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Construction - Basic


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Robinson Coupling

Splicing Bottles #1

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Servo Timer II




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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 25 - Polaron III, J4 II, Acceleron and more underwater launches
Trimming the fins so that there is enough clearance for the launcher.
Preparing Polaron III for its maiden flight.
Last minute consultations ...
Launch. We are investigating why the water column looks the way it does.
A diagram of Polaron III's twin parachute deployment mechanism.
A well lit view of Polaron III on the launch pad.
Did the rocket camera finish recording?
A video frame taken from the onboard camera, with superimposed calibration measurements. This image was used to estimate the rocket's altitude.
A kids' hard life. ... Sometimes you have to get up pretty early to chase rockets.
J4 II pressurised and ready to ....
.... go. J4 II also exhibited the same sort of water column that Polaron III did.
We didn't use the launcher extension as there was no cross-wind.
Descent shots of the three rockets flown on the day.
John said that the coloured water tasted good. He is hoping for a little more during launch.
Preparing Acceleron for its one flight.
Good lighting on the water columns.
A bit blurry, but nice colour.
Getting ready to submerge the rocket. The tank stays above the surface.
At a depth of ~2m pressurised to 130psi.
Launch. It is hard enough to catch the rocket above the surface. The video shows the launches.
Date: 18th February 2007      6:45am - 8:25am

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 III 8 L A new rocket rebuilt from the last launch attempt after rocket crashed.
Acceleron 12.75 L A booster under development. New fins have been fitted since the last launch day.

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

Number of launches: 7 (part 1), 3 (part 2)

This was an excellent day for flying rockets, nice and mild, and no wind whatsoever. We had an early start today because we didn't want to be chased off the field before we were done. We managed to get seven launches in on the day, and we were really happy with the performance of the rockets.

Later in the day we launched the Cena rocket a few times from underwater again but from a greater depth.

Flight Day Events - Part 1

  • The launcher has been working really well for us, but we haven't needed to use the launcher extension yet. That will be handy when there is going to be a cross breeze. It provides a very stable base for the rocket launches.
  • When we loaded Polaron III for the first time on the launcher we discovered that the fins just fit inside the launcher ring. There was only a few millimeters to spare all around, so we got out the scissors and took about 1 cm off the end of each fin. Better to have a little less weight and drag ( read stability ) than catch a fin on the launcher.

    We loaded up the parachutes and inserted the camera. This was Polaron's first time to 120psi so we were happy nothing leaked. We wanted to make sure we got one good launch in with a camera rather than risk damaging the rocket with too high a pressure.

    The rocket flew a beautiful flight with the rocket deploying the parachute right at apogee. The onboard video shows that as the rocket just stops ascending, you can hear the release motor and chute ejection.

  • Water rocket in-flight video - Polaron III

     (If the video does not play, try downloading the latest Flash player from Macromedia)
  • From the video we were able to measure the altitude of the rocket, because the camera looked straight down at apogee as it was over a baseball diamond on the field, which is a known size. We measured the diamond later in the day with a tape measure. It was 26.87 meters diagonal.

    Then at home we measured the camera's Field of View (FOV) (by taking a picture with the camera of A4 paper at a distance of 1 meter) using the similar triangles technique, we got an estimate of 121 meters ( ~397 feet).  See diamond image on left.

    We are confident that the measurement is quite accurate, as entering the rocket parameters into a simulator gave an apogee of 119 meters. That's close enough in our book.
  • We flew Polaron III two more times after that at 130 psi, and both times it performed very well. We are surprised that the rocket doesn't spin very much, but that is likely due to the low acceleration, low top speed and its the fairly large diameter. Its fins are just eyeball aligned as they are held under rubber bands. This aspect of the fin design seems to be working very well and I think we will use more of it.
  • J4 II has had a new nosecone fitted that sits much better on top of the rocket. J4 II's first two flights were excellent with the single parachute deploying right around or just past apogee. It was too high to see when it deployed. On J4's last flight the parachute opened perhaps a little early, but the flight still looked great.
  • Acceleron was also launched once, but with a few modifications this time. The water holes for the dummy payload were closed up about 2/3 to prevent the water emptying out too soon after burnout. If the water empties too early then the rocket also looses stability early. The other major mod was the use of new larger, rubber band attached fins. These allow the rocket to hit the ground without snapping a fin off.

    We launched it with its highest pressure to date of 120 psi. You can sure see the difference in acceleration and flight at the higher pressure. The take off was great and it went mostly vertical, the water in the dummy payload looked as if it emptