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A 3/8" line
is marked inside the two AS5048 airfoil templates and then the marker
is held extended from my finger tips and the hand slides along the
profile to give an even line the whole way. Staples and
icy pole sticks secure the template which has a chord length of 44"
verses the 48" template at the fuselage. |
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2" thick
foam is cut to fill the bottom skin. I then carve the sides
down to the lines that I marked previously. |
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The foam is
then lifted out and I have carved channels with the surform down to the
carved out areas on the sides. This sets the levels to which
I need to remove the rest of the foam. |
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...almost
done. |
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When placed
back in the stub wing, the shape conforms to the 3/8" lines perfectly. |
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These carbon
fiber straps are left over elevator gap seals and are good for stopping
the foam from falling through and onto the garage floor. The
plastic around the sides will allow me to cleanly remove the skin when
the resin is set which will make fitting the tanks easier. |
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The
microballoons slurry is coated on the foam outside of the stub wing
just
because it is easier. The plastic sheet layup method is used
to then apply the carbon fiber which is positioned on the 45o
angle. |
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The whole
composite skin is then lowered into position and rests on the straps.
Clamps and timber just stop the edges from lifting. |
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After
the composite had dried I removed it and the airfoil templates from the
spars. I used a cheap adjustable hole cutter attachment and
added
some lightening holes to the 4 templates. The gap between the
holes and the template edges is 1 1/2" which leaves plenty of
structural rigidity. Out of curiosity I weighed the removed
disks
and discovered my KR is going to be 10oz lighter! |
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I wasn't
happy with the valley depth along the spars that would have to be later
filled with micro so I
epoxied a 1/8" strip of hoop pine across the top and bottom of the
spars and sanded them more closely to the contour of the
templates. I
have cut the supports out of the bottom of the templates which make
them easy to slide down into position and then remove while sanding. |
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With the
lower skin held in place from above and below, I have begun making the
primary strengthening supports for the fuel tank. These will
be floxed in situ and then shaped to accept the fuel tank before being
covered in carbon fiber. |
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I have cut
out the basic shape of the tank and then placed some sand paper on the
supports. |
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The
tank then gets put on top and the sandpaper is pulled out while holding
the tank in position. This is the best way to get the foam to
exactly match the tank contour. |
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The
carbon fiber has been layed over the foam ribs which had a small layer
of flox applied. Where the CF meets at right angles, the foam
at
that corner is sanded down and the triangular void filled with flox.
When cured, this makes the edges and indeed the whole rib
incredibly strong. |
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Before
using carbon fiber tape to hold the lower skin in place, I have epoxied
in three tabs on each spar which hold the skin until dry.
This
allows me to check the fuel tank fit before permanently securing the
skin. |
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Everything
was fine so the carbon fiber tape was used to secure the skin to the
spars. I use a piece of 2" thick foam to start the upper
skin.
I gave some thought to setting up a jig to sand the inner
side
but have chosen to sand the shape by hand using the rib template as a
guide. |
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Carbon
fiber is applied to the inner skin in the usual way and peel ply layed
over the top to soak up any excess resin. This I do on the
workbench and leave for about one hour. This gives the carbon
fiber time to become quite tacky so when I invert the skin, it will
remain in contact with the slurried skin. Plastic has then
been
layed over the peel ply As the skin has been shaped
from a
flat piece of foam, the top side is still flat. I have
clamped
some particle board flat across the top to hold everything in shape
until the skin dries. After then the panel will be lifted out
and
the plastic and peel ply will be removed. |
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With
the inner skin dried it is now time to add strengtheners as I did to
the bottom skin. These will help hold the fuel tank firmly in
place but are also the beginnings of the wing walk. |
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The inside
of the upper skin is now finished along with additional cross
strengthening in the wing walk area. |
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The
early construction of the leading edge has begun. 2 pieces of
2"
foam are shaped internally to match a 3/8" - 1/2" line drawn around the
inside of template. The foam was then held together in the
"V"
shape and expanding foam drizzled along the internal join.
