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The
top and bottom rib templates for the vertical stabilizer have been made
using same method as all the other templates. Cut paper,
stick to
plywood then cut plywood. Easy! The top airfoil
template
sits on top of the tailpost and the lower template sits 5" above the
longeron. I leveled the front of the fuselage on the bench
and
used the laser to shoot the vertical down to the stabilizer, making
sure the forward spar is in fact vertical. |
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With
the HS resting in place and the VS spars sitting in position, I can get
a good idea of where the "N" verticals and webbing support are
going to be. I have measured from the tips of the horizontal
stabilizer to the firewall making sure they are equal before marking
its position on the top longeron. This is where the "N"
verticals
will be epoxied. |
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The
aft webbing has been cut and is now drying between the "N" verticals.
The lower gusset blocks are also in position. The
bottom of
the forward VS spar passes through two layers of webbing so I will be
setting everything in place and then marking on this piece of webbing
where to cut the first hole. Once done I will work out where
to
cut the hole in the second piece of plywood which is yet to be
epoxied into position. The "N" verticals are turned on their
axis
so the plywood webbing can be epoxied on the flat sides. This
means the edges facing the outside of the fuselage need to be sanded or
planed flat so the external plywood will have some kind of a surface to
adhere to.
|
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I
have used a thin straight edged piece of pine which has a sharpened tip
and passed it through the templates where the VS forward spar will go. |
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I
mark on the webbing where the sharpened tip touches and then join the
four corner dots. This area is then removed with a jigsaw |
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With
the lower template held off the bottom longeron 5", the forward spar
passes through the webbing perfectly. It will be trimmed to
length after I have added the forward webbing to the "N" verticals. |
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To
set the forward vertical stabilizer spar at the correct height, I first
set the fuselage level using the point between the forward and rear
main spars on the top longerons. I want the top of the HS and
rudder to be level with the fuselage, which is a piece of cake when
using the digital level. |
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I
now know where to cut the forward VS spar at the webbing by using a
piece of 5/8" pine and marking with a pen. 5/8" x 5/8" pine
is
then epoxied to the webbing and along either side of the spar,
along with wedges to secure it in place. |
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At this
stage the horizontal stabilizer is clamped in place rather than
epoxied. I will set its angle of incidence after the vertical
stabilizer is finished. The forward VS spar is now epoxied to
the webbing which means the HS can not be removed from the fuselage
without cutting timber. Dr. Dean hinges are used on the
rudder. |
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The
rudder
horn was shaped from 1" x 1½" 6061 T6 aluminum angle.
Whilst the AN3 bolts will be replaced with correct length
ones
shortly, the nut plate and nylon lock nuts are epoxied in place.
I have set the rudder horn up high on the rudder in an
attempt to
reduce its exposure to the air stream and thus decrease drag.
The
cables will enter the fuselage just below the upper longeron and
connect to the tail wheel cables within the fuselage instead of
outside. The rudder horn and cables will be covered by a
fillet
between the HS and fuselage. |
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As usual
expanding foam is used to stick the urethane. Clamps keep
everything in place until the foam sets. |
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I
tossed around a few ideas for an antenna including copper tape,
aluminum tape, coax cables and more but decided to use a regular pair
of TV "rabbit ears". The main reason being that they are
solid
and also adjustable in length which should make tuning easier.
