keesje
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Next Gen NB Engines : Contra Rotating Turbofan Fan

Fri Apr 27, 2007 8:25 pm

Snecma is looking at contrarotation fan as an option for next generarion Narrowbody aircraft.



Wonder how GE thinks about it.

RR (3 spool) and Pratt (GTF) are also testing the water. I wonder what they will say at the Paris Airshow.

http://www.flightglobal.com/articles...uture-engine-concept-revealed.html

[Edited 2007-04-27 13:26:46]
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JAAlbert
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Fri Apr 27, 2007 8:48 pm

Very interesting. (I think). Those fan blades rotating in opposite directions should have a very effective garbage disposal effect should any bird find its way into the engine!
 
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SEPilot
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Fri Apr 27, 2007 8:54 pm

I am not an expert in jet engines, but just from basic physics and engineering principles the idea is fascinating. The idea of eliminating the need for fixed blades by having contrarotating blades has enormous potential, as well as substantial difficulties in getting it right. If they can do it and get it right it will be a magnificent acheivement. The next step for ultimate efficiency would be a geared contrarotating fan. Anyone seen Rube Goldberg lately? Oh, that's right, he's dead. Summon his ghost, the industry needs him. Seriously, it would be enormously difficult to make a geared contrarotating engine reliable enough, but if it could be done it would be the holy grail of jet engines.
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Fri Apr 27, 2007 11:49 pm

You're up early Keesje....a most interesting article on a very timely subject.

On the subject of ultra high bypass fan engines I worked on a few Garrett ATF3s back in the day. They were used on the USCG HU25A and the French Navy equivalent, mating the engine to a modified Falcon 20 airframe. There was an extensive teething process with numerous service bulletins which required some of the mechanics to go to the airplanes and modify the engines. One of our guys spent seven weeks in Tahiti on that show.

The original task was to produce a very efficient engine with very low IR signature for a high altitude pilotless drone that Teledyne Ryan was going to build-which sounds a lot like Global Hawk.

That project got shelved but the ATF3 eventually got built. There was some internal dissension within Garrett as the ATF3 was a Torrance design and all the other engines came out of Phoenix. Well, I could be wrong about that part of it because it has been about 25 years
.
The ATF3 turned the airflow a bunch of different ways and ejected its exhaust into the fan air path midway through stacks. It was said that the ATF3 produced 93-95 per cent of its thrust from the fan, and it was a three spool engine.

Ultimately the ATF3's efficiencies were attained using 70s technology and materials, which was a very expensive way to do it. New materials and processes allowed simpler and less expensive engines to reach the same high degree of fuel economy.

There is a very interesting ATF 3 site that is worth a trip, particularly the part about the Tacit Blue engines and how they disappeared and reappeared..

http://www.pocketprotectors.com/atf3/index.htm

http://www.area51zone.com/aircraft/tacitb.shtml
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DAYflyer
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sat Apr 28, 2007 12:48 am

A very intersting subject indeed, Keesje.

I work for a company that manufactures high speed turbine impellers for commercial applications. Couter-rotating is indeed possible, but tricky. But let me tell you, the ones we have done here for non-aircraft use move HUGE volumes of air at tremendous speeds. I wonder what engineering problems and success they are having with this at Snecma??
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sat Apr 28, 2007 1:20 am

Quoting SEPilot (Reply 2):
Seriously, it would be enormously difficult to make a geared contrarotating engine reliable enough, but if it could be done it would be the holy grail of jet engines.

Don't propfans contrarotate?
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scbriml
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sat Apr 28, 2007 1:32 am

Call that contrarotatring?

These bad boys are contrarotating at its finest:

View Large View Medium
Click here for bigger photo!

Photo © Steve Brimley
View Large View Medium
Click here for bigger photo!

Photo © Steve Brimley


 wink 
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sat Apr 28, 2007 1:45 am

Quoting N328KF (Reply 5):
Don't propfans contrarotate?

