Fastback 12 – Vert Stab Modification


The Showplanes Fastback is slightly higher than stock at the intersection of the turtle deck and the vertical stabilizer. As a result, the front of the vertical stabilizer must be trimmed to allow sufficient clearance. 175 degrees to be exact. I bought a protractor on my way to the shop today, and presto here’s the result. Before this photo was even taken, I removed all the appropriate rivets. 

As you can see, this doesn’t allow the existing rivet holes to be placed nicely in the new layout. The new line is close to the second hole, and essentially bisects the next two. I gave careful consideration to how I should approach this problem. Online I found a few pictures, but nothing with enough detail. I found one builder who build a new rib. I briefly considered doing this as well. Getting the existing rib to fit, turns out to be a challenge.
  

Next, nothing to do but start the cut!

I really didn’t want to have any chance to harm the front spar so I protected it with some scrap aluminum I had laying around.   

Here’s the part that has only one photo, but took a ton of time!! Fitting that rib into position. I wound up fluting the nose and redoing some of the flange bends to narrow the nose of the rib down. I also redid the rear flange bend to pull the entire rib aft. This is a better solution (in my mind) than creating a new rib from scratch (which for me, is something I’ve never done).   

Here’s a good picture of where the previous rivet holes are after the cut. Not optimal. If I keep the same holes in the rib, there will likely be some of these that are very close together, especially those closes to the spar. I measured, and the aft most rivet (not in the spar) would almost touch one another. That won’t do!

The best solution I came up with was to create three new rivet locations aft. You can see them marked here. I was able to keep approximately the same spacing, and ensure that there was ample edge distance for every new hole.   

As for the old holes, I flattened them, and made sure they were as smooth as possible. They each have a firm new rivet on either side of them, which according to the acceptable methods of aircraft repair is the appropriate method.

I filled in the holes with a little JB Weld. Not for strength, but to build the primer / pain on to later.

Here’s a good picture of the end result. I’ve tried to diagram where the original holes are in the rib, and where the new ones are. The original holes in the skin are fairly obvious.   

Apparently I missed the note to leave these spots empty for the fairing. I did the same thing on the elevator. Man, what a newb I was then!

Next, I pulled the horizontal stab down, and removed the elevators. (They were just placed there temporarily for storage). I’m considering taking care of Service Bulletin 14-01-31 before installing the empennage. This is a bear of a project, so I’m not convinced yet. It isn’t required unless cracks form in the spar. Until such time the only requirement is yearly inspection. However, this project will not become easier after installation.   

I do not have the required relief notches. Upon review you can see them in the drawings, but there are no reference to them in the instructions.

Again with the fairings!  

Session time: 7 hours

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