Originally Posted by Mike S
Are these holes possible tooling alignment holes??
They don't appear to be alignment holes. Those holes are used to attach the HS-00916 stringer web to the HS-1004 inspar rib in only two locations. Vans uses the same part on the two inspar ribs outboard of the stringer web (four total ribs), but the web only spans the two on either side of the centerline.
The overview drawing of the HS on page 08-01 shows holes at the web/rib interface, but no holes on the other identical ribs. I wish they would have not punched some or all of those holes for us in this case. I'd rather match drill them.
Originally Posted by Aluminum
An authoritative answer to this would require the kind of structural analysis only Van's engineers are qualified to perform.
My $.02: material this thin gets wrinkled even by -3 rivets properly driven, which will transfer loads elsewhere etc. It's a critical area that has been significantly beefed up compared to the older RV models. I say leave good enough alone since it's not called out in the plans.
I agree that the specific static loads and load spectra would only be available to Vans engineers, however, this particular issue doesn't require that information. Good engineering practice for large transport aircraft dictates open holes are filled with a rivet to lessen the possibility of a crack forming at the hole. Rivets put compressive stress in the holes which gives significantly better protection from crack initiation. I've seen a number of cracks in the fleet (big planes, not Vans) where the crack initiated at an open hole. I've been involved in creating service bulletins to inspect for and fix such issues.
You bring up a good point about possible wrinkling of 0.025 in. sheet. Before I put in extra rivets I'll test it out on some scrap of the same thickness. If it wrinkles then I could fabricate a small doubler, or, more likely, just forget about filling the holes.
But first I need confirmation that these four ribs do not use those holes for anything.