last updated: 21st october 2023 - Day 226 to Day 230 - Various Experiments

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Construction - Basic


Ring Fins

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Construction - Advanced

Robinson Coupling

Splicing Bottles #1

Splicing Bottles AS#5

Reinforcing Bottles

Side Deploy #1

Side Deploy #2

Mk3 Staging Mechanism

Multi-stage Parachutes


Construction - Launchers

Gardena Launcher

Clark Cable-tie

Medium Launcher

Cluster Launcher

Launch Abort Valve

Quick Launcher

How It Works

Drop Away Boosters

Katz Stager Mk2.

Katz Stager Mk3.


Dark Shadow Deployment


Recovery Guide


How Much Water?

Flying Higher

Flying Straight

Building a Launcher

Using Scuba Tanks


Video Taping Tips

MD-80 clone

Making Panoramas


Burst Testing





Servo Timer II




V1.3, V1.3.1, V1.3.2


Deploy Timer 1.1

Project Builds

The Shadow

Shadow II


Polaron G2

Dark Shadow

L1ght Shadow

Flight Log Updates

#230 - Tajfun 2 L2

#229 - Mac Uni AON

#228 - Tajfun 2 Elec.

#227 - Zip Line

#226 - DIY Barometer

#225 - Air Pressure Exp.

#224 - Tajfun 2

#221 - Horizon Deploy

#215 - Deployable Boom

#205 - Tall Tripod

#204 - Horizon Deploy

#203 - Thunda 2

#202 - Horizon Launcher

#201 - Flour Rockets

#197 - Dark Shadow II

#196 - Coming Soon

#195 - 3D Printed Rocket

#194 - TP Roll Drop

#193 - Coming Soon

#192 - Stager Tests

#191 - Horizon

#190 - Polaron G3

#189 - Casual Flights

#188 - Skittles Part #2

#187 - Skittles Part #1

#186 - Level 1 HPR

#185 - Liquids in Zero-G

#184 - More Axion G6

#183 - Axion G6

#182 - Casual Flights

#181 - Acoustic Apogee 2

#180 - Light Shadow

#179 - Stratologger

#178 - Acoustic Apogee 1

#177 - Reefing Chutes

#176 - 10 Years

#175 - NSWRA Events

#174 - Mullaley Launch

#173 - Oobleck Rocket

#172 - Coming Soon

#171 - Measuring Altitude

#170 - How Much Water?

#169 - Windy

#168 - Casual Flights 2

#167 - Casual Flights

#166 - Dark Shadow II

#165 - Liquid Density 2

#164 - Liquid Density 1

#163 - Channel 7 News

#162 - Axion and Polaron

#161 - Fog and Boom

#1 to #160 (Updates)



Each flight log entry usually represents a launch or test day, and describes the events that took place.
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Day 24 - Underwater Launches and New Launcher
Fully assembled new launcher. Here it is shown with the 2 meter guide rails.
Launcher with the top 1 meter of guide rails removed.
A detail of the adjustable ring.
Detail shot of the foot. There is a thread in the leg that allows the foot to be adjusted up and down.
Detail of the release mechanism lever and pulley.
Looking straight down the launcher.
Detail of the brace position adjustment. There are two of these per brace.
The launcher packs up for easy storage. Most nuts are wing nuts to allow for assembly without tools.
J4 II loaded into the new launcher.
J4 II pressurised and ready for takeoff.
An interesting shot, the rocket is already lying on the ground but the chute is still open.
Loading Polaron II into the new launcher.
Polaron II crashed after I forgot to turn on the flight computer during a hasty launch.
Setting up the old launcher and Cena rocket for its maiden underwater launch.
Cena breaks through the surface from a depth of 1 meter.
Another flight at higher pressure.
Just out of camera shot, the rocket is held down by a line to prevent it flying into the neighbours yard.
Cena pressurised to 90 psi.
Reloading Cena for another 90 psi launch.
Its not every day that you get to pose next to an underwater water rocket.
"Look what happens when I pull this string"
Both the rocket and operator are pressurised by air from a SCUBA cylinder.
Date: 3rd February 2007      7:00am - 8:15am

Location: Denzil Joyce Oval. (launch site #4)

Conditions: Warm, calm, partly cloudy.