Contrarotating is not that difficult as far as shafts/bearings are concerned; what is difficult is the blade contours. Contrarotating between a prop and a turbine is easy; it is geared anyway. The difficulty starts when you gear between the fan and turbine within the engine; first, where do the gears go and second, how do you make them reliable enough? That is what P & W is working on, and as I understand it it is not easy. Then add a contrarotating shaft in there that also needs to be gearded and you have just squared or cubed your problems. I'm not at all sure that it can be done.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sat Apr 28, 2007 1:49 am

[quote=SEPilot,reply=7]Contrarotating is not that difficult as far as shafts/bearings are concerned; what is difficult is the blade contours. Contrarotating between a prop and a turbine is easy; it is geared anyway. The difficulty starts when you gear between the fan and turbine within the engine; first, where do the gears go and second, how do you make them reliable enough? That is what P & W is working on, and as I understand it it is not easy. Then add a contrarotating shaft in there that also needs to be gearded and you have just squared or cubed your problems. I'm not at all sure that it can be done.[/quote

Why not have two HP turbines, with two stages on each, each driving one fan. Then you don't need any gears.?
 
justloveplanes
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sat Apr 28, 2007 1:53 am

why are so few prop applications counter-rotating?
 
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sat Apr 28, 2007 2:00 am

Quoting Justloveplanes (Reply 9):
why are so few prop applications counter-rotating?

In a nutshell, cost and complexity. Howard Hughes's plane that crashed (I forget what the model was) had counter-rotating props, and the failure of one of them is what caused the crash.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sat Apr 28, 2007 2:03 am

Quoting Keesje (Thread starter):
Snecma is looking at contrarotation fan as an option for next generarion Narrowbody aircraft. Wonder how GE thinks about it.

What must really be on their mind is the future of the CFMI partnership...
 
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lightsaber
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sat Apr 28, 2007 2:31 am

Quoting Keesje (Thread starter):
RR (3 spool) and Pratt (GTF) are also testing the water.

Pratt proposed one for the Sonic Cruiser.  bigthumbsup 

Quoting SEPilot (Reply 2):
Seriously, it would be enormously difficult to make a geared contrarotating engine reliable enough, but if it could be done it would be the holy grail of jet engines.

 checkmark 

Hence why Pratt is focused on the simple GTF. But is this a concept of high merit? Yes!

Quoting TristarSteve (Reply 8):
Why not have two HP turbines, with two stages on each, each driving one fan. Then you don't need any gears.?

But that is effectively a triple spool without the benefit of getting the turbine's mach number into its optimal range. The current triple spool has higher efficiency than your proposal. Why? By having the intermediate spool turbine and compressor spinning at their optimal mach number (which must be at a higher RPM than the fan based on diameters and temperature increases to compression heating) the engine gains in efficiency.

Should this be done long term? Yes! But we're talking engines in the 2020 timeframe.  Sad This is pretty far out technology.

Short term I'm still a fan of the GTF. This concept is far more complicated than a two shaft GTF.

Lightsaber
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SEPilot
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sat Apr 28, 2007 2:36 am

Quoting TristarSteve (Reply 8):
Then you don't need any gears.?

You miss the point. The idea is to have a gear reduction between the fan and the turbine, and then have contrarotating fans/turbines as well. That is what I was getting at.
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
Dougloid
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sat Apr 28, 2007 5:20 am

Quoting Scbriml (Reply 6):
Call that contrarotatring?

These bad boys are contrarotating at its finest:

Damn, now you've gone and done it....talk about yer heavy metal thunder......I love it.
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A342
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sat Apr 28, 2007 5:39 am

Well, the Russians are some steps ahead in this aspect:

http://motor-s.ru/NK93_en.htm

http://www.kmpo.ru/indexe.htm

IIRC the engine has already run, but Tu204 can probably tell you more about that.
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sat Apr 28, 2007 6:51 am

Lightsaber, why couldn't this just be a 3 spool design? I saw your response to TristarSteve, but I didn't quite follow what the problem would be...if you were hooking up the two fans to their own spools and making the core the a single spool, it could work and still be fairly conventional and simple, no?

