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Day 114 - Reefing Parachutes
Mounting the camera so that it can track the
parachute from deployment...
... to full inflation.
Reefing ring made from a key ring with heat
shrink tubing to stop the lines catching.
The reefing ring is pulled up all the way to
Parachute packed and ready to go.
Axion III launched at 100-110psi with a 9mm
We used the break wire trigger for the Servo
Launch and recovery crew.
Turning on the camera.
Parachute starts to inflate...
The ring starts sliding down.
... a little more...
Parachute almost fully inflated
Recovery crew is quickly on the scene
Filling and filming ... a little more
training and we'll be able to sit back and
Another one of the six launches on the day.
Reefing ring about half way down the shroud
Way too much fun.
Filling up for the next experiment.
Experiment #2 - Twisting up the shroud
Packing the parachute.
The shroud lines have just emerged from the
Still somewhat twisted up.
Just prior to the canopy starting to fill.
The wind is picking up and the rockets are
...Kids these days ...
Still trying to find a caption for this one
December 2011, 7:45am - 8:45am
Location:Denzil Joyce Oval, NSW, Australia
Conditions:Calm 0 -10km/h wind, warm, blue
Team Members at Event:John K, Paul K, Jordan K, PK and
As we look to potentially open parachutes at higher
speeds, we are trying different ways to
reduce the shock on the parachute and the
rocket. Today we tested a couple of simple
techniques to reef a parachute so that it
does not snap open.
The first technique used a reefing
ring threaded onto the shroud lines, and the
second technique simply put a few
twists in the shroud lines themselves.
The reefing experiments used the
material - flat sheet
parachute and shock cord
Weight of rocket
Length of shroud
Number of shroud
We used fluoro yellow
cord for the shroud lines and black for
the shock cord to make them easy to
distinguish to see how much the shroud
lines were separated.
Looking at the parachute in flight
In order to get a better sense of how the
reefing works in flight we decided to mount
a camera on the shock cord where it attaches
to the rocket. We wanted the camera to
follow the parachute from the time it
deployed to the time it fully inflated, and
then continue to follow it until landing.
Initially the parachute deploys sideways
and then swings to the back of the rocket
where it inflates, and then swings out to
the side again when it has reached terminal
velocity. Just mounting the camera
directly to the shock cord would have
introduced a lot of roll and would have been
hard to see anything. So we attached the
camera to a little Coriflute platform
suspended between a triangle made out of
another cord and attached at two points to
the rocket. This
eliminates the roll but still allows us to
mostly follow the parachute.
We also filmed the rocket from the ground
with zoom both in HD and slow motion to try to get a better idea
of the process from a
We arrived at our local park at 7:45am,
with beautiful blue skies and almost no
wind. We had the three boys with us, and now
being older they are a lot more help in
carrying gear and setting up. We had the
first rocket on the pad within 10 minutes of
arriving at the park.
The first flight was with the reefing
ring and the rocket was only filled to
100psi. The park is fairly small and so the
rocket can drift a long way if we pump up
the rocket too much. The flight went well
and the reefing ring appeared to also work well.
We had set the deploy delay to 3 seconds
which was right around apogee as we didn't
know what may happen and so we wanted to
give the parachute maximum amount of time to
We flew the same configuration again on
the next flight, and the parachute worked
well again. On the third flight we increased
the pressure to 110psi and set the deploy
delay to 4 seconds to get the parachute to
open a bit later while the rocket was coming
down. Again, the reefing ring appeared to
When we later looked at the on board and
ground videos you could see that the reefing
ring did stop the parachute from snapping
open and nicely ballooned out before fully
inflating. It was also evident that the ring
only made it half way down the shroud lines
on all three flights. This was enough for the
parachute to be almost fully inflated and
bring the rocket down safely. The ring
wasn't being caught on anything as one video
showed that as soon as rocket touch down the
ring slid down the rest of the way.
The ring's position on the shroud lines is determined by a
number of factors including the friction
between the ring and the lines and the
amount of force being exerted on the shroud
lines by the canopy
Twisting the lines
This was always going to be an
interesting one because you normally try to
stop tangles. The key assumption here was
that the parachute will want to unwind
itself when a force is applied to the shock
cord and shroud lines. Of course
aerodynamics could also want to twist the
parachute in the other direction and twist
up the shroud lines even more.
As a first test we only twisted the lines
5 full revolutions. This was perhaps less
than ideal for effectively reefing the
parachute but it was a toss up whether we
wanted to potentially crash the rocket or not. The flight
went well again and both ground and onboard
video showed that the twisted lines worked a
little bit to reef the parachute but not as effectively as the
reefing ring. The shroud lines did untwist
all the way so the shroud lines were fully
separated - which was good.
We repeated the experiment again with a
second flight, and again the parachute
deployed well and fully inflated. We suspect
that some of the twist in the shroud lines
was transferred to the shock cord on opening
and hence untwisted faster than expected.
As a control, the sixth flight of the day
was a normally packed parachute without any
reefing arrangement so we could compare the
other techniques to it. You could clearly
see that the parachuted snapped open quickly
and you could also hear the pop of the
parachute. Something you didn't really hear
with the two reefing methods.
Here is a highlights video from the day:
We packed up after the 6th flight as the
wind started picking up and was blowing
towards the road. We used the simple
wire trigger for the Servo Timer II on
all the flights as we were using lower
pressures and restricted nozzles. The
trigger worked really well on all the
flights. A good day all round and happy to
get all rockets back without damage.
Next we'll need to try to deploy the
parachute at higher speeds to see what
happens - both on the way up and on the way
When we were testing the reefing ring the
night before by swinging the parachute
around, we noticed that it did not work at
all if the parachute had a hole in it. The
reefing ring will only work if the entire
canopy is closed.