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A320 & Boeing 737 Successor, Open Rotor?  
User currently offlineKeesje From , joined Dec 1969, posts, RR:
Posted (5 years 1 month 1 week 1 hour ago) and read 16686 times:

The Boeing 737 has been around for 40 years and has seen major upgrades in the mid eighties and late nineties. The A320 also has passed 20 yrs. Both Airbus and Boeing indicate they don’t see the need for new narrow body aircraft being developed before 2020 earliest.

Question is what the airlines will think if oil goes through the roof again. Who will buy Boeing 737/A320's from 2017 for use until 2042? Is it still a good investment? Public & government pressure to reduce levels of green house gas emissions are also growing.

Counter rotating open rotor technology (CROR) promises 25 % fuel efficiencies improvements over todays engines..


Source : http://www.nlr.nl/smartsite.dws?id=12618

43 replies: All unread, showing first 25:
 
User currently offlineMSNDC9 From , joined Dec 1969, posts, RR:
Reply 1, posted (5 years 1 month 1 week ago) and read 16687 times:

Not a chance. Too much noise.

User currently offlineRoseFlyer From United States of America, joined Feb 2004, 9585 posts, RR: 52
Reply 2, posted (5 years 1 month 1 week ago) and read 16681 times:

I'm more of a believer that eventually making laminar flow through the engine will be where we go. Open rotor technology isn't that impressive. It doesn't get you much more than a high bypass engine does. Open rotors were a good thing to look at when engines were lower bypass as in the 727/DC9 days. The new engines with less than 10% going through the core defeat the purpose of open rotor in my opinion. If you want to go towards higher efficiency, then go for a full turboprop, and not a basterdized more efficient low bypass engine. The open rotor concept was really popular in the 80s for development, but the noise, lower altitude, lower speed could not help it overcome the fuel improvement, especially when the ultra high bypass engines gave almost the same improvement.

Now where we can see some big gains is if we go towards laminar flow. The technology has been around for decades on submarines, and Pratt & Whitney is trying to do it with air. Changing the speed of the fan blades is not an easy task though. Getting reliability out of all those extra moving parts operating at the extreme conditions in an engine will be an incredible challenge. They'll certainly blow a lot of stuff up in the process. If someone can do it and get it to work though, they are going to have a huge money maker, although the risk and cost are probably as high to an engine manufacturer as the 747 was to Boeing. It appears though that Pratt & Whitney is willing to bet the company. The others still seem to believe that the bigger the fan, the better off you are.

[Edited 2009-07-16 15:44:55]


If you have never designed an airplane part before, let the real designers do the work!
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 3, posted (5 years 1 month 6 days 18 hours ago) and read 16603 times:



Quoting Keesje (Thread starter):
Who will buy Boeing 737/A320's from 2017 for use until 2042?

Everyone, unless somebody comes out with a viable competitor. Although using an older technology aircraft isn't a great value proposition for an airline, it's better than having no aircraft. That's assuming you actually want to have an airline at all. Thus the old joke about how to make a fortune in the airline business...

Quoting Keesje (Thread starter):
Is it still a good investment?

Relative to what? If it's the only option then it's the only investment...unless you choose to exit the business, you need aircraft.

Quoting Keesje (Thread starter):
Counter rotating open rotor technology (CROR) promises 25 % fuel efficiencies improvements over todays engines..

*If* they can solve all the integration issues. CROR promised exactly the same thing in the 80's with and it never went anywhere.

Quoting MSNDC9 (Reply 1):
Not a chance. Too much noise.

Last month, RR claimed their latest open rotor would meet Stage IV by a comfortable margin.

Quoting RoseFlyer (Reply 2):
If you want to go towards higher efficiency, then go for a full turboprop, and not a basterdized more efficient low bypass engine.

That kills your speed worse than an open rotor. If fuel really goes through the ceiling the time/fuel trade might drive us that way, but the open rotor is an attempted compromise to get a step change in fuel burn while fitting in the same route/schedule structure as the existing products.

Of course, by the time we replace the A320/737, the A400M engines will finally be available and we'll have a nice big turboprop to play with...

Tom.


User currently offlineMSNDC9 From , joined Dec 1969, posts, RR:
Reply 4, posted (5 years 1 month 6 days 18 hours ago) and read 16595 times:



Quoting Tdscanuck (Reply 3):
Last month, RR claimed their latest open rotor would meet Stage IV by a comfortable margin.

Yes, but fans are doing so by a wide margin.