The FlightGlobal article points out that the front fan has noticably fewer fan blades than the rear one. That hints at a simple 3 spool, but different than what RR is doing. Standard HP core, fairly standard LP driving the rear fan and lead stage(s) and another LP (VLP?) beyond that driving the lighter front fan only. It would certainly reduce the complexity of the problem down dramatically from any kind of geared solution, no?
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lightsaber
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sat Apr 28, 2007 8:29 am

Quoting Lemurs (Reply 16):
Lightsaber, why couldn't this just be a 3 spool design? I saw your response to TristarSteve, but I didn't quite follow what the problem would be...if you were hooking up the two fans to their own spools and making the core the a single spool, it could work and still be fairly conventional and simple, no?

It could be a 3-spool.

But by using two of the spools to turn the fans, you limit each spools Mach number at the fan (Feel free to think RPM). Thus, you lose the benefit of RR's triple spool of having the low compressor and low turbine spinning fast enough to be efficient.  Smile

I've read a bit more about this offline, and am now convinced that the added complexity of the 2nd part of the gearbox wasn't as bad as I feared. So move the EIS up by 5 or so years.  spin 

I still think a geared solution is simpler. But that's me. I've been exposed to the ugly sides of GTF's and haven't been scared off.  bigthumbsup 

Lemurs, love the quote in your signature.  Smile

So now I'm in favor of this as a 2nd generation turbofan. You really need to get the low turbine Mach number (again, feel free to think RPM) up. Dramatically! There is too much efficiency being thrown away in a low Mach number turbine.


Lightsaber
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Lemurs
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sat Apr 28, 2007 8:52 am

Quoting Lightsaber (Reply 17):
But by using two of the spools to turn the fans, you limit each spools Mach number at the fan (Feel free to think RPM). Thus, you lose the benefit of RR's triple spool of having the low compressor and low turbine spinning fast enough to be efficient.

Ah right, I always lose sight of that. Low pressure systems in current turbofans are inherently about picking the least ugly tradeoff, aren't they? I don't suppose the configuration of the fan would dramatically change the optimal rotational speed for a given diameter, would it? There's only so fast the outer edges can go before they stop doing their job well, right? (i.e. would that front fan with fewer blades have a higher optimal RPM than a conventional fan, allowing for a less painful tradeoff?) Still obviously not as good as letting everyone spin at their most efficent speed, like a gearset would allow, I realize.

Quoting Lightsaber (Reply 17):
Lemurs, love the quote in your signature.

Thanks! It's both fun and practical. It sort of acts as a self-selection mechanism. I know almost without fail that I will enjoy talking to anyone who "gets" it without me having to explain. I have a large body of experience using it, so I know it works. Let's just say I am not shocked you got it.  Wink
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RayChuang
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sat Apr 28, 2007 10:39 am

Combine this with the upgraded CFM56 engine core and we could see 8-14% fuel efficiency improvements without having to go to a new airframe for a 737 or A320 Family replacement. That could make the A320 Family viable for the next 25 years.
 
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sat Apr 28, 2007 10:53 am

Quoting RayChuang (Reply 19):
That could make the A320 Family viable for the next 25 years.

NO

The MX benefits of the construction methods used for the 787 make the 737RS unbeatable given that any existing engine could very well be used on the 737RS if it works on a A320. Not to mention the 737RS will be cheaper to make than the 737NG despite having more toys stuffed in it.

The A320 dies the day the 737RS enters service, the only question is how long does the body keep twitching.
 
keesje
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sun Apr 29, 2007 2:11 am

Quoting XT6Wagon (Reply 20):
Quoting RayChuang (Reply 19):
That could make the A320 Family viable for the next 25 years.

NO

The MX benefits of the construction methods used for the 787 make the 737RS unbeatable given that any existing engine could very well be used on the 737RS if it works on a A320. Not to mention the 737RS will be cheaper to make than the 737NG despite having more toys stuffed in it.

The A320 dies the day the 737RS enters service, the only question is how long does the body keep twitching.

