I hate it when work gets in the way of an interesting thread!
|Quoting astuteman (Reply 48):|
To be fair, he says 68" is "the right size for the airframe". Insofar as 68" has already caused additional changes to be required of the 737, 81" could well be expected to add considerable weight and complexity to an airframe that's not really designed to accommodate it, and which may in overall cost terms, be counterproductive.
I assume 81" (or 78" for CFM) is "the right size for the airframe" for an A320 in the same way.
Perhaps worth remembering that the A320's engines are already 68" compared to the 737's 61", so the relative change in size isn't actually as big as is made out.
Thanks for the insight.
BTW Guy Norris (in AvWeek blog posting linked earlier) quotes Albaugh as also saying: "I think we made the right decision for us" .
And in a new, longer article at AvWeek
, Norris quotes 737 Chief Program Engineer John Hamilton as follows:
The 68-in. fan size is the largest possible that can be accommodated beneath the wing without extensive modifications to the landing gear. Although the 68-in. fan does not strictly require a nose leg extension, Hamilton says, additional design space will enable a more optimized design. "We've allowed our designers to remove that restraint, and the nose gear will float up a little bit," he said, adding that a nose gear dimension has not been selected.
So there in blue and white from the mouth of the 737 Chief Program Engineer is the constraint
mentioned elsewhere: go any larger than 68" and you get hit with "extensive modifications to the landing gear"
, presumably meaning you need to change the MLG and thus you hit the wingbox and then you have moved into a very different and much costlier design space.
He's vague about the source of the "additional design space" but FlightBlogger's updated article says:
The question of whether or not a nose blister for the larger gear comes into the fray, however, a year ago Boeing said it had essentially cracked the problem by relocating equipment from the forward electronics equipment bay and creating a larger nose landing gear wheel well for the extended strut.
It'll be interesting to see if that cuts into cargo space or not.
As for FBW, AvWeek says:
Even the planned change to fly-by-wire spoilers, confirmed by Hamilton on Thursday, is being made in a less disruptive way by adapting a tried and trusted architecture based on the 757. Such a system does not require the same levels of redundancy as a primary flight control system, "so the weight impact is not the same," says Hamilton.
It'd be interesting to know how that approach contrasts itself with the one on 747-8.
|Quoting Baroque (Reply 73):|
Am I not interpreting it correctly or have there been requests that GE produce a more efficient for for the small fan Leap than the larger fan Leap?
's posting of the Boeing PR
in reply 43 states "a continued focus on engagement with customers and partners to optimize the engine core architecture.".
So, yes, Boeing is leaning on CFM to optimize the core. Whether or not it happens at all, or whether or not the impovements are suitable for the A320 either directly or via PIPs is still an open question AFAIK.
|Quoting Baroque (Reply 73):|
There is going to be a lot of "competition for Astuteman's peanuts".
|Quoting rheinwaldner (Reply 77):|
Like others (e.g. ebbuk) I am really annoyed by Boeing's twisting PR.
Yes, that was really where I was going with my earlier posts.
|Quoting Baroque (Reply 64):|
You also might be justified to conclude that if only a 78" fan would fit under the wings, this too would be an optimised solution. In other words 68" is as far as she will go, hence it is now optimised.
Yes, confirmed above. Going any further brings in more pain than can be tolerated within the scope of the project.
|Quoting tdscanuck (Reply 87):|
They have two lines to do the -5 and -7 right now (A320 and 737NG)...why would that suddenly change? They're not the same engine, they shouldn't have the same core.
It's not clear to me from what I've read that the -5 and -7 cores have different sizes. I've done some googling, wikipdeding etc and haven't found a definitive statement. Do you have a reference? I'd appreciate one if you had it.
Wiki makes the engines sound more similar than different:
It (CFM56-7) incorporates features from the CFM56-5 series such as FADEC, double-annular combustor (as an option), and improved internal design.
