|Quoting tortugamon (Reply 88):|
Some have speculated that the OEW could be less than the 77W as the wing will be substantially lighter and the stretch is small.
|Quoting ThReaTeN (Reply 89):|
while the OEW figure on Wikipedia (415,000 lbs) was (perhaps intentionally) released as too high
The 777-9's OEW will certainly be higher than 77W's. I can't provide a link to this but behind Leeham's paywall, Bjorn/Ferpe told me in a comment that Randy from Boeing quoted him a 407,000lb OEW for 779. So that's probably the floor for OEW, 415,000 wouldn't be unreasonable.
While CFRP will help with weight, we have to consider the fundamentals of wing design as well: span and area-dependent weight. A rule of thumb is that weights are 40% span-dependent and 60% area. Breaking these out:
-Span-dependent weight rises with (1) cube of span and (2) ultimate load. Effective span is increasing by ~8% (230/213 - the tips aren't fully loaded). By cubic escalation that causes ~25% span weight delta. The ultimate load is also increasing with the longer, heavier fuselage. The stretch is ~3.5% (238/230) but fuse weight increases more than linearly due to bending moment of longer fuse. Total span-dependent delta should be ~30%, thus span-dependent contributes ~12% wing weight delta.
-Wing area is increasing by ~10%. That's a ~6% wing weight delta.
-Total wing weight delta, before CFRP, would be ~18% on this calculation.
-If CFRP saves 10% of weight, total wing weight delta (.9*1.18) is ~6%. If wings are 40% of OEW, OEW delta is ~2.4%.
-If fuselage+floor beams+furnishings is 40% of OEW, and this increases by 4-5%, that's another ~2% OEW delta.
-Between wings and fuse, basic fundamentals would predict ~4% OEW delta. Much higher if CFRP doesn't quite save 10% of weight.
-GE9X will probably be heavier than GE90-115B, even with lower thrust. Its cruise thrust is around equal, but will have a bigger fan and much heavier core to achieve 62 OPR.
-Considering center wing box stays aluminium, empennage size is increasing, and engines should be heavier, total OEW delta should significantly exceed the 4% laid out above. Plus reinforcing the fuselage for 6,000ft pressure and thinner sidewalls will cost weight.
I bet Boeing is setting MSP
for more realistic pax loads. With 350 pax @225lbs, a 146,000 MSP
still leaves room for 67,000lbs of cargo. At 139.5ft3 usable volume per LD3, 11lbs/ft3 cargo, that would allow for 40LD3's. The 77W's higher MSP
comes into play only when you're carrying 500+ pax with few bags and a lot of cargo in the belly. Having a higher MSP
would require heavier wing spars, probably just not worth it.[Edited 2015-07-01 16:16:04]
[Edited 2015-07-01 16:20:33]