brindabella
Posts: 562
Joined: Fri Apr 30, 2010 10:38 am

Re: Could the 787 be scaled to create the 797?

Thu Jul 11, 2019 12:57 pm

RJMAZ wrote:
LDRA wrote:
Rather than scale 787, just make a 787-8 V2 for MoM. Redesign structure for 200T MTOW, using lessons learned from 1st gen 787 structure, new 5000lb MoM engines, center wing box tank deletion, done!

7 across is rather inefficient use of space anyways

Smaller end of MoM space can be covered by NSA

This is why I think it will definitely be 8ab and slightly shorter. Any disadvantage to a stubbier fuselage is more than made up by the superior aisle efficiency of 8ab versus 7ab.

I always thought the 787-8 lightweight was a good option. It is worth noting that 200T MTOW on the 787-8 is still way too high for the NMA mission. It does reduce the MOM gap significantly though by providing a big efficiency boost to the 787-8 on shorter missions.

Boeing has different takeoff weights on their ACAP's and a standard 787-8 can fly 250 passengers nearly 5500nm with a 200T MTOW. Removing say 10,000kg of empty weight would increase range even further with that 200T MTOW. Removing that weight would actually be easy as the 787-8 has so many parts shared from the heavier 787-9/10. These parts are simply derated like the engines or overbuilt for the 787-8.

The centre fuel tank on the 787 is pretty large so unless the empty weight could come closer to 100T deleting the centre tank might not allow it to fly over 5000nm.

The more changed that get made to improve the 787-8 the closer you get to a cleansheet.


Yes, I've always seen the most prudent strategy as an NMA at "generous" 7ab also allowing a :crowded: 8ab.

This allowing better volumetric efficiency as well as preventing a future AB 8ab "overunning" a "strict" 7ab BA bird - that is, avoiding the 767 vs A330 redux.

However an alternative strategy might go like this:
1) the NMA is indeed set at a "strict" 7ab, thus minimising cross-section/weight/drag/cost and maximising competitiveness with A321X/A322X in the specific MOM space; (**)
2) meanwhile in the event of AB subsequently launching a clean-sheet 8ab, then the 787 fuse is in turn given a whole new wing/wing box/gear/powerplant/empennage(?)


That is, in a direct competition, a good 8ab will defeat a good 7ab ... ("apples vs apples")
however in similar direct competition, a good 9ab will in turn defeat a good 8ab ... ("apples vs apples")
and BA already have the basis of the "good 9ab" ...

What think you?

cheers Bill

(**) not to stress that the NMA offer-for-sale IMO marks the start of the big wheels turning which will eventually produce the NSA ... and the closer the NMA is to the NSA, the more-accurately the evolved NMA production-system will scale-down to the 6ab NSA

just sayin' ... :D
Billy
 
brindabella
Posts: 562
Joined: Fri Apr 30, 2010 10:38 am

Re: Could the 787 be scaled to create the 797?

Thu Jul 11, 2019 1:11 pm

gtargui wrote:
rikkus67 wrote:
The 767 Section 41 cockpit was used on the 777. IIRC the "adaptor" section to increase the cockpit diameter to meet up with the larger fuselage section was quite a design challenge, so Boeing had to use a smaller portion of the 767's Section 41. This is why the 777 has such a distinctive "forehead".


I had always wondered why the 777 looked the way it does. This explains it all now!


Yep; that section from the cockpit roof back aways is as ugly as hell ... :ashamed:

cheers
Billy
 
RJMAZ
Posts: 1450
Joined: Sat Jul 09, 2016 2:54 am

Re: Could the 787 be scaled to create the 797?

Fri Jul 12, 2019 5:19 am

brindabella wrote:
That is, in a direct competition, a good 8ab will defeat a good 7ab ... ("apples vs apples")
however in similar direct competition, a good 9ab will in turn defeat a good 8ab ... ("apples vs apples")
and BA already have the basis of the "good 9ab" ...

What think you?

I think in terms of 7ab vs 8ab the 8ab will always win. With 8ab you can run two skinny aisles and have the same aisle percentage of the cabin width as a 6ab aircraft.

The problem with 7ab is there is a minimum aisle width of 15inch so the aisle percentage of the cabin width has to be higher than both the 8ab and 6ab. This means a few extra percent of fuselage wetted area and empty weight per passenger. This is hard for the 7ab design to overcome.

But in terms of 9ab vs 8ab it is less clear cut. Both aircraft can have the same aisle percentage of the cabin width. At any given cabin area the 9ab will have to be stubbier and have more space wasted in the nose and tail tapers.

There is also the problem that if two aircraft have equal CASM and range airlines will always choose the smaller aircraft. Passengers prefer frequency and smaller aircraft allow more point to point connections. So a cleansheet 8ab will easily beat a semi-optimised lightweight 9ab 787 design.

This is why I am certain that the 797 will not be 7ab.
A tight 8ab cabin with a new container will be unstopable.

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