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rotating14
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69 Inch Fan For The MAX

Fri May 18, 2012 12:47 am

http://seattletimes.nwsource.com/htm...echnology/2018232657_boeing18.html

Boeing has decided to go with the 69 inch fan and not the 68. Does this make a huge difference?? Thoughts
 
RickNRoll
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 12:49 am

Looks like they are wanting to increase weight and drag.
 
mffoda
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 1:00 am

It's actually 69.4" as reported by the WSJ... With no change to the NLG.
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Stitch
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 1:11 am

Quoting rotating14 (Thread starter):
Does this make a huge difference?

According to some, every inch counts.


Quoting RickNRoll (Reply 1):
Looks like they are wanting to increase weight and drag.

Ssh! You'll honk off the "fan size is magic" crowd.  
 
WarpSpeed
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 1:36 am

Shouldn't the focus be on By-Pass Ratio rather than fan diameter anyway? Larger Fan, Smaller core = more BPR.
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mffoda
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 1:48 am

Quoting WarpSpeed (Reply 4):
Shouldn't the focus be on By-Pass Ratio rather than fan diameter anyway? Larger Fan, Smaller core = more BPR.

Funny you should bring that up... On the Leeham website they're speculating (via Buckingham Research) that as well.

http://leehamnews.wordpress.com/2012...anges-to-the-cfm-leap-1b/#comments

Buckingham Research, citing Boeing at the investors’ day, wrote that Boeing talked about a 70 inch fan. Jon Ostrower–now at the Wall Street Journal–confirmed the larger fan, but at 69.4 inches (70 inches apparently was a rounded number) as well as pursuit of a smaller core.

The smaller core is important for two reasons: a larger fan and a smaller core provide for a higher by-pass ratio, increasing fuel burn reduction performance. The smaller core also enabled the engine to be mounted closer to the wing, which in turn means the previously announced 8 inch nose gear extension remains valid.
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Byrdluvs747
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 6:53 am

Boeing has had years to address this problem. They should have confronted the 737's design flaws the moment they decided not to green light a clean sheet Y1. How much recertification would be needed to increase the length of the rear landing gear?
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scouseflyer
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 7:40 am

Quoting Byrdluvs747 (Reply 6):
Boeing has had years to address this problem. They should have confronted the 737's design flaws the moment they decided not to green light a clean sheet Y1. How much recertification would be needed to increase the length of the rear landing gear?

Very large, they'd be looking at having to design one of the most complicated parts of the plane in the centre wing box and along with the wing changes to take the larger, heavier engines you're starting to look at a largley new plane along the lines of the 748 which increases costs ever further.
 
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BreninTW
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 7:46 am

Quoting Byrdluvs747 (Reply 6):
How much recertification would be needed to increase the length of the rear landing gear?

I believe there is also the complication that the 737 is right up against the limit that allows it to not have slides/rafts for the window exits. Any lengthening of the MLG would mean that Boeing has to add slides/rafts to the window exits of the 737.
 
sweair
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 8:43 am

Imo the NSA was the better way, they should have done a minimum reengine on the 737 and gone full ahead on the NSA. The 737s age is showing, as any upgrade is about compromises all the time.

Maybe its the huge blunder the 787 became that has scared Boeing into going the minimal route into the future. The 777NG is also the minimal way forward. Age will catch up to a frame eventually like it has on the 737 now.

Will we even see a new model done before 2030 at Boeing?
 
sweair
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 10:27 am

Quoting clydenairways (Reply 10):
According to some, every inch counts.

69 is a nice number...
 
murchmo
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 12:22 pm

Quoting sweair (Reply 9):

I would say its worth noting that Boeing clearly wanted a NSA. It's the airlines forcing them into these decisions.
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rheinwaldner
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 3:59 pm

Quoting Stitch (Reply 3):
According to some, every inch counts.

According to Boeing I would say. Nobody proves that point better than Boeing. Increasing the fan size multiple times despite the earlier claims, that the optimum for the 737 has truly been found.

Seems the earlier optimums for the MAX were not good enough... And...how can we be sure that this will be final?
 
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ODwyerPW
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 4:00 pm

Quoting RickNRoll (Reply 1):
Looks like they are wanting to increase weight and drag.

Thanks for putting the smile on our collective faces!

This is good news that they went for the 70inch fan (69.4). So different than the talk a year ago about 'settling' on a 66inch fan. They have spent the additional money (nosegear) to permit the engineers a bit more latitude to pursue higher efficiency.

Will be interesting to see if we get to keep the almost round nacelle inlets with this 1 1/2" increase of the previous 68". Or perhaps the renderings already accounted for the 70"?
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DocLightning
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 4:08 pm

Quoting murchmo (Reply 12):
I would say its worth noting that Boeing clearly wanted a NSA. It's the airlines forcing them into these decisions.

