The spar box is an assemblage that includes two HS-1211 spar caps joined by four HS-1212 in spar ribs, with the HS-1202 fwd spar and HS-1203 aft spar. It is definitely a big, sturdy piece of work. The horizontal stabilizer ribs and skin will be attached to this.
After the spar box was complete, we fitted the WD-1207 and WD-1208 upper and lower control horns. Then we did the same with the WD-1222 counterbalance brackets and the WD-1223 counterbalance arm.
It's interesting that the counterbalance arm and brackets need to be turned 90 degrees in order to match drill the holes which will be used to bolt them together. I don't think the plans specified why, but the reason that made sense to me was that it was easier to check alignment of the parts. When the counterbalance arm was turned 90 degrees, we could check alignment with a level.
One issue: after final drilling the cb brackets with a #30 bit, I noticed the holes still are not quite wide enough to fit an AN470 rivet. Not sure how others have handled this.
Put the level on the spar box...
Then put it on the end of the counterbalance arm to check alignnment.
