747400sp From United States of America, joined Aug 2003, 3301 posts, RR: 2 Posted (2 years 5 months 2 weeks 4 days 9 hours ago) and read 4296 times:
I know Boeing, knows what they doing, but when I read that they de-rating the GE 90 with GE 90X to 99000 lb thrust engines for the 777-X, I thought, something does not feel right about this. I see that the 777-X has a beast of a wing span, I believe it's around 134 ft, (larger than the 747-8) which should give the 777-X, amazing lift, but with de-rated engines, there may-be a problem. Now I can see where the de-rated GE 90X, could help the program, by burning less fuel. So will the de-rated GE 90X hurt the 777-X or help the giant twin jet?
tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 81
Reply 7, posted (2 years 5 months 2 weeks 3 days 19 hours ago) and read 4022 times:
Quoting thegeek (Reply 2): Quoting gigneil (Reply 1):
The point is that the 777-X should be much much lighter and burn, and therefore need, much less fuel.
But then you have a wing too big for the MTOW.
That's not at all unusual...the 777-200 (original), the 767-200, the 787-8, the A380-800, and soon the A350-800 are all in exactly the same situation. "Oversize wings" tend to provide very good aerodynamics and provide room for future growth at much lower cost.
XT6Wagon From United States of America, joined Feb 2007, 3300 posts, RR: 4
Reply 9, posted (2 years 5 months 2 weeks 3 days 6 hours ago) and read 3749 times:
Don't forget that its likely to have HUGE margin for hot and high operations at higher thrust than "max". Only compared to the current GE90-115, this might not have the fairly large penalty to MX intervals given its lower base thrust on the same core size.
ferpe From France, joined Nov 2010, 2767 posts, RR: 59
Reply 10, posted (2 years 5 months 2 weeks 3 hours ago) and read 3346 times:
A wing is characterized by it's span and it's wing area.
The span is a good thing asit reduces induced drag. A CFRP wing can be made with a higher aspect ratio (ie more span with the same wing area) then an alu one. The original 777 wing was alu and was dimensioned for MTOWs in the 250t range (777-200), for the 350t only swept wingtips was added. Given the chance B has now increased the span and aspect ratio a lot=good.
The wing area gives the lift (area * lift-coeffcient) but it also produces weight (lots of structure) and drag (wetted area) so you don't want more then you need. We don't know the area for the new wing but don't expect it to increase as much as the span. MTOW/Wing area seems to lie in the range 650kg/m2 (today 800kg/m2) when you start fresh so expect the area for the 720-740t 777-8-9X to lie in the range of 500m2 (today 435m2).