User currently offlineKeesje From , joined Dec 1969, posts, RR:
Reply 5, posted (5 years 1 month 6 days 14 hours ago) and read 16550 times:



Quoting RoseFlyer (Reply 2):
Open rotor technology isn't that impressive. It doesn't get you much more than a high bypass engine does. Open rotors were a good thing to look at when engines were lower bypass as in the 727/DC9 days. The new engines with less than 10% going through the core defeat the purpose of open rotor in my opinion. If you want to go towards higher efficiency, then go for a full turboprop, and not a basterdized more efficient low bypass engine.

I think counter rotating open rotor technology is more efficient then a single prop. A single prop creates a swirling airstream. A CROC a more straight one. That should be good enough for an additional 5% energy effieciency. I think CROR have a bypass ratio in term of 1 to 30/40 so only 3-4% of the air going through the core.

CFM and Pratt are developing the LEAPX and the Geared Turbo Fan (GTF). Both these engines could fit under the wings of A320 and 737 (though with considerable modifications). Those engines promise fuel consumption reduction of around 15%.

However a further 10% improvement could be achieved by introducing counter rotating open rotors (CROR) as shown on GE stand at the Paris airshow (CFM LEAPX prototype in front).



So the promises of the new improved CROR are high. Last month GE / Safran were openly claiming its 10% better then their LEAPX (in front).


User currently offlineFaro From Egypt, joined Aug 2007, 1540 posts, RR: 0
Reply 6, posted (5 years 1 month 6 days 10 hours ago) and read 16505 times:



Quoting RoseFlyer (Reply 2):
Now where we can see some big gains is if we go towards laminar flow. The technology has been around for decades on submarines, and Pratt & Whitney is trying to do it with air. Changing the speed of the fan blades is not an easy task though. Getting reliability out of all those extra moving parts operating at the extreme conditions in an engine will be an incredible challenge. They'll certainly blow a lot of stuff up in the process. If someone can do it and get it to work though, they are going to have a huge money maker, although the risk and cost are probably as high to an engine manufacturer as the 747 was to Boeing. It appears though that Pratt & Whitney is willing to bet the company. The others still seem to believe that the bigger the fan, the better off you are.

Very interesting, first time I've heard of laminar flow in the context of jet engines. Is this a direct result of GTF and a slower turning fan? Can it be applied to compressor/turbine flow too or only to the fan? Are we talking of all engine surfaces including the nacelle duct or the aerodynamic airfoils only?

Also, why would it be a bet-the-company innovation for PW? What is so difficult to implement about laminar flow in a fan engine?

Faro



The chalice not my son
User currently offlineMSNDC9 From , joined Dec 1969, posts, RR:
Reply 7, posted (5 years 1 month 6 days 6 hours ago) and read 16432 times:



Quoting Keesje (Reply 5):
I think counter rotating open rotor technology is more efficient then a single prop. A single prop creates a swirling airstream. A CROC a more straight one. That should be good enough for an additional 5% energy effieciency. I think CROR have a bypass ratio in term of 1 to 30/40 so only 3-4% of the air going through the core.

But an ultra high bypass fan combined with bio-fuel makes the open rotor idea relatively dead idea, yet again...


User currently offlineKeesje From , joined Dec 1969, posts, RR:
Reply 8, posted (5 years 1 month 6 days 3 hours ago) and read 16370 times:



Quoting MSNDC9 (Reply 7):
But an ultra high bypass fan combined with bio-fuel makes the open rotor idea relatively dead idea, yet again...

The most ambitious turbofans at this moment have bypass ratios of about 1:10-12. Making them even bigger makes cowlings very heavy.

The most modern turbofan currently under development and to enter service around 2015 is the LEAPX, it has a BPR of about 10. GE and Safran hope it will have provide a fuel efficiency improvement of about 16%.



Still CORC offers a 10% advantage, to much to ignore. That's why despite the LEAPX, GE are investing in it, together with NASA. http://www.gereports.com/ge-and-nasa...est-open-rotor-jet-engine-systems/

Biofuel or whatever alternative fuel can also be put in an CROC, that's not the issue.


User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 9, posted (5 years 1 month 6 days 2 hours ago) and read 16357 times:
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DATABASE EDITOR



Quoting Keesje (Reply 8):
a fuel efficiency improvement of about 16%.

I have a question. When engine manufacturers state percentages like this, are they using common definitions and conditions?