It was really Airbus forcing them into the decision. Boeing had wanted to wait for some newer technology to get a bit further down the pipeline, which would have allowed them to design a new airframe around the next generation of engines (whether GTF's, open rotors, or whatever else). Instead, Airbus launched the NEO. When this happened, Boeing's original intent had been to continue incremental improvements to the NG, but the airlines made it clear that this was not sufficiently competitive with the NEO. Having loyal customer AA place an order for NEO's must have stung like crazy.

A clean-sheet design would have meant that the result might have been incompatible with the next generation of engines. So what was left?

It's obvious that this is the last 737.
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Stitch
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 5:08 pm

Quoting rheinwaldner (Reply 13):
According to Boeing I would say. Nobody proves that point better than Boeing. Increasing the fan size multiple times despite the earlier claims, that the optimum for the 737 has truly been found.

Seems the earlier optimums for the MAX were not good enough... And...how can we be sure that this will be final?



If Boeing continuing to tweak the design as they move towards Firm Configuration makes the MAX that much more competitive with the neo, the only ones who will care are Airbus and the Airbus Aficionados.
 
roseflyer
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 5:13 pm

Quoting rheinwaldner (Reply 13):

According to Boeing I would say. Nobody proves that point better than Boeing. Increasing the fan size multiple times despite the earlier claims, that the optimum for the 737 has truly been found.

Seems the earlier optimums for the MAX were not good enough... And...how can we be sure that this will be final?

The article does a very good job of answering that question. Of course every inch counts! Too large is too much weight and drag, and additional airframe modifications. Too small is opportunity left for improvements in propulsion efficiency. Where the final number ends up is based on very thorough analysis and it is engineers with a PhDs making those determinations.

http://seattletimes.nwsource.com/htm...echnology/2018232657_boeing18.html

A bigger fan produces more efficient propulsion. On the negative side, it also adds weight and drag. Engineers must come up with the optimal engine size to produce the greatest overall benefit to the airplane.

Penning said 69 inches is "looking like the best balance of weight, drag and performance."

However, on fan size, Airbus insists that bigger is better. Its executives argue that Boeing simply can't make the 737 MAX fan as big as it would like because the jet sits lower to the ground than the Airbus A320 and there isn't enough clearance to fit a bigger fan.

...

Some in the industry have speculated that, because of the ground-clearance limitation on fan size, Boeing is struggling to come up with a design that will match the fuel efficiency of the Airbus neo.

But in a note to clients Wednesday, Richard Safran, aerospace analyst with Buckingham Research Group, wrote that "the revised engine fan size has more to do with optimizing the engine than a means to overcome performance deficiencies."

And Scott Hamilton, industry analyst with Leeham.net, said that with the MAX still five years away from entry into service, "Boeing is doing what it ought to be doing in trying to get every little advantage out of its redesign."
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sweair
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 5:15 pm

How long will they keep the NSA on the back burner?
 
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ODwyerPW
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 5:18 pm

Quoting rheinwaldner (Reply 13):
According to Boeing I would say. Nobody proves that point better than Boeing. Increasing the fan size multiple times despite the earlier claims, that the optimum for the 737 has truly been found.

I don't think the word 'Truly' was ever used. There has been no design freeze. Of course, we cannot be sure that 69.4" is final, until they freeze the design. We may see further tweaks. The key is implementing improvements that don't substantially raise the overall costs, negatively impacting Boeing's total Value proposition for the MAX.

Who cares? I enjoy seeing the NEO and MAX both getting better!
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Revelation
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 5:21 pm

Quoting rheinwaldner (Reply 13):
Increasing the fan size multiple times despite the earlier claims, that the optimum for the 737 has truly been found.

  

Just last month Boeing's Jim Albaugh explicitly said that the number was still being investigated and won't be firm till the end of the year:

Quote:

CFM has initially sized the engine with a 1.74m-wide fan, but the precise dimensions could change before the design is frozen in the fourth quarter.


Ref: http://www.flightglobal.com/news/art...-other-details-for-737-max-370602/

Don't be surprised if it changes yet again.
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lightsaber
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 5:49 pm

Quoting mffoda (Reply 2):
It's actually 69.4" as reported by the WSJ... With no change to the NLG.

It sounds like a slight move of the engine enabled by the *small* core shrink.

Quoting Stitch (Reply 15):
If Boeing continuing to tweak the design as they move towards Firm Configuration makes the MAX that much more competitive with the neo, the only ones who will care are Airbus and the Airbus Aficionados.

Boeing's engineers are doing a good job. This will help.

Any rumors/PR on if the LEAP will receive a variable nozzle for the fan? That should help 1.5% or so. The cruise efficiency does not have to be compromised for takeoff and climb stall margins. Note: I normally quote 2%, but I'm SWAGging that engine/wing interactions might limit the benefit.

