"Ah. So 6 abreast economy on B747 is not serious, for some reason?"
I tried to specify economy class once on 744 upperdeck yrs ago with a big airline, limiting factor became the luggage stowage. Seatwise you can accomodate about 60-64 passengers. Logistical (galley, crew (de-)boarding but speciallly luggage wise) you create an operational drama.
http://www.boeing.com/commercial/air...s/7474sec2.pdf
Boeing shows the ways to get 72 seats (page 25) and even 85 seats (page 28) on upper deck. I cannot see where the supposedly allowed 110 seats could go.
But as for luggage, the upper deck width between the outsides of armrests is shown as 346 cm (page 29), and 345 cm (page 31). Comparable with 707/727/737/757 single deck. The height of main deck is given (241 cm), but the height of upper deck is not.. Generally, the overhead space on 747 upper deck is less than on Boeing narrowbodies - but 747 has the floorlevel bins lacking on narrowbodies. How does the total available luggage space compare?
Do you happen to know the actual height of 747 upper deck - floor to top of ceiling vault?
I think the A350XWB / 787 and A380 also do not have circular pressure vessels which are threoretically ideal. However this is not the only factor determining weight & operating costs. If you make the nearly circular damage can be limited.
767 is not a circular pressure vessel, either
But if you cannot have circle, your next best choice is double bubble. Still a pure tension structure, though now the floor carries pressurization loads, holding the walls together.
P.S how do you do Quotes on this forum?
Looks difficult, yes, because there is no Reply with Quote option. I use Quote icon above the reply box (the last to the right) and then have to copy and paste from the thread presented beneath.