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represents a launch or test day, and describes the
events that took place.
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Day 79 - Acceleron Vb Explosion and Axion V
flights
Axion IVb gets filled with 1.3L of water and
foam.
Standing on a crate makes it easier to load
the second stage.
Getting ready for test Flight #2
Coming up to pressure at 130psi... ....Ooops!
Photo: David Kelleher
Only Casualties:
1 ring brace
1 2L spliced pair
1 lowest bottle on sustainer.
Sustainer nozzle is still locked in the
staging mechanism.
You can see half of the failed bottle here.
Top part of the booster was prevented from
flying away by the parachute cord.
Lowest sustainer bottle. Blew up as a result
of the explosion next to it.
Broken ring brace. One of the servo wires
running along it was also severed.
The altimeter and camera are now located
under the top bottle for protection.
Repaired Axion IVb with new
fin set becomes Axion V.
Photo: David Kelleher
Good landing
Cloudless and windless sky.
Axion V - flight #1
(120psi)
Axion V with some red food
colouring to make it look faster.
The lowest bottle has a very streamlined
shape. You can't buy them anymore. :(
Axion V launched at 130psi.
Flight #2
Photo:
David Kelleher
This time the rocket reached 468' (143m)
Changes seen at Doonside with the
construction going on.
It came down very close to the rocket eating
trees.
Axion V - flight #2
(130psi)
Helping to prepare a regular rocket motor
for John's rocket.
Running back into camera position.
Flight #3 pitched over a little bit after
take off....
Just washing the sky with a bit of soap.
Launch area and car park. (Descending under
parachute)
... and landed a fair way down range.
The lost alarm on the flight computer could
be heard ~20m away in the open.
Axion V - flight #3
(130psi)
New MD-80 camera next to FlyCamOne V2.
Despite the size the MD-80 weighs about the
same as the flycam, but is more ruggedised with
an alloy body.
We used Ed's (Houston water rockets)
corriflute alignment and shaping technique for
Axion's IV fins. Note the holes drilled in the
middle for better glue grip.
New booster nozzle seats for the cluster
launcher. The special shape allows the nozzles
to pivot as bottles expand. These seal the
nozzles from the inside. They simply screw onto
the existing launcher.
Acceleron booster nozzle evolution. Each
Acceleron rocket uses three nozzles.
Date:25th
July 2009(8am - 1:30pm)
Location:Doonside, NSW, Australia
Conditions:Cold in the morning, (5 degrees
C), warming up to 17 degrees, no wind and no
clouds.
Team Members at Event:PK,
GK, AK, Paul K and John K.
After reviewing the first test flight we
have incorporated a number of changes into
the booster and sustainer in order to help
improve the chances of flying vertically.
Sustainer
We replaced the fins on the
sustainer with ones about three times
the surface area of the previous set. We
made these from corriflute material and
glued them directly to the lowest bottle
rather than using the removable fin set
like we have been using. We tried a
couple of small improvements this time
around:
- We drilled the little holes in the
corriflute material on the inside so
that we could use much less glue to
attach the fins. This was done to try to
avoid extra weight of glue used on the
fillets.
We mounted the new MD80 camera (see
below) along with the altimeter under the first bottle
to help protect it from possible impacts.
Switched to using V1.6 of the flight
computer for deployment.
We reduced the amount of water in
the sustainer to 1.3L.
Booster
We modified an older set of nozzles to
give a 15.6 mm ID in order to increase the
thrust on take off. The takeoff acceleration
is almost doubled now compared to
Acceleron V. The inside of the nozzles
were also polished.
We switched over to the older
pressure switch (TDD) that we have flown
on previous Acceleron rockets.
We have reduced the amount of water
in each of the booster segments to 2.5L.
This gives slightly lower performance,
but it helps with stability. Once
stability of the rocket is verified we
will increase this back up to ~3.2
liters.
Dad made a new narrow seal stamping
tool and we made a number of seals from
three different rubber sheets. The
narrow seals were designed to prevent
the seal partially blocking the nozzle.
Launcher
We made new nozzle seats for the new
nozzles for the launcher. These simply
screw into the existing launcher.
Because the nozzle diameter is now big
enough, we have switched to sealing the
nozzles from the inside. The o-rings are
on the launcher now. (see picture) The
special shape of the nozzle seats allows
the nozzles to pivot while remaining
sealed. This is important because the
bottles stretch during pressurization.
New Camera
Having had the need to replace the
smashed FlyCamOne V2, we thought we'd give
this camera a try:
The resolution is 640 x 480 @ 25fps and
it takes up about 1/3 the volume of the
FlyCamOne! You can fit this pretty much in
any rocket including T8 FTC.
The low light response is great although a
little grainy, which is miles ahead of the
FCO2 that shows mostly black. The frame rate
is also good. The overall image quality I'd
say is slightly lower, and the colour also
seems not to be as rich as the FCO2.
The big plusses are that it does not
suffer from the audio lag and dropped
frames, and there are no battery issues with
it. The build is very solid and the case
looks like it is made of alloy.
It came with a 2Gb micro SD card which gives
around 1.5 hours recording at 640 x 480 @
25fps. Operation is extremely simple. Turn
it on, push button to record. Push again to
stop.