Quoting Roseflyer (Reply 16):
Too large is too much weight and drag

Due to technological improvements, the MAX is not there. The larger the fan diameter, the longer the mission the MAX will be optimized for as a larger fan does add weight and nacelle drag (plus engine/wing interaction drag for the 737), but it also improves cruise propulsion efficiency. The LEAP is not yet at a diameter that is severely impacting cruise fuel burn (from a fan diameter engine aerodynamics standpoint that ignores weight and external drag).

Quoting Roseflyer (Reply 16):
http://seattletimes.nwsource.com/htm...echnology/2018232657_boeing18.html
"Some in the industry have speculated that, because of the ground-clearance limitation on fan size, Boeing is struggling to come up with a design that will match the fuel efficiency of the Airbus neo."

This will help with engine performance. I keep hearing of little improvements here and there (no links, this is from my rumor mill) that will also help the 737. It isn't that Airbus isn't doing the same thing, it is juts that the A350 and other projects are distracting them more. Boeing is about one year away from releasing engineers from the 748 to help with the 737 too... (Note: My estimate, my rumor mill refuses to give me any such proprietary schedule information right now.)

Lightsaber
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 7:30 pm

Quoting lightsaber (Reply 20):
It sounds like a slight move of the engine enabled by the *small* core shrink.

Right. The Leeham article just says "pursuit of a smaller core" without saying anything about how much smaller. What would the tradeoffs be? Meaning, at what point does improved performance via less weight and more bypass ratio overtake the cost hit to CFM of having two different sized cores?

From what I've read in the usual public sources, Boeing seems to be more public than CFM is about how different the Leap 1B is from the other variants.

In looking for more info, I ran into this cat-fight between PW and GE over use of CMC vs use of advanced cooling systems:

Quote:

P&W's approach on the geared turbofan introduces no new materials, but adds an all-new "super cooling" system to keep the geared turbofan's metallic turbine blades below melting temperatures.

"Cooling air is still the best way to increase turbine inlet temperature," P&W's Adams says.

Adams concedes that rising core temperatures will eventually force cooling systems to become more sophisticated in the absence of advanced materials. Instead of simply piping the air straight into the turbine, the coolant itself will have to be cooled. This means the extracted air first must be routed outside of the engine core and through heat exchangers, then returned to the core and down into the hottest section of the turbine.

For GE, such an approach seems too risky.

"For a commercial application such as the Leap we don't need to use the additional complexity of active cooling when we have a superior material solution at hand," Carlson says.

But the readiness for CMCs for all but the most benign environments in the engine core is still debated. CMCs have been studied since the mid-1980s in the US by NASA, and finally introduced in stator vanes of the third-stage low pressure turbine of GE's now-cancelled F136 fighter engine.

But CMCs have been slow to enter commercial production because of the high cost of manufacturing and questions about the reliability of the material in operational service. P&W's Adams estimates that CMCs still cost between 10 to 100 times more to manufacture than conventional materials. Moreover, Adams says, GE may be forced to use CMCs because the company lacks the advanced cooling technology developed within P&W.

Carlson responds that GE has resolved the problems that prevent P&W from immediately applying the new material.

"What Pratt & Whitney doesn't have is access to our trade secrets and proprietary information in how we design and build CMC parts," Carlson says. "It's quite a unique process and we've figured out how to do this."

Ref: http://www.flightglobal.com/news/art...-technology-for-cfm-engine-371586/

Interesting times ahead!
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flylku
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 7:37 pm

In what part of the flight envelope does a larger fan generate more drag?
...are we there yet?
 
Airboe
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 9:13 pm

Boeing has previously stated they could not go beyond 68.4 inches without major and costly structural changes.

But - voila - now they can, - now the new sweet spot appears to be 69.4 inches.

I think is is pure magic how they succeed in finding another new sweet spot one time after another.
I guess they have received some magical help from poor Harry Potter, I do not hope Mr Voldemort is hiding in the wardrobe.

Expect to see first flight in 2016 - late.   
keep it free of the propellers
 
CM
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 9:24 pm

Quoting airboe (Reply 23):
Boeing has previously stated they could not go beyond 68.4 inches without major and costly structural changes.

I'm pretty sure you made this up... Source?
 
tdscanuck
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 9:25 pm

Quoting lightsaber (Reply 20):
Any rumors/PR on if the LEAP will receive a variable nozzle for the fan?

The 737 ecoDemonstrator (CFM56-7 engines) will test variable area fan nozzles...I won't be at all surprised if they show up on the MAX:
http://atwonline.com/eco-aviation/ar...g-commits-737-ecodemonstrator-0624

Quoting flylku (Reply 22):
In what part of the flight envelope does a larger fan generate more drag?

All of them. Bigger frontal area, same drag coefficient = more drag.

Tom.
 
ikramerica
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 9:48 pm

Quoting airboe (Reply 23):
Boeing has previously stated they could not go beyond 68.4 inches without major and costly structural changes.

But - voila - now they can, - now the new sweet spot appears to be 69.4 inches.

For every 0.5 shrink in Core Radius, that's 1" increase in Fan Diameter assuming the full shift can be accommodated in front of the wing.