In other words, when an engine manufacturer says an engine will be 16% more efficient than a certain engine in service today, do they mean:

- The new engine will burn 16% less fuel in a ground-based test stand at XX% N1

or do they mean:

- The new engine will burn 16% less fuel when mounted on an aircraft and flown from airport A to airport B

As I understand it, there is a significant difference. Awhile back, I read an interview with an opponent of open-rotor technology (proponent of the GTF), and if I recall correctly, he stated that the open-rotor can exhibit lower fuel burn in the stand, but due to other factors, the advantage decreases or disappears on actual flights. Possibly because the open-rotor must be throttled up for a longer period of time...maybe due to weight and/or aerodynamics.

So which conditions does everyone refer to? Test stand or point-to-point? And does it really matter?

2H4



Intentionally Left Blank
User currently offlineMSNDC9 From , joined Dec 1969, posts, RR:
Reply 10, posted (5 years 1 month 6 days 1 hour ago) and read 16332 times:

Quoting Keesje (Reply 8):
The most ambitious turbofans at this moment have bypass ratios of about 1:10-12. Making them even bigger makes cowlings very heavy.

Size of the cowling is moot compared to the diameter of unducted blades. Your argument makes no sense.

Quoting Keesje (Reply 8):
The most modern turbofan currently under development and to enter service around 2015 is the LEAPX, it has a BPR of about 10. GE and Safran hope it will have provide a fuel efficiency improvement of about 16%.

The PW GTF is a 20% per seat burn improvement over the 717-200 and A-318. Your point is again moot.

Quoting Keesje (Reply 8):
Still CORC offers a 10% advantage, to much to ignore. That's why despite the LEAPX, GE are investing in it, together with NASA. http://www.gereports.com/ge-and-nasa...tems/


Waste of time and money.

Quoting Keesje (Reply 8):
Biofuel or whatever alternative fuel can also be put in an CROC, that's not the issue.

Irrelivant. The point is the fan gains coupled with biofuel being enough to relegate the open rotor to the dust box again. You might see it on a nextgen RJ but you are seriously out of touch if you think you're going to see it on a 150 seater.

Just because you can, doesn't mean you should.

[Edited 2009-07-17 14:03:37]

User currently offlineKeesje From , joined Dec 1969, posts, RR:
Reply 11, posted (5 years 1 month 6 days ago) and read 16318 times:

During the last year Rolls Royce has been doing extensive testing on new open rotor concept.

Strategic Marketing Manager-Future Programs Paul Randall said the open rotor is "the true game-changer" and could provide a 25%-30% fuel efficiency gain over turbofans powering narrowbodies today and be 10%-15% more fuel efficient than advanced turbofans that may come on line in the next decade. "Now the open rotor has moved from being a physics problem to an engineering problem," he said. "It is real and it is being realized."
http://www.atwonline.com/news/story.html?storyID=16749



RR open rotor being tested in large wind tunnel in the Netherlands last yr.

I think progress has been been made with the help of CFD that wasn't there 20 yrs ago. Wing tip vortexes don't hit each other anymore and smart ways to manage engine pylon wake are developped.


User currently offlineMSNDC9 From , joined Dec 1969, posts, RR:
Reply 12, posted (5 years 1 month 5 days 19 hours ago) and read 16250 times:



Quoting Keesje (Reply 11):
"Now the open rotor has moved from being a physics problem to an engineering problem," he said.

Thats a big problem.


User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 13, posted (5 years 1 month 5 days 18 hours ago) and read 16239 times:
AIRLINERS.NET CREW
DATABASE EDITOR



Quoting MSNDC9 (Reply 12):
Thats a big problem.

Historically, it's been easier to overcome engineering challenges than it has been to overcome laws of physics.

2H4



Intentionally Left Blank
User currently offlineMSNDC9 From , joined Dec 1969, posts, RR:
Reply 14, posted (5 years 1 month 5 days 18 hours ago) and read 16233 times:



Quoting 2H4 (Reply 13):
Historically, it's been easier to overcome engineering challenges than it has been to overcome laws of physics.

2H4

Unless the engineering problem winds up turning in to a new physics problem once you attach it to an airframe.


User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 15, posted (5 years 1 month 5 days 18 hours ago) and read 16232 times:
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DATABASE EDITOR



Quoting MSNDC9 (Reply 14):
Unless the engineering problem winds up turning in to a new physics problem once you attach it to an airframe.

