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RH Spar Riveting

Here are some pictures of riveting the right hand spar.  The first picture is using a tungsten bucking bar we borrowed from a friend.  It weighs a lot since the density is so awesome.

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This next photo shows a really difficult area to buck the rivets.  Not even the little tungsten bar would fit between the angles.  We fabricated this bucking bar from a piece of round stock and a bolt.  Notice we had to machine one side of the bolt, we also rounded the edge so it would fit in the radius of the spar angle.  These rivets are pretty long so they take a little more from the gun to set.  (We had a fun discussion about the physics of why they took more to set than the others.)

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Below is the completed row, they came out pretty well.  I would like to know how people rivet this row when they use the Sonex hammer and bolt head process.  I imagine they back rivet and machine a bolt like we did.

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In the next picture the rivets are on the top row were -12’s and were a hair too long by the rivet gage.  We borrowed this gauge from a friend and it is really nice to check the rivet length before and the shop head diameter and height once set.

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Well we tried the -12 and a couple were OK but then they started to dump, or mush to one side.  We think I was tilting the bucking bar up a little and the long rivet would mush over from that misalignment.  We drilled those out, which is a pain since they are so long.  We shortened the rivets to match the gage length.  We used a belt sander but they got hot quickly.  I didn’t want to over heat them  in case that would change their properties.  I’ve heard about rivet cutters, but pretty expensive for a handful of rivets.    In the end we got them all done.

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Main Spar (right)

So many small details that we have documented with photos and emails back and forth but so few posts on the web site.  We need a secretary….

In November of 2012 the right wing box was assembled for the first time and in December and January (2013) the ribs were match drilled to the spar, up drilled and the gussets were attached.  Many web sites (Blogs) keep track of hours meticulously but we are really bad at it.  I (Dan) try to spend some time each available day in but there are many days that do not allow any time to work on the plane.

Regardless, in late January everything was in place to begin assembling the right spar.  Counter sinking was done, dimpling was done as well as de-burring and light priming.

On Monday night I drove the first few (flush) rivets on the right spar.  They turned out pretty good but we are using conventional riveting with a pneumatic rivet gun (3x borrowed from Gary Hall, our Harmen Rocket builder friend) and bucking bars.  We found the quality of the flush rivets was very good when using the conventional method with the proper counter sink depth.  I wrote up a little analytical evaluation of the countersink calculation that seemed to be pretty reliable.  The bottom line is that for a 110 degree countersink and 0.032″ skin, an AN426-AD-5x rivet required a minimum of 0.022″ more diameter countersink than the rivet head width at it’s widest.  I will have to post the calculations but the rivet head is 0.275″ wide so the counter sink needs to be in the order of 0.300″ diameter.

Counter sink diameter

After driving a small number of rivets it became apparent that this job would be much easier with two.  So the following night, Tim and I got together and started driving rivets.  As was expected, we got progressively better at it as each rivet was driven.  That was until we go to the section of flush rivets on the spar where the rivets are buried between the upper spar cap and an angle brace.  Our best efforts resulted in driving a couple less than ideal rivets and drilling out most that we put in due to them being dumped on the shop side.  We debated back riveting (putting the flush head against a smooth metal surface and driving the shop end with a hammer and bolt like Sonex advocates)  these are hard to get at rivets and eventally decided to sleep on the issue.

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