While nothing is linear, a linear calc becomes a massive improvement in BPR, as much as an additional +1. If BPR was 9 at 68.4, it could be as much as 10-10.5 at 69.4. Question is how hot this core will be and if it's smaller size reduces efficiency, offsetting the BPR gain.
Of all the things to worry about... the Wookie has no pants.
 
Airboe
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 9:55 pm

Quoting CM (Reply 24):
m pretty sure you made this up... Source?
http://www.flightglobal.com/news/art...ne-fan-size-options-to-two-361438/

Actually the sweet spot in the late summer of 2011 apears to be 66 inches.

"What we're trying to do is optimse the integrated design of the airplane and we believe the sweet spot for that integrated design solution is going to be 66 or 68 inches."

"We have that built into our reserve for the development of this programme and we have it built into the reserve for the schedule," he said of the 173cm fan.

"Clearly with the heavier engine, you'll have to do some changes to the wing, some changes to the side of body join, some localised stiffening of the airplane," said Albaugh.

If the fan diameter will increase with the same speed the next year or two, the landing gear will be so long I will look like a ostrich.
keep it free of the propellers
 
PITingres
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 10:16 pm

Quoting airboe (Reply 27):
http://www.flightglobal.com/news/art...ne-fan-size-options-to-two-361438/

Which nowhere that I can find says what you claimed:

Quoting airboe (Reply 23):
Boeing has previously stated they could not go beyond 68.4 inches without major and costly structural changes.

Unless you are claiming that lengthening the nose gear is a "major and costly structural change" (which claim would be incorrect anyway).

Accuracy in reading, please!
Fly, you fools! Fly!
 
Airboe
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 10:29 pm

Quoting PITingres (Reply 28):
Unless you are claiming that lengthening the nose gear is a "major and costly structural change"

I would gladly clarify: Very costly, very-very costly:

http://www.flightglobal.com/news/art...ined-737-fan-size-decision-361001/


A design shelved earlier this year, designated the 737RE, featured a 177cm (70in) fan, which required an 8in nose gear extension to meet the required 43cm (17in) engine nacelle ground clearance to avoid hitting taxiway lighting.
....
The 737 could have accommodated up to a 170cm (67in) fan before requiring any changes to the landing gear.

According to that now-defunct plan, the longer nose landing gear would have prompted a redesign in the lower lobe of the forward 41 section, requiring Boeing to modify the electrical equipment (EE) bay to find new routing for wiring and equipment racks.




End of story for me.

Edited: Typo


[Edited 2012-05-18 15:40:38]
keep it free of the propellers
 
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lightsaber
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 10:42 pm

Quoting Revelation (Reply 21):
What would the tradeoffs be? Meaning, at what point does improved performance via less weight and more bypass ratio overtake the cost hit to CFM of having two different sized cores?

It is a decision to have one core with 99% of the parts common (fuel injectors and a few other parts never are common due to variations in case diameter) or not. Once GE committed to even a fractionally different core, they committed to a separate set of logistics as once the core is shrunk, that is new rotors, shafts, blades, etc... Some might be left common (e.g., bearings) or re-engineered depending on the degree of the shrink. Certain features won't change (e.g., oil flow path from the oil coolers to the bearings will be left as unchanged as possible, how the rotors 'spin cooling air' through the engine will not fundamentally change, etc.) But as soon as the blades differ, the hubs must have different 'fir trees' to prevent one part from going into the wrong engine.

So it is either a common core or two sizes. Sometimes the decision is a family of cores: PW1200 and 1500 have one core while the 1100 and 1400 share the larger core. In this case, the 'sole source' option on the 737 motivates GE to be willing to spend the billions (yes, billions), to have another core. However, by being sole source, GE makes about another $600k to $800k *per engine!* If Boeing is really at 1,000 frames (2,000 engines) in un-announced sales as I've heard rumors of, than GE has already broken even on customizing the core and thus eliminating IAE (or Pratt) off the airframe.

It should even be enough of a difference that Boeing will come out ahead in the long term too. (Due to the custom core allowing the larger fan diameter that will reduce 737MAX fuel burn perhaps 0.7% (my SWAG).

So the decision must be A320NEO core or a new core. Once that decision is made (a multi-billion dollar decision), than it is best to optimize the core for the airframe. The other alternative was for Boeing to declare "not good enough for an exclusive" and let IAE/Pratt devour GE's profits. As I already noted, I believe the 737MAX has already hit breakeven for GE to customize the core by avoiding the competition.

Now Boeing has to find other ways to cut fuel burn (weight, the new winglets, new tailcone, I suspect wing/body fairings, and perhaps something else?).

