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First
things first. The bottom of the seat is calculated using some
timber between the lower longerons. I sat on it and angled
some
makeshift seat backs. Moving the "seat bottom" timber fore
and
aft, I found the legroom length I was happy with. Whilst the
photos do not show it, I used a piece of cardboard and made a very
rough outline of the seat by holding it up against the fuselage side. |
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Getting
in and out of the KR was made easy by securing clamps to the spars on
both sides and having them touch the ground, giving the KR stability
much like a Harrier Jump Jet. |
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From the
cardboard template I cut out the first of three profiles and made sure
that it lined up.
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The
box section has now been built and work can now begin lining the shape
before then applying a layer of clear contact as a release agent for
the carbon fiber layups. |
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I
keep changing my mind on how to build the seat. Here I have
cut
four pieces of foam and used expanding foam to glue them together but
not to the box section. |
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I
have divided the seat into two sides and then marked shapes
that
are similar to my car seats. I then shaved the centers down
about
1cm at the bottom. |
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Expanding
foam has been used to glue the thigh bolsters in place. These
will be sanded away to form very shallow mounds maybe 1cm high.
Just enough to provide some lateral support. |
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I have used
the electric sander to carefully remove the overflowed expanding foam
from the joints at the back of the seat. |
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This
is the piece of timber removed from one of the seat profiles made
earlier. A length of sand paper stapled to the bottom and I
now
have a perfectly shaped sanding block to make the corner angles rounded. |
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Whilst
I have not finished the sanding yet, you get the idea of how I want the
two seats somewhat contoured. Looking down on the lower seat
backs you can also see how they have been slightly shaped too. |
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Trial
fitting the seat seems OK with about 1" clearance from the fuselage
floor. I made my "Flip-O-Matic" in 30 seconds flat.
It
ain't fancy but it works a treat and what's more an engineering degree
isn't needed to build it. |
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I have
applied gaffer tape and plastic to the center spars to stop the first
layer of carbon fiber from sticking to them. |
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As with any
other layup, I have used the plastic sheet method and then
draped the carbon fiber over the inverted foam seat. |
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Apply
the peel ply and fit the seat into place. I have left enough
carbon fiber to drape over the front and rear spars which has been
stapled to hold it in place until dried. |
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Everything
went perfectly well until I went to remove the peel ply. I'd
been
staying back at work until late working on the WAFs. I didn't
get
to removing the peel ply for three days and discovered that by this
time it had become brittle as the epoxy had completely hardened within
it. Peeling it off was akin to peeling a price sticker off a
CD.
What has been peeled off in this pic took in excess of one
hour!
My sense of humor wore thin to say the least so I will start
all
over again but will use this skin as a mold for the next. |
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I started
on the new seat by marking out the plastic sheet for the beginning of a
new layup. |
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I cut
a piece of carbon fiber to the size marked on the plastic, layed it on
top and then squeegeed through the resin/hardener mix until it was
wetted out. Peel ply was then layed on top and pressed by
hand to
remove any air bubbles and to make sure that it had absorbed any excess
resin. Another piece of plastic was then layed on top of the
peel
ply to create a "sandwich". I then flipped over this sandwich
and
layed it on the mold to make sure everything was going to be fine. |
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Looking
at the photo above, there is no peel ply between the plastic and carbon
fiber showing, so I carefully peeled off the plastic and layed down a
piece of peel ply, then replacing the plastic. So what I have
here is a "sandwich" of; plastic - peel ply - carbon fiber - peel ply -
plastic. This layup is so easy to handle. While
making room
on the bench I just picked it up by the corners and draped it over the
side of the aircraft. Between the plastic, nothing moves. |
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I
layed the sheet over the underside of the mold and used staples to hold
it in place. The mold was then set in place over the spars
and
allowed to cure overnight. |
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The next
morning I peeled off the first layer of plastic and peel ply to reveal
this beautiful looking piece of carbon fiber. |
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I then just
popped the seat off the mold and then removed the plastic and peel ply
from the other side. |
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The
beginning of the new seat has gone quite well. Still a lot of
work to do but I am happy so far. |
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The
vertical reinforcing structures that would normally be between the seat
bottom and fuselage floor, I have decided to build into the seat
itself. The first step is to get some 1/2 " square foam
strips
which I made a simple timber form to create. |
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Pop some
foam in, shave it level and pop it out. |
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Here's
a view of how the reinforcing will sit from front to back.
There
will also be some from side to side. As each of these
miniature
square beams will be covered with carbon fiber and connected to each
other, the seat should end up being structurally very sound. |
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Trying
to wrap the wet carbon fiber around a small beam that has just been
painted with microslurry is no easy task as it wants to unroll.
So I have given up on that idea for the moment... |
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...and
will try to do it again when the microslurry has dried. So in
the
mean time I have set the beams to the shape I want on the seat and held
them in place with some light weight whilst they dry. |
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Here
is one of the beams wrapped in CF which is held in place with pins.
Soon after this shot I tried to wrap it all in peel ply.
What a disaster! The whole thing wanted to unwrap
itself.
A valuable lesson was learned. Do not try to reinvent the
wheel.
