flipdewaf wrote:morrisond wrote:mjoelnir wrote:
Your 12,000 lbs / 5.5 t payload difference is an assumption and a bad one at that. As Boeing states the MZFW for the 777-9, but neither MSP nor OEW, you can not find your number in regards to Boeing statements.
The only way is to look at the OEW of the 777-300ER, 186 t, and assume a reasonable increase of the OEW in regards to the stretch of the fuselage, heavier engines and new bigger and heavier wing. The upper point is fixed with the MZFW of 255 t.
I assumed a 68 t MSP for the A350-1000 resulting from the MZFW of 233 t and a conservative OEW of 155 t. Real world numbers seem to reach 70 t.
If we assume a 5.5 t difference in MSP between the 777-9 and A350-1000 and assume the MSP for the A350-1000 with 68 t, than the 777-9 should offer a MSP of 73.5 t.
That would mean, that the OEW of the 777-9 would be 179.5 t. (255-73.5)
The OEW increase over and above the 777-300ER would than be only 11.5 t. I would say you are operating with rather optimistic numbers.
Increase in length, 2.2 each meter (same number as the stretch from the -200 to the -300) 3 m stretch gives us 6.6 t.
Engines, the GE9X will be heavier than the GE90-115B. A very conservative 1 t per engine. 2 t
(The numbers I found for the GE9X weight are astonishingly high so I disregard them here, the original plan was the GE9X coming out lighter than the GE90-115B, but that seems to have been a misconception. Perhaps some early estimates of the OEW increase are with lighter engines)
That would leave about 2.9 t for all other changes.
The other changes.
- bigger windows. weight increase as windows are heavier than skin. Not a lot each window, but it adds up.
- lower height of frames (to increase inside diameter) should increase weight of the fuselage.
- Eventual strengthening of some areas of the fuselage to match increased MZFW and MLW.
- The new big wing with folding wing tips should be heavier, though it is made from CFRP. It is far bigger than on the 777-300ER and the hinges and actuators for the folding tips are plain additional weight.
I would assume an OEW increase over above the 777-300ER of 15 t is quite conservative. That would bring the MSP of the 777-9 down to 70 t.
That is a good list. However you also have to look at where Boeing could have saved weight.
I believe they redid the avionics to use lighter 787 systems.
Interior fittings could be a lot lighter by using 787 tech as well.
It has new gear and a new wing box as well. MLW will have gone up - but you are talking 25 years of design time - you would think they could have taken some weight out here and there.
They have known the A351 numbers for some time - you would think they would have spent quite a bit of time trying to take weight out of it.
Yes I'm sure it will be heavier but maybe not as heavy as some are expecting.
But no way of knowing until the numbers are out.
If it’s not heavy then why is it using so much fuel to get 426pax to 7285nm. I would expect that number to be significantly higher with reduced fuel fractions ( lower slope on first section of payload/range chart).
Either Boeing are holding something back, it’s overweight but the aero is good but the payload availability not or the structures are good but the aero/engines stink.
My gut says Boeing are holding something back but I’m not quite sure what/why.
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I would agree they are holding something back. No way of knowing until the final numbers are released.
When you think about it what is left of the Original 777W?
The outer mold line of the nose and cross section?
New Wing, new tail, new gear, new wing box, a lot of new systems, new interior fuselage structure.
The Original 777 was described as very overbuilt. Given the 777x wing/fuselage structure failed almost perfectly at 149% (missed by 1%) you would have to assume they have shaved the margins quite a bit.
This is essentially a brand new aircraft and probably should have certified as such.
The 777X may have about as much in common with the 777W/L/F as the F18 A/B/C/D does with the F18 E/F.