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MAX / NEO Engine Optimization Issues?  
User currently offlinemffoda From United States of America, joined Apr 2010, 1083 posts, RR: 0
Posted (2 years 4 months 4 weeks 2 hours ago) and read 3931 times:

Engine optimization issues?

There’s been a lot discussed on the subject of engine optimization, particularly regarding the MAX/NEO. While there have been some very excellent posts from our engine guru’s, (lightsaber and others) there have also been a lot of negative posts by those who portray their opinions as fact. Anyway, it got me to thinking about other factors beside fan diameter.

For example: If we look at the 787 and its engine options the GEnx and RR T-1000. We can see the similarities as well as the differences.

GEnx: 111 inch fan dia., Dry weight = 12,822 lbs. & BPR 9.5 :1.
T1000: 112 inch fan dia., Dry weight = 12,710 lbs. & BPR 11 :1.

While these numbers might not be exact. They do show that while similar in weight and fan dia. They are clearly different in BPR.

Next, if we look at the spec fuel miss (approx. 3%) by both engines at EIS. Both engines have PIP (or package ABC in RR case) programs. With GE’s PIP2 expected to recover the balance of the shortfall in early 2013 (certification starts Jun/Jul 12). And RR package B to recover most (still 1% shortfall) by early 2013 and the remainder with package C by the end of 2013 (earliest).

My observation is:

Despite the T-1000’s slightly larger fan dia., lower weight and significant BPR advantage?? The two engines will still be just on par with each other.

***The next thing that comes to mind is the NEO’s engine options?

While it has been argued that the MAX is “Compromised” because of its wing to ground ratio (can’t fit larger fan). That is not the case for the NEO. Yet, the GTF has a 81” fan and the Leap-1A has a 78” fan (originally 76”). Many have speculated that the GTF will provide better sfc then the Leap? There was obviously something to it because the Leap-1A grew by 2”. And still some believe the GTF will still provide better sfc.

The obvious question is:

If the NEO is unencumbered by the 81” GTF, why not have an 81” Leap-1A if the simple answer were 1"=.5% sfc?? Since it is frequently argued that the fan dia. and BPR are the “be all, end all” of the conversation. It would seem that CFMI is leaving some low hanging fruit.

***Which brings me to engine optimization…

But, before we do. Let’s look at NEO/MAX engines as we now know them.

And as I stated above, I’d like to consider other factors besides Fan dia. & BPR.

GTF = 81” fan, BPR 12:1? and installed thrust of 24k – 33k. (9k range).
Leap-1A = 78” fan, BPR 10:1? and installed thrust of 24k – 33k. (9k range).
Leap-1B = 69.4” fan, BPR Unk? and installed thrust of 26.3k – 27.3k. (1k range).

It occurs to me that this installed thrust range may tell us part of the story?

If we just use the Leap’s as an example, the 24k A319neo is carrying the same Fan and Core that the 33k A321neo is. Which brings the question, which NEO is the core optimized for? The MAX family is covering a range of just 1K of thrust between the models.

I may be wrong, but optimizing the Leap-1B core would seem to be an easier task then on the Leap-1A. Since it does not have to scale very far between applications.

Anyway, just some thoughts I had… Perhaps others have something to add?

Regards,


harder than woodpecker lips...
9 replies: All unread, jump to last
 
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 1, posted (2 years 4 months 4 weeks 2 hours ago) and read 3908 times:

Quoting mffoda (Thread starter):
My observation is:

Despite the T-1000’s slightly larger fan dia., lower weight and significant BPR advantage?? The two engines will still be just on par with each other.

There's a very important caveat here...the engine spec's are not necessarily the same. A 1% shortfall on a GEnX does not necessarily give you the same tsfc as a 1% shortfall on the T1000.

The engines are, though, on par with each other for total cost of ownership. They have to be or the sales would be far more lopsided than they are.

Quoting mffoda (Thread starter):
Anyway, it got me to thinking about other factors beside fan diameter.

