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The
main spar caps for the AS5048/45 airfoil are 2" high and 2.16" wide
which means I need 8 x 1/4" thick laminations per cap. I have
ripped 1" hoop pine into 89" lengths which are 2 1/2" wide.
This
is slightly larger than planned. I have done it this way as
it
leaves room for trimming the ends to length and machining the sides
perfectly smooth and flat. Each length is then ripped
vertically
down the middle to split it into 2 pieces 3/8" wide. (My saw
blade is 1/4" wide). The laminations are then given a run
through
the thicknesser a few times until they end up 1/4" thick. |
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Here
are all sixteen completed laminations, machined and ready for bending
for the upper and lower spar caps. My german shepherd enjoys
the
building process and is keen to go flying too. |
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Before
setting up the spar jig I had to work out a few dimensions and angles.
The horizontal section is 33" wide and then angles upwards at
4o
which is what I have set the dihedral at. The bent sections
are
both 28" long and at their ends, rise 1.95" (5cm) above the horizontal.
I have drawn these lines on the bench and screwed down
straight
pieces of hardwood along them. |
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I
have layed down plastic and have laminated four pieces of the spar
before letting it cure over night. Every time I added another
lamination, the tension was released from the others and I felt it was
best to let the epoxy do its thing rather than continually breaking its
tight grip. The other four laminations can wait until
tomorrow. |
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Eight
laminations and I now have a bent spar cap. It is perfectly
straight along all three angles and exactly 5cm above horizontal at
both ends. |
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I have
ripped and machined some hoop pine into a length of 2 3/16" x
1/2". I then clamp a timber block to the saw guide so every
vertical spacer will be exactly the same length of 4 3/16". |
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After
cutting the spacers, I jigged the drill press so as drill each exactly
in the same spot for no other reason that I want the holes to line up
perfectly. |
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The
spar jig was screwed back in place and the epoxy applied to the bottom
spar cap and the bottom edge of the vertical spacers. Plastic
sheet underneath naturally to stop epoxy overflow from gluing the spar
to the workbench. |
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In
order to avoid the vertical spacers from sliding, I will only epoxy
them to the bottom spar cap initially, using the top spar cap to apply
even pressure. The holes in the vertical spacers are to
equalize
internal spar air pressure with the surrounding atmosphere. |
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Even
without the plywood side webbing the main spar is rock solid.
I
am waiting on a delivery of plywood so will get to "box" it out soon. |
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I
have marked lines on the top and bottom spar caps so I know how far to
shave them down with the electric plane. The forward side of
the
top cap is angled down 4.7o from the
rear, which means it is 4.5mm lower at the front. At 6.6o,
the forward side of the lower spar cap needs 6.4mm shaved off.
I
use the marker to indicate the aft edge of the caps. I know
that
planing the angles is going OK as long as I do not remove the marker
line. Note the cap.........on my head. |
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As
my wings and thus spars are going to be straight from root to tip, the
rear spar caps need to be laminated and bent in the same manner as the
main spar. Unlike the main spar however, the rear is going to
not
only bend up, but also forward as it exits the fuselage. The
trailing edge of the wing will be a straight line from root to tip
instead of from the end of the stub wing to tip. This will
allow
wider more effective flaps. There will also be no need create
a
bend in the WAFs. The photo shows how the rear spar caps are
initially laminated bent up and then ripped vertically, ready to be
laminated again with a forward bend. |
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Prior to
fitting the spar webbing I wanted to take a quick look at what the wing
will look like. The root and stub wing templates have 48"
and 44" chords respectively. I ran out of spray adhesive for
sticking the paper templates to the plywood, so resorted to a skill
learned in kindergarten. Flour and water! I am not
kidding. The beauty of this stuff is that it is
super sticky, you can clean up any overflows by licking them and the
left over flour and water can be used to make an Aussie damper. |
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This one of
the aft main spar caps showing how it is bent up and forward, though it
still need to be planed. |
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With
the forward main spar and one rear spar cap in place you can get the
idea of how the trailing edge will go straight from root to tip. |
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Laminations
have begun for the second aft spar cap. To the right on the
edge
of the bench is the outer wing spar caps. Each made up of two
pieces of 1" hoop pine roughly cut to shape and then epoxied together.
I have made both spar caps and clamped them together.
Final
shaping will be done when they are dry. |
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The
plywood webbing was epoxied to one side of the main spar and allowed to
cure overnight. I then used the router to trim it flush.
I
have decided to use straight epoxy to varnish the inside. To
make
the epoxy easy to spread I mixed it up in a cup and then placed the cup
inside a larger container half filled with hot water. This
thins
the epoxy but the heat also reduces its workability time to about 10
minutes. It is applied with a 1" wide brush which has had the
bristles trimmed to 1" in length. Pipe cleaners have been
used to
coat the holes in the spacers. |
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Each
cap of this outer main spar is made by laminating two 1" x 2" lengths
of hoop pine. When dry, I ripped the top and bottom caps from
roughly 2" x 2" at the stub end, down to about 1" x 1" at the tip.
I then finished the camber on each using a hand plane.
As
you can see I used the same width spacers which I then shave down with
the electric plane and finish off with the hand plane and then sander. |
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To epoxy
the spacers between the aft bent spar, I have done it in sections as
there are three flat sides. |
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Now
that the aft bent spar is dry and the cambers shaped, all that needs to
be done is to sand the spacers flush with the caps before epoxying the
webbing. |
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My
son Noah, trims the webbing using the router. Soon after this
we
got the fuselage down from the "loft" and took it outside the garage
for a few photos. |
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Now,
the incidence and washout have not been set and the driveway has a
slope in it, but I wanted to take a look at the left hand wing
and
assure myself that the calculations for the forward bent rear spar and
shorter stub wing rib template were all good. The picture
says it
all.
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I
double checked the required length of the stub wing template with the
laser. It's 44" which matches the calculations I made on
paper.
83 hours
since beginning the spars and they are now all built and shaped.
It took much longer than I had anticipated. |
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I
leveled the fuselage left to right and front to back before passing the
main spar through. My level point is measured on top of the
upper
longeron and between the front and rear spars. As the bent
forward spar exits the fuselage at a 4o angle,
there has been a need to insert shaped blocks as support on the bottom
longerons. |
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The same
goes for the rear spar however the wing root has to be set for 1o of
incidence. Luckily this is easy to do as "Level line
for 1o incidence"
is already marked on the 48" wing root template. I passed the
rear spar through the fuselage and then just slid the template over the
two. I then raised the rear spar until the incidence line was
perfectly horizontal with the top longeron by using the digital level. |
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The
decreased AS5048 wing root incidence and taller spars over the original
RAF48 airfoil mean the rear spar sits noticeably higher off the bottom
longeron. |
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Here
is the making of the jig used to drill holes through the spars
in
a straight line so that the WAFs (wing attachment fittings) line up
perfectly |
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I used a
scrap piece of 4x2 Aussie hardwood, drilled it, cut it and then
chiseled it. |
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10 minutes
later.......a jig. |
