In a message dated 12/29/01 4:03:01 PM Central Standard Time, RWM@RWMann.com writes: > I suspect the reference was to "double bubble" fuselage section, i.e. not a > simple "hoop", but two joined, partial hoop sections of different diameter, > designed to achieve more section height than width. > > A circular hoop section is in (essentially) pure tension when pressurized. > A > double-bubble is in tension, and also in bending at the join. > I believe the DC-9/MD-80/MD-90/B-717 series have that type of construction, don't they? I realize that the 747 has some shape changes that could be considered a "double bubble" because of the upper deck. I think I understand more. Jim Proud to be an American, Jim Hann Waterski J-41 Captain STL