Rockets: (click the name for rocket details)

Name Capacity Notes
J4 II 5 L A newer rocket now equipped with 4 x 1.25L Robinson coupled bottles.
Polaron II 6 L A new rocket rebuilt from the last launch attempt that failed on the launch pad.

Team Members at Launch Event: PK, GK, HK, AK, IK, JK, John K and Paul K.

Number of launches: 4 (part 1), 4 (part 2)

On this day we conducted a couple of new tests and experiments. The first was the test of our new launcher. In testing the new launcher we launched a couple of new rockets as well. The new launcher is discussed in detail in the Design and Development section below.

The second experiment was launching a water rocket from underwater (see part 2). Why would we want to do that? Why not? We hadn't seen it done before, and we had no idea what would happen.

Flight Day Events - Part 1

  • We assembled the new launcher and adjusted it for the first rocket. The setup was quite straight forward, and doesn't take long, although it is a little more complex than our old launcher. Since there was virtually no wind we only used the 1 meter guide rails.
  • J4 took off very well out of the new launcher and proceeded almost vertically, the nosecone deployed well, but the parachute didn't unfurl properly almost all the way down. The parachute opened about 3 meters above ground which caused the rocket to swing around horizontally and land undamaged on its side. A pretty close shave!
  • We launched it a second time and this time the nosecone came off just after the air pulse so basically the parachute opened at very high speed, the nosecone line ripped from the rocket and the nosecone kept going up, but the parachute brought the rocket down safely. I am glad we have learned to put strong parachute lines on the rockets, they can prevent hours of work in repairs.
  • Second up was a rebuilt Polaron rocket. It was in a different configuration since the last attempt. The rocket had only 3 bottles and a new set of fins. The fins were constructed of a fairly thick pieces of plastic, and only held in place with rubber bands. We are now looking at using this technique to hold fins onto the rockets because tape tends to come off easily especially when the bottles stretch. Some tapes also leave a pretty nasty sticky residue when they are removed for repairs. Because of the length of the rocket, we decided to dispense with the fin strut extensions so the fins are now directly mounted on the last bottle.

    The flight computer was set and the rocket pressurised to about 80 psi, and one of the joints started slightly leaking. We hadn't pressure tested the rocket prior to launch day, so it was hardly surprising. It turns out that it just wasn't tightened enough.

    Since the leak was only slight we decided to launch anyway. The rocket flew a beautiful flight, and on the in-flight video you could see that it only spun on its axis a few degrees. The parachute opened as expected and as the rocket was coming in to land close to the launch pad, I raced after it and caught it before it hit the ground.

    Polaron Inflight video

      (If the video does not play, try downloading the latest Flash player from Macromedia)
  • Since the launcher was configured for Polaron, we reloaded it into the launcher and started filling it. We were going to go for 110psi, but at around 90psi the joint started leaking again, but a little more this time, so in a quick hurry I told dad to launch it and gave a quick countdown. The rocket took of great but as it was on its way up ... I called out something like "s**t I forgot to turn the computer on!!!" Well you can imagine what happened next. The parachute will not deploy if you do not turn the computer on and arm it. So instead we watched it crash pretty hard. The payload section was completely smashed in, one of the flight computer's PCB's snapped in half and most of the release mechanism components were bent. The launch detect micro switch lost its armature. Later when I checked the little motor and gearbox, I noticed that it was sticking. I thought that one of the gears must have also split, but on disassembly it turned out that there was a tiny grain of sand from the crash stuck in one of the teeth. Cleaning it out resolved the gearbox problem.

    An interesting artefact of the crash was the fact that the fins, being attached by rubber bands, allowed them to come off in a triangular pattern a couple of meters from the impact site. They weren't damaged and were easily reattached.
  • The one big thing we learned from this crash, was that procedures and checklists are needed for these more complex rockets and launch sequences. There will not be any more rushed take offs. If in doubt, DO NOT LAUNCH.

