Each flight log entry usually
represents a launch or test day, and describes the
events that took place.
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Day 18 - New
Rocket, good in-flight video.
The new J4Y rocket. Looks like the rockets
are growing faster than John.
Packing up the parachute for the maiden
After several in-field repairs, the J4Y
rocket finally takes off.
Frankovka III with a 7mm nozzle takes off at
a bit of an angle.
Another shot of Frankovka III going up to
see the world from a different perspective.
J4Y' bottom section, the top section blew
off on the launch pad.
Frankovka III with 7mm nozzle - that is
still the water column!
Our new lathe, this makes it much easier to
manufacture rocket parts at home. (Still covered
in grease from shipping)
New couplings flown on the new rocket.
Diagram of how the coupling fits together.
Seal cutters made on the lathe. These cut
out the exact seals we need from a rubber sheet.
The end of the long tool showing where it
slots into the coupling nut. The tool helps
tighten the nut in the bottle.
First version of the ground support
vehicle. After it was made we discovered it
didn't easily fit in the car....
Overcast, light breeze, temperature ~20 deg
This is a new rocket made out of
three 1.25L bottles. It is our
tallest rocket to date. Parachute
deployment is achieved using the
Rocket is typically filled with 1.1
liters of water.
This is an older rocket designed to
carry a video camera and a flight
computer. On this day, it was flown
with the camera and the flight computer
for the first time. This is a 2 x 2L
rocket. Typical fill is 1.25L of
Team Members at
PK and GK.
of launches: 12
This day was a little different from
others in that we decided to go fly on a
weekday rather than on the weekend. We met
up for an early start at 6:30am so we could
get a few launches in before work. It was an
overcast morning with only a slight breeze.
Great day for shooting rockets.
Flight Day Events
First on the launch pad was the new
rocket J4Y. The J4Y rocket was named
after John because it was his 4th
birthday on the day the rocket was
finished. As we got up to 50psi one of
the couplings started leaking. This was
a bit disappointing but it was the
maiden flight so you would expect a few
teething troubles. We launched it
anyway, but it only went up about 5
meters before dropping. We found that
the problem was actually the plastic
bottle cap part of the coupling which
appeared a little distorted. This is
something that can be easily fixed with
a longer thread bottle cap. The other
coupling was holding up quite well.
While repairs were being made to
J4Y, Frankovka III was fuelled up and
placed on the launch pad. Today was the
first time we launched the flight
computer along with the video camera. We
purposefully set the deployment delay
back to 5.5 seconds so that we could get
a nice clean in-flight video of the
rocket passing through apogee and a
little beyond. It always looks a little
scary from the ground when the parachute
doesn't open near apogee as we are use
to. The video can be seen below. This is
probably our best in-flight video to
(If the video does not play, try
Flash player from Macromedia)
We set up J4Y on the launch pad
again, but again it leaked. It was
looking like we would not be able to
make field repairs to it. But we
retightened the bottle and tried again.
This time as we approached about 90 psi,
the cap failed and the top two bottles
with the nosecone ripped themselves out
of the lower bottle and flew about 10
meters in the air. You can imagine our
surprise we haven't had one of these
couplings let go like that yet. The
lower bottle was fine, still full of
water, and the top two were okay as
well, so we screwed it back on, thinking
that it won't happen again, and we were
going to launch it at a lower pressure.
Well, at around 70 psi the top blew
off again. Arghh!! so what now? Well,
you screw it back on, get some glass
fiber reinforced tape and you tape the
top section to the bottom section so it
(hopefully) can't happen again. After we did that we
happily launched it 4 more times
increasing the pressure by 10 psi each
time. The bad coupling managed to hold
up to 90psi without leaking. Replacing
the cap back in the workshop should
solve the problem.
On the final flight the rocket went
really well, so we are looking forward
to pumping it up to 140psi, although I
suspect, the park is a little small for
this rocket now.