A
channel has been cut in the back end of the leading edge urethane foam
and the antenna is held in place with expanding foam. The
second
half of the antenna will angle forward into the fuselage which is the
opposite to most installations but will make no difference to
reception. It means I will be able to have the lower antenna
length set at the full 22" of there abouts. |
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When
it comes time to tune the antenna inside the VS, a small pair of pliers
can be inserted through a hole I have left in the foam near the top of
the antenna. There is room for about 4" extension within the
VS
itself which is heaps. Once tuned correctly, a small "
blob"expanding foam will be put in the hole which will also hold the
top of the antenna in place. A fiberglass patch will then
cover
the hole. You can see the bottom of the antenna poking out
the
bottom of the VS. |
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Plastic
protected the aircraft from resin drops when the vertical
stabilizer had the micro slurry applied as well as the
fiberglass
layup. Naturally, fiberglass is being used in the vertical
stabilizer as radio frequencies travel freely through it unlike carbon
fiber. The leading edge will have two fiberglass layers and
the
rear half one layer. The stabilizer has been modified to
allow
for a balance horn on the rudder. |
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Once
the resin has dried I give the stabilizer a rough sand which reveals
any low spots. These areas are exposed as they remain clear
and
are unsanded. |
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A
stiff micro is mixed and applied evenly to the stabilizer making sure
to fill the low spots. When it is dry the sanding begins.
|
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The
rudder is sanded with the straight edge using short strokes across the
plywood templates. When it is about finished I do
6 or so
strokes with the templates to remove the miniature ripples left by the
initial sanding. |
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200
gram fiber glass has its size over cut by 1 inch and is cut on the bias
so that the weave runs diagonally. The 85 gram sheer fiber
glass
cut square and over cut by 2 inches just to be safe. All this
is
layed out on the outlined plastic. |
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Because
the heavier fiber glass is cut on the bias, it wants to move about when
trying to squeegee the resin around. To minimize this I spot
the
resin around the edges to hold it all in place. Much like
spot
welding. |
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When the
resin is poured on and evenly squeegeed, the fiber glass takes on a see
through effect with no dry areas showing. |
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As
with fiber glassing on all the KR foams, a micro slurry is applied then
the plastic and fiber glass sandwich is layed on top and squeegeed
before the plastic is peeled off. Peelply is then layed on
top
(not shown) which absorbs excess resin and makes for a good surface
when it is removed 12 hours later. |
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One
side of the rudder is done now so it is flipped over and the last inch
of trailing edge foam/micro is removed with a wire brush and a straight
edge.
|
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A
stiff flox is mixed and used to fill the trailing edge which sets rock
hard. The foam is slurried and fiber glassed at the same time
so
it all dries together. |
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In trying
to keep the KR as aerodynamic as possible I used the laser level seen
at the lower right had corner of this photo, to define a continuation
of the fuselage line over the rudder. It shows that a ¼"
angle needs to be removed from the bottom of the rudder. |
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Foam
was then removed before filling the cavity with flox. The
reason
I did this was 2 fold. Flox will better protect the bottom of
the
rudder from stones that may spray up from the tail wheel. And
given that there is no plywood rib at the base, the flox also adds
rigidity. |
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I
have attached foam to the leading edge of the rudder with 2 part
expanding foam. The top and bottom leading edge templates
have
been pushed into the urethane and sit in the expanding foam.
Once
dried, the clamps are removed and then the foam is sanded to the
contour of the templates. |
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A quick
twist of the spade bit exposes the eye bolt hinges below the foam. |
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A
razor blade is used to remove foam above and below the eye bolts to
make room to insert and tighten the AN3 bolts. A rat tail
file
puts a nice rounded groove either side of the hinge. This
widening is necessary to allow the rudder to move freely from hard left
to hard right. |
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With the
rudder at full right I sand the exposed foam leading edge so it is
level with the vertical stabilizer. |
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With
full left rudder applied I hold this makeshift gap seal on the vertical
stabilizer and line it up so that it just touches the rudder. |
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Without
moving the gap seal the rudder is then applied full right to check for
nil contact between the foam and seal. |
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I
am always on the lookout for ways to achieve aerodynamic
improvements. The alloy rudder horn sits out in the breeze
and I
think could be faired in in some way. In Kent Paser's book
"Speed
With Economy", a brilliant read by the way, he writes of extensive
efficiency benefits gained with fairings. On page 74 he says
that
a teardrop shape 3.7 times longer than it is wide is the best shape for
fairing in, say a wheel. I have roughly shaped a foam fairing
using the 3.7 rule and aligned it at the same angle of incidence as the
horizontal stabilizer. |
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Paser
speaks highly of Dr. Sighard Hoerner's book "Fluid-Dynamic Drag".
