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Day 92 - Fiberglass flights
Two fiberglass reinforced rockets ready for
launch. We didn't fly the larger one due to the
6L Axion G1 prior to it's maiden flight.
Filling rocket to 220psi in about 1 minute.
You can see the parachute on it's way out
half way down the rocket.
A portable rocket. All the important
The main casualties were a 9V battery and a
Rockets really obey the laws of gravity.
After quick repairs, we replaced the
nosecone, top bottle, and used a stronger
Here grandpa, let me show you how to do
Launch #2 @230psi, parachute is again seen
The guide rail extensions are removed and
the launcher is set up away from the trees.
We set the time delay to 8.5 seconds to
reduce the drift in the strong wind.
The rocket was launched at 230psi.
A long walk to pick up the rocket. The most
painful part? The spiky grass seeds in my shoes.
A panorama from flight #3 from around 695'.
Altitude plot from flight #3.
The fourth launch was powered by 245psi. Our
highest launch pressure to date.
Altimeter plot from flight #4.
The end of the rocket is capped with a
regular bottle cap and a plastic reinforcing
ring over the threaded section.
Pressure testing a Tornado tube (red) with a
hose connection at one end and a PET bottle
pre-form on the other. The tornado tube was okay
High pressure panel (left) next to our lower
pressure one on the right.
Location:Doonside, NSW, Australia
Conditions:Warm 25C, mostly cloudy
Team Members at Event:PK,
GK, Paul K and
We had a very busy week of preparations
in getting two fiberglass rockets ready for
launch day. It's actually good having the
fixed launch schedule, because it forces you
to finish things on time otherwise you have
to wait another two weeks until the next
launch opportunity hoping the weather will
co-operate on the day.
Starting to work on the higher pressure
rockets is like starting all over again as a
lot of components need new construction
techniques and things need to be retested or
replaced. We also need to make new tools for
making the stronger components.
During the week the last of the 8
reinforced spliced-pairs finished curing and
so we tested them to 270psi (18.6 bar)
individually. There are 4 x 90mm
spliced-pairs and 4 x 110mm spliced-pairs.
Thankfully they all held up well to the
pressure without any leaks. Because of the
higher pressures we also needed to test a
whole slew of our regular components to
those pressures. The big unknown were the
new Tornado tubes we wanted to use. Thanks
to Clifford H. for sending us some PET
bottle pre-forms which let us pressure test
the couplings to high pressures. We used the
pre-form to plug the other end of the
coupling and we used our special bottle neck
/ air hose adapter from the other end. The
tornado tubes held 270psi without
We then fully assembled the rocket with
the tornado tubes and pressure tested it.
One of the the tornado tubes sprung a small
leak, and so we tightened it further until
it stopped. These are merely
plastic-on-plastic seals so a little
trickier to seal. We pressure tested it
again and all was good.
So we assembled the
larger rocket and as we were really
tightening up the last coupling it cracked.
Major OOOPS! So we inspected the other
couplings and found one with lighter stress
marks showing where the thread was
underneath. Although not cracked it was
definitely a concern. The next day dad
suggested we swap all of the couplings on
both rockets to our old couplings made out
of polypropylene. Although the first rocket
was already tested to the full operating
pressure, the stresses in the over-tightened
couplings may become worse over time, and we
decided to play it safe. So we had to
re-test our old couplings with o-rings to
full pressure as well. Thankfully they also
We were going to use 4 spliced pairs in
the smaller rocket, but we couldn't quite
get the last bottle to line up straight with
the rest of them. We suspect that the bottle
is bent ever so slightly when it was
originally glued with the Sikaflex glue. Not
wanting to launch a bent rocket, we decided
to leave the rocket with just 3 spliced
To seal the end of the rocket we just use
a normal bottle cap, but have a plastic
reinforcement ring over the thread section
to prevent the cap from flying off. We have
tested this to 300psi (20.7bar).
All the tests were carried out with our
high pressure (300psi) control panel as it
was going to be the one we launch the
rockets with as well.
Our medium launcher
has nice long guide rails fitted, but we
don't have a brass release head for it with
stainless steel ball bearings that hold on
to the nozzle. For the higher pressures we
did not want to rely on the plastic tabs
like in regular Gardena mechanisms. The
nozzle was going to be aluminium to hold up
to the pressures as well. Because our
cluster launcher already has a built in
brass release head with the ball bearings,
we simply modified the base to accept the
guide rails from our medium launcher.
Launch Day Report
We arrived at the usual 8am timeslot
and set up the launcher. The wind was
already starting to pick up and heading
in the wrong direction back over the
rocket eating trees.
We filled the Axion G-1 rocket with
foam and 1.6L of water. We are using the
jet foaming insert in the tornado
coupling to produce foam on the way up.
The new control panel allows us to fill
the rocket quite rapidly to the higher
pressures. We can get the rocket up to
pressure in around 1 minute. We have switched
to using a longer hose as well as a
longer launch string. You just don't
want to be anywhere near the rocket at
those sorts of pressures.
As we launched the rocket at 220psi,
it very quickly became apparent that the
chute was out a bit early ... well
actually ...as soon as the rocket
cleared the guide rails. It promptly
decided it did not want to participate
in the rest of the flight and fluttered
down next to the pad. The rocket barely
blinked as the parachute cord broke and
continued to climb to 605' (184m). That
wasn't too bad considering the parachute
slowed it down somewhat.