Quoting tdscanuck (Reply 25):
The 737 ecoDemonstrator (CFM56-7 engines) will test variable area fan nozzles...I won't be at all surprised if they show up on the MAX:

Good to hear. IMHO, a variable nozzle is 'low hanging fruit.' Normally, the trend is to justify adding technology into an engine. However if GE knows anything about the GTF flight testing (trust me, they know a bit...), then they know this is a "must have" and GE knows how to do this from their military nozzles (albeit, it must be done much simpler for a commercial engine, hence why only the fan variable nozzle is 'low hanging fruit' today. A core variable nozzle adds more maintenance than is economical right now... give it a few years.)

Quoting airboe (Reply 27):
"What we're trying to do is optimse the integrated design of the airplane and we believe the sweet spot for that integrated design solution is going to be 66 or 68 inches."

That was based on the prior core. With a new core customized, the engine is able to be moved a little allowing a slightly larger core. If the variables are opened, the optimal engine size changes. If the 737 had tall landing gear, the optimum engine would be in the 76" to 79" range (my best guess). So we're discussing engine size compromised by the short gear.

Lightsaber
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aerokiwi
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 11:31 pm

The forward landing gear extension has now gone from 6 inches to 8 inches. Does this mean the MAX will lose its nose-down attitude on the ground? The NGs noticeably had this whereas the Classics appeared largely "flat".

Just an aesthetic point really, but I can't get a sense of this from any of the images I've seen so far.
 
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RE: 69 Inch Fan For The MAX

Fri May 18, 2012 11:38 pm

Quoting lightsaber (Reply 30):
So the decision must be A320NEO core or a new core. Once that decision is made (a multi-billion dollar decision), than it is best to optimize the core for the airframe.

Clearly CFM would be able to make even more money if they could make one core work, but...

Quoting lightsaber (Reply 30):
The other alternative was for Boeing to declare "not good enough for an exclusive" and let IAE/Pratt devour GE's profits

... it seems Boeing has been all over CFM to pull out all the stops, including use of CMCs as described above, and they of course have loads of leverage.

Quoting lightsaber (Reply 30):
As I already noted, I believe the 737MAX has already hit breakeven for GE to customize the core by avoiding the competition.

Yes, all things considered it does pay for CFM to do it, but as above, they'd make even more money if they could get away with just one core.
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ikramerica
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RE: 69 Inch Fan For The MAX

Sat May 19, 2012 12:15 am

Quoting airboe (Reply 27):
If the fan diameter will increase with the same speed the next year or two, the landing gear will be so long I will look like a ostrich.

You quoted something but didn't seem to understand it. They found 68" (68.4") would be the optimal in that it allows for a larger fan without overdoing the cost of adjusting the structure of the aircraft.

Since that time, they have NOT changed that view. What has changed is that they were able to get CFM to alter their engine design so they could physically lift the engine core up .5", allowing for an additional 1" diameter of fan without impacting their structural limitations.

It's really quite clear. Not sure why so many people are having trouble with this.

Boeing has not said and will never say that they wouldn't welcome an even larger fan. What they have said is that the design adjustments they have made to the rest of the aircraft are optimized on that 68" fan size. Working with CFM, they were able to get a bit larger fan in the mean time, but not through changes to the 737 itself.
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lightsaber
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RE: 69 Inch Fan For The MAX

Sat May 19, 2012 1:10 am

Quoting Revelation (Reply 32):
Yes, all things considered it does pay for CFM to do it, but as above, they'd make even more money if they could get away with just one core.

Agreed. But by having a more competitive airframe, it will have a longer sales life. I'm not sure which case would have the higher ROI. I can see justification for both. But Boeing would have been silly to not 'put on the pressure' and the result is a better engine for the 737MAX.

Quoting ikramerica (Reply 33):
What has changed is that they were able to get CFM to alter their engine design so they could physically lift the engine core up .5", allowing for an additional 1" diameter of fan without impacting their structural limitations.

Nicely said. Thank you. Changing the core changed the optimal engine position and thus optimal fan diameter.

Lightsaber
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CM
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RE: 69 Inch Fan For The MAX

Sat May 19, 2012 1:37 am

Quoting airboe (Reply 27):
If the fan diameter will increase with the same speed the next year or two, the landing gear will be so long I will look like a ostrich.

You are under the incorrect assumption that each increase in fan diameter requires a new increase in landing gear length. This is simply not the case. The nose landing gear was extended 8" last year in order to give CFM and Boeing engineers the design space to work with larger fan diameters - up to 70". When this change happened, Boeing immediately announced they would increase the fan diameter to 68.4", which was a sweet spot for the previously defined core.

Quoting airboe (Reply 29):
According to that now-defunct plan, the longer nose landing gear would have prompted a redesign in the lower lobe of the forward 41 section, requiring Boeing to modify the electrical equipment (EE) bay to find new routing for wiring and equipment racks.

This is not how the landing gear extension was accomplished. Boeing has left the gear trunnion location alone and has grown the gear forward (in the retracted position) rather than aft. This has permitted the gear extension while leaving the E/E bay untouched.

Quoting aerokiwi (Reply 31):
Does this mean the MAX will lose its nose-down attitude on the ground?

