747400sp
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Is It A Good Ideal To De-Rate The 777-X Engines?

Thu Sep 22, 2011 11:48 pm

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?
 
gigneil
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RE: Is It A Good Ideal To De-Rate The 777-X Engines?

Fri Sep 23, 2011 1:13 am

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
 
thegeek
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RE: Is It A Good Ideal To De-Rate The 777-X Engines?

Fri Sep 23, 2011 3:31 am

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.
 
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Stitch
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RE: Is It A Good Ideal To De-Rate The 777-X Engines?

Fri Sep 23, 2011 3:38 am

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?
 
HaveBlue
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RE: Is It A Good Ideal To De-Rate The 777-X Engines?

Fri Sep 23, 2011 4:59 am

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!
 
thegeek
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RE: Is It A Good Ideal To De-Rate The 777-X Engines?

Fri Sep 23, 2011 6:43 am

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.
 
747400sp
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RE: Is It A Good Ideal To De-Rate The 777-X Engines?

Fri Sep 23, 2011 1:32 pm

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.
 
tdscanuck
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RE: Is It A Good Ideal To De-Rate The 777-X Engines?

Fri Sep 23, 2011 1:36 pm

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.
 
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Stitch
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RE: Is It A Good Ideal To De-Rate The 777-X Engines?

Fri Sep 23, 2011 3:34 pm

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.
 
XT6Wagon
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RE: Is It A Good Ideal To De-Rate The 777-X Engines?

Sat Sep 24, 2011 3:11 am

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
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RE: Is It A Good Ideal To De-Rate The 777-X Engines?

Tue Sep 27, 2011 5:25 am

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).
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