So it's still not clear to me.
|Quoting SEPilot (Reply 94):|
My take on all of this is that the A320NEO boxed Boeing into a corner that they would have liked to have avoided. They clearly did not want to do another 737 upgrade, but would have preferred to go directly to a new model, but not until the 787 was well under control (including the 787-10.) But with Airbus pushing the NEO button, they ran out of time, and while if they could have guaranteed a new, better plane with EIS before 2020 they might have been able to get away with it, but after the 787 fiasco nobody was going to believe them (not even me, and I am a die-hard Boeing fan.) So in order to maintain market share they were forced to offer the MAX; and if anyone still believes that the NEO had nothing to do with the timing then I have such a deal on a bridge in Brooklyn for them. It also appears to me that the AA deal is what pushed them over the edge.
I agree with this narrative. It matches all the statements being made in the press at the time. At the time of the AA
deal, the Seattle Times said Boeing had to "scramble" to come up with a propoal, only after AA
had already signed a MOU with Airbus, to get a chunk of their orders.
|Quoting RoseFlyer (Reply 118):|
The fact that Boeing is saying that a 68'' diameter engine is optimized is not the same thing as saying a 68'' engine is the largest that will fit on the plane. They can go bigger. Main gear can change, nose gear can change, mounting can change.
Thanks for your interesting post, but to add some perspective, as above Mr. Hamilton is saying that changing the MLG is a step too far for this current program.
I did ask the question earlier about what the optimal aircraft would be if Boeing did not have this constraint, but no one has hazarded an opinion on it.
|Quoting tdscanuck (Reply 122):|
GE can read the market just as well as Boeing and Airbus...even if the 737MAX was a "poor" performer in the market it would still tell way more than enough frames to justify creating a separate version.
It seems inconsistent to me to say that GE
will throw several hundred millions of dollars at a special core for the MAX, yet Boeing won't throw a billion or so to reprofile the MAX's wing.
Purely speculation on my part, but I can imagine if you make a smaller core for the MAX, it really is an all-new engine. There will be next to zero parts commonality, the temps and pressures at almost every part of the core will be different so you will have to redo the CFDs to make sure you get things right, etc. It makes a reprofiled wing look positively simple, at least to me, who admitedly is not a aerospace engineer.
has shown it's reluctance to make special engines for each aircraft. Witness the A350XWB where GE
has given RR
the windfall of a lifetime just because it didn't want to do a special engine for the aircraft.
|Quoting lightsaber (Reply 104):|
Nitpick, the LEAP-X core is too large for the 737. In other words, the low pressure compressor will have to deliver less mass flow of air for the lower required maximum thrust vs. the A320NEO LEAPX. Thus, the overall pressure ratio for the LEAP-X on the 737MAX will be lower costing 1.5% (by my SWAG) in fuel burn. So half of the missing fuel burn will be recovered if Boeing is able to convince GE its worth spending a few hundred million more designing a 10% to 12% smaller flow number core on the 737MAX LEAP-X.
Yes, and this is what makes me think the work for the smaller core is akin to doing a new engine.
BTW is Pratt varying the core size on its various PW1100G family memebers?
|Quoting seabosdca (Reply 128):|
I very much doubt this is actually the case.
I suspect a lot of early work was done on NSA that will prove very valuable in the future.
I don't know. If you re-read FlightBlogger's three part interview series with Mike Bair on the NSA, it seems they were no where close to doing any detailed engineering. It seems they were still working out what mission the plane would have, and what technolgies were of interest, etc. Seems to me they were struggling mightly in the requirements analysis phase, with no clear way forward. This was after he had a year or so working on the project at a VP
level, and after something like three years of attention by his predecessor who was at a director level which means to me they probably had sizeable staffs under them for significant periods of time.
I think a lot of what NSA will be will come from the 787 team working with their current technology and working with their partners on what the next generation approaches will offer.
|Quoting seabosdca (Reply 128):|
I think Boeing's problem was not that it wasn't doing anything but that it didn't read the tea leaves correctly on the question of how many airlines wanted new aircraft very soon.
I'd spin this a bit to read that Boeing was wishing that its customers would wait so it could be spared the distraction of the MAX and go full forward with NSA. The Boeing and BCA CEOs were publicly badmouthing the NEO which shows to me an active disinformation campaign rather than just poor tea leaf reading.