Step 11.2, Empennage fairing

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.

Step 11.1, Canopy jettison mechanism

Imagine you're flying along and suddenly everything has just gone to hell.  You have no choice at all, but to leave the aircraft in midair.  In an airplane with a sliding canopy, one just slides it open and out you go.  Alas, it's not so easy in a tip up canopied airplane when the canopy opens against the prevailing wind.  To overcome this obvious design oversight, Van's has thoughtfully provided a canopy release mechanism. Under dire circumstances the canopy may be released from its hinges via the canopy release handle.  The canopy can then be pushed upward and free of the aircraft.

The utility of the canopy release is a ready topic of discussion on-line.  The two main arguments being, one, that it is unlikely that one would be wearing a parachute in the first place, and two, that the release mechanism may not work as designed, especially since its never been tested in flight.  Either way, I think it's still a nice thing to have.  I look at it as a kind of Jesus handle -- pull the handle under emergency circumstances and you'll be meeting Jesus in a jiffy.

But there is another use for the canopy release mechanism, and that is, if you want to remove the canopy for maintenance.  With out the canopy in the way, the interior of the aircraft is much easier to access.  So for this reason I have decided to install the canopy release hardware.

To begin there are a bunch of UHMW (Ultra High Molecular Weight) blocks of polyethylene plastic.  This is the same or very similar to the kind of plastic used for kitchen cutting boards.  It offers excellent durability and very low friction which makes it ideal for use as hinge pin guides and bell crank bearings.

The basic mechanism is a handle protruding through the instrument panel that pulls on a lever attached to a bell crank.  The bell crank turns the action 90 degrees such that when the handle is activated the bell crank pull inward on connecting rods which in turn pull the pins from the canopy hinges.  In the photo below, the lever and connecting rods are visible -- the bell crank assembly is upside down.

And here is the bell crank installed showing the connecting rods withdrawn.

A wider view looking backward towards the back of the instrument panel.  The canopy hinges on the left and right sans canopy. The lever can be seen at center, left of forward deck central rib.  The release handle, not shown, connects to the lever and continues rearward through the instrument panel.

I'll leave the attachment of the handle until after the instrument panel is complete.  So for now, the canopy jettison mechanism is finished.  And so is this post.