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The Boeing 377 Stratocruiser - a civilian adaptation of the C-97, a military transport which would also later be developed into the KC-97 - were derived from the B-29/B-50 family by grafting a large, bulbous passenger/cargo compartment onto the B-29/50 fuselage; this created a sharp cusp in the fuselage cross-section, as can be seen in this photo of a half-built Stratocruiser:

Stratocruiser fuselage cross-section

(Image source)

Such a sharp discontinuity in the fuselage profile would be expected to serve as a stress concentrator in a pressurised aircraft, like the 377/C-97/KC-97 series, and cause accelerated fatigue cracking in and around the cusp, shortening the lifespan of these fuselages; did these aircraft, in fact, experience fatigue problems emanating from the fuselage cusp, and, if so, how were they dealt with?

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  • $\begingroup$ The floor in these aircraft takes part of the stress caused by the cabin pressure. It might not be as bad as it looks. But I am no expert in this stuff by any means :D $\endgroup$
    – Jan
    Jan 25, 2019 at 7:27

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You can actually see the same effect happening with soap bubbles when they touch and form a flat film connecting them. You can actually still see this type of fuselage in use in the Boeing 717 (Douglas/McDonnell Douglas DC-9). A lot of other narrowbody airliners also have it, but the outer panels fair over the intersection between the two fuselages.enter image description here

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It is not the stress concentrating type of sharp corner. That is the natural shape that allows the parts to be in a nice smooth tension at lowest energy. If you made an elastic rubber balloon with a divider membrane creating two chambers and inflated it you would get a similar load distributing shape.

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