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Day 129 - Inverter Rocket & Shadow II flights
Paul getting ready to celebrate Australia
Prepping the rocket.
All set up on the pad.
Preparing for launch.
Pressurised to around 420psi. Launcher
springs a leak
So we quickly launch before the pressure
drops too far.
Frame grab from the video.
Rocket landed just past the rocket eating
Easy to find on a mowed field.
zLog altimeter was added for this flight.
Preparing the Inverter for its first Flight.
The kids are becoming a great help in
setting up the rockets.
We attached a camera just above the
Rocket takes 6.5L of water.
Ready to go.
Very sloooowww launch.
Accelerates when it clears the launch tube.
The water phase lasted for over 1 second.
Max-Q ... parachute is forced out from under
Parachute starts opening
Just prior to getting shredded.
6 Seconds after launch the servo releases
the now imaginary parachute.
Only fairly light damage due to the drag on
The top 6 bottles need to be replaced.
Only reached 245 feet.
Launching the Axion II rocket at 120psi.
On the second flight the rocket landed
within easy reach.
Sam retrieving the rocket after the second
Splicing shaped bottles.
Bottles re-shaped ready for splicing
The bottles fitted together.
They were spliced with Asymmetric splice #5.
Burst test showed the splice held to 170psi.
Location:Doonside, NSW, Australia
Conditions:Overcast, light winds < 10km/h
Team Members at Event:GK,
PK, Paul K and John K.
This was a bit of a mixed day with some
good successes, but also some failures. We
first started off the year again by helping to
mow the grass at the Doonside launch site as
it tends to grow more over summer.
We had prepared the Shadow II rocket
earlier in the week to get it ready for
launch. There really wasn't much that needed
to be done, but the deployment ejection
piston was re-greased with silicone, and the
deployment system was tested again. We
decided to include the AltimeterOne
altimeter on the rocket as there was empty
space for it in the payload bay. It was a
backup in case the zLog altimeter failed to
record the flight. The AltimeterOne will
shut down after about 1 hour of inactivity, so we
simply turned it on and then attached the
payload bay to the rocket. There was no need
to drill another hole to turn it on. It was
located in exactly same section of rocket as
the zLog, because we wanted to see how close
the two are.
The target launch pressure was 440psi
(30.3bar) for this flight, but just as we
got past 420psi, the launcher popped an
o-ring on the quick connector. With the
small, but significant leak going we decided
to quickly launch. Because the parachute
deployment is time based if the pressure
drops too far, there is a danger the rocket
would start falling sooner and we could have
a high speed deploy. From the video it
looked like the pressure was just about
420psi (29bar) when it launched.
The flight was perfect, and straight up.
The rocket just kept going and going with
the 9 second delay it seemed to hang in the
air for a long time. The rocket drifted past
the rocket eating trees and landed on the
AeroClub's mowed section. The altimeter on
the AltimeterOne read 1256 feet (383m),
and the zLog gave a peak altitude of 1241
feet (378m). This was difference of 15
feet which means they agreed on the altitude
within around 1%. So for this flight we are
averaging the two readings which gives us:
1248 feet (380m). This is very much
comparable to the last flight flown at
Unfortunately the on-board video camera
failed to record the flight. :( I'm not sure
why that was, the camera has worked well on
numerous other flights, and I am "pretty
sure" I had turned it on. There just weren't
any files on the SD card. Perhaps the
acceleration or the landing somehow jarred
it and it stopped recording? I tried to
record on the camera in the workshop and it
recorded just fine. Oh well it was a cloudy
From the altimeter we also get a flight
duration of 72.5 seconds and ground video
also shows 72 seconds.
John said that the rocket was easy to
launch, so the arm extension on the launch
leaver had done it's job.
We checked the launcher for why the
o-ring popped, and it looks like the quick
adaptor wasn't screwed all the way into the
base and must have left a tiny crack. We
tightened it and it should be good to go for
the next flight.
We switched over the release head on the
launcher and set it up for the Inverter
rocket. Setup was straight forward and it
was put on the launcher dry. We then removed
the PVC air manifold and filled it up with
approximately 6.5 liters of water. This was
just below the launch tube in the top
We strapped a camera to the top bottle
looking down over the parachute. We also
taped an AltimeterOne altimeter to the side
of the rocket so we could get an idea of the
Everything was armed and running, and as
I was walking away from the rocket, I
thought I'd double check the release
mechanism. I had forgotten to set the mode
to the break wire trigger, and because the
timer was mounted sideways the G-switch
wouldn't have worked. So I quickly switched
to the correct mode. Simulations said this
was going to be a very slow launch and so we
decided to go with the break-wire.
We pressurised it to 120psi and tried to
launch, but the rocket did not take off. The
collar was dropping down correctly but it
looked like the nozzle was wedged in the
release head. We depressurised the rocket
and had a closer look. Everything had been
greased so that wasn't the problem. We
rotated the release head in relation to the
nozzle hoping that it was something about
the location of the locking tabs on the
We pressurised it again to 120psi, and
this time it launched without problems. The
take off up the launch tube was very slow
with the rocket and water weighing around
8Kg. As soon as it cleared the launch tube
the rocket accelerated nicely. The rocket
looked nice and stable on the way up, and
just as it passed through Max-Q the
parachute slipped out from under the door,
opened, and promptly shredded all but two of
the shroud lines. The rocket continued to
power skyward but with the high drag of the
flapping parachute it soon tipped over and headed
toward the ground. Luckily it didn't hit at
full speed and so only the top 6 bottles
were damaged. All the payload had survived,
and even the PVC air manifold had survived.
Only one of the cap retaining rings broke
loose, so that will be glued back on.
At first we weren't sure what caused the
early deploy, but the on-board video showed
clearly what happened. The air pressure on
the parachute probably coupled with the
burst of acceleration during the air pulse
simply caused the parachute to slide out.
The parachute bottom wasn't resting on
anything and the friction between the
parachute and the plywood brace just wasn't
enough. I had wanted to use two rubber bands
on the door for stronger support but I
suspect even that wouldn't have been enough.
This is an easy fix and so that will be done
before the next launch.
The altimeter read 245 feet (75m)
which isn't surprising with all the extra
drag, and the big hit to upwards velocity
the rocket would have received when the
chute opened. Two of the knots on the nylon
shock cord were actually fused by the
opening. It sounded great though on the
way up. :)
We've already stripped the rocket down
and have started repairs. Because of the
impact on the manifold we will re-test it to
130psi. Stay tuned to the rebuild progress
on the Inverter build
Here is a
highlights video from the day:
After the Inverter flight we swapped the
release head on the launcher once again to
the 9mm one and launched the Axion II a
couple of times. Both flights went well.
Paul also launched his Thunderbee Hero on a
1/2A3-4. The rocket lost it's streamer, but
because it is so light no damage was done.
Shaped Bottle Splicing
Recently we were asked if it was possible
to splice those shaped coke bottles
that don't have straight sides and have all
sorts of protrusions. We had a go using the
same narrow sleeve asymmetric splice
technique we normally use on the straight
wall bottles, with one additional step in
We let the splice cure for 3 days, and
did the burst test. The splice held
170psi before it burst. That's about
20psi shy of the normal burst pressure of
the bottles. The splice would work fine for
the regular un-reinforced bottles that are
launched at 130psi. (same as the straight
walled splices). After the burst test we
inspected the splice and it had pulled apart
at the glue line, but we noticed that the
glue was still a little soft. It looks like
it hadn't fully cured yet. We'll try another
splice and let it cure for a full week.
We'll add the extra step into the
splicing procedure for those who wish to use
the shaped bottles in their rockets.