brindabella wrote:morrisond wrote:enzo011 wrote:
You ever wonder why this is? Seems like it is a market where a suitable solution is hard to come by, even for engineers and designers at both OEM's.
It also just takes a lot of effort to push the state of the art a bit. Just think how long it has taken to make a Geared Turbo Fan work.
If the rumours were right - this was the cross section or something similar that Boeing was going to use for NSA back in 2011 and the rumours have stayed pretty consistent since then.
They gained a lot of experience with the 787 and the 777X new wing - they are understanding composites a lot better - new composites are available, computing power has multiplied exponentially, Machine learning is helping to make structures lighter and and knowledge has been gained in terms of how to efficiently produce complex composite structures (like the 777X wing) to radically reduce labour hours - maybe it has just taken this long to get to the point where we can start to progress beyond the basic round tube and wing.
Not to belabour it, but I'm going too - one of the main takeaways from that article was realizing how little of the length of the belly of a 2-3-2 would have the floor beam in compression where you would have a big hole in the monolithic floor beam/ lower floor frame for the cargo compartment. Due to all the pressure bulkheads in the ends for things like wheel well and gear bays - those sections should really not have any issues and it should be a lot easier to deal with the loads as they would also probably taper to circular anyways.
Plus then you have the section above the wingbox - the wingbox is essentially rectangular with only a Round cross section above it in the Ostrower Double Circle 2-3-2 concept - just like a 3x3. The leaves only about 50% of the length of an NMA-5 - maybe 20% in front of the wingbox and 30% behind that would have to deal with some non-standard loads. As I laid out above in another post that could be overcome with some innovative thinking - effectively turning the Cargo bay into a large keel beam.
Plus this 2x3x2 is really not that far off round. If it is 168"H x 185"W a circle of equivalent circular diameter would be about 176" x 176" - it's very mildly elliptical. You only have to taper out 8.5" on each side of the aircraft over 22' in the nose to get to round - (I'm sure not that hard to do in 5-6' if you wanted too) and in the tail you have 37' of length to work with. This is not an extreme shape.
Do I think that an NMA that has 9% less skin area, 2% less volume than a comparable capacity/technology 3x3 would weigh less? Probably not - but I don't think it would weigh a lot more - most likely low single digits - as only about 50% of it's length would be non-standard.
Lets go to an extreme - say that the non- standard cabin part is 20% heavier by equivalent Capacity - however those sections would not be 50% of the weight of the aircraft - the wingbox and nose sections and tail have to deal with a lot of loads are probably a high percentage of the weight - call it 60% - so 40% left over for the cabin that is not part of the wingbox - making the NMA fuselage 8% heavier for the same capacity at worst - and it could be a much smaller delta.
I posted a study many times over the last year ( that I can't find now) that shows that an A320 fuselage is about 5% of the MTOW - the study shows that done in carbon this drops to 3%.
So an increase of 8% of 3% is a whopping .24% - if you take an example that is pretty extreme. That is only 500lbs. The NMA could use shorter gear than an equivalent capacity 3x3 to get the same rotation angles - I'm sure you would make that up with the lighter gear and less structure(due to shorter lighter gear) in the wingbox and nose bay/nose gear.
It's a rounding error - and also less than the gain you get from a mild PIP or minor change to wingtips.
It should not be that much more complicated to manufacture as most of it will be automated - and about 50% of the fuselage won't be materially different than a 3x3 - the rest of the aircraft is the same - wings, tail, wingbox and most of the nose once circular. Plus the 2-3-2 will have fewer parts (frames, etc.. than an equivalent capacity 3x3) in the passenger compartment as it's shorter - it will just take design time to make it light and deal with the more complex loads in the non standard sections.
You have to guess that Boeing has not stopped working on refining this 2-3-2 even after NSA was scrapped and have been building and testing cross sections in a secret lab somewhere getting it ready for prime time.
Just like I am sure Airbus is doing as well (working on new concepts). Given that article originated in Germany (On the Double Circle with non-pressurized cargo bay) who knows that that idea didn't come out of Airbus engineers originally anyways?
Much as I admire your presentation, I would counsel caution on the "shorter/lighter gear" argument.
1) as far as we know, the newly-revealed MoM-5 model is in addition to the previously suggested -6 and -7 models.
So the gear will have to allow significant fuse extensions. Can't make it too short!
2) using "shorter gear" as an advantage seems to be heading back towards the 737 problem which has so badly warped development of the successive 737-family iterations.
Quite possibly - I guess it really depends on what the -6 and 7 are - if you look at the Aviation Week Articles rendering - -6/7 look like they have different wings/tails/gear again.
It is not inconceivable that after NMA and NSA - there is an NMA-XL with another a different wingbox/wing - not constrained by SA gate spacing even with folding tips ( I suspect NMA-5 would have folding tips - NSA - no folding tips. NMA-XL would fit in 767 sized gates that could launch in 2035 or so.
The NMA-5 with 322 Capacity would be quite small at less than 40M. There would probably be a longer version say at 45M that you are right you would have to account for. However a 3x3 of equivalent size would be even longer that would have to be taken into account for.
Given the growth in passenger volumes eventually I could see the following:
NSA - S - 34M - 3,500 NM range 175 Y Seats at 32" pitch
NSA- L - 39M - 3,000 NM Range 217 Y Seats at 32" pitch
NMA - S(5) 39M - 5,200 NM Range 217 Y Seats at 32"
NMA- L 44M - 4,700 NM - 259 Seats at 32"
NMA- XL - S 49M (762 Length) - 6,000 NM - 301 Seats at 32"
NMA-XL - L 54M (763 Length Approx) - 5,200 NM 343 Seats at 32" - the real 2040's Transatlantic monster.
All using the same basic systems architecture/cockpit/nose(just like 757/767/777) - all with one cross section - over what could easily be 20,000 frames in the lifetime of the program.
Basic Structures like wings and /wingboxes are not so hard - especially with modern computers and where they would be in 10 years at NMA-XL launch. It's the systems and control work that consume a lot of the testing and certification time.