XT6Wagon it seems a bit premature to present a non existing aircraft (not event sketches available) as a winner over another aircraft because of an unproven technology.
"Never mistake motion for action." Ernest Hemingway
 
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sun Apr 29, 2007 8:27 am

Quoting Dougloid (Reply 3):
One of our guys spent seven weeks in Tahiti on that show.

The horror.
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keesje
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Thu May 03, 2007 6:02 am

Bombardier recently with regards to their C-series:

“Now we’ve got until 2013, this fits in well with geared-turbofan technology. It also fits with Rolls-Royce which is thinking of a new engine and it fits with CFM as well.”

Scott says that Bombardier has been impressed by Pratt & Whitney’s geared turbofan, which has not been mirrored to date by its rivals.

“They’ve been working on this technology for a long time and it’s now matured to a point where we can put it on a new aircraft. It’s a very good option, but it’s not going unnoticed by Rolls-Royce and CFM.”


the pressure on the industry to come up with new smaller turbofan is increasing it seems..

[Edited 2007-05-02 23:36:41]
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sanjet
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Fri May 04, 2007 2:02 am

Quoting XT6Wagon (Reply 20):
NO

The MX benefits of the construction methods used for the 787 make the 737RS unbeatable given that any existing engine could very well be used on the 737RS if it works on a A320. Not to mention the 737RS will be cheaper to make than the 737NG despite having more toys stuffed in it.

The A320 dies the day the 737RS enters service, the only question is how long does the body keep twitching.

LOL thanks for the outlook XT6...  Embarrassment
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Boeing7E7
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sun May 06, 2007 4:01 pm

Going out on a limb here.... ie... Beta vs. VHS...

They all get together and develop an engine that combines all of their technologies in one way or another.
 
keesje
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Tue May 08, 2007 8:57 pm

Quoting Keesje (Thread starter):
Wonder how GE thinks about it.

CFM studies 'open rotor' concept for next generation airliner engine


CFM International is conducting preliminary studies of open rotor and other potential "game changing" architecture concepts for future narrowbody engines as part of its LEAP56 technology study, new details of which have just been revealed.

The open rotor concepts, one of which was revealed recently by CFM partner Snecma, include pusher, counter-rotating designs very similar to the General Electric GE36 unducted fan (UDF) study of the 1980s, as well as puller-type designs.

Both options, as well as a low-noise optimised counter-rotating fan study, would build on the foundations laid by LEAP56, says CFM. LEAP56 was launched in 2005 to develop the technical foundation for the next generation of CFM56 engines.


http://www.flightglobal.com/articles...-for-next-generation-airliner.html

New fan technology seems to be the core of next generation developments, probably enabled by new materials / production techniques an advanced fluid dynamics analyses.
"Never mistake motion for action." Ernest Hemingway
 
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Tue May 08, 2007 11:36 pm

Quoting Keesje (Reply 26):
New fan technology seems to be the core of next generation developments,

No pun intended?  Wink
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keesje
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Tue May 15, 2007 12:00 am

CFM is also studying different fan options. One off the problems with UDF es if I remember well the charaterictics of the noise it makes (irritating frequencies) and cooling of engine when the fan is aft positioned. http://www.flightglobal.com/articles...cfm-ready-for-narrowbody-leap.html



Meanwhile PW remains confident the GTF will prove superior option (as is another member here on a.net  Wink ) for the NB's. http://www.flightglobal.com/articles...fan-concept-has-the-edge-over.html
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Stitch
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Tue May 15, 2007 6:52 am

Both the GTF and LEAP56 programs appear to have the fuel savings needed to justify the launch of the 737RS and A320RS programs... And if the GTF can do that while hanging under an existing A320, that would give Airbus valuable "breathing room" and allow them to launch the A320E to "hold the fort" against the 737RS.
 