We need to let fan diameter go. It's a meaningless number. People frequently use it as a proxy for bypass ratio, which is far more important, but they're not the same thing at all. You can have a 20" fan with a bigger BPR and better TSFC than a 120" fan.

Quoting mffoda (Thread starter):
If we just use the Leap’s as an example, the 24k A319neo is carrying the same Fan and Core that the 33k A321neo is. Which brings the question, which NEO is the core optimized for?

The 33k. The core is most efficient when running closest to its limit; that is the highest thrust setting. All lower thrust ratings are packing "more" core than they actually need.

Tom.


User currently offlinemffoda From United States of America, joined Apr 2010, 1083 posts, RR: 0
Reply 2, posted (2 years 4 months 4 weeks ago) and read 3725 times:

As always, thanks Tom.

Quoting tdscanuck (Reply 1):
There's a very important caveat here...the engine spec's are not necessarily the same. A 1% shortfall on a GEnX does not necessarily give you the same tsfc as a 1% shortfall on the T1000.

Agreed Tom,

However, one would have to assume that the original spec requests were pretty darn close... yes?

Quoting tdscanuck (Reply 1):
We need to let fan diameter go. It's a meaningless number. People frequently use it as a proxy for bypass ratio, which is far more important, but they're not the same thing at all.

Again totally agree Tom, which is why I was considering other parameters.


Quoting tdscanuck (Reply 1):
The 33k. The core is most efficient when running closest to its limit; that is the highest thrust setting. All lower thrust ratings are packing "more" core than they actually need.

Therefore, It makes perfect sense to develop a custom core for the MAX. Since it requires 20+% less thrust then the NEO core at its highest thrust setting. Do I have that right?

Thanks again Tom...

[Edited 2012-05-26 14:41:22]


harder than woodpecker lips...
User currently offlineTWA772LR From United States of America, joined Nov 2011, 2184 posts, RR: 1
Reply 3, posted (2 years 4 months 3 weeks 6 days 19 hours ago) and read 3470 times:

The specs on the RR T1000 may be better than the GENx, but there are also maintenance costs, company preference/alliance (I've noticed BA uses mostly RR instead of GE or PW (yes I know both companies are English)), or maybe an airline doesn't need the extra umph (like Piedmont getting lower rated engines on their 762's back in the day).


Go coogs! \n//
User currently offlinelightsaber From United States of America, joined Jan 2005, 13250 posts, RR: 100
Reply 4, posted (2 years 4 months 3 weeks 6 days 18 hours ago) and read 3405 times:
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What isn't being discussed is optimal mission range. While increasing fan diameter does reduce TSFC, it increased weight and nacelle drag. It also hurts fuel burn durning climb. Thus, a smaller diameter engine is optimized for shorter missions. I had the pleasure of working a widebody engine optimization. We found a 3" smaller fan was *much* cheaper to produce as the most efficient vendor just couldn't make fan blades beyond a certain length economically. So the engine was optimized for that fan diameter (well... a little less 'just in case') and we were shocked that it improved the average mission economics entirely due to the reduced climb fuel burn. (We had been *way* to focused on the longest missions, but that wasn't how the launch customer used their widebodies.)

So I see the MAX being optimized for shorter missions than the NEO. Or more precisely, the A320 will improve nicely versus the 737 on longer missions. Since the 737 currently has a range advantage, this is just 'closing the gap.' I could see airlines with shorter missions (such as WN) being very happy with the MAX. I could see airlines with longer mission lengths being very happy with the NEO (e.g., B6). In between? a.net fodder.   

Quoting tdscanuck (Reply 1):
The engines are, though, on par with each other for total cost of ownership. They have to be or the sales would be far more lopsided than they are.

Excellent point to start the discussion. What matters in the end is the economics. CFM/GE is willing to guarantee more than Pratt is. Read into that what anyone wants, the customer buys on the guarantee and not the promise.

Quoting mffoda (Thread starter):
While these numbers might not be exact. They do show that while similar in weight and fan dia. They are clearly different in BPR.

