Kees, The 74's Section 41. I know it well. Your characterization of the elements under bending stress is certainly clearer than was mine. Best to you in 2002. - Bob Mann Kees de LezenneCoulander wrote: > > RWM <RWM@RWMann.com> wrote: > > >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. > > > >- Bob Mann > > Bob, > A double bubble fuselage consists of two circular sections, which > are each under pure tension as far as pressurization loads go (there > is of course shear or bending for other loads). The cabin floor has > to be at the joint line, and the floor beams are under tension. As > such, in a double-bubble fuselage, the floor beams are an essential > part of the pressure hull (in a circular fuselage, the floor beams > do not carry any pressurization loads). > A double-bubble fuselage always has a sharp crease line where the > two sections meet. This may be faired over for aerodynamic reasons, > but the actual pressure hull should have a 'figure 8' cross section. > In the front fuselage, it is usually impossible to maintain purely > circular sections all the way, and then the frames will carry some bendin= > g. > The most famous is of course the front fuselage of the > Boeing 747 and the non-circular sections cause considerable fatigue > problems. Ask any owner of old 747s. > Kees de Lezenne Coulander > -- = > > C.M. de Lezenne Coulander > Aircraft Development and Systems Engineering B.V. > Hoofddorp, The Netherlands > > = -- - R.W. Mann & Company, Inc. >> Airline Industry Analysis Port Washington, NY 11050 >> tel 516-944-0900, fax -7280 mailto:RWM@RWMann.com >> URL http://www.RWMann.com/