The nosecone was destroyed, but the
flight computer survived, with
only a bent connector and a broken power
switch. Both of which can be easily
fixed. The servo motor was destroyed and
the 9V battery completely
disintegrated. The camera and altimeter
were located between the 1st and 2nd
bottles so they were protected from most
of the shock and survived, though the
camera did not record the launch or it
did not close the video file properly. The
MD80 camera has an alloy body so I suspect
it helped protect it.
The top bottle was completely crushed,
and even though the neck that was
connected to the coupling was also
broken, the coupling sustained no
We replaced the broken spliced-pair with
the bent one and fitted a spare deployment mechanism to top. We replaced the broken parachute
cord with a much heavier one and the
rocket was ready for the next flight. I
was surprised to see that none of the
shroud lines were broken or pulled out
of the canopy. They are simply attached
through a hole in a piece of electrical
tape stuck on the ripstop nylon.
We set up the rocket again hoping
that it was only a one-off. ... Nope...
the second launch at 230psi was
identical. The parachute fell out as
soon as the rocket launched, but the
heavier cord stopped the rocket from
flying too high and the rocket landed
close by without damage. We did get
onboard video, but only partial
altimeter data as the parachute cord
slipped down the rocket and hit the
altimeter power switch and turned it
At this point we were quite stumped
as to what was happening. We had used
these two nosecones on quite a few
rockets but never had this problem. At
first I thought the acceleration must be
too high forcing the parachute out, but
that really didn't sit too well. The
theory was that the guide rail
extensions were rubbing against the
rubber band between the door and the
servo and pulling it off as the rocket
launched. This seemed reasonable and so
we removed the top guide extensions.
We also relocated the launch pad next to
the rocket eating trees to give the
rocket a clear path down wind. The wind
was quite strong at this point and it
was a 50-50 decision to launch or not.
Not much more could have gone wrong at
that point and so we decided to try
As we started to pressurise the rocket
the parachute fell out again. We stopped
pressurising and I repacked the parachute.
Started pressurising and the parachute fell
out again. Dang ... just one of those days!
So I repacked it, but did not arm the
rocket. We pressurised it to 230psi again
and only after the air stopped that I armed
the rocket and then we launched it.
rocket flew great and went to 696' (212m).
It was definitely noticeable how much more
power the rocket had. I thought it was quite
a reasonable flight considering it was bent
and only 6L capacity.
Even with a longer 8 second deployment
delay, it drifted around 300m down range.
Feeling pretty confident that we had
solved the problem we set the rocket up
again and this time pressurised it to
245psi (16.9 bar). We waited until
the rocket was fully pressurised before
arming the flight computer again. This
is our highest launch pressure to date.
went up beautifully to 744'
(226m). Which we thought was a great
result for this rocket considering it
used a small 9.5mm nozzle and no launch tube.
Running several simulations later that
were surprised at the altitudes we were
getting when they were predicting around
610'. I believe the foam has a lot to do
with it as we have seen on a number of
From the onboard video it was noticeable
that the rocket was spiralling quite a
on the way up probably the result of the
So what actually happened? It looks like
the culprit is the modified launcher base.
It has a built in non-return valve fairly
close to the rocket. With the higher air
pressures and flow rates it started
hammering (vibrating) pretty badly and the
vibrations travelled up the rigid rocket and
caused the G-switch on the flight computer
to detect launch and deploy the parachute.
The reason we did not notice it on the first
two launches was because the guide rail was
holding the parachute door closed even
though the servo had activated. Having
removed the guides we were then able to see
the fact the parachute was being deployed
during pressurisation. You can hear and see
the vibration in the on-board video as well.
We did have an audible warning though which
we didn't notice in the excitement of
launching a new rocket. The FC beeps when it
is armed. When it detects launch it stops
beeping. We did not notice it had stopped
beeping because we were further away than normal.
I may update the code to make sure the FC is
making a different tone if it is in the
launch detected phase.
Seeing how far the rocket was
drifting we decided not to launch the
bigger rocket (12.4L Polaron G-1) that
was expected to go higher with a bigger
Next we would like to get the bigger
rocket up in the air and see how it does. We want to launch it with a 15mm
nozzle and launch tube. This in itself
brings new challenges in designing for
We are also going to
see what the actual burst pressures are of
the 90mm and 110mm spliced-pairs. This will
give us a better idea what the safe
launch pressures are.
These flights showed that there is quite
a bit of performance potential in these
rockets. So we are going to pursue this
further in upcoming, single stage, boosted
and two stage flights this year.
We need to buy more fiberglass as
we've used up our 3m. I think we'll get a
10m roll next which is good for about 25
We are also going to have a go at
sealing the tornado tubes with either
o-rings or soft seals so they don't have
to be tightened so much.
Parachute fell out
just after clearing guide rails.
Parachute opened but the string
broke and the rocket proceeded to
climb. Nosecone destroyed, 9V
battery dead, servo motor destroyed.
Minor damage to flight computer.
Camera and altimeter survived. Good
altimeter data, no video recorded.
again just after launch, but strong
string prevented rocket from flying
away. Rocket landed without damage.
Good video, but no altimeter data as
the cord switched the altimeter
power switch off.