if I have a wing, which is split in the middle of it and attached at each side of the aircraft (like in any commercial aircraft today), I get a bending moment at the root of the wing.

What if I have an continuous wing (box) like an oblique wing on the top of the fuselage? A friend of mine says, that this way the wing itself would carry its bending moments. How can I imagine this? Is this just like a beam? Does anybody has some papers about this?

  • $\begingroup$ does this answer your question? aviation.stackexchange.com/q/3428/1467 aviation.stackexchange.com/q/52092/1467 $\endgroup$
    – Federico
    Nov 3, 2020 at 13:31
  • $\begingroup$ you mean like this? $\endgroup$ Nov 3, 2020 at 15:37
  • $\begingroup$ I think your understanding is flawed. Every commercial aircraft I can think of has a single wing structure from wingtip to wingtip. The main spar either passes through the fuselage below the cabin floor, or above the cabin roof. $\endgroup$ Nov 4, 2020 at 0:59
  • $\begingroup$ @CatchAsCatchCan, the wings are, at least for airliners, definitely manufactured separately, as you can see on the first image here. Yes, there is a structure inside the fuselage that is direct continuation of the wing and carries the load, but the overall structure is riveted or bolted from three parts: the left wing, centre section embedded in fuselage, and right wing. $\endgroup$
    – Jan Hudec
    Nov 4, 2020 at 13:09
  • $\begingroup$ I am not really sure what you are looking for. There isn't much difference between structure joined from multiple pieces and one build from one piece. $\endgroup$
    – Jan Hudec
    Nov 4, 2020 at 13:28

1 Answer 1


The bending moment is produced by the lift generated by the wings and the weight of the fuselage in the middle, or on the ground the weight of the wings and the support (gear) mounted on the fuselage or fairly close to it. So it is always there.

The only choice you have is how to build the structure to carry that load. You can:

  • Have a central spar, a solid beam that carries the load, and unstressed or lightly stressed skin. That's how all the early planes with fabric-covered wings and fuselage were built.
  • Have a hollow wing with stressed skin supported by mesh of ribs and longerons. That's how most aircraft are made today. You have tension load on the bottom and compression load on the top and the centre is not doing much, so not having it there makes a lighter structure.
  • Anything in between, with solid spar, but some load carried by the skin.

Independently of that, you can

  • Build the structure in one piece and and attach the fuselage to it (from above, below or build it around).
  • Build the structure in several pieces and join them with rivets, bolts or glue.

In either case the structure is continuous through the fuselage. The fuselage walls would have no chance of handling the load if you didn't have any connecting structure inside and would bend easily. The only difference is whether it is joined from multiple pieces or not.


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