Structural Question

[Kyle Boatright]

This example isn't on an experimental, it is on the EAA's B-17 - Aluminum Overcast, which is grounded for the time being with a wing attach issue. Anyway, at the bottom of the linked page is a sketch of the wing mounting structure that caused the aircraft's grounding. What I found interesting is that there are attach points for the upper and lower spar caps - a very common attach method. But there is also a middle attach point. Doesn't that middle attach point make the entire mounting concept structurally indeterminate - where you can't easily calculate the load path? It just seems really odd to me.

Here's the link: Update on EAA B-17G Aluminum Overcast - Aero Vintage Books

Can someone help me understand the how/why of that middle attach point?

 

[BJC]

 

[bmcj]

 

[dave wolfe]

 

[Hot Wings]

 

[trimtab]

 

[Toobuilder]

 

[BBerson]

 

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[Riggerrob]

 

[Jay Kempf]

 

[D Hillberg]

 

[bmcj]

 

[wsimpso1]

 

[Map]

 

[John Halpenny]

 

[ragflyer]

 

[crusty old aviator]

 

[pylon500]