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The recovery harness anchor
straps for Starfire are 1/2" tubular Kevlar webbing that has a thin steel
band inserted into it. The steel band is positioned inside the
tubular webbing at the place where the webbing will bear against the end
of the body tube when the shock cord comes tight. This
steel band reinforces the webbing and assures that it can not be sliced
through by the antizipper band
installed into the end of the body tube. The Kevlar alone
is extremely tough and very difficult to cut, but the steel bands
eliminate that concern all together. The tubular Kevlar
webbing is available from various rocketry vendors for about $1.25 per
foot. One such vendor is
Giant Leap.
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The steel bands are cut
from large hose clamps. The ends have been ground into a semicircle
to eliminate the sharp edge. These bands are about 10 inches long by
1/2" wide. They are fairly thin and flexible to allow the Kevlar to
bend as needed.
This photo shows the full
length of Kevlar webbing and the three steel bands that were used to make
three anchor straps for Starfire. Only
one is actually needed, but three are used as redundancy backups for each
other. This is because these anchor straps are subjected to the hot
ejection charge gasses and must tolerate a great deal of "wear and tear".
If one should happen to fail, the others will still hold. |
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Inserting one of the steel
bands inside the tubular Kevlar webbing. The band is held in place
inside the webbing by sewing the webbing shut with Kevlar thread at each
end of the steel band. I got the Kevlar thread from
McMaster-Carr.
The part number was 8800K81. It is trade size 69, 0.014" diameter, 375
yard/spool for $13.50. |
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A simple water knot is used
to create a loop in the end of the Kevlar anchor strap. This photo
shows the first step in tying that knot. Double the end back along
the strap for about 6-8 inches. |
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Then just execute a simple
overhand knot and pull all the webbing neat and tight.
The loose end is then just touched up with some epoxy to keep the Kevlar
from fraying. The knot itself is very strong. Don't add epoxy
to the knot itself. |
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Next step was to make a
flame shield big enough to hold all the recovery harness for Starfire.
The flame shield was cut from a bolt of Kevlar cloth. This photo
shows how I used a metal pin, a string and a Sharpie pen to mark the cloth
in a circle.
I got the Kevlar cloth from
Thermostatic
Industries, Inc. Their part number for it is 8K-60. It was
$100 for 3 yards x 60
inches (45 sq ft). |
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Flame shield as cut. |
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To cut the Kevlar flame
shield I used some special shears that look like scissors and are
available from CST
for $17.95. (Part number E814.) These work really well!
Regular scissors can just barely cut the Kevlar and it takes a long time
and a lot of effort. And besides that, when you are done, the
scissors will be dull! These shears snip right through the Kevlar. |
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The outside edge of the
flame shield was sewn with an overcasting stitch that prevents the raw
edge of the cloth from fraying. |
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The three Kevlar anchor straps pass through a small hole in the middle of
the Kevlar flame shield. Then the water knot is tied into each end
and some epoxy is added to the loose ends to keep the tubular Kevlar from
fraying.
These anchor straps are now ready to be installed inside Starfire using
some metal quick
links. |
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