As we get to the last of the flap repair (for this wing anyhow) I'm learning more skills that will come in handy later for my build.
So far, I've had the opportunity to work with blind "pop" rivets (the predominant style in the Zenair line of aircraft) and solid "bucked" rivets. Both have their place and use.
Last night I started working with flush rivets. Designed with a smooth flat top they too are bucked or squeezed to form a bond between two sheets of metal. The advantage these have however is that they leave the top surface smooth and thereby more aerodynamic. It also looks real cool! Most modern metal aircraft use this style for aerodynamic reasons. They are particularly handy around windows trim and landing gear plates where thickness tolerance of adjoining parts is important.
In the case of our flap repairs, we wanted to come up with a way to clean up the trailing edge and correct the ham-fisted attempts at a straight edge by the original builder. Ron made up a sleeve which will be flush riveted to the trailing edge.
It starts with marking out the rivet lines and drilling small #3 holes, the size of the rivet shank:
Next, the hole is very carefully countersunk with a bit in the cordless drill:, to a depth that matches the shoulder of the rivet. Holes for larger rivet are usually countersunk using a dimpling tool, but this tool works here:
Here is a picture of a typical flush rivet. Note the smooth flat top, angled shoulder and round shank:
Making the hole match the rivet so it lies flush is the goal here. Too shallow and the rivet won't lie flush, too deep and it can't hold the bond adequately enough nor be completely smooth on the surface:
Work a little at a time, test fit often and eventually the rivet will sit perfectly flush with the surface... smooth!:
Now repeat 30 times along the trailing edge :)
Ron and I flipped the wing over on the bench and I removed the damaged nose skin:
I know at this point I shouldn't be surprised by anything I find with this repair, but this was interesting. There was a "perfectly" blended rectangle, held in place by rivets and covered by the magic of cheap paint located at the back edge of the nose skin. It is hard to make out in the picture below but I really didn't notice until I took off the skin what it actually was, so I don't have a before picture.
Once the skin rivets were removed, and the damaged nose skin removed did the curious patch reveal itself, again nothing surprises me anymore:
My only guess is that this was some sort of Mickey Mouse access panel to get at the wing strut mounts, but I can't for the life of me figure out how anyone thought this was an acceptable patch..... jeebus.
On a happier note, I recently confirmed my attendance this fall at the Zenith Factory open house in Mexico Missouri. It's a two day drive from here, but most importantly William Wynne will be there demonstrating the build up of Corvair engines. As a bonus I'll be able to take my core items for assessment and perhaps send my heads away for rebuilding at the same time. Can't wait to atttend and learn even more!
Next up, more finishing work on the wing repair and prepping the bench for slat building.
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Husband, father and 911 dispatcher. Long time pilot with a licence that burns a hole in my pocket where my student loan money used to be. First time aircraft builder. Looking to fly my own airplane.