Partially this is component efficiency. The LEAP-X has an amazing number of additional low turbine stages (Seven versus only three). Normally, this is a HUGE maintenance burden. If CFM/GE is willing to 'eat the part costs,' than as far as the customer is concerned, they are equivalent. By eat the costs, I mean still make a profit on the spares, but just not as much.

I'm personally amazed how light the LEAP-X is. I'm still trying to get my mind where the weight was removed (due to all those stages). But that is my own issue... what matters is what is delivered.

Quoting mffoda (Thread starter):
Despite the T-1000’s slightly larger fan dia., lower weight and significant BPR advantage?? The two engines will still be just on par with each other.

The GTF helps in three areas: Fan efficiency, low compressor efficiency, and low turbine efficiency.

CFM is putting in a far more advanced fan (the GTF will not benefit as much by the newer blade profiles as the fan is at a more optimal mach #).

CFM is also using a scalloped compressor vs. the GTF's standard compressor. I give the advantage in component efficiency to the GTF, but I haven't found the overall pressure ratio. GE is going pretty high (for a narrowbody) for the LEAP-X (40:1). This is just a penalty in turbine inlet temperature (high turbine durability).

For the low turbine, I've already noted the extreme number of stages for CFM.    Normally I would say the weight penalty would be huge. I'm still trying to figure out how the two engines are in the same ballpark. (What did CFM due with low turbine material to save weight? What did I miss?)

My only concern with the LEAP-X is high turbine durability.

Quoting mffoda (Thread starter):
Since it is frequently argued that the fan dia. and BPR are the “be all, end all” of the conversation. It would seem that CFMI is leaving some low hanging fruit.

It isn't the end all. Fan diameter is a function of mission optimization. It is a penalty on shorter missions. Now, the sub 250nm market is pretty much dead (outside of Hawaii and a few other regions) thanks to the TSA, high speed rail, and car reliability improvements.

Lightsaber



Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 5, posted (2 years 4 months 3 weeks 6 days 17 hours ago) and read 3358 times:

Quoting mffoda (Reply 2):
However, one would have to assume that the original spec requests were pretty darn close... yes?

They will be close but not the same, since the engines are actually different and optimized in slightly different ways. The difference between engines is probably on the order of the spec shortfall so the water is really muddy.

And the end of the day, total cost of ownership is what matters. Since engines burn fuel, TSFC is a major part of that but, as lightsaber has noted in far more detail, it's more complicated than just TSFC.

Quoting mffoda (Reply 2):
Therefore, It makes perfect sense to develop a custom core for the MAX. Since it requires 20+% less thrust then the NEO core at its highest thrust setting. Do I have that right?

It absolutely makes performance sense; if the MAX thrust numbers are right it can have a smaller core (also a way to get higher bypass out of a smaller diameter fan). However, that doesn't necessarily mean it makes business sense for CFM. They have to be assured they can get enough business to cover the cost of developing two cores. That's probably not an issue for the kind of sales numbers they're talking about but it is something they have to look at; even if it makes fantastic sense for the airplane, if it doesn't make business sense for CFM then it won't happen.

Tom.


User currently offlinelightsaber From United States of America, joined Jan 2005, 13250 posts, RR: 100
Reply 6, posted (2 years 4 months 3 weeks 6 days 17 hours ago) and read 3352 times:
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Quoting tdscanuck (Reply 5):
That's probably not an issue for the kind of sales numbers they're talking about but it is something they have to look at; even if it makes fantastic sense for the airplane, if it doesn't make business sense for CFM then it won't happen.

The exclusive makes it worth while. Pratt is also implementing too many variations of the GTF (and other engine commitments) to offer an exclusive core. IMHO, a MAX exclusive is worth much more than the costs of a custom scaled core.

As you note, at the end of the day it is TCO, not just fuel burn. TCO will be mission dependent for the two NEO engines... It will take years to fully understand the costs with each. I suspect later sales will be very dependent on each engine's optimal mission.