Precisely! In the end, it's the physics problem that is most difficult to overcome, and is the limiting factor.  yes 

2H4



Intentionally Left Blank
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 16, posted (5 years 1 month 5 days 18 hours ago) and read 16232 times:



Quoting Keesje (Reply 5):
I think counter rotating open rotor technology is more efficient then a single prop. A single prop creates a swirling airstream. A CROC a more straight one.

This is true from a purely aerodynamic point of view, but the CROC has to be much much heavier and more complex in order to achieve the aerodynamic gain. At the moment, CROC's can't beat turboprops on installed efficiency, although the gap will eventually close up since a CROC taken to its extreme is just a counter-rotating turboprop, which is ~50 year old technology.

Quoting 2H4 (Reply 9):
As I understand it, there is a significant difference. Awhile back, I read an interview with an opponent of open-rotor technology (proponent of the GTF), and if I recall correctly, he stated that the open-rotor can exhibit lower fuel burn in the stand, but due to other factors, the advantage decreases or disappears on actual flights. Possibly because the open-rotor must be throttled up for a longer period of time...maybe due to weight and/or aerodynamics.

I've heard that as well, although not due to weight or aerodynamics but due to integration problems. You need to do a lot of things to the airframe to accomodate the open rotor and, apparently, those compromises eat up most of the initial advantage that the engine had in isolation on the test stand.

Quoting 2H4 (Reply 9):

In other words, when an engine manufacturer says an engine will be 16% more efficient than a certain engine in service today, do they mean:

- The new engine will burn 16% less fuel in a ground-based test stand at XX% N1

or do they mean:

- The new engine will burn 16% less fuel when mounted on an aircraft and flown from airport A to airport B

Typically the former. The engine makers usually wash their hands of the airframe integration problems, which is where most of the difference between the two comes from.

Tom.


User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 60
Reply 17, posted (5 years 1 month 5 days 18 hours ago) and read 16229 times:
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Quoting Tdscanuck (Reply 16):
Typically the former. The engine makers usually wash their hands of the airframe integration problems, which is where most of the difference between the two comes from.

Very interesting, indeed. Thanks for the info.

2H4



Intentionally Left Blank
User currently offlineFaro From Egypt, joined Aug 2007, 1540 posts, RR: 0
Reply 18, posted (5 years 1 month 5 days 13 hours ago) and read 16203 times:



Quoting Keesje (Reply 11):
During the last year Rolls Royce has been doing extensive testing on new open rotor concept.

CFD may be a boost to the progress achieved with the CROR concept but the pic of the Rolls Royce set-up resembles the Kuznetsov MK-12 as installed on the Tu-95/Tu-114. I wonder whether this older technology installation is to a certain extent being refined with today's CFD tools.

Faro



The chalice not my son
User currently offlineKeesje From , joined Dec 1969, posts, RR:
Reply 19, posted (5 years 1 month 4 days 2 hours ago) and read 16017 times:



Quoting Faro (Reply 18):
CFD may be a boost to the progress achieved with the CROR concept but the pic of the Rolls Royce set-up resembles the Kuznetsov MK-12 as installed on the Tu-95/Tu-114. I wonder whether this older technology installation is to a certain extent being refined with today's CFD tools

The RR testconfiguation is for accoustic testing. Extensive CFD modelling and testing let to significant noise and efficiency improvements compared to late eighties research. Blade tip vortex streams are among the key research areas. Shapes, lenghts, numbers, speeds of these rotor are incomparable to previous generations.

Progress has been made. Thats why GE and RR are investing and developping. 10 Percent on top of new gen turbofans within noise regulations cannot be ignored. PW is nervous. GE, Safran and RR are betting on two horses.


User currently offlineAffirmative From France, joined Jul 2009, 351 posts, RR: 0
Reply 20, posted (4 years 8 months 1 week 4 days 7 hours ago) and read 13422 times:

What about the design of NK-93? I guess the ducting of the counter rotating fans greatly reduces the noise but it still has all the savings of the open rotor concepts. It surprises me that noone else have tried this solution. This also facilitates the mounting under the wings which would be a problem with the open rotor.


I love the smell of Jet-A1 in the morning...
User currently offlineStitch From United States of America, joined Jul 2005, 30862 posts, RR: 86
Reply 21, posted (4 years 8 months 1 week 4 days 7 hours ago) and read 13416 times:
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You're still going to need a pretty large duct around the rotor, so you either need a high-mounted wing or stilts for landing gear.

