Riveting the stiffeners to the skins3h
June 20, 2022
Today I started riveting stiffeners to the skins.
The first thing I did was to dimple the trim access reinforcement plate and counter-sink the holes for the nut plates. Instead of dimpling the part and the nut plates, I went with the NAS1097 (also known as "oops" rivets). They have a smaller head than the "regular" AN426 rivets, which allows two uses.
The first case is to use them for damaged holes, so you need a larger shank. For example, a hole for the AN426AD3 could be upsized to -4 size. Then you can use a NAS1097AD4 rivet, which will have a factory head size similar to the AN426AD3 rivet.
The other use is to use them to attach nut plates. A smaller head size allows to counter-sink thinner materials (such as skins or various reinforcement plates) instead of dimpling them. This avoids the need to dimple the nut plate itself (which usually distorts it somewhat).
Then I riveted the nut plates using NA1097AD3-3.5 rivets.
Dimpled the skins.
And installed the plate and the stiffeners for one of the sides on both of the skins.
I did not buck the last rivet in the row (the aft one) as it would require bending the skin a lot, and if you don't do that, there is a risk that the stiffener will not sit tight against the skin (bending the skin pulls the skin from the stiffener).
I have already ordered a double offset back rivet set which should allow easier access to these rivets.