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?