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Nutplates on tail section longeron

JDA_BTR

Well Known Member
I'm trying to synthesize the plans steps to machine things correctly before assembly and I'm a little stumped.

Running fore to aft the side skin attaches to the longeron (1418) with a lot of rivets and a row of nut plates at the aft end. The nut plates go inside the longeron according to a prior question. These plates are used for the fairings later in the project and I think that the nut plate screw holes should take a flush screw. So it seems that I should be dimpling the center nut plate hole on the skin, and then countersinking the longeron for it.

But I can't find an explicit instruction to do that. I did find one for the nut plates taking flush screws on the access cover - I'm planning to do that.

But are the fairing cover screws flush and need additional steps, or not? Or is it in the instructions and I just can't put it together correctly?

Second question: on the access cover flush screw installation - it says to machine countersink the skin and longeron to take the dimple of the cover. So do I countersink the longero/skin sandwich like it says, or do I dimple the skin and countersink the longeron. The nut plate is attached and it seems that c/s the sandwich is the way to go.
 
First question

No there are no countersinking in this section as you are attaching fiberglass that is thick and countersunk.

Second question

If you want to follow the plans countersink as requested.

If you want to dimple then you will end up with a slightly deeper countersink in the longeron. Will that effect the structure? I don't know, The dimpled skin sitting in the countersunk hole might actually make it a bit stronger.
 
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