Re-framed- Skin shear flow with ribs

[jpaero]

At the outset, this question in some fashion is a follow-up of my previous question but I feel is worth asking as a separate one.

Let us say I have a wingbox as shown below subjected to pure torsion at one end and cantilevered at the other. I understand that I can calculate the shear flow as q=T/2A, where A is the enclosed area, which in this case is 40x10. The enclosed area is the same for all the bays and the only load input is the torsion at the free at. Under these conditions:

1. Will the shear flows in the skin/spar vary across the bays if all the bays enclose the same area? If they do vary, what causes the change, and what factors determine this variation?
2. If the shear flows remain constant across the bays, I assume this would indicate that the ribs are not carrying any shear loads. In that case, would removing a rib impact the shear flows at all?

Intuitively, it seems like removing the ribs would reduce the torsional stiffness of the box. However, this feels contradictory if the shear flows don’t vary and the ribs aren’t loaded in shear.

In summary, the question is: Do the ribs play any role if the wingbox (a const. cross-section one) is subjected to pure torsion?

 

[SWComposites]

Yes, the box will buckle and/or collapse without the ribs.

Do you think aircraft designers have added ribs to wing boxes for 100+ years for no reason?

 

[jpaero]

Yes, the box will buckle and/or collapse without the ribs.

Do you think aircraft designers have added ribs to wing boxes for 100+ years for no reason?

Just in case you missed, the questions were:

1. Will the shear flows in the skin/spar vary across the bays if all the bays enclose the same area? If they do vary, what causes the change, and what factors determine this variation?
2. If the shear flows remain constant across the bays, I assume this would indicate that the ribs are not carrying any shear loads. In that case, would removing a rib impact the shear flows at all?

 

[rb1957]

with your very idealistic loading, the shear flows in the skin are constant. But the ribs break the skin into panels and this determines the shear buckling allowables

 

[WKTaylor]

The OP's posted image looks like a classic illustration from EF Bruhn's 'Analysis and Design of Flight Vehicle Structures'.

Re-do the problem using classic Bruhn 'hand stress analysis'... including torque, shear and bending in both configurations. I suspect that load redistribution around any missing elements will be very evident... and maybe catastrophic much like battle damage.

 

[Ng2020]

Shear flow is constant in all bays.

As others mentioned, the purpose of a wing box rib is manifold -
It provides a means to maintain wing aero profile under load, it prevents upper skin collapsing onto lower skin as the wing bends, conducts skin out of plane pressure loads into spars, it provides a means of distributing discrete loads introduced to the wing (pylons etc), it provides column support for spanwose elements like stringers and spar caps, panel buckling support for skins, a stiffener for spar webs, baffle for integral tanks...

 

[SWComposites]

the shear flows in the bays will be the same IF there is no change in thickness, depth, width, material in the skins and spars down the length.

 

[rb1957]

shear flow (due to torque) depends only on the enclosed area. Shear stress is shear flow/thk.