Strathpeffer
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Wed May 16, 2007 4:49 pm

I was really intersted to read the full article that includes this info in this week's printed FI.

http://www.flightglobal.com/articles...-for-next-generation-airliner.html

Back in the late 80s, when I was first getting hooked on aviation, UDF was THE buzzword for future propulsion. Between the UDF and the UHB geared ducted fans there were some pretty outlandish designs - many of which can been seen in the first edition of Gordon Swanborough's 'Modern Commercial Aircraft'.

As a generalisation, would it be fair to say that technical issues, huge improvements in turbofan technology and a gradual downward creep in the 'real' price of oil put pay to them?

For me, its really exciting that these concepts are being discussed again - twenty years after they were first mooted! I wonder if technological progression, especially with computerised blade design and airflow modelling, makes them more likely to be successful these days.

As I recall, noise was the most significant problem with the UDFs and I expect it will remain so - for this reason I think I will put my $5 on contra-rotating ducted fans.

PJ

[Edited 2007-05-16 09:52:39]
Another Technical Problem?
 
MarkC
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Thu May 17, 2007 10:36 am

The airframers are not ready for new tech engines now. They would rather keep selling their narrow body cash makers for the forseable future. An engine revolution does not benefit either A or B as the engines would be used on both, and both would incurr the expense of new or modified airframes to match.

The push will come from the operators. If airlines think they can get 10 or 15% from a GTF or other, they will camp out at the airframers doors for it. And I am guessing that is the plan.
 
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jetmech
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Thu May 17, 2007 1:30 pm

Quoting MarkC (Reply 31):

True, but I think a more realistic scenario would be Airbus or Boeing scrambling to get some sort of exclusivity deal with an engine maker that produces a significantly more fuel efficient design. It may cost the air-framers some money to develop and adapt new airframes for these engines ( plus any cost associated with an exclusivity deal ), but the almost guaranteed windfall from the airlines will be more than worth it.

Regards, JetMech
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XT6Wagon
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Fri May 18, 2007 2:14 pm

Quoting MarkC (Reply 31):
The airframers are not ready for new tech engines now

Wrong, Boeing wants to do the 737RS ASAP. They will produce the two side by side for a few years like they did with the 737 and 737NG so the "we would rather sell the old ones" argument is weak. More so since the 737RS will be CHEAPER to make. Airbus wants to do the A320 replacement now, but can't... so they want to get as much from the A320E as soon as possible.

Never mind the 737RS very likely can top 1000 orders in its first year. If allowed to WN alone would take 35-40 a year for a decade in their first firm order alone. Ryanair, and AA both would also be standing just behind WN. Just 3 airlines could pay off the program on "day 1" sales. Begs the question why anyone would claim that Boeing wants to wait. United is just one of the many converts to the A320 that Boeing wants to win back, and I've seen hints they they may be actively asking to be converted back.
 
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Stitch
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Sat May 19, 2007 1:41 am

Quoting MarkC (Reply 31):
The airframers are not ready for new tech engines now.

I depends on how that tech can be integrated into existing designs. P&W believe their GTF will fit under the wing of the current A320 family (but not the 737NG), so Airbus could adapt it to their existing plane with probably little effort.

I'm not sure how LEAP56 compares in dimensions to the current CFM engine hanging off the wings of A320 and 737NG family members so it may also be able to be fitted to current models.
 
thegeek
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Wed Jan 02, 2008 3:29 am

At the risk of reviving an old thread, wouldn't this result in effectively a two stage fan and a low bypass ratio? Wouldn't that be counter productive for fuel burn?
 
tdscanuck
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RE: Next Gen NB Engines : Contra Rotating Turbofan Fan

Wed Jan 02, 2008 5:56 am



Quoting Thegeek (Reply 35):
At the risk of reviving an old thread, wouldn't this result in effectively a two stage fan and a low bypass ratio? Wouldn't that be counter productive for fuel burn?

Having a two-stage fan doesn't automatically lower the bypass ratio...provided they lower the disk loading accordingly, they could hold the same bypass ratio and just put half as much power into each fan. Not sure how that improves fuel burn, but it's not a given that bypass ratio has to drop.

Tom.

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