to bring this up on a fairly regular basis.

Quoting bikerthai (Reply 31):
I was told by GE (way back when) that the failure of the composite blade is different from a metal blade and any failure would result in smaller pieces flying off instead of large chunks. Were they proven right after all these time?

Composites don't crack into chunks like metals, that's true. They tend to split (think a tree trunk breaking) or turn into loose assemblages of fibers and powdered resin.

Quoting rampart (Reply 32):
What advantage or disadvantage is there with 8 ft of strut above a wing (a scaled up Hondajet) or 8 ft of strut out the side of the aft fuselage (I'm envisioning a wider MD80 strut, right?).

Because if it's over the wing you don't need an 8' strut. You hang the fan off the back (or front) edge of the wing. The engine core is over the wing (or slightly forward or slightly aft). Then you just need to make sure the centerline is 8' from the ground...the core could be snuggled right up against the wing like the 737-100 or Sonic Cruiser.

The only way to do that with a fuselage mounted engine is to have it so far aft (or forward, hypothetically) that the fans clear the end of the fuselage and, even then, you need to keep them separate from each other. That's fairly clearly a non-starter.

Quoting rampart (Reply 32):
And a high wing/low slung engine configuration would not help with shielding noise or controling uncontained failures, correct?

True.

Quoting fcogafa (Reply 36):
Why is the risk of that different to a Dash 8 or ATR today?

More energy per rotor. The thrust ranges we're talking about here are only barely approached by even the largest turboprops in existance. You also have way more blades, making them more likely to interfere with each other during a failure.

Tom.
 
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 9:17 pm

Quoting Revelation (Reply 12):
To me, the biggest problem is safety, in particular the blade failure scenarios.

  Do open-rotors or propfans run faster than props mounted on a Dash-8 or an Avanti, or where does this fear come from? Besides, if the propellers are mounted quite aft, I don't see how this could be more dangerous to the airframe or passengers than the propellers mounted right next to my head in the 8th row of an ATR.
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 9:18 pm

Quoting lightsaber (Reply 30):

Just like a Q400?? I can't believe that no one has seriously considered a 120 seat turboprop - or have they and we just haven't heard about it?

These UDF's being discussed, are they 'puller' or 'pusher' units? All I can imagine at the moment is a CF6 or similar without the nacelle! How far away is this from the reality?
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 10:49 pm

Quoting tdscanuck (Reply 22):
Quoting nasula (Reply 14):If this happens for the A330 and gives a 10% reduction +
They're not going to fit a laminar flow wing to the A330 in production. Laminar flow would be relofting the wing.

Actually, to get accurate inflight test readings, they will probably mount the 'wing' as a canard, or something on their test bed A-340. The 'wing' will of course be scaled down, but its shape will be accurate.

This has been done on B-707s, B-720s and B-747s by several companies, including Boeing.
 
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Thu May 31, 2012 10:59 pm

Quoting fcogafa (Reply 36):
Another problem with this proposal is passenger resistance to props

There is some. But the higher speed will prevail.

Quoting tom355uk (Reply 41):
Just like a Q400?? I can't believe that no one has seriously considered a 120 seat turboprop - or have they and we just haven't heard about it?

Ok, bad analogy as the open rotor is significantly faster than a turboprop.   

Quoting tom355uk (Reply 41):
All I can imagine at the moment is a CF6 or similar without the nacelle! How far away is this from the reality?

Take a CF34 with triple the fan diameter, and you have the idea. The CF6 derived open rotor would be for a HUGE platform.

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RE: Airbus: Open Rotor A320-replacement Prior 2025

Fri Jun 01, 2012 12:28 am

Quoting Semaex (Reply 40):
Do open-rotors or propfans run faster than props mounted on a Dash-8 or an Avanti, or where does this fear come from?

Seems you and Tom were writing at the same time, see his #39 for the answer.

Quoting Semaex (Reply 40):
Besides, if the propellers are mounted quite aft, I don't see how this could be more dangerous to the airframe or passengers than the propellers mounted right next to my head in the 8th row of an ATR.

I can guarantee you I would not want to be in an ATR if it had a prop blade failure.

You take a system with that much weight spinning at that rate and destabilize it with a prop failure, and all hell can break loose.

Here's some input on the blade-out issue from two folks who know an awful lot about designing airplanes:

http://seattletimes.nwsource.com/htm...ge_on_radical_airplane_design.html has some concerns:

Quote:

The pod that encases an engine today, called a nacelle, must by regulation be capable of containing any parts that break off in operation, including fan blades.

With no nacelle covering the propellors, a nightmare scenario is a blade flying off into the fuselage or wing, something referred to as a "blade-out."

In a discussion last year, Boeing engineering legend Joe Sutter dismissed the open rotor as unrealistic because this problem is insurmountable. (See this blog entry from last year, at the bottom.)

"If I were chief engineer, what would scare the hell out of me is the first day I lose a blade and lose an airplane," Sutter said then.