There will be time to test and build a "better mouse
trap"
after my KR is flying. Every day wasted on these things is a
day
I am further way from flying. |
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So
it's back to KR seat Mk 3. This is similar to the first seat
but
for the yet to be shaped 2" thick piece of foam which will sit on top
of the forward spar. |
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When
shaping the bolsters on first seat I managed to sand through to the
expanding foam used as adhesive. Being harder than the green
foam, it was a pain to sand. So I decided to carve out areas
where I wanted the bolsters to go. |
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I then cut
2" foam to size and slid it into the cutouts. |
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The
foam was then glued from behind with the expanding foam. I
did
learn that the expanding foam is very easy to sand about 10-15 minutes
after mixing. At 20 minutes it is too hard again. |
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This
left no hard foam joints to sand through. After shaping the
bolsters I used a very stiff micro to fill some minor gaps. |
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The
pre-molded seat skin has had peel ply layed on the back with a drizzle
of resin to make it sit in place when turned up the right way.
I
have done this because there are tiny holes between the carbon fiber
weave that will allow the resin to seep through a little. The
CF
has then had resin squeegeed over the top in readiness for the
contoured foam which has had the reverse side painted in the
microslurry. |
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I
placed the seat in its proper position in the KR and weighted the foam
with anything I could find that had some weight in it including a bag
of dog biscuits. |
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The
following day I lifted the seat out and covered it with a layer of
runny micro. |
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I
then wet out a piece of CF on a plastic sheet and draped it
over
the seat, peeled off the plastic and squeegeed the CF into close
contact with the foam. |
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Peel ply
was then layed on top to draw out the excess resin and then the seat
placed back in position to cure overnight. |
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The
following morning I removed the peel ply to reveal the final form of
the seat with small bolsters and slight sculpting in the lower back
area. At this stage the seat is held in position by hooking
the
carbon fiber over the front and rear spars. Strengthening
ribs
will be added shortly to the underside. |
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1" thick
foam has been used to create some strengthening ribs. Each is
a 2 piece affair which is glued together with expanding foam and then
sanded to a depth of 1½ - 2". |
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Each rib
has been coated with a slurry before carbon fiber and peel ply is added
to the sides only. |
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These
are then layed in position over the seat bottom which is protected by
plastic sheeting. I do not want them to adhere to the seat
yet. |
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After
about 2 hours the carbon fiber and resin has hardened enough that it
has stuck to the foam but still soft enough to easily trim with a razor
blade. The ribs are removed and all the overhanging carbon
fiber
trimmed off before putting them back into position to fully harden. |
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When
completely hardened I removed about 1/16" of foam from the underside of
the ribs and a little more at the edge where the foam meets the carbon
fiber. This was the filled with flox (resin and chopped
cotton)
which provides incredible strength when adhering the ribs to the seat
bottom, which has a line of flox added in readiness. |
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1"
bi-directional carbon fiber tape was then wet out and used at the rib
to seat junction to provide additional strength to the joint.
Peel ply soaks up any excess resin. |
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The CF tape
creates aesthetically pleasing edges too. |
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This
side of the rib gets the same flox treatment as the other before
covering with a layer of 3" uni-directional carbon fiber tape.
The uni-directional tape has all the CF filaments running in
one
direction which in this case is length ways. This therefore
means
that all its strength is length ways too. The reason I have
used
this tape is that this side of the rib only needs uni tape and I've had
a roll of it sitting around for ages anyway. |
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As with all
layups, I have used peel ply. |
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The
seat is almost finished but it still needs to be trimmed where it meets
the fuselage and some carbon fiber tape added to the edges.
I have sat on it in situ and bounced up and down and there is
zero movement. |
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I'll be
having head rests built into my seat backs which will be split
folding. I have made the the seat shoulders 2½"
above the level of the parcel shelf. The head rests are
shaped
using whatever I could find laying around. In this case the
plate
did the job. |
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Cut out and
place in position to make sure it will fit, I'm pleased with the look. |
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The
carbon fiber was added to one side at a time and then sanded to the
seat contour. The plastic sheet method was used but I lowered
the
foam onto the wetted out layer like putting a jigsaw piece in a puzzle. |
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All of the
edges get a layer of CF which have to be held in place with clamps
until the resin cures. |
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Where
carbon fiber, or fiber glass for that matter, meets at a right angle ,
the corner has to be strengthened by removing a little foam in that
corner and then filling the void with a stiff flox mix. The
oxide
color in this picture is the micro slurry. |
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I
fitted the seat back in the fuselage a found that it had a 1/4" twist
which made it sit out at one end of the shelf. The solution
was
as easy as supporting it out in the sun and adding a weight to the
corner. 10-15 minutes in the Aussie sun softened the resin
enough
to reshape the seat back. Perfect! |
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I
have decided for a number of reasons not have a split hinged
seat
as originally planned. I don't think I would use the split
folding seat in flight and the added seat back area above the parcel
shelf would hit the fuselage walls if folded forward. I still
wanted the ability to remove the entire seat back to gain access to the
area behind. As there will be no hinge I have shaped these
"monster teeth" out of foam and carbon fiber. They will be
epoxied to the CF that overhangs the rear spar. |
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Now that
they are epoxied in place, the "monster teeth" also provide additional
rigidity to the CF overhang. |
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The seat is
easily removed when I need to access the back. |
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And it
rests securely against the supports and parcel shelf. |
