Step 13.2, Horizontal Stabilizer, SB

Vans aircraft announced a Service Bulletin a while back that applies to my plane.  The SB requires recurring inspection of a section of the main spar of the horizontal stabilizer that has been shown to develop cracks on some aircraft over time .  This is not a particularly worrisome development -- GA airplanes get these types of service bulletins or ADs (Air worthiness Directives) all the time.

What is a Service Bulletin and how does it differ from an AD?  SB are maintenance recommendations from a manufacturer and do not carry the force of law.  Air worthiness Directives are mandatory compliance issues that come from the FAA.  An AD may reference an SB in which case the SB does become mandatory.  Even though an SB may not be mandatory, it is probably not a good idea to just ignore them.

That Vans Aircraft has responded with the SB and provided a retrofit kit is a good thing and shows that the company is safety conscious and is proactive in maintaining their good reputation. The SB states that the retrofit kit is not required until cracks have developed. As a preventative measure, I have decided to implement the fix anyway since the horizontal stabilizer is not yet on the plane and has not been painted.  There will never be a more convenient time to do the work so I might as well do it now even though it will delay my completion date a few days.

The first step is to disassemble the center section.  This means removing the inside ribs and the attachment flanges.  There are a lot of rivets in here.  The last time I worked on this piece was in early 2012.  I always hoped that I would be get to fly the plane a little before I started tearing it apart.

The rivets attaching the inside ribs are removed.

The horizontal stabilizer main spar is that thin piece of sheet metal in the foreground.  The area of concern are the four rounded notches right at the edge of the skins,  This is, evidently, a high stress area, which is why the notches are placed there in the first place.  The theory behind the notches is that the slow curvature of the inside edge of the notch would allow the stress to flow around this area rather than build up at a single point, resulting in crack formation. 

The theory has worked on most planes, but a few have developed cracks which led to the service bulletin.

The retro fit kit further beefs up this intersection with doubler plates on each side.

The doublers are clecoed in place prior to riveting

This is the front mostly riveted.

And the rear with the doublers visible.

Now the ribs are re-installed.

The final step is to complete the painting.

Horizontal stabilizer service bulletin (and painting) complete!

Step 13.1, more painting

Sand, sand, primer, sand, sand, base, base, base, sand, clear, sand, sand, buff. done.  Ok, good, now on to the next piece.  Obviously it's needless to say, but painting is a slow, messy, and often very tedious business.  I comfort myself in the knowledge that I'm saving big bucks here  -- enough to buy fuel for about 5 years worth of flying (assuming the average GA pilot flies about 50 hrs/yr). I plan to fly more than that, but who knows.

After the primer is sanded down to #800, the masking for the stripes begins.  Here the wing tips are masked and ready for the first stripe.  I don't know if this is the most efficient method or not, but I start with the gray stripe.  The when that is on and dry enough, I peel the tape up and re-apply it over the gray, but on the other side of the line so I can mask off the just painted stripe.

Then the blue is applied and re-masked for the white.  Here is Carol preparing the tape for the blue stripe.

Finally after all of the base colors are on there are two coats of clear applied over the top.

On to the next thing.  Carol sanding primer on the left wing.

Here I'm applying 3-M fine line tape to follow paper templates for the stripes.

Here is a wing in the blue stripe phase.

Wing tips and wing after clear coat in the paint booth.  I think the flash must have been off.  I don't think it was really that dark in there.

So at this point, I've done no color sanding or buffing because that can wait. Indefinitely, I think, because there will always be something more fun to do.  I've completed about 1/2 of the painting now with just one really big item, the fuselage to go.  Of course there are numerous smaller items such as the cowling,  the vertical stabilizer, rudder, wheel pants, and fairings to go...