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Is It A Good Ideal To De-Rate The 777-X Engines?  
User currently online747400sp From United States of America, joined Aug 2003, 3498 posts, RR: 2
Posted (2 years 10 months 1 week 2 days 22 hours ago) and read 4468 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?

10 replies: All unread, jump to last
 
User currently offlinegigneil From United States of America, joined Nov 2002, 16347 posts, RR: 85
Reply 1, posted (2 years 10 months 1 week 2 days 21 hours ago) and read 4431 times:

The point is that the 777-X should be much much lighter and burn, and therefore need, much less fuel.

If that is the case, a lighter engine is wise.

NS


User currently offlinethegeek From Australia, joined Nov 2007, 2638 posts, RR: 0
Reply 2, posted (2 years 10 months 1 week 2 days 19 hours ago) and read 4391 times:

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. It still doesn't feel right to me. I guess the too big wing could work out if operated at higher average weights.

It doesn't feel right to me either.


User currently offlineStitch From United States of America, joined Jul 2005, 30579 posts, RR: 84
Reply 3, posted (2 years 10 months 1 week 2 days 18 hours ago) and read 4388 times:
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Quoting thegeek (Reply 2):
But then you have a wing too big for the MTOW.

That has been presented as a plus for the A350 and A380, so why would it be a negative for the 777X?


User currently offlineHaveBlue From United States of America, joined Jan 2004, 2098 posts, RR: 1
Reply 4, posted (2 years 10 months 1 week 2 days 17 hours ago) and read 4355 times:

Quoting 747400sp (Thread starter):
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)

Misprint? I know its not 134' and its also not 134' longer than the 747-800.



Here Here for Severe Clear!
User currently offlinethegeek From Australia, joined Nov 2007, 2638 posts, RR: 0
Reply 5, posted (2 years 10 months 1 week 2 days 15 hours ago) and read 4333 times:

Quoting Stitch (Reply 3):
That has been presented as a plus for the A350 and A380, so why would it be a negative for the 777X?

Could that be salesmanship? I don't know that I buy that the A358 having the same wing as the A359 is a plus, unless its for a longer range version.


User currently online747400sp From United States of America, joined Aug 2003, 3498 posts, RR: 2
Reply 6, posted (2 years 10 months 1 week 2 days 9 hours ago) and read 4195 times:

Quoting HaveBlue (Reply 4):
Misprint? I know its not 134' and its also not 134' longer than the 747-800.




Yes, you are right, I meant 234', and that is wider than a 747-8.


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 7, posted (2 years 10 months 1 week 2 days 8 hours ago) and read 4194 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.

Tom.


User currently offlineStitch From United States of America, joined Jul 2005, 30579 posts, RR: 84
Reply 8, posted (2 years 10 months 1 week 2 days 6 hours ago) and read 4134 times:
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Quoting thegeek (Reply 5):
I don't know that I buy that the A358 having the same wing as the A359 is a plus, unless its for a longer range version.

Maybe the lower wing-loading helps with long-range cruise efficiency? It certainly helps field performance.


User currently offlineXT6Wagon From United States of America, joined Feb 2007, 3392 posts, RR: 4
Reply 9, posted (2 years 10 months 1 week 1 day 19 hours ago) and read 3921 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.

User currently offlineferpe From France, joined Nov 2010, 2800 posts, RR: 59
Reply 10, posted (2 years 10 months 5 days 17 hours ago) and read 3518 times:

A wing is characterized by it's span and it's wing area.

SPAN
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.

WING AREA
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).



Non French in France
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