This
was allowed to set for 10 minutes and then sanded with a curved wood
rasp before it got too hard. |
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Tape is
applied to the gear bracket and spar caps as a releasing agent. |
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A
single layer of carbon fiber lines the inside. After
smoothing
out the wrinkles in the peel ply I lightly stapled it on the ends to
keep it pulling the carbon fiber firm. I left it resting on
the
table in this position for an hour to ensure the layer was sticking
well enough to the foam |
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After an
hour, The leading edge is held in place against the main spar until it
dries. |
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I score the
foam around the template just as a rough guide. |
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I have
found the best way to sand a bulk amount of foam quickly. |
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Here
it is after the driveway sanding. A quick going over with
the sand paper straight edge between the templates, then the
leading edge will be the perfect contour. |
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So it is
now sanded and I have the plastic marked out ready for cutting the
carbon fiber. |
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The
nights are cold at the moment and the resin doesn't like to flow and be
absorbed into the peel ply. I use the heat of the 500 watt
light
to warm the resin and make it more viscous. |
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It
is held in place with staples through the peel ply and into the spar
caps. The templates are stapled into the cured carbon fiber
on
the ends of the leading edge. |
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The
morning after and it pops clean off due to the gaffer tape.
When
the rest of the stub wing is finished I will cut a straight line from
front to rear and carbon fiber the ends properly. |
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I
have decided to go with the split flap option which means the upper
skin will be one smooth surface from front to back with no gap.
Here is the beginning of the upper surface. It has
been
shaped and will have a layer of carbon fiber applied on this under side
but only as far back as the foam ridge. Aft of here to the
tip of
the trailing edge will be shaped later. |
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Both the
inner surfaces of the top skin (above) and this flap have been covered
with one layer of carbon fiber. |
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Both
time has come for me to finally epoxy the templates in place with the
pine wedges. The partially built flap sets the distance apart. |
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As
this panel is going to be a flap I intend to build it separately.
Its level is set along the 1/2" line using clamped blocks and
the
large sliding clamps. The under surface is the sanded to the
templates with the straight edge. |
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A line is
then marked where the rear edge of the flap has to be sanded. |
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The
rear edge is then sanded and 3/4" of foam removed. This
recess
will have the micro removed to expose the carbon fiber and then be
filled with flox to create an incredibly solid edge. The cut
outs
in the bottom corner are there to clear the WAF nuts. |
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The
flox and carbon fiber skin have been added to the lower side of the
flap. I do this on the workbench and let it cure for around 2
hours. That way I can then clamp it into position and not
have
the CF skin peel off, yet it is still pliable enough clamp into its
final curing position. |
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Here is a
shot from beneath showing the aluminum straight edge and the curing
carbon fiber which also has the peel ply on it. |
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The
flap will pivot using piano hinge which is attached the same way as for
the rear deck. Epoxied to hoop pine which is floxed to the
flap
and long screws which stick in extra deep pockets of flox. |
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This is how
the flap will look in the pivoted down position. It's clear
to see the
need for the cutouts around the WAF nuts. |
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The
stub skin above the split flap has had the inner carbon
fiber done
and is now resting on clamped blocks and has been given a rough sand. |
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This
is how I sand foam down to an even 3/8" thickness for some internal
bracing. I cover both sides with carbon fiber and
allow it
to dry. What I then have is a very strong composite sandwich
which is cut with a jig saw to the shape of the bracing. |
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When
looking in from the back of the trailing edge you can see how the flap
is braced on the diagonal to reduce any torsional twisting when it is
lowered. As the upper skin of the stub wing is going to be
one
big unbroken profile, I am concerned that someone may ignore the
signage and momentarily stand on the trailing edge which is not built
to take weight. Whilst it will be fixed to the plywood ribs
at
either end, I have added a strengthening composite brace in the center
which will also be epoxied to the aft spar. |
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The stub
wing is now ready to be closed in. The fuel tank is connected
to the fuel line. |
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I
prepare the 2 part expanding foam which has no reaction when initially
combined. I left it like this for 15 minutes and nothing
happened. Give it a brisk stir and it rapidly starts heating
up
and expanding. I then get about 20 seconds to pour it evenly
into
the valleys before it becomes too thick to work with. |
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You
can see how the foam has expanded out from under the tank, like bread
dough rising. I needed to be careful not use too
much as it
continues growing for around 1/2 hour. My first foray into
wiring
begins with the fuel tank sender. For this I am using 16 GA
Tefzel unshielded wire. The wires are white with a red stripe
for
positive and a black stripe for negative. They are routed and
secured with cable ties and "sticky mounts" |
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The
expanding foam between the tank and rear spar ended up oozing above the
tank line so I waited about 45 minutes before sanding it down with a
fine wood rasp. |
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Just
before epoxying the upper trailing edge in place I have covered the WAF
nuts with tape as I would like to reserve the right to tighten them
should it be deemed to be necessary in time. I have protected
all
my WAF and landing gear bracket nuts and bolts from epoxy for this
reason. |
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This
is the upper skin with wet carbon fiber strips in place. It
is
ready to be flipped over and the strips stuck to the spar and plywood
profiles. |
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The inside
of the upper skin has the foam poured along the ribs and "blobs" in the
other areas. Flox is applied to the edges that come into
contact with the front and rear spars. |
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The
main foam skin was weighted down with timber and a piece of railway
line to stop the expanding foam from possibly lifting it. The
tag
in the corner is attached to some tape covering the tank hole and makes
it easy to pull this cover free when ready. |
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24 hours
later and the stub wing is sanded between the plywood profiles using
sand paper stapled to a straight piece of 4" x 1". |
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The
removable pitot tube will extend out from the leading edge.
