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Day 137 - Axion G4 with Boosters
31st August 2013
Location:Doonside, NSW, Australia
Conditions:Overcast, light winds 5km/h
early, 15km/h later,
Team Members at Event: PK, GK,
Paul K, and John K.
Over the last several weeks we've been
continuing with the Polaron G2 phase 2
development. This is a project that has
dragged on for a long time (since September 2010),
so we are keen to get it finished. A lot of
work still needs to be done, but we now have
a way forward with one of the main issues
and that was holding us up and that was how to attach the boosters at
higher pressures. The glued pins and tubes
work well for lower pressures, but would
not be sufficient for high pressures. To test
how well a part of this retention mechanism
would work we tried it on our Axion G4
rocket this week.
We also purchased a couple more
zLog altimeters from Hexpert Systems.
These are the newer Mod 6 (Z6R) versions
that have a neat USB connector that
allows you to directly plug it into your
computer and download the data without the
need for a cable.
The one thing we really
like about these altimeters is that you can
start them recording on the ground. Some
commercial altimeters have specific launch
detect criteria that work well for model
rockets, but with some of our slow foam
launches, these often fall outside the
criteria and would fail to detect launch.
These altimeters are also very thin and can
run from a single LiPo battery.
The main aim for the day was to get at
least a couple of flights in of the Axion G4
rocket. We wanted to test the
Flying a high pressure rocket with a
small nozzle to get a nice long burn.
Booster clamp with thrust
ring as a proof of concept for the Polaron G2.
New zLog altimeters
We ended up using the
old Gluon boosters since they were already
made and sitting in storage. They also
already had their recovery systems so that
made it even easier. Since we have never tried a
higher pressure main stage before we weren't
sure what was going to happen. We decided
for a conservative 200psi on these launches.
(This rocket has flown at 245psi previously.)
Rocket and launcher setup took about
45 minutes because you have to assemble the
whole rocket on the pad.
The assembly procedure is as follows:
Boosters go on the pad first
The main stage is threaded onto the
boosters and locked down
The guide rail is threaded onto the
rocket and attached to the legs.
Boosters are filled with water from
top and capped.
Main stage is filled with water and
foam from top and capped.
Nosecone is attached.
Booster parachutes are packed and
parachute doors are locked with wire
connected to main stage.
Main parachute is packed and stowed
in the nosecone.
Deployment mechanism is armed,
camera and altimeter started.
Rocket is ready to be pressurised
The nozzle has a 7mm internal diameter
and uses a standard Gardena launcher. We
made this nozzle a few years back, but
haven't really used it. We have mostly used
it's plastic brother on low pressure
launches. We decided to use the brass
version because of greater pressures were
used in the main stage, but especially
because this nozzle also had to hold down
not only the rocket, but also the 3
boosters. That is a combined force of around
70 kgf (690N, or 155 lbf) The entire nozzle
is held down by 3 ball bearings in the
release head, and if we had used plastic the
ball bearings would have made neat little
grooves in the nozzle.
7mm brass nozzle used on the
Axion G4, next to a standard 9mm
Because the boosters are not reinforced
we had to use our dual pressure panel where
we can supply different pressures to the
main stage and the boosters. We have to run
two separate hoses to the launcher for this. We fill
each of the boosters with a different
colour. Not only does it look better on
video, but it lets us see if there is a
specific leak as to which part is
responsible. It also helps us to identify
booster problems during flight. We also have
matching coloured tape on each booster
nozzle so that we can check for nozzle seal
issues post flight if we see unusual flow
from a booster,
Dual pressure control panel
1L into each booster
Packing booster parachutes
Filling main stage
Gauges marked with target
Ready to go.
Because it is difficult to simulate these
flights due to the use of foam we chose 6
seconds as the deployment delay. The
boosters were pressurised to 120psi but as
the main stage passed about 120psi a leak
developed near the nozzle. It was spraying
quite considerably so we quickly decided to
launch as 120psi was sufficient pressure.
The actual launch pressure was somewhere
between 120-150psi as could be heard dad
calling the pressure out from
The rocket took off nicely and the boosters
all separated at the same time. The rocket
had a nice slow and long burn, but it had a
bit of a roll and ended up spiralling
upwards. The rocket reached 623 feet (189m)
and it looked like the parachute opened just
a little bit prior to apogee. So a good
flight overall despite the leak. The burn
time was around 5.5 seconds.
Rocket landed nice and close...
...about 1m next to me.
Prior to apogee
The rocket landed only 1m away from me so
that made it easy to retrieve. The only
damage done was that one of the fin can
leaves slipped out from under the booster
clamp when the fin hit the ground. We just
loosened the clamp and slipped it back
Here is the flight #1 altimeter plot from the zLog
We weren't quite sure why the nozzle
leaked, but it was a non-standard nozzle
that we don't normally use. We attached the
nozzle to just a single bottle and
pressurised it to 120psi without any
trouble and released it. So we re-attached it to the rocket
for another go. The most likely cause was an
improperly seated seal.
After the rocket was put on the pad and
filled with water we noticed that we forgot
to put the reinforcing ring around the
nozzle cap. We had it in place for the first
flight. The reinforcing ring helps hold the
cap on the bottle at higher pressures. We had a
bit of fun lifting up the rocket out of the
launcher without loosing too much water and
slipping the ring back on. It took 3 of us
to get all the pins and tubes aligned again.
We topped off the main stage with another
100mL of water to cover the stuff we lost.
We had already added 100mL extra to the
rocket just in case we had another leak.
This time pressurisation went smoothly
and we got the main stage up to the target
200psi. The launcher released the rocket
easily and the rocket went up again fairly
straight. The boosters separated from the
rocket simultaneously again. You could
visibly see and hear how much longer the
burn was and the rocket kept going and going
spiralling it's way up to apogee. The
parachute delay this time was set to 7
seconds, but from the on-board video you
could see that it was just a little
too early again. This time the rocket went
up to 760 feet ( 231m ). It would be
interesting to see how this rocket would go
at 245psi like was used on the Axion G2
flight. The burn time was over 7 seconds.
Boosters separate simultaneously
Parachute opens just before
Turning off camera and altimeter
Back to civilization
Here is the altimeter plot from the zLog
for flight #2
When comparing the altimeter plots we
noticed that the descent rate was quite
different for the two flights which was
quite strange. It was the same weight
rocket with the same size parachute.
Both descent rates looked constant so it
was unlikely it was caused by a thermal.
The only thing I can think of is if the
rocket had a different attitude hanging
under the parachute. In both instances
we can see that the parachute had opened
cleanly. The rocket also may have
spiralled more under the parachute which
could increase the descent rate because
the canopy is at an angle.
Flight #1 had a descent rate of 18.2
feet/s and flight 2 had 25.4
feet/s That's a
difference of 7.2
We were quite happy with the performance
of the booster clamp and thrust ring and we
did not see any damage after the two flights
We're now going to go ahead and make a
bigger version of the clamp for the G2. The
zLog altimeter also worked great. It was a
lot of fun seeing the very long burn on the
second flight. I'm really looking forward to
the 10+ second burn of the G2.
The next step will be to make similar
clamps for each booster, but with the loops
replaced with the pins made from folded
sheet metal. The thrust rings will also be
glued to the boosters, but under the clamp
rather than on top of it.
We also flew the Axion rocket by itself
with water. We tried yellow food colouring
this time, but it looks way too much like
urine! :) I think we'll be sticking to the
other colours next time. The rocket launched
at 120psi went up well and landed without
problems as well.