![aircraft design - Why does the DC-9-80/MD-80 have this cusp in its fuselage? - Aviation Stack Exchange aircraft design - Why does the DC-9-80/MD-80 have this cusp in its fuselage? - Aviation Stack Exchange](https://i.stack.imgur.com/2GuZU.jpg)
aircraft design - Why does the DC-9-80/MD-80 have this cusp in its fuselage? - Aviation Stack Exchange
Do modern airliners like the Boeing 787 and Boeing 777X still use circular cross sections because it is less expensive to build? - Quora
![aircraft design - Could some one explain me with the mathematical relations on how the double bubble fuselage cross section (example A380) is designed. - Aviation Stack Exchange aircraft design - Could some one explain me with the mathematical relations on how the double bubble fuselage cross section (example A380) is designed. - Aviation Stack Exchange](https://i.stack.imgur.com/t6jxm.jpg)
aircraft design - Could some one explain me with the mathematical relations on how the double bubble fuselage cross section (example A380) is designed. - Aviation Stack Exchange
![This cross-section of a Boeing 727 fuselage (located at Syracuse, NY, USA airport ✈) : r/mildlyinteresting This cross-section of a Boeing 727 fuselage (located at Syracuse, NY, USA airport ✈) : r/mildlyinteresting](https://external-preview.redd.it/_6pmxPGarwVvKEd_In7x5C-roQSye5ckW8SW1WbkMQM.jpg?auto=webp&s=e2dd2889a9166608a148d934fe4e00e3f16e540d)