Open Rotor does have a fuel advantage over "traditional turbine" and GTF designs in a laboratory environment, but Pratt is pretty confident that once you actually attach it to an airframe and put it into revenue service, the extra weight of the mounting unit and extra insulation and armor for the cabin/control surfaces will negate much of that.


User currently offlineAffirmative From France, joined Jul 2009, 351 posts, RR: 0
Reply 22, posted (4 years 8 months 1 week 3 days 8 hours ago) and read 13245 times:

But with the current NK-93 design the fan diameter is 290mm which would be about the same as the GE90 and I would guess you would be able to scale it somewhat.. All newer designs are growing the fan compared to the compressor itself so I guess no matter how you spin it you'll need more space underneath the wing eventually or go for a mounting on top of the empannage.?

My technical knowledge is restricted when it come to this, but since the NK-93 at it's current form has a output of ca 16t.. What would be the equivalent GE/RR/PW engine?



I love the smell of Jet-A1 in the morning...
User currently offlineStitch From United States of America, joined Jul 2005, 30862 posts, RR: 86
Reply 23, posted (4 years 8 months 1 week 3 days 7 hours ago) and read 13219 times:
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According to Pratt, an Open Rotor providing 24,000 to 30,000 pounds of thrust would require between 450 and 500 centimeters of clearance. You're not going to be able to do that with a low-mounted wing unless you're undercarriage is modeled after a stork's.  Smile

They claim a GTF could do that with a nacelle diameter under 250 centimeters and that they could squeeze it under a 737NG (thanks to a more forward mounting position allowing them to lift the top of the nacelle up close to the wing's leading edge, which evidently brings it's own benefits.


User currently offlineMax777geek From Italy, joined Mar 2007, 538 posts, RR: 0
Reply 24, posted (4 years 8 months 1 week 3 days 6 hours ago) and read 13209 times:



Quoting Keesje (Thread starter):
Counter rotating open rotor technology (CROR) promises 25 % fuel efficiencies improvements over todays engines..

And 300% more troubles for the noise.... so that's not convenient


25 Keesje : I think the configurations in the opening post & GE presentation are no coincidence. RR says they made progress due to new configurations, shapes and
26 Stitch : Indeed. However, NIMBY's concern for the plight of polar bears end in their backyards. So they're going to be interested in reducing both fuel consum
27 Post contains links Affirmative : Ok, so after browsing what little info I could find on the NK-93 I found that the 18t (not 16t) of thrust equals about 35-40.000 pounds of thrust. So
28 SEPilot : I think that the UDF is always going to come up short against turbofans, for two reasons. One is noise, and the other is speed. Fuel efficiency alone
29 Keta : Even with all the problems of noise and structure, the savings on fuel consumption may well be of enough importance to think about this propulsion sys
30 Stitch : For a 737/A320 thrust range, the GTF's fan is 203 cm, so you'd probably be looking at 340+ cm for an NK-93 with nacelle?[Edited 2009-12-16 08:54:44]
31 Affirmative : Ouch.. Well, I guess that's out of the picture unless they can refine that technology. I do think that the whole counter rotating and variable pitch
32 Tdscanuck : Aviation Week & Space Technology had an interesting article on this topic this week...in an nutshell, they've got GE on record as claiming they can g
33 Stitch : Didn't the GE36 eventually meet Stage III noise regulations?
34 SEPilot : That will be very interesting if they can do it; but that still leaves the problem of speed. I do not see how they can even approach the current spee
35 Post contains links Keesje : Both GE claims 26% fuel saving over their CFM56 (market standard) and about 10 % over their future LEAPX concept, as can be seen in early replies. RR
36 SEPilot : If they can achieve this then it may be viable, provided the noise targets are met. That is assuming that they do not make more advances on fanjets i
37 DocLightning : Which is fine for flights under about 2000 statute miles. But for a flight like JFK-SFO, you'll still want turbofans.
38 Okie : Mount a single MTU off the A400M on the nose of a 37, that ought to pull a 37 about 330kts. Okie
39 FLY2HMO : Now now, we have to keep aesthetics into account. It may work but I don't even want to picture how ugly that would look
40 Tdscanuck : It would sure show those Canada Geese who's boss. You want to take down an A320? Well how about *these* apples! Tom.
41 Erchen : Approximately how big is the difference in noise in dB?
42 Okie : I am not sure exactly, but living close to an Air Force Base, I can tell you there is a significant difference between some of the older low bypass e
43 sirtoby : By the time an open rotor would enter service, we will have eventually Stage V - should be another 10dB below Stage 4, what makes it hard to believe
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