The other option it has is to start
recording when the sound level goes above a
certain value and then stops recording after
2 minutes if the sound level drops off
again. This I think would be ideal for
rockets. ... turn it on to standby. ....
yell at the rocket just before launch (or
tap it a couple of times) and then launch
within 2 minutes. The sound of the launch
should be enough to keep it recording for
most of a flight.
Flight Day Report
The launch day was about as perfect as
they come. There were no clouds in the sky
and no wind. Although there was a little bit
of frost on the ground when we arrived, that
disappeared quickly.
We had to set up the launcher in a
different place again due to the
construction going on that morning.
The setup was quite straight forward
with no issues.
As we came up to 130psi ( 9 bar )
pressure and the rocket was holding
awaiting launch, one of the middle
spliced pairs of bottles blew apart in
the splice.
Luckily it was one of the boosters with
a parachute so no electronics were
affected by the immediate blast. The
blast also ruptured the lowest bottle on the
sustainer. We were lucky again because that bottle was
mostly full of water so no major
explosion occurred there.
The top part of the booster flew upwards
with quite a bit of force and tore
through the ring brace braking it in 4
places. The booster was stopped from
flying further because of the parachute
cord that is attached to the top as well
as the bottom section of the entire rocket.
When the bottom sustainer bottle blew
the Robinson coupling in the upper
section acted as a nozzle and the
sustainer flew off downrange where it
landed safely on its side in the tall
grass.
If the ring brace had not broken, we had
enough spare parts with us to repair the
rocket and try for another flight.
None of the electronics on board the
rockets were damaged, and all the other
components like the staging mechanism,
base plate and launcher also were
unharmed.
Overall the repair bill will be under $5
as we need to make up a new 2L spliced
pair to replace the one that blew,
replace the sustainer lowest bottle and
re-attach its fins. The ring brace being
made of balsa and fiberglass can be
glued back together. (Repairs are
already under way)
We put the booster aside and set up
our Medium launcher. We brought a number
of rockets with us in case something
like this happened.
Within 10 minutes we removed the
tail section of Tachyon V rocket and
screwed it into the top section of the
Axion IVb sustainer that just blew as it
was already fitted with the new camera
and altimeter. We packed its parachute,
reprogrammed its flight computer and
were ready to launch again.
We ended up flying the new rocket (Axion
V) three times on the day with foam and all
three flights went really well. The flights
were nice and straight in the windless
conditions and the parachute always opened
near apogee. We ended up with good onboard
video, and the second flight managed to
reach 468' (143m).
We also ended up flying three of the
boys pyro rockets. All landed well, so
despite the initial failure we ended up
having a great day.
What's next
We will rebuild the rocket in the same
configuration, but will most likely only
launch it at 120psi on the next test.
Although the bottles get tested to the full
operating pressure for 2 minutes, multiple
pressurization can eventually cause them to
fail at lower pressures. Once we get at
least a couple of good flights in we will
again bring up the pressure. Since our
launcher allows it and we are all set up for
it with the control panel, as an
intermediate step we may pressurize the
booster to 120psi and the sustainer to
130psi.
Flight computer
settings
New updated settings for
Acceleron Vb and Axion IV when using a
lighter water load. 2.5L for Acceleron and
1.3L for Axion.
CATO on pad at
130psi. Sustainer bottom bottle
destroyed, fin damage. Booster 1
spliced pair destroyed, two inter
bottle separators damaged, and ring
brace broken in 4 places. Booster
camera failed to record. Good
onboard video. All electronics and
mechanical components survived
without damage.
2
Rocket
Pod 2 (Paul's)
Motor
C6-5
Altitude / Time
?
Notes
Good straight
flight, with very little roll.
Parachute deployed near apogee and
the rocket landed well. No damage.
Nice flight, but
slightly pitched over. Parachute opened
after apogee. Good landing. Good
altimeter data and video.
7
Rocket
Thunder Bee 7 (John's)
Motor
1/2A3 - 2
Altitude / Time
?
Notes
Good straight
flight, streamer deployed well at
apogee. Safe landing.
More Thermal Testing
About a month ago when disassembling one
of our rockets we noticed that the threaded
section of a couple of the bottles had
shrunk and distorted. The threaded sections
were inside the black Tornado couplings.
There are really only two sources of heat
that could have caused this: The sun and/or
pressurising the rocket.
We know from experience that black tape
on bottles and sun don't mix. So we setup up
a mock up of the joint and placed an
electronic thermometer (thermocouple)
against the inside of the threaded section
of the bottle inside the coupling. We placed
the section along with the inter bottle
separator in the sun.
The ambient temperature was 17 degrees C.
Within 30 minutes the temperature on the
inside of the coupling reached 38 degrees C
and remained stable at that point. To
simulate conditions on a hot day and during
transportation, we moved the experiment into
the car and closed all the windows with the
Tornado coupling still exposed to the sun.
Again within about 30 minutes the
temperature inside the coupling climbed to
54 degrees C at which point the LCD panel on
the thermometer turned all black from the
heat. We should have placed the thermometer
in the shade. We stopped the experiment at
that point. When the LCD screen cooled down
again it went back to normal.
Conclusion
This temperature increase due to the sun
is significant, because if a rocket is left
out on the pad in the sun and then is
pressurised, the further
temperature increase due to air compression
can very easily push the temperature over
the critical 65 degrees C at which point PET
plastic starts to become soft. The force as
a result of the pressure at the same time
could make the coupling fail.
We will now be covering any tornado
couplings with a roll of white paper to
protect against heating.
