Yeah, I have changed my mind in some respects.
The thread from last September was mainly about traditional 3 engined planes like DC-10, B727, Trident etc. I said that they will never happen again. ETOPS twins will take their place simply because ETOPS has been "invented" in the meantime.
A BWB plane with engines in the back can, however, have any number of engines, 2, 3, 4 or 5.
But where I may have changed my mind is concerning the narrow balance limits of a BWB plane. Commercial transport planes have the operational disadvantage compared to bomber planes that the centre of gravity is not too well known at take off. It is compensated with a relatively large tailplane which gives a wide margin. That's not possible on a BWB since it has no tailplane. But I think that it can be overcome by automated centre of gravity shift by pumping fuel around between different tanks for proper trimming.
Such trimming is already performed on some of the newer Airbusses, but only for optimising fuel burn during cruise, not for reducing stability margins. It would have to be a much faster and more active system on a BWB, and safe flight would depend on it, not just fuel burn figures.
The Concorde has the same problem, and in addition it has to deal with a centre of gravity shift needed for supersonic flight. It has a manual fuel transfer system operated by the flight engineer. It scrapes by with this somewhat rude system because the payload in any case is such a small portion of the total weight.
A BWB plane on the other hand... it's major advantage is that it can have a greater payload to MTOW ratio than any other type of plane - less metal, more passengers, that's the name of the game.
About the YB-49:
The whole truth may never be known. And certainly John Northrop and general Symington (USAF chief of staff in late 40'es) never agreed. The debate over the YB-49 continued more than 30 years after the cancellation of the YB-49 program. I think that it is pretty well summed up on http://www.nurflugel.com/Nurflugel/Northrop/yb-49/yb-49_blurb/yb-49_blurb.html
It also has a link to an article in Los Angeles Times from December 8th 1980 where John Northrop's version is well documented, read http://www.nurflugel.com/Nurflugel/Northrop/xb-35/xb-35_blurb/conspiracy/conspiracy.html
The whole truth has gone with the people involved, but I am totally convinced that the XB-35/YB-49 program, which suffered all sorts of problems, also was "ahead of its time" because a much needed active computer based stability control system was not available yet. The B-2A took advantage of that. And the fact that the computers on the bomber will always know the plane's centre of gravity within a fraction of an inch.
New subject (almost):
You may also have a look at http://www.zagi.com/html/slope_zagis.html
- I play with such a thing when flying my $1k+ carbon fibre model gliders becomes boring. It's extremely funny and thousands of such things are flying all over the world. But they are only fun when you get the centre of gravity absolutely correct. Ordinary model gliders fly safely with a wide range of centre of gravity, although with a performance penalty. But the Zagi has to be right, so has a BWB transport.
Happy landing, Preben Norholm