Each flight log entry usually
represents a launch or test day, and describes the
events that took place.
Click on an image to view a larger image, and
browser's BACK button to return back to the
Day 150 - Rocket Salvos, Foam Experiment
Location:Whalan Reserve, NSW, Australia
Conditions:Sunny, calm, 22C
Team Members at Event: PK, GK,
Paul K, and John K.
For this launch dad had the idea to fly a number of rockets
from the new cluster launcher, but rather than launching them
all at the same time as you do in a drag race, we were going to
launch them one at a time in quick succession. The middle one
would go first and film the others with a couple of cameras as
they overtook it.
We had to update the firmware on the launcher to give us
200ms delay steps that we could adjust out in the field. A
problem with doing it this way was that the air manifold that
normally equalizes the pressure between the boosters had to be
modified to prevent air escaping through the fill tubes of those
rockets that had already launched.
We added simple removable non-return valves to the tops of the fill
tubes so that later we could reuse the same fill tubes for
launching regular boosters. Here is a diagram of the removable
Non-return valve added to each
Filling up the small rockets
A beautiful cloudless and windless day awaited us when we woke up
and as we headed out to the launch site. 10 minutes from the
site we drove into really dense fog. This was going to be
good, because it usually means that the morning is going to be
nice and calm, and sure enough within half an hour the fog had
burned away, leaving that great cloudless sky with virtually no
Salvo 1 - The rockets were set-up on the
cluster launcher easily. We didn't use any guide rails so not all the
rockets were pointing directly vertically. The sliding nozzle
seats allowed us to move them back far enough to give clearance for the 12 fins
now on the pad. We put 1L of water in each of the
smaller rockets, and 1.5L and foam in the middle rocket. The
timing was set so that the second rocket
would get released 800ms after the first. The others would then get
released at 400ms intervals.
As we started pressurising the rockets, one of them self
launched at around 10-20psi and went up maybe 30 feet before
crashing nose first into the ground. The nosecone fairing was
crushed, but was easy to pop back out, and since the deployment
mechanism still worked fine we set it up again. We believe that
we simply forgot to lock this rocket into the launcher, Ooops.
We locked it in this time, armed it, and as we started
pressurising the parachute deployed from the same rocket.
This time I forgot to twist the wires properly on the break
wire. Double Ooops. I put the parachute back, properly secured the break wire,
and we were able to go up to 120psi without any further
Launch was good, although without the guide rail the main
rocket veered of to one side a little, followed shortly by the
other 3 rockets. It was a great sight to see and all 4 rockets
deployed their parachutes at apogee landing back on the mowed
It was time to download the on-board video, but to my
embarrassment I noticed that one of the cameras had its tiny lens cap
still on. Triple Ooops! At least the other camera caught good action of the
rockets going up. The way it veered off course actually gave it
a good view of the remaining rockets. We
will paint the lens cap orange to make
it easier to notice that it is still on.
Salvo 2 - We set the rockets up again on the pad, but
this time we adjusted the timing so that the second rocket
launched only 400ms after the first, and then the others followed
200ms apart. This time the launch went well without any issues
or lens caps and the timing was a lot more impressive. We got
good onboard video again from both cameras.
Salvo 3 - The next salvo was also set up in the same
way with the same timing as salvo #2. Again the launch went well
and all the rockets came back safely under parachute. This time
while reviewing the video on the #11 cam, we saw that it stopped
recording after about 1 minute while the rocket was still on the
pad. We saw similar behaviour with it when Daniel flew it on his
remote control plane. There the video also cut out after about a
minute. I'm not sure what the cause is, but will need to do
further testing. The other camera got a good shot of the launch,
so we were happy with that.
We had 8 cameras covering this
launch. 2 x on-board, 1 at ground level looking up, 1 on a
tripod giving static shot of the pad, 2 x tracking the rockets,
2 x still cameras. Here is a highlights video from
the day from multiple angles:
The last launch of the day was
a test to see how well foam generation works during
pressurisation with a large nozzle. We
filled the rocket with a water and foam mix, but this time we
doubled the amount of bubble bath in the mix. One problem with
this test was that the launch tube went almost all the way to
the top of the first spliced pair, and therefore there was no
way to fill the rocket without filling the launch tube first. If
it was a little lower we could have used the funnel tube to fill
around the launch tube. For best performance the
launch tube should be hollow.
Even as we poured the solution in we noticed that not a lot
of foam was forming in the lowest bottle as we see normally.
This was a little odd, but we didn't pay much attention to it.
When we started pressurising the lowest bottle foam started
getting generated so it was good for a while but as we kept
going, the foam level started decreasing, so by the time it was
time to launch the rocket, there was virtually no foam left! We
had no idea what was causing this.
Later that night, we thought that it perhaps may have been
another additive that was causing the foam to collapse. We had
used a good dose of silicone grease on the bottle to get it to
slide onto the o-ring. The launch tube was a tight fit and as
the bottle was slid down
that had coated the launch tube as well.
When we got back we performed a small experiment
of putting some foam and water in a bottle and shaking it up. The
foam held well inside the bottle. We then added a little silicone
grease and shook it up again, and sure enough the foam started
collapsing quickly. After a while there was very little foam left.
So off to check with the interwebs and it turns out that silicone is often
used as an anti-foaming agent due to its low surface tension.
Here are a couple of references:
So lesson learnt, we'll use less silicone grease in foam
powered rockets. Conversely, this may be a useful additive when using the Jet
technique that generates foam during flight, but leaves a lot of
foam in the rocket. The silicone
may help prevent too much foam from staying behind in the
Here is a
video showing the observed launch, as well as the de-foaming
So all up a great day
for flying rockets with a total of 13
launched, plus the one that self