Now, apparently Boeing has concluded that Sutter is right.

Bair in his Paris presentation ruled out the open rotor option as an alternative he had to think about.

"Those are 14 feet to 16 feet in diameter, very large blades that spin very fast," said Bair. "We cannot envisage an engineering solution for a blade-out."


It'd be interesting to see what kind of data there is today about turboprop blade-out causing hull loss.

Can you imagine if you spend $billions developing open rotor, and you do have a hull loss due to blade-out? One bad event could wipe out that investment, IMHO.
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Fri Jun 01, 2012 12:47 am

Quoting Revelation (Reply 44):
Can you imagine if you spend $billions developing open rotor, and you do have a hull loss due to blade-out? One bad event could wipe out that investment, IMHO.

OK, how about a ducted prop? Why are ducted props limited so far to blimps, RC aircraft, and the occasional experimental homebuilt? Perhaps it would diminish the effeciency?? But if it's a minor diminishing, the safety allowance may be worth it.

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RE: Airbus: Open Rotor A320-replacement Prior 2025

Fri Jun 01, 2012 1:00 am

Quoting Revelation (Reply 12):
To me, the biggest problem is safety, in particular the blade failure scenarios.

I'd wager that the propellers on a Brazilia are just as dangerous. If anything, these are less dangerous because they will be mounted aft of anything important.

What I don't get is the love affair with canards. I understand the aerodynamic benefits and the benefits in controllability, but how are you supposed to taxi into a gate with a jet ramp there? Most jet ramps angle up once they leave the aircraft. Most jet ramps will obstruct the canard from entering (or be at risk for hitting it when put into position). Why do designers keep putting them on concepts?
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Fri Jun 01, 2012 1:11 am

Quoting rampart (Reply 45):
OK, how about a ducted prop?

That's a GTF. Seriously.

The advantage of an open rotor is:
1. Weight (no duct/shroud)
2. Larger fan (due to drag/weight optimization shifting to a greater diameter fan blade)

The disadvantages:
A. Blade tip losses (its why all turbofans have the nacelle surrounding the fan)
B. Lack of stators after the fan (straighten out the airflow for best propulsion efficiency)
C. Lack of a nozzle (A variable nozzle is even better as take-off, climb, and cruise are best at different expansion ratios due to the different mach # of the aircraft.)

Point #1 means the Open Rotor benefits aircraft less than 200 seats the most (above that, the disadvantages might outdo the weight advantage).

Point #2 means a nice bypass ratio. This means a more efficient take off and a far more efficient cruise.

Point A means that the speed of the blades must be backed off below what would be optimum for a shrouded fan (GTF). This is part of the reason for a lower cruise speed. Its also an efficiency hit that is overcome by the propulsion efficiency of the large diameter fan.

Point B is an efficiency loss. Because of B, the large fan (#2) must be taken advantage of or there is no reason doing an open rotor. Hence why we look at body mounted or above wing (a la Hondajet) placement of the engines. In other words, unless the fan diameter is large, don't bother with an open rotor.

Point C means both an efficiency loss (overcome by the large diameter), but also a lower optimum cruise speed (hard to separate from Point A).

As soon as the shroud (duct) is put on, one wants a nozzle to improve cruise efficiency and that is a GTF. For blimps or RC aircraft, their top Mach # is low enough that a nozzle isn't warranted (in a blimp) or affordable. (Note: I've seen RC aircraft with proper nozzles to optimize thrust. But I'm sure my old RC crowd was on the geeky side...) A blimp shrouds the propellers for noise control (brought by managing the blade tip losses...). RC aircraft are trying to simulate jet engines. Now that RC jet engines are far cheaper, the number of shrouded props flying seems to be declining, but that is just my impression.

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RE: Airbus: Open Rotor A320-replacement Prior 2025

Fri Jun 01, 2012 1:32 am

Quoting DocLightning (Reply 46):
Most jet ramps will obstruct the canard from entering (or be at risk for hitting it when put into position). Why do designers keep putting them on concepts?

Because airlines/airports consistently find work-arounds for ground facilities when there are substantial economic gains offered by an inconvenient design feature. Examples:

- 777 wingspan is a category higher than DC-10, airlines opted for larger gates rather than the folding wingtip
- 787 wingspan, airlines again were not dissuaded by being pushed into a larger category.
- 737NG winglets, AA initially declined to add winglets because of gate spacing, but retrofit them when the fuel savings cost was compelling
 
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RE: Airbus: Open Rotor A320-replacement Prior 2025

Fri Jun 01, 2012 2:03 am

Quoting Revelation (Reply 44):
Here's some input on the blade-out issue from two folks who know an awful lot about designing airplanes:

The only way I can see it is if they are mounted pusher with no critical systems inline with the fan. Bonus points if you put them 2-3 degrees off axis so that the fans don't intersect. Ruin your gains from open rotor, but might be better than having an armored vertical stabilizer between the two to prevent a blade out from removing the other rotor.

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