Yes. It will sit relatively parallel with the ground after the nosegear extension.

Quoting ikramerica (Reply 33):
Since that time, they have NOT changed that view. What has changed is that they were able to get CFM to alter their engine design so they could physically lift the engine core up .5", allowing for an additional 1" diameter of fan without impacting their structural limitations.

  

Quoting RickNRoll (Reply 1):
Looks like they are wanting to increase weight and drag.

  

The new core is smaller, not only increasing bypass ratio, but decreasing engine weight. Furthermore, it appears Boeing has fit the added fan diameter within the currently defined nacelle, meaning this fan diameter increase has been achieved with no added drag - probably an indication they knew when they took the current nacelle lines into the wind tunnel, they had a pretty good idea the fan diameter was going to grow. I suspect the delay was because it took CFM a while to define a fan/core optimized for the 737 thrust levels and wing height. Regardless, the end result is a lighter engine with higher BPR and no change to drag or the basic airplane architecture. Together it means this change should pay off handsomely for the MAX.
 
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kanban
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RE: 69 Inch Fan For The MAX

Sat May 19, 2012 3:02 am

Quoting tdscanuck (Reply 25):
Bigger frontal area, same drag coefficient = more drag.

Tom,
is there any chance they found a way to reduce the nacelle thickness by rearranging some of the engine support hardware tubing and ducting allowing for a larger fan but no nacelle diameter increase?
 
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lightsaber
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RE: 69 Inch Fan For The MAX

Sat May 19, 2012 4:37 am

Quoting kanban (Reply 36):
is there any chance they found a way to reduce the nacelle thickness by rearranging some of the engine support hardware tubing and ducting allowing for a larger fan but no nacelle diameter increase?

Possible, but the nacelle thickness is more for aerodynamic shape.

Most people only see the metal of the nacelle. For example, the nozzle for the air exiting the engine. By shaping the nacelle, one can have an effective different nozzle at takeoff and a better nozzle shape for cruise by taking advantage of the compressible properties of air flowing over the nacelle. While a bigger fan could be used, it gives up propulsion efficiency by not having as variable of nozzle properties. Or one could go with a mechanical variable nozzle... but the outer aerodynamics still play a role. There is a point where a thinner nacelle would actually increase fuel burn.  

Note: I'm an aerodynamic engineer by training. I'll let Tom (or someone else) talk to the structure.

Lightsaber
"They did not know it was impossible, so they did it!" - Mark Twain
 
tdscanuck
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RE: 69 Inch Fan For The MAX

Sat May 19, 2012 4:59 am

Quoting kanban (Reply 36):
Tom,
is there any chance they found a way to reduce the nacelle thickness by rearranging some of the engine support hardware tubing and ducting allowing for a larger fan but no nacelle diameter increase?

It's possible but, like lightsaber said, there's more going on than just nacelle thickness. The 787 has a significantly *thicker* nacelle (larger radii on the leading edge) as a price for getting natural laminar flow over more of the nacelle. Boeing obviously thought it was worth the trade.

I was thinking earlier today that I suspect CFM is working hard to take everything off the bottom of the engine that they can so that they can get maximum clearance. Normally you've got at least a few inches of wire harnesses, drain tubes, etc. wrapping around the bottom and, in this game of fractions of an inch of clearance, that might be a big win.

Quoting lightsaber (Reply 37):
I'll let Tom (or someone else) talk to the structure.

I freakin' hate nacelle structure. I did nacelle structural repair design for a couple of years; it's a thankless task and a very tough design problem because nobody wants to spend any weight (more than usual) on non-primary structure but it's strapped to the engine where it gets vibrated and heated and cooled to heck and it's a magnet for ramp rash. It's basically the worst intersection of abusive environment and low-margin design on the entire aircraft, except maybe the APU exhaust. And you've usually got three or four vendors all coming together in a very tight space (engine, nacelle, engine mount, and strut).

Tom.
 
PlanesNTrains
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RE: 69 Inch Fan For The MAX

Sat May 19, 2012 5:11 am

Quoting ikramerica (Reply 33):
It's really quite clear. Not sure why so many people are having trouble with this.

"Having trouble" or "creating trouble"? Seriously, in this and a few other MAX threads, it appears to be the latter.

-Dave
-Dave
 
astuteman
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RE: 69 Inch Fan For The MAX

Sat May 19, 2012 6:49 am

Quoting lightsaber (Reply 30):
So the decision must be A320NEO core or a new core

I'm not sure I'm following this to be honest.

There seems to be a bit of "Boeing's MAX will get the "fancy new Leap-X core", whilst Airbus (and COMAC) will be left with the "old dogs dinner one" going on here.

I can't for the life of me see why CFM won't back-fit as many of the improvements as the can into the whole Leap-X range, to restore as much commonality as they possibly can......

