Wednesday, December 23, 2009

Riveting the Tail Fuse Frames

The first two and a half were easy. Blind rivets - not too much can go wrong.

The third frame, however, has a very beefy structure on top. That can mean only one thing: it is going to have a very important job to do, and will therefore require big, fat #4 solid rivets. Ok, it means two things. It will have a very important job to do, it will require big, fat #4 solid rivets, and they will be a bear to squeeze. Ok, it means three things.

So, what's the critical function that will be the responsibility of the upper half of the smallest frame? Funny you should ask. That extension coming from the top of that frame is where the four bolts that hold the vertical stab and rudder will go. Given that the plane probably can't fly without the vertical stab, keeping a tight grip on it is an important role indeed!

There are 18 rivets to be squeezed, and they are a bit tricky to get at. There are. as seems to often be the case, flanges that get in the way. After attempting multiple contortions and invoking any number of profane incantations, I came across an angle of attack (so to speak) that allowed the access I needed, although it still required quite a bit of facial scrunching and bulging arms to get them squeezed:

I know I make it look easy, but really, you should consult your physician before trying this yourself. Facial contortions lasting longer than four hours should be considered a medical emergency.

In addition to the circus act needed to get the squeezer into position, there was also a special pattern required to work around the clecos. Here's the order that I found to work best:

Here's the ugly side that no one will ever see again once the tail is buttoned up:

After all of that effort, the frames ignominiously joined the tail skins back on the parts shelf while other parts are prepared. The first of those is the piece that a threaded O-ring will go into to provide a tie-down hoop at the back end of the airplane:

There's a template that provides directions on holes to be drilled and corner to be cut:

The manual calls for a 3/8 x 16 (3/8" diameter with 16 threads per inch) tap to be used to thread a one inch deep hole that the tie down hoop will screw into. My tap set has two 3/8 taps, one labeled 3/8 x 24 and the other simply labeled 3/8. My assumption that the plain old 3/8 tap assumed a thread per inch count of 16 was proven with this side-by-side comparison:

There's a rather cryptic command on the drawing that says "Cut To Tangent of 1/4" Hole." I'm not sure exactly what it means and will research it before proceeding, but my initial guess is that a line drawn from the tangent of the holes will intersect the two little semi-circles on the edges, and that I am supposed to remove the metal from the part underneath the template that resides under that line:

Note also the 5/16" drill bit that will be used to pre-drill the hole into the part. The masking tape marks one inch of depth.

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