We were launching the J4Y rocket
with a custom made new 7mm nozzle to get
a slower more spectacular lift-off.
Later we launched the Frankovka III
rocket with the 7mm nozzle a couple of
times at 130 psi and got some very
impressive slow acceleration high
the ground support vehicle were made to carry the
various bits and pieces to the launch
site. We can carry everything now to the
launch site in one go.
We had to call it a day and head off
to work, but an hour of flying was just
enough to keep us happy.
As this rocket
reached 50 psi, one of the couplings
started leaking, so it was launched.
Rocket flew to around 5 meters.
Parachute deployed but did not open.
No damage was done to the rocket.
First flight with
both flight computer and on board
video. Deploy delay set to 5.5
seconds. Very good flight and good
video. Rocket went mostly straight
up. Parachute deployed at the
5 Second setting on
chute deploy. Very good flight, but
the rocket angled a little on take
off. Despite the flight away from
the launch pad, wind carried it back
to a landing 2 meters from the
Again leak from the
same coupling. Better flight this
time about 25m in altitude and a
good chute deploy. The rocket used a
After some attempted
repairs the top two bottles and
nosecone blew off the rocket while
pressurising. Flew to around 10
meters. Failed at the leaky
coupling. Fitted with 7mm nozzle.
Again the top two
bottles blew off at 70 psi.
More repairs, this
time the rocket launched properly
and with the 7mm nozzle was a good
slow take off. Relatively low
altitude but reasonable flight with
good parachute deploy.
Again 7mm nozzle,
angled a little off the launch pad
but a good flight and higher than
previous. Good deploy.
7mm nozzle, a very
good flight with the parachute
deploying just before apogee.
7mm nozzle, good
straight flight up, highest for the
rocket for the day. The parachute
deployed a little too early but the
rocket landed well.
We fitted the 7mm
nozzle to this rocket to see how
slowly it will take off. The rocket
carried no video and the FC was set
for 5 second deploy. Rocket angled a
little on take off as is quite
common for us with a small nozzle,
but then flew very straight and very
very high, great deploy, drifted
down range about 130 meters. landed
1 meter from large tree. Flight time
~ 26 seconds
Almost exactly the
same flight as #11. The rocket
landed about 5 meters from where #11
landed. The slow takeoff and the
long acceleration are really fun to
Design and Development
As we develop new rockets we
often need to manufacture custom parts
such as new nozzles or couplings. To
make this a whole lot easier and more
convenient we decided to buy a small
metal-working lathe. Every water
rocketeers' workshop should be equipped
with one of these. Fortunately dad has
known how to use a lathe for most of his
life and can churn out accurate parts
very quickly. The lathe can cut both
imperial and metric threads which is a
One of the reasons we did not fly
last week was because we are upgrading
the workshop to accommodate the new toy.
We have now made 4 new "Robinson" style
couplings for testing. Two of them are
made with an 11mm hole and the other two
have an 8mm hole. Some photos and a
diagram of how the couplings fit
together are shown on the left. A slot is cut into the
bottom of othe coupling nut to
enable a special tool to be used when
tightening the coupling in the bottle.
We found that a fourth seal between the
inner coupling and the bottle cap is not
necessary as the cap is soft enough to
provide a good seal. We tend to omit it
so that the amount of thread available
to hold the upper bottle is maximised.
The lathe was also used to create
seal cutters that enable us to punch
seals out of a rubber sheet that are
exactly the right size.
When testing the 11mm couplings with
1.25L bottles we found that we just
could not get a good seal above about 80
psi. The outside diameter of the
coupling was just too big for the shape
of the bottle. These may work better
with slightly larger 2L bottles.
The 8mm couplings worked really well
and were pressure tested up to 140psi.
We don't know how much more they will
hold but, we are getting up towards the
failure level of the bottles and so we
will need to test with re-enforced
We used two of the 8mm couplings on
the J4Y rocket.