F-904b dwg 22 question

[FlyGuy65]

On dwg 22 there is a note to countersink the F-904B to seat rivets.

So, first question, do they really mean F-704B, the anodized bulkhead?

Secondly, is it just the bulkhead/rib intersection? Top and bottom? And why if it can be dimpled? Are the ribs that stiff that they would not flex enough to get over a dimple in the flange, or am I missing something bigger?

I've been searching regarding the bottom skin and F-704 bulkhead, and the consensus seems to be to dimple (except the few locations called out in the directions on the fwd part of the bulkhead.) Was just about to run amok dimpling when I saw the note....

Thanks in advance!

Edit: As usual, about 10 minutes after posting I came across more info. Vans website, support, tech Q and A, 2nd item discusses some of the issue.

 

[bjdecker]

On dwg 22 there is a note to countersink the F-904B to seat rivets.

So, first question, do they really mean F-704B, the anodized bulkhead?

Secondly, is it just the bulkhead/rib intersection? Top and bottom? And why if it can be dimpled? Are the ribs that stiff that they would not flex enough to get over a dimple in the flange, or am I missing something bigger?

I've been searching regarding the bottom skin and F-704 bulkhead, and the consensus seems to be to dimple (except the few locations called out in the directions on the fwd part of the bulkhead.) Was just about to run amok dimpling when I saw the note....

Thanks in advance!

This is a typo caused by the commonality of some of the RV-9 fuse parts. You are correct, there isn't an F-904B in the RV-7, and yes, the F-704B is the center section aft bulkhead in the RV-7

Because it (F-x04B) is anodized, you should countersink those holes requiring flush rivets.

 

[sahrens]

Seat pans

Your seat pans will lay over that area so you want a nice smooth surface.

Due to the thickness of the 704B you can distort or even create cracks attempting to dimple the flange on the center section. Plenty of room for a counter sink, just go slowly as you can’t afford to over countersink that area.