|Quoting faro (Reply 8):|
Do structures people use some rule of thumb figure in terms of %/ratios of OEW, MZFW, etc beyond which wing weight is deemed non-optimal for the mission? It's interesting to see how A & B interpret this differently in launching short baseline models vs long baseline models with the A330/787/A350.
If one want to get some feeling for the weights involved in a modern aircraft this is the best reference I have found:
Go down on this PianoX model of the 787 and you find the structural weights for the different pieces. Now this model is based on a version of 787 from 2005 with 216t MTOW but you also get the relations, e.g. wing 12,61% of MTOW. The wing at the time was slightly different (58,7m span instead of 60m) but the information is the best we got. Relations don't change that much when you grow the frame to regain payload-range so one can use these relations.
The wingloading for the final 788 at 228t ended up at 700 kg/m2, higher then A350 (600) but still not where the 77W is at 800 kg/m2.
Now B could use this wing also for the 789 (780 kg/m2) and finally for the 7810X. That this final frame is a shorter range model is typical, the shorter the range design point, the lighter and therefore smaller the wing. Why, well to my reasoning the climb segments gets more pronounced in the overall flight profile for the shorter range frame (lower weight is good) and the cruise segments for the longer range one (lower drag due to lift is good at the higher FLs desired).
A does the opposite, they produce an optimal wing for the mid model (333 or 359) at around 600 kg/m2 for the initial weight variants and then shorten the fuselage to get a longer range frame (drag due to skin friction is lowered, ref 332 or 358) with a lower wing loading still (until they up the MTOW to the same as the mid model to get even more range).
[Edited 2011-11-09 02:02:48]