Building, testing and operating an experimental aircraft

Horizontal Stab Quality Control

20 Apr 2010

After completing the horizontal stab, we performed a little QC inspection of the work we’d done, and despite being as meticulous as possible while squeezing rivets around the edge, we noticed that we had a few bad ones.

Squeezing Rivets Squeezing Rivets

For some reason, while using the Cleaveland squeezer, we ended up with some “clubbed” shop heads, illustrated below from MIL-R-47196A, the military specifications for driven rivets.

Clubbed Shop Head Clubbed Shop Head

Although we carefully aligned the flush sets of the squeezer, and watched the shop heads as they formed, the fact that these rivets had “dumped over” escaped our attention until we took a closer look. Some example photographs are included below.

Clubbed Rivets Clubbed Rivets

With the tiny AN426AD3-3.5 rivets, it’s difficult to get a properly-sized shop head that adequately covers all of the drilled hole beneath it. If we moved the set or bucking bar just a little off center, we got results like these. We found we had a much easier time forming acceptable shop heads with the bucking bar rather than with the hand squeezer.

Unacceptable Rivets Unacceptable Rivets

At this point, we’re still not comfortable using the squeezer without it being solidly mounted to the workbench.

Bad Rivets Bad Rivets

We called our Tech Counselor, Tom, and he graciously agreed to return just a few days after his first visit, to confirm our suspicions that these rivets needed to be replaced. Before his arrival, I carefully inspected each accessible shop head with a flashlight, then marked any suspect rivet with a permanent marker.

Drilling Rivets Drilling Rivets

Tom agreed that some of the clubbed rivets would need to be replaced, but also added that the odd rivet here or there with an imperfect shop head might be considered acceptable, while several bad ones in a row should be drilled. We’re still developing our own sense of quality workmanship, so Tom’s advice was again invaluable. Thanks again, Tom!

The Aftermath The Aftermath

So, after completing the vertical stab, we went back to the HS, and spent a couple of hours drilling out and replacing rivets. We got fairly adept at the process, and won’t have any reservations about replacing bad rivets in the future.

The good news, however, is that the horizontal stab is now done! Both the HS and the VS are now in temporary storage, as we move on to the empennage control surfaces.

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