| Empennage Fiberglass
I have decided to attach my fiberglass tip to the airframe with screws
rather than pop-rivets. I don't know that I'll ever want to take them
off, but if a reason comes up I want to be able to get them off with minimal
fuss.
Did I tell you that I hate the new counterbalance design? I read somewhere that Van's motto
is "Simplicate and add lightness." Somebody
at Van's decided that they might save a few grams if they rotated the lead
weight 90 degrees and moved it to the forward face of the tip ribs.
Maybe so, but it sure complicates closing the tip. They kept the
original tip ribs and surface skins, and changed the counterbalance skin to
accommodate the forward shift. It may add lightness, but it sure don't simplicate.
 When
you try to mount the elevators, the old HS skin pattern interferes
with the new counterbalance length and must be trimmed.
The molded flanges on my tips were too long and butted against the rib
flanges inside the skins. If necessary, sand the flanges until the
molded flange seats against the skin.
 I
started with the elevator tips. Having them in place will help you
position and align the HS tips. Same goes for the vertical parts - do
the rudder first. Mount the elevators to the stab, being careful to
ease the counterbalance between the over-sized tabs on the HS tips. (I
didn't get a photo of the overlap on the -7. I'll post a cheater from
the -8 as soon as I get to it.) You also have to trim the forward inch
or so of the fiberglass flange where it slips inside the counterbalance skin
to clear the lead and trim the forward length to clear the HS tip.
With the elevator tip trimmed to length, I made a fiberglass a patch to
close the open end of the tip that faces forward.
Figuring out how to make the patch and get it to stay where I put it took
several tries before the light came on. The one that finally worked
goes something like this...
 I
glued a scrap of foam art board to the open end of the tip. This is
the HS tip, but you get the idea. It doesn't need to be strong - it's
really just a form that I'll tear off later. When the glue is dry,
turn it over with the cavity facing you, foam scrap down. Cut two
pieces of fiberglass fabric (mat or cloth, doesn't really matter) to lay
flat against the paper face of the foam. Cut another piece of glass
1/2-inch or so over size and tuck it in on top of the first two plies with
the edges curled up the insides of the tip. Work out the wrinkles - a popsicle stick makes a great wrinkle-smoother, but
sand the edges first or it will pick at the glass cloth.
Cut a fourth piece 1/2-inch bigger and work it in on top of the first three.
Work as many of the wrinkles out as you can, and make relief cuts as
necessary to get rid of the rest. When you're happy with the fit, mix
a batch of epoxy and pour it on the glass. Work the epoxy in to the
glass and up the sides of the tip. Drip out the gross excess and set
it aside to cure.
A few hours later, the matrix should be cured enough to handle without
pulling it apart. Ease a sharp knife between the foam patch and the original fiberglass and the paper facing on the foam board should tear loose
without any trouble, leaving the fiberglass bulkhead behind. If it's
still slightly soft, you can trim the glass with a sharp knife or scissors,
leaving less to grind and sand later. Set it back down on a flat
surface to finish curing or the soft matrix may sag.
 I
filed, whittled and shaved for days trying to get the fiberglass tip to fit
over the chunk of lead that's hanging out in the wind. File a little
and slip the tip in place. The lead is soft enough to show scratches
where it needs to be trimmed. When it stops interfering, the tip
will stop leaving marks on the lead and you can stop filing.
 Now
find a way to put back some of what you took off. With the trim servo
mounted in the elevator, I had to add a stack of fender washers to get it to
balance, and it still needs paint. You could probably get away with
balancing both elevators as a unit, but I don't like it. More than
balancing stick forces, we're trying to avoid flutter, right? Seems
better to balance each surface individually.
 Incidentally,
can you find the safety issue in this photo? I need to move the
nutplate to the inboard side of the counterbalance rib and put the weights
outboard. If the bolt backs off in this position, it will jam the
elevators. A small poke-hole next to the nutplate will allow me to
check the hidden weight for snug during pre-flight. Pictures at a
later date...
  OK
- it's a later date. Here are the counterbalances on Gene McNeely's
RV-8 elevators. I'll correct the RV-7 elevators the next time I take
the parts down off the wall. Note that the nutplates are on the
inboard side, putting the weight and bolts outboard. After I took this
picture, I drilled the #30 hole (mentioned above) about 1/2" aft of the
nutplates. I'll also use a drilled-head bolt and safety wire, just for
good measure.
  When
you're happy with the fit around the lead, you can make preparations to
mount the tip to the skin. I match-drilled the attach holes and dimpled
the holes that needed it - you may have dimpled the aft-most holes earlier.
Next I drilled and countersunk for nutplates. Rivet the nutplates to
the glass and mount the tip.
Use a light touch when setting rivets in fiberglass. Squeeze the
rivets just enough to hold the nuplates in place. If you try to get a
proper shop head, the rivets will probably swell too much and split the
glass.
   
 
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