Flight Day Events - Part 2

  • Later on in the day we decided to cool off in the pool, but this time we took the old launcher and an older rocket with us. We had been talking about this for a couple of weeks, so it was high time we did it. The rocket that we used has served us very well from the first few days of experiments, and has continued to do so.
  • There was virtually no adaptation of the rocket and launcher for these experiments. We only tied a string to the rocket so it would not fly over the fence, and we had to weigh the launcher down with lead weights so that the rocket would not lift it off the bottom.
  • The first launch was only at 40 psi. We played it conservatively at first so that we could see what would happen. The rocket only flew a couple of meters above the surface, but had no problems from getting above the surface, having penetrated about 1 meter of water.
  • We increased the pressure to 70 psi and launched again, this time the rocket went higher and would have gone more had it not been for the string. The submerged string caused a lot of drag on the rocket.
  • Later we launched the rocket a couple of times again from the same depth with 90psi. The rocket had no problems in leaving the water and would have gone to a considerable height had it not been for the string.

    (If the video does not play, try downloading the latest Flash player from Macromedia)
  • It was a fun experiment, and what did we learn from it?

     - It is difficult for the diver releasing the rocket to communicate the count down with the surface personnel. Holding a camera in one hand, the release string in another and a regulator in their mouth was the problem.

    - The water provided less drag than was expected.

    - It is feasible to launch water rockets from under water.

If you have questions or comments feel free to visit our blog and leave a comment.

Flight Record

Launch Rocket Pressure (PSI) Notes
1 J4 II 100

Very straight flight up, the nosecone came off a little early, but the parachute again tangled and it opened about 3 meters above ground and brought the rocket to a safe landing.

2 J4 II 130

Good take off but failed to get any reasonable height due to very early parachute deployment. The nosecone ripped off and kept flying. Rocket landed well.

3 Polaron 80

Very good flight although relatively low in altitude due to the low pressure. Rocket started leaking, but launched with computer set to “4” setting. Good in-flight video obtained. Rocket was caught as it was landing.

4 Polaron 90

Started leaking and launched hastily, forgot to turn on the computer. Flight was good and straight, although rocket was heavily damaged on impact.

5 Cena 40

Good launch, from a depth of 1 meter, only went about 2 meters above surface.

6 Cena 70 Better launch, went higher. Tether limit was reached.
7 Cena 90 Good flight. Tether limit was reached.
8 Cena 90 Good flight. Tether limit was reached.

Design and Development

Last time we attempted to fly a couple of long rockets we discovered that our launcher was inadequate to support them when there was even a minor cross breeze. The relatively short guide rails also tended to provide less guidance for rockets - which as a result were more likely to stray from vertical.

So we decided to build a new adjustable launcher that will support the next phase of development. We are calling this the medium launcher, as the rockets we are planning in the more distant future will need an even bigger one.

Medium Launcher

The launcher has 4 feet, having one fixed in the middle to support the weight of the rocket and the other three adjustable to allow the launcher to be levelled on uneven ground, or be angled in a specific direction.

The launcher has three 2 meter guide rails that support the rocket’s cylindrical body. The guide rails do not require the rocket to have any special guiding attachments. The guide rails are in separate 1 m lengths to allow for easier storage and allow rockets to be placed more easily on the launcher.

The guide rails are supported by a cross member at the end of each foot for stability. Each guide rail can be moved and locked into position in 5mm increments relative to the center of the launcher, allowing rockets of various diameters to be launched. The guide rails are connected by supporting rings that ensure the correct rocket clearance is maintained along the full length of the launcher. One ring is at the 1 meter mark and the other is at the two meter mark.

Each ring has a separate adjustment for each guide rail, so fine tuning of direction and clearance can be achieved. Each ring is also supported by 6 tensioning lines to prevent the guide rails from twisting. The rings are also designed to provide clearance for rockets with both conventional and ring fins.

The release mechanism is based on an all brass Gardena hose attachment. The release mechanism stands off the launcher about 30 cm allowing rockets with ring fins to be launched. The base of the release mechanism has a quick connect hose fitting for air and a small lever and pulley for the release string. The Gardena hose attachment was modified to include a custom return valve to prevent water entering the hose.

Line tensioning is achieved using the same technology that tents use to tighten lines – a piece of bent metal with two holes in it. Very simple and very effective.

The launcher can be used with just the 1 meter launch rails for smaller rockets, or in the 2 meter configuration for longer rockets.

The launcher set up time is about 8 -10 minutes.

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