On page 103 of Kent's book he goes on to say, "From
Hoerner's "bible", when designing a fairing for a protrusion from an
existing aerodynamic form (like a bolt head), the nose and tail parts
of the fairing should each be 6 times the height of the fairing, or a
total fairing length of 12 times the height, for minimum drag".
Now
this leaves me feeling that the protruding rudder horn needs a fairing
6 times longer than high, as in this photo, and one equally as long in
front of the horn, down the side of the fuselage. I will put
it
to the KRnet guys for discussion then decide later. |
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Here
are all the materials I need for terminating my first cable.
3/32" stainless steel control cable. It is
7x19 which
means the cable is made up of 7 strands and each strand is made up of
19 wires. There is a nicopress sleeve and thimble, a swaging
tool
with spanner to tighten it and a cable cutter. |
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The
instructions that came with the swaging tool are pretty straight
forward. Place the cable through nicopress sleeve then loop
it
back through. Place the thimble in the loop and pull the
cable
and thimble tight against the sleeve leaving a small length exposed on
the other side. Evenly tighten the swaging tool all the way. |
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And
here is the finished product. The 7x19 stainless steel cable
is
flexible and is strength rated to 920lbs. The cable and
connections should be tested to 60% of the rated strength before being
put into service. |
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I
have drilled a hole in the fuselage for the rudder cable to pass
through. This hole is in direct line with the rudder horn
fairing. At the moment I am waiting on some shackles so have
used
a cotter pin and washer just to hold the cable in position while I work
out the best way to route the cable within the fuselage. |
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I
have made this cable guide from 6061 T6 aluminum. The gap
between
the bottom of the phenolic pulley and the aluminum angle is small
enough that the cable will not be able to fall off the pulley.
A
number of these pulleys will be used to guide the rudder cables all the
way to the rudder pedals. |
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The
AN219 pulley forward of the main spar is larger than the AN210-1B
pulleys aft. This is because the allowable cable deflection
on
the smaller ones has to be no greater than 15o to
avoid damage to the cable. The front pulley guides the cable
from
the rudder pedal, under the spar to a small pulley which guides to the
next small pulley under the rear spar. The cable is able to
pass
under the main spar because the dihedral begins just inside the
fuselage and leaves a small triangular gap. |
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The
cable then goes to the pulley on the rear cross member and out
to
the rudder horn. In fact the cable takes a straight route
from
the large front pulley all the way to the rudder horn. All
pulleys are made as per above and are held in place using T-88 epoxy
which I tested on some ally earlier. As usual with T-88 the
wood
broke before the glue joint. I couldn't imagine applying
enough
rudder pressure that the cable would be able to break a pulley mount
from the timber. |
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Months
have passed since routing the cables high and I have changed my mind on
having the rudder horn under the horizontal stabilizer.
Attaching
cables from the rudder cables to the tail wheel horn was just going to
be too tricky to make it all work smoothly. I guess the
beauty of
building with timber and composites is that a change of mind is easily
accommodated. |
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Now
I can't remember where I saw it but this is a simple way of making a
cable fairing. Grab two blocks of flat timber and hold them
together on the side of the KR where the rudder cable exits the
fuselage. Rule a line on the blocks from the exit hole to the
rudder horn. Clamp the blocks in a vise and drill through the
middle along the line. |
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Plastic
or duct tape would have been no good in this situation as I wanted no
creases in the finished product. So I used rubber gloves to
act
as a release agent. The ally tube was fed through one hole
and
then the wetted CF, light weight FG sheet and peel ply were layed on
top before the second gloved block was placed on top and the whole kit
was clamped in the vise over night. |
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This is the
finished product, albeit these gloves are not the originals but are
ready for the next fairing. |
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And there
it is. All 2.4 grams of it. |
