Building, testing and operating an experimental aircraft

Skin Riveting & Murphy's Law

05 Jan 2010

We’ve really been making some headway over the last few days, so today we wanted to knock out as much of the skin-to-understructure riveting as possible. Unfortunately, that pesky old Mr. Murphy decided to exercise his famous law.

HS-707 Nose Rib Clecoed HS-707 Nose Rib Clecoed

Riveting began by wrestling the HS-707 nose rib into place on the left skin. This baby does not want to squeeze its way forward very easily, and takes some muscle to get the skin into position over the holes. Then, once it’s finally in place, the forward nose of the rib doesn’t like to “sit down” on the skin. We had put a flew clecoes in the bottom side of the rib as well, just to hold things together while riveting the top side.

HS-707 Nose Rib Riveted HS-707 Nose Rib Riveted

This was our first real test of riveting skin to ribs since completing the Van’s airfoil practice kit. We set the air compressor output to roughly 38 psi, and adjusted slightly down from there with the Brown Tool swivel regulator on the gun. We also followed the advice of several builders on the VAF Forums, and covered the factory head and surrounding skin with a couple short strips of masking tape to help eliminate slippage and scratching from the flush rivet set.

Everything worked beautifully. I think we may have drilled out one rivet with a malformed shop head due to lifting the bucking bar off the rivet too early, but other than that I think our confidence and skill are definitely improving. Oh, and we’re also getting pretty good at drilling out rivets.

Rear Spar Bent Rear Spar Bent

Then, while moving things around in preparation for the next few steps, we dropped the rear spar assembly, causing one of the HS-603s to bend about 20° toward the flanges, just outboard of the ends of the riveted HS-609s.

Rear Spar Damage Rear Spar Damage

Using the hand seamer, we were able to mostly straighten it back out, but there are still some damaged areas visible from the bend line. I was concerned that we may have caused unseen structural damage, so I decided to email some photos to Van’s.

Spar Damage Spar Damage

Several hours later, Van’s Aircraft builder support rep Ken Scott returned my email, with this reassuring statement:

Probably not any disaster. Certainly the fix is straight enough to use. There’s no way of knowing what the future holds, but it seems unlikely that there will be problems. If that’s not enough reassurance, simply taking the spar apart and installing a couple of new HS-603s will eliminate all uncertainty. It might add a day’s work to your airplane project…

So we decided to at least cleco the spar to the ribs and skin, to see if we could salvage the part.

Almost There Almost There

We got everything to align fairly well, and the damage seems minor, so at this point I think we’ve decided to “build on” after a brief hiatus. The right side of the rear spar on the stab will just have to be a place we keep our eye on down the road for any abnormalities.

I’m sure this little catastrophe is only the first of many to come.

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