Foam
has been removed from behind and a piece of Australian hardwood floxed
in place. The hardwood has a hole pre-drilled and this steel
tube
is just pushed in to align the hole while everything dries.
The
tube has tape around it so flox will not stick. |
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Here is the
hardwood back block. Clear PVC tubing will be attached to the
small ally tube which is floxed in. |
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I made
these mounts out of 5/8" cube offcuts which were drilled and floxed in. |
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I
have not totally made up my mind as to what lights I will end up with.
So I have run three pairs of 16G Tefzel wire and one 14G pair
for
any landing lights. One of the 16G pair will connect to the
fuel
sender wires and the other two pairs would be for strobe and the red
position light. All these wires will terminate at a block
that
will be secured to the end of the main spar. A connecting
block
will make disconnecting the wires from the outer wing a breeze.
The wires are identified with masking tape at both ends
before
being run. |
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A
pvc tube protects the wires from abrasion as they go through a hole in
the rib and and into the fuselage. Anywhere the wires are
tied to
the brake line, a piece of pvc hose is clipped to the aluminum.
I
don't want any wiring to be touching metal components.
Rubber grommets are also used to protect entry points into
the
fuselage. |
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The
leading edge has now been floxed to the main spar and ribs.
The
KR is shown out of the garage and has been turned upside down.
The final sanding has been completed and blown off with the
vacuum outlet. |
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The
familiar plastic sheet method for laying up is used. I cut a
slit
in plastic, carbon fiber and fiberglass before squeegeeing any resin.
This slit is for the landing gear leg which has had plastic
taped
to it to protect it from wet resin as the sheet is slid down and into
place. As the leading edge already has one layer of carbon
fiber,
this now makes two layers. This new layer extends around the
point of the leading edge by two inches. The same will happen
with the layer on the upper surface of the wing which means the point
of the leading edge, and two inches either side, will be three layers
thick making it virtually indestructible to bugs, stones and the odd
stray kangaroo. |
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To
make sure the layup is properly oriented, I have marked both spars on
the plastic sheet, the fuselage and fuel cap sides and the front with
big arrows. |
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As
with every other trailing edge tip I have made, this one also is flowed
before the carbon fiber and fiberglass is applied. The
urethane
is microed and the spats have some resin painted on in readiness. |
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After
the layup has dried for around 3 hours, I pierce the leading
edge
and insert a split pin and AN4 bolt into the fuel vent and pitot holes
that are underneath. |
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While
the layup is not fully cured it is a good opportunity to cut the fuel
cap hole with a razor. The slight indent left by the spar is
intentional and is filled with a stiff micro down the track.
A
spar that is taller than the foam is impossible to blend in to the
shape of the airfoil and getting its height spot on is difficult.
Stiff micro in the 1/16" spar valley is straight
forward.
It is clear in this photo and the one above, that the carbon
fiber weave has been aligned at 45o which
provides maximum strength to the wing skins. |
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The
plastic protected the timber from a light shower but the KR2S looks
more like an aircraft every day. Two stubs wings are now
complete. |
