Brief Description: Rear Spar to Countersink or Dimple?
As you will frequently hear after the empennage is completed the manual instructions become less detailed (less hand holding) and you need to spend more time with the drawings as they are the master, which is at it should be. Rivet callout is king but you also need to study carefully as to what those rivets are going through and this is a good example.
At the very outboard section of the rear spar the holes will align a doubler plate, outboard rib and the Aileron Hinge Bracket. The plans call for AN426AD4-5 on the four outboard holes and where the red arrow points an AN426AD4-7. Now this is where reading the plans is so important; in Image 2 at the red arrow tip is a black vertical line - this is the Aileron Hinge Bracket and this is where the rivet head will go - NOT on the doubler plate - the main clue is the rivet length.
There are two options for the outboard holes - dimple or countersink. Section 5E of the manual gives you the information on which to make your decision "minimum thickness for AD4 countersink is .050" and "..the interlocking nature of a dimpled rivet line is stronger". Now the rear spar is .050" so it is JUST thick enough to countersink however, what swung it for me (and thanks to Dans RV7 Factory website for this) was that dimple joints are stronger. I just have to remember now to dimple the outboard ribs!
This a a good time to dimple the top rear spar flange above the doubler plates and reinforcement bar as access will not be possible once they're rivetted in.
Finally you can tape off the reinforcement plate holes that will later be rivetted in assembly or I just taped around the cleco's which seemed to work fine. Big day when I finished rivetting the rear spars - not one rivet drilled out! Boy am I pleased and am I pleased I bought the pneumatic squeezer - expensive but for me it's worth it.