I don't feel that it's anything liks as black-and-white as "either/or".
I remain to be educated though

Rgds
 
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RE: 69 Inch Fan For The MAX

Sat May 19, 2012 7:39 am

Quoting astuteman (Reply 40):
There seems to be a bit of "Boeing's MAX will get the "fancy new Leap-X core", whilst Airbus (and COMAC) will be left with the "old dogs dinner one" going on here.

I can't for the life of me see why CFM won't back-fit as many of the improvements as the can into the whole Leap-X range, to restore as much commonality as they possibly can......

I didn't really see much of the A320NEO leap-x will suck compared to the 737MAX leap-x here, but I think some people are reading too much into the "new" core bit. I'm sure you will be correct that CFM will continue its practice of updating the A320 and 737 in alternating fashion. So the bits that work well and pay thier way onto the A320 will get there in a few years along with new shiny ideas, materials, and other advances not on the MAX engine.

The interesting question will be if any of the other programs using the Leap-X will use this smaller core now that its "paid for" by the thousands of units needed by the 737.
 
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RE: 69 Inch Fan For The MAX

Sat May 19, 2012 9:17 am

Quoting ikramerica (Reply 26):
For every 0.5 shrink in Core Radius, that's 1" increase in Fan Diameter assuming the full shift can be accommodated in front of the wing.
Quoting ikramerica (Reply 33):
You quoted something but didn't seem to understand it. They found 68" (68.4") would be the optimal in that it allows for a larger fan without overdoing the cost of adjusting the structure of the aircraft.
Quoting CM (Reply 35):
You are under the incorrect assumption that each increase in fan diameter requires a new increase in landing gear length. This is simply not the case. The nose landing gear was extended 8" last year in order to give CFM and Boeing engineers the design space to work with larger fan diameters - up to 70". When this change happened, Boeing immediately announced they would increase the fan diameter to 68.4", which was a sweet spot for the previously defined core.

I understand that very well.
What you fail to understand is, that I am quoting Boeing statements - about 9 month old.

9 month ago, it was Boeings assumption that 1 inch bigger fan, was the same as 1 inch bigger engine pylon, and (more or less) one inch longer landing gear.
But now - voila - they can make the core smaller, or they can to this or that. And it is all very costly, - and making the core smaller is also a risk.

And why do they do it? Of course, because the fuel consumption not is where they want it to be.
The engine simply can't deliver the fuel consumption they expected.

They are in the same situation as Airbus was, when they hang a couple of new engines under the A330 and called it the A350 - and only a very few bought it.

And it is painful to see.

The Boeing guys has always been good at talking, but when it comes to fuel consumption you can measure it very it very precisely, and then the talking must come to an end. They are trying to get there with a minimum of investment, but the bill is just getting longer and longer.
Just as it did with the 787 - and the 748.


Will they reach the goal? Probably, but with a must larger investment than they assumed a year ago, - meaning we are going to live with the 737MAX much longer than 2020.

+
keep it free of the propellers
 
RickNRoll
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RE: 69 Inch Fan For The MAX

Sat May 19, 2012 11:08 am

Quoting airboe (Reply 42):
And why do they do it? Of course, because the fuel consumption not is where they want it to be.
The engine simply can't deliver the fuel consumption they expected.

I think everyone knew that, but more a case of what they wanted than expected. They have been since been working hard at making sure they meet what they want. Both companies put on their bravest face when they make announcements, then, like a duck, are paddling as hard as they can underwater to get it to happen.
 
Oykie
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RE: 69 Inch Fan For The MAX

Sat May 19, 2012 11:09 am

Quoting lightsaber (Reply 30):
fan variable nozzle is 'low hanging fruit' today.

In what stages of flight will this improve fuelburn? During climb or cruise? Or both? Will this help performance on shorter routes than longer?

Quoting astuteman (Reply 40):

I can't for the life of me see why CFM won't back-fit as many of the improvements as the can into the whole Leap-X range, to restore as much commonality as they possibly can......

I am sure they will try to incorporate as many improvements on the whole range. When CFM launched their CFM56-7BE, they offered a similar update for the CFM56-5B engine. I am unsure if the Evolution design has flown on the -5B yet, or if it is still pending.

Quoting XT6Wagon (Reply 41):
The interesting question will be if any of the other programs using the Leap-X will use this smaller core now that its "paid for" by the thousands of units needed by the 737.

I wonder how much of the core would find its way to the next gen E-jet? I know that they have not decided on an engine, but I am sure this tweaking done by GE will help their case for the NG E-Jet. The GE CF34-10E is derived from the CFM 56 engine.

Quoting airboe (Reply 42):
The engine simply can't deliver the fuel consumption they expected.

The performance improvements for the MAX has not been idle. It is slowly improving and the improvement target has increased since the launch last year. Maybe they do know how to design improvements after all? It seems a good strategy to start of with modest design goals and then exeed them, rather than the other way around.
Dream no small dream; it lacks magic. Dream large, then go make that dream real - Donald Douglas
 
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par13del
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RE: 69 Inch Fan For The MAX

Sat May 19, 2012 12:02 pm

Quoting airboe (Reply 42):
9 month ago, it was Boeings assumption that 1 inch bigger fan, was the same as 1 inch bigger engine pylon, and (more or less) one inch longer landing gear.

If a non engineer can weigh in, you are correct Boeing settled on the inch longer gear to accomodate the fan.

Quoting airboe (Reply 42):
But now - voila - they can make the core smaller, or they can to this or that. And it is all very costly, - and making the core smaller is also a risk.

Also correct, but you seem to think the voila is Boeing, it is not, it is the engine makers. My read on the article and the a.net experts who have weighed in is that the engine makers have shrunk the engine core more than Boeing initially expected, what that has meant is that the engine will be lighter, thus creating additional efficiencies which they can accept as if, modify the fan size to take advantage of the lower weight etc etc etc.
 
PlanesNTrains
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RE: 69 Inch Fan For The MAX

Sat May 19, 2012 1:43 pm

Quoting airboe (Reply 42):
They are in the same situation as Airbus was, when they hang a couple of new engines under the A330 and called it the A350 - and only a very few bought it.

No. The A350 was up against a new build frame. The MAX is up against another re-engine, albeit a very compelling one.

-Dave
-Dave
 
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Revelation
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RE: 69 Inch Fan For The MAX

Sat May 19, 2012 2:11 pm

Quoting airboe (Reply 42):
And why do they do it? Of course, because the fuel consumption not is where they want it to be.
The engine simply can't deliver the fuel consumption they expected.

IMHO your logic is flawed.

First of all you have no idea what Boeing promised the customers so you have no idea if the engine is hitting the fuel consumption target they expected and/or needed.

Secondly, you have no way of knowing if they are missing targets elsewhere (structures, aerodynamics, etc) and need to get more out of the engine.

Thirdly, why wouldn't Boeing go beyond whatever goal they initially set if that doesn't change the development cost much? Right now the design is still open, and it's in Boeing's and CFM's best interest to make the product as good as possible, no?

Bottom line to me is that Boeing had a lot of focus elsewhere (NSA) but now they have lots of resources dedicated to MAX, and now have a lot of liberty to tinker with it, and that's what's happening.

Clearly the cheapest thing to do would have been to reuse the LEAP-1A, but the MAX application is different than the NEO (in both beneficial and detrimental ways), and the market is big enough for CFM to do the LEAP-1B and optimize it for the MAX, and that's exactly what's happening.

I have no idea why a.net goes nuts when Boeing changes the fan size. The further Boeing goes on the MAX project, the more they learn, so the optimal point can and is shifting, and wil continue to do so. Keep in mind Airbus is still tinkering with the A380 and Boeing is still tinkering with the 787 years after protoypes first flew, and fuel burn of the 737NG improved several percentage points over its production run.

Right now GE may be adding or subtracting hundreds of degrees of temperature from the hot section, or finding it has to radically change the way it cools the hot section (see above), and that would cause way more impact than adding an inch to the fan, yet because it doesn't affect the size of the fan, a.net is blissfully unaware.
Inspiration, move me brightly!
 
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Stitch
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RE: 69 Inch Fan For The MAX

Sat May 19, 2012 2:12 pm

Quoting astuteman (Reply 40):
I'm not sure I'm following this to be honest.

There seems to be a bit of "Boeing's MAX will get the "fancy new Leap-X core", whilst Airbus (and COMAC) will be left with the "old dogs dinner one" going on here.

As I read it, enough units of the LEAP-X1B will be sold to justify giving it a core optimized for a 69" fan as opposed to using the core of the LEAP-X1A, which is optimized for a 78" fan.

And that making the decision to use a core optimized for the 68" fan, this will create a core for the X1B that could run hotter and harder than the core of the X1A. And to that end, CFM will make some changes to materials to address that - material changes not necessary for the X1A engine.

And having a later EIS than the X1A, CFM could introduce some items on the X1B not available or ready when the X1A first enters service. Such items may be retrofittable to an X1A via PiP or could be slipstreamed into later X1A builds.

So not a case of CFM crippling the X1A core (which is ludicrous since they're competing with the GTF on the A320neo), but instead a case of making both engines the best they can be for their respective airframes, but not needlessly adding complexity and cost to the X1A core if it doesn't need it (where the X1B core might).
 
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kanban
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RE: 69 Inch Fan For The MAX

Sat May 19, 2012 4:27 pm

Quoting tdscanuck (Reply 38):
I suspect CFM is working hard to take everything off the bottom of the engine that they can so that they can get maximum clearance. Normally you've got at least a few inches of wire harnesses, drain tubes, etc. wrapping around the bottom and, in this game of fractions of an inch of clearance, that might be a big win
Quoting lightsaber (Reply 37):
Possible, but the nacelle thickness is more for aerodynamic shape.

Thanks.. both of you.. yes that is a cramped place..supported both spares and engine build up at different times...

so could they be looking a flatter lower lip?

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