[Dag Viking]

Og da har Boeing havnet på 69,4" fan, samt forsøk på å redusere core. Begge deler for å få høyere BPR, og dermed lavere forbruk. Tydelig at 66" og 68" ikke er bra nok når man skal konkurrere med NEO som har 78/81"" på sine motorvarianter

http://seattletimes.nwsource.com/htm..._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."

En liten quote fra en på a.net som pleier ha bra peiling på motorer og aerodynamiske ting og tang

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?).

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.)

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.