About Vibration

[Lee Jordan]

I'm drilling the holes into the flange of HS-405(rib) using the skin as a template. The 405 rib is linning up nicely as I work the holes from the aft spar, heading toward the front, to spar (HS-702). When I get to the last hole I need to drill I see that the 405 rib has "hooked" out from under the skin by 3/32s of an inch. The entire rib looks great, except for the very last hole I need to drill.

If I press against the front edge of 405 with my thumb pretty dog-gone hard, I can get it back under the skin. I could then drill and pin it in place and everything would look great.

What I'm wondering, is if there is a concern with lateral loads on the shank of a rivet. I'm pushing hard on the rib to get it in line with the skin, once it's rivetted, the force I used to push the rib into place is now going to be applied to the rivet, as the rib wants to go back to it's natural state.

With all of this occurring on the tail of the plane, do I need to be concerned with vibration creating a "sawing" effect on the rivet?

Would I be better off just trimming away the (3/32) the half inch piece of flange, or do I really need all the metal that's on the flange? The piece sticking out is 1/64 on one end, and protrudes out to 3/32 a half inch later.

Seems kinda silly to worry about a sliver of metal, but it's my butt in the seat and I want to make sure I'm doing this the best way possible.

Thanks
Lee Jordan
RV-8 (tail)

[dan]

The dimples are going to do a good job of reducing or maybe eliminating that shear tendency. Dimples nestling together help lock the parts together shear-wise, so there shouldn't be any load on the rivet. I'm no engineer, but that's my take on it.

But when you get down to it, you ought to flute your ribs and bulkheads so they don't bow or curve unnecessarily. You want nice, straight lines of holes. A little fluting here and there can eliminate that "hook" you're talking about.

And if it's the tip of a rib that already has relief cuts between holes, then fluting won't do diddly. In that case, you should be able to massage the rib (bend accordingly) so that the line of holes is straight.

Hope this helps,
)_( Dan
RV-7 N714D
http://www.rvproject.com

[DGlaeser]

The reason it is so hard to push in place is because the skin traps the flanges like a vise. If you were to remove the clecos aft, and let it open up a bit, it you could position it just fine (been there...) Even if you don't relieve the pressure, push it in place and drill it. After you've dimpled, the dimples will help align it for final assembly. When you re-assemble for riveting, start clecoing from LE back and things will be just fine.

Dennis Glaeser
7A - wings