While this discussion is facinating, Its also amusing, With all these experts, especially Mr Twistedenginestarter, critiqueing this design, I think that Boeing could save Millions by just hiring the members of Pprune! While its true that the US SST never got off the drawing boards, I wonder if the manyfacturers of the Concorde would have liked to trade places with Boeing vis a vis the 747...I know their accounting departments would have! One must take it on faith that alot of the research has already taken place, and that Boeing is not going to proceed with such a project unless its feasible. For all the critisism about Boeing being conservative, old fashioned etc You have to admit that not alot of their designs have failed commercially. So sit back, relax, have faith in the Boeing engineers, and if they are able to pull this off, it will undoubtably be a great airplane to fly...Just like the A-380, If Airbus can pull this off Not one of you out there would pass up the chance to fly one.