This week's task is to finish the empennage fairing. I've been wanting to take the empennage (vertical and horizontal stabilizers) apart now that they have been fit, so that I could ready them for painting. One last detail before I can remove them is to fit the empennage fairing. The fairing is a molded fiberglass part that comes with the finish kit. It is designed to cover the intersection of the vertical stabilizer, horizontal stabilizer, and fuselage. As it comes from Van's, the fiberglass is a bit too rough for painting and the fit is, well, less than perfect. A heat gun is used to make minor adjustments here and there, but some new fiberglass and much sanding is required to fine tune the fit.
In addition to generally improving the fit, I also want to add a lower fairing to it so that the fairing covers the gap above the horizontal stabilizer as well as below it.
So here is the basic fairing as it comes from Van's after trimming the excess. It's not visible in the picture below, but the fairing does not extend underneath the horizontal stabilizer. The Van's way to fill this lower gap is to fit a piece of aluminum trim to the fuselage that extends upward to the bottom of the horizontal stabilizer. I've decided to follow the lead of a number of other builders who think it nicer to add a fiber glass fairing to the bottom of the Van's supplied piece. More on that later...
The elevator torque tubes come from the center of the fuselage area and extend through the fairing. Carol worked on finding the limits of the tube's movement relative to the fairing. A template was made and the curve transferred to the fairing. The fiberglass was cut back to the blue line that leaves clearance for the elevator control.
A few other notches and trims later, the fairing was fitting nicely.
The next step is to build the lower fairing. The aluminum skin is protected with a layer of packing tape. Then modeling clay is globbed on to pack the lower gap. I cut a piece of aluminum with the radius that I wanted on the fairing and proceeded to scrape off all of the clay that didn't fit the radius profile. I slapped on some automobile past wax as a release agent and I was ready to mix epoxy. Well almost, I cut out the strips of fiberglass first.
Next came the fiberglass and epoxy. Four layers of 9oz. BID glass with West Systems epoxy.
It's a couple of days later and much to my surprise, the fairing comes off easily. There may be a little more epoxy in the layup than is necessary. The new glass is 10 to 20 thousandths thicker than the Van's supplied piece. I didn't know ahead of time how many layers Van's used, so I consider myself pretty lucky to get even that close. Here is the new glass (foreground) grafted on to the Van's piece after the rough trimming.
For filler I used a mixer of epoxy and micro-spheres. The micro spheres are just little glass bubbles that take up space. When combined with epoxy they make a very lightweight filler material that is fairly sandable.
These leading edges don't look too good, so I'm forced to go for another round of epoxy. To get a better fit on the mating surfaces of the vertical and horizontal stabilizer, I'm going to lay up a thin layer of glass on the HS and VS directly over the leading edge part where the fit is poor. Then, after that is almost set I will re-install the fairing with some wet epoxy on the inside to bond with the thin layer.
Now the fit is pretty good around the entire perimeter.
At this point its just a matter of smoothing everything down, filling pin holes and other minor imperfections in the surface, and match drilling the mounting holes through the fairing to the aircraft structure.
After a coat of primer it's ready for paint.
The empennage fairing has taken much longer than I expected. Oh, well. It's the journey not the destination that's important -- I just have to keep reminding myself.
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