RV9/7 center section rivet callout on web stiffener

[alpinelakespilot2000]

The center section is really where Van's really leaves you on your own (and the drawings don't seem to be helping in this case)...

Ref: dwg 16--
The F-904M web stiffener (that goes on the back of the fwd center section web) calls for flush rivets to attach the stiffener to the web with the flush heads fwd (so that the cover support rib can sit flush on the forward side of the web). The call out is for 426-4-5 rivets. However, the fwd center section web that must be countersunk is only (as best I can tell with my calipers) about .040" thick. Since the minimum c-sink thickness for 426-4's is .050", what gives? If it would have called for 426-3's, I wouldn't have thought twice but a 426-4 really seems too big for countersinking in this case.

I assume the 7 uses the same web stiffener/center section set-up so if any -7 builders have encountered this issue I'd sure appreciate their help as well.

Thanks.

 

[LettersFromFlyoverCountry]

Steve: I recall asking Van's about this. The structural element of that stiffener isn't going to be the rivet to the stiffner, it's going to be the screw going into the nutplate on the stiffener. The work of the rivet is to hold the stiffener in place until the screw goes in the nutplate.

 

[alpinelakespilot2000]

Thanks Bob. Out of curiosity, on a related note, I suspect the rivets holding the spacer bars serve only the same purpose, since the two bolts hold everything together. Per plans, I used the 2 AN426-4-14 rivets and got almost NO shop head after setting them, it's like the bar swallowed up the rivet. Have others found the same happening here? I just want to make sure that I'm not supposed to have a "normal" shop head before I move on to other things.

 

[LettersFromFlyoverCountry]

Per plans, I used the 2 AN426-4-14 rivets and got almost NO shop head after setting them, it's like the bar swallowed up the rivet.

You mean the doubler bars on each end of the center section? Yep, same deal here and I asked Van's about that too. The answer was the same. The rivets are not performing a structural task here other than to hold the bar in place as the wing spar is inserted.