Lightsaber



Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently offlinemffoda From United States of America, joined Apr 2010, 1083 posts, RR: 0
Reply 7, posted (2 years 4 months 3 weeks 6 days 6 hours ago) and read 3216 times:

Quoting lightsaber (Reply 4):
Quoting mffoda (Thread starter):
While these numbers might not be exact. They do show that while similar in weight and fan dia. They are clearly different in BPR.

I'm personally amazed how light the LEAP-X is. I'm still trying to get my mind where the weight was removed (due to all those stages). But that is my own issue... what matters is what is delivered.

Thanks lightsaber,

My comparison above was to the T-1000 & GEnx, not the LEAP-X and GTF... I have found no data on the LEAP-X's weight? Perhaps, you could venture a guess?

 
Quoting lightsaber (Reply 4):
Quoting mffoda (Thread starter):
Since it is frequently argued that the fan dia. and BPR are the “be all, end all” of the conversation. It would seem that CFMI is leaving some low hanging fruit.

It isn't the end all. Fan diameter is a function of mission optimization. It is a penalty on shorter missions.

I wonder what your thoughts are regarding the NEO itself? I understand you're a P&W guy... But, the LEAP-X size is not restricted on the NEO. Do you believe it is restricted by weight? Like as not to effect additional aircraft modifications/ strengthening?

Thanks again lightsaber and Tom...



harder than woodpecker lips...
User currently offlinelightsaber From United States of America, joined Jan 2005, 13250 posts, RR: 100
Reply 8, posted (2 years 4 months 3 weeks 6 days 3 hours ago) and read 3162 times:
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Quoting mffoda (Reply 7):
I have found no data on the LEAP-X's weight? Perhaps, you could venture a guess?

Oops... need more sleep. That would have been the weight of two engines (and maybe nacelles).

I would imagine the LEAP-X should weight about 600lbm more than the GTF. The stages add about 900lbm, but subtract about 300lbm for the GTF's gearbox, bearings, structure, etc.

I'm not a structures engineer, I'm aerodynamics. So my weight estimates are truly SWAGs.  

I don't know the LEAP-X's weight. Due to the 7 low turbine stages, I would expect them to be heavy. Even hollow nickel blades have quite a bit of weight...

Quoting mffoda (Reply 7):
I wonder what your thoughts are regarding the NEO itself? I understand you're a P&W guy... But, the LEAP-X size is not restricted on the NEO. Do you believe it is restricted by weight? Like as not to effect additional aircraft modifications/ strengthening?

I believe bypass ratio on the NEO is limited by shock wave interactions with the nacelle and the wing.

Lightsaber



Societies that achieve a critical mass of ideas achieve self sustaining growth; others stagnate.
User currently offlinemffoda From United States of America, joined Apr 2010, 1083 posts, RR: 0
Reply 9, posted (2 years 4 months 3 weeks 3 days 22 hours ago) and read 2740 times:

Lightsaber and Tom (tdscanuck),

It appears Randy T is following this thread, as he commented on the same issues that we have addressed.

There could be a potential business opportunity for you guys at Boeing? 


Quote:

"Identifying the thrust demand from the CFM International Leap-1B powerplants will confirm the type's maximum take-off weight and range. Meanwhile, the airframer is dismissing rival Airbus's focus on the Max's smaller fan diameter compared with the A320neo.

"Physics doesn't work in Europe the way it does everywhere else," says Boeing Commercial Airplanes vice-president of marketing Randy Tinseth.

He says both airframers are designing thrust requirements around their largest re-engined aircraft - the A321neo and 737-9 - but says the Airbus twinjet needs 20% more thrust, and this allows the 737 to employ a smaller core and smaller fan. Tinseth adds that the A320's empty weight per set is higher than the 737's - by 5-10% across the family range - and the larger A320neo fan will simply add more weight to the aircraft.

"We've worked hard to optimise the performance of the [737 Max]," he says, insisting that weight affects the operating costs in terms of fuel-burn, maintenance and landing charges."


[Edited 2012-05-29 16:16:14]


harder than woodpecker lips...
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