to tear a couple of Dacron straps off
the jacket. After the second loop was
torn, I stopped attaching the modules
to the bottom split rings and began
attaching both the parachute and
lower modules to the split rings at
the top of the airframe. Four lift lines
— or short lengths of woven Dacron
kite line — span the distance between
the lower module and the split rings.
After switching to using only the
top split ring to tether parachutes and
lower modules, I didn’t do away with
the bottom split rings. I repurposed
them. I run the link lines from the
lower module through the bottom
split rings without actually attaching
the link lines to the bottom split ring.
The bottom ring’s small interior
diameter seems to prevent the
airframes from swinging wildly like a
pendulum. I like this so much that in
the new design, I created restraining
loops at the bottom of the harness.
In this case, however, I added four
loops of Dacron kite line to the
harness. On the harness at a point
one inch above the bottom of the
airframe, I melted a hole through all
four arms of the harness. To
strengthen the hole for the Dacron
loop, I inserted an opened rivet
through the hole. Then, I cut a short
length of woven Dacron kite line and
melted the cut ends with a lighter to
prevent the kite line from unraveling.
I tied a loop with the kite line by
folding it in half and tying a simple
overhand knot in the end.
Next, I pulled the folded end of
the Dacron kite line loop through the
center of the rivet using a pair of
tweezers. The knot at the other end
of the loop is so large that it can’t be
pulled through the rivet. The loop of
Dacron left sticking out of the rivet
replaces the split ring I used to
restrain the swinging of modules.
Before attaching the harness to
the airframe, I added a bumper to
the bottom of the airframe. My older
modules had a landing bag at the
bottom of the airframe. The landing
bag protected it in case it landed on
a hard surface like a road. The
landing bag consisted of a one inch
thick sheet of foam rubber placed
between the Styrofoam
bottom of the airframe
and the inside of the
bottom of the abrasion jacket.
I took a hint from hard hats
when I replaced the landing bag in
the new design. Hard hats protect
heads two different ways. First, the
elastic band inside of them spreads
out an impact’s length of time,
thereby reducing the force of the
peak impact. That’s how the landing
bag functioned in my previous
airframe design.
Second, hard hats have a hard
shell that spreads out the area of the
force of an impact, thereby reducing
the peak pressure of the impact. I
chose the second method to protect
the airframe in the new design.
I spread out the area of the
landing impact by adding a
lightweight plastic plate to the
bottom of the airframe. The plastic
was a 1/4 inch thick sheet of
Correplast, or corrugated
polypropylene plastic. This impact
bumper attaches to the bottom of
the airframe with bolts that also
attach the harness to the bottom of
the airframe.
The largest and oldest conference for amateur near space explorers is the Great
Plains Super Launch (GPSL). It takes place every summer in a location in the Midwest.
The 2014 Great Plains Super Launch will take place in Hutchinson, KS — the home of
the second largest air and space museum in the United States: the Cosmosphere. The
dates for the conference are June 12 and 13, with the 12th set aside for presentations
and the 13th reserved for near space launches. If you would like to begin your own
program or investigate how and what near space explorers do, then plan to attend the
next GPSL. While you're there, be sure to look for me. By the way, I want to give Zack
a big hand for hosting GPSL again.
A six inch loop of Dacron was folded in half and tied
at the end with a simple overhand knot. Note that
the cut ends of the kite line are melted to prevent
them from unraveling over time.
In this bottom view of the airframe, you can see the
impact bumper attaches to the bottom of the
airframe using the same bolts that attaches the four
arms of the harness to the bottom of the airframe.
The knot in the
Dacron loop will
remain inside the
rivet after the
harness arms are
attached to the
sides of the
airframe.
64 November 2013