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Finished up riveting the fwd wing skin, the rivets didn't sit as flush as I thought they would. During the dimpling I thought they would sit just fine, but after riveting some of the rivets they are not completely flush. I saw some threads that the dimple dies don't exactly match up with the new CS rivets from Sonex.

I suppose I can sand down the heads a bit. Does the design have to have a completely smooth airfoil on the leading edge?

Can you share a picture? I suspect the wing would be fine aerodynamically without countersinking any rivets, but doubt anyone has actually tried it (so from your description, I doubt you'd notice any difference aerodynamically). I'd be more concerned that the rivets are fine structurally and would probably only bother sanding them for aesthetics.

Have you tried setting these rivets in a couple pieces of scrap to figure out why they are protruding?

I would guess that the nestling of the two pieces of aluminum together that is provided by
dimpling adds to the strength of the leading edge portion ahead of the spar.

RT