Brief Description: Prime Skins and Stiffeners; Back-rivet same
21-3 Step 8:Primed skins and stiffeners then back-riveted all per the instructions. I added in a recessed back-rivet plate into my torsion buld table to ease the task for both aileron and flap construction. I prefer using the long back-rivet set as it seems to promote being more square to the rivet when setting the rivet. It required more air pressure to obtain the same results as the short set because of its larger mass. I used about 45 psi at the compressor side regulator which is probably about 35 or 40 psi at the gun (3x gun). The 426AN3-3 rivets were just a tiny bit shorter than perfect but they set fine and for these stiffeners I think were acceptable.
This image shows side and middle back riveting surfaces