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Need help interpreting instructions on 13-3 Wing Spar countersinking

salty

Well Known Member
Empennage is pretty much done now, getting into the wings. Apparently I still need more practice interpreting the plans... I think I'm reading too much into them.

Initially, I was having a heck of a time figuring out which holes exactly they were talking about in bold below. none of the rib to spar flange attach rivet holes appear to actually be in line with nut plate attach rivet holes. But then when I read step 3 it seems like it's saying to CS all the holes anyway, so maybe the comment in step 2 is more to make sure you don't miss them as they are hidden in the row of nut plate holes. But if that's the case, then I don't understand why they qualified the statement with "inboard of the most outboard fuel tank attach nut plate" if you're going to do them in step 3 anyway. :confused:

Step 2: Machine Countersink the nutplate attach rivet holes in the flanges of the W-SPAR ASSY-L Spar Assembly - Left. Machine countersink those rib to spar flange attach rivet holes that are in line with the nutplate attach rivet holes and are inboard of the most outboard fuel tank attach nutplate.

Step 3: Machine Countersink the skin and rib attach rivet holes in the flanges of the W-SPAR ASSY-L Spar Assembly - Left. Countersink just deep enough to fit the dimples in the wing skins. Make a dimple test sample by drilling and dimpling a scrap of .032 aluminum for an AN426AD3 rivet. See Section 5E.
 
Grab a rib and see how it fits into the spar. There are two -3 rivet holes in the flange of the rib that mate up with holes in the flange of the spar. For the outboard leading edge they get used to attach the leading edge and the wing skin. The forward most of those get covered by the tank and get a flush rivet installed before the tank is installed. The aft set of holes are used to attach the wing skin for the whole span. That's why you have two different sets of countersink operations: 1) for flush rivets for the nutplates and these holes under the tank and 2) deeper for accepting the skins.

Double check everything before you start making chips. There are about 1000 holes and countersinks to make in the spar and you can make a very expensive mistake if you aren't 100% sure what's going on!
 
Okay, I see one is CS for the rivet and the other is CS for the dimpled skin.

I'm still fuzzy on the specifics they are calling out. I'm thinking it might be good to do section 14 through page 4 first and fit everything together to see it. Should be self evident at that point.

What do you think of that idea?
 
I was confused by the step as well. If it makes you feel better, every single hole in the spar flanges will be countersunk when you're done. The difference is the depth. The holes for the nutplate attach holes and the holes described in this step are countersunk for a rivet only, the rest of the holes are countersunk deeper for a dimpled skin. Like was already said, the holes in this step are the forward holes of several of the ribs which will be riveted to the spar but not the skin above because the fuel tank will be installed over top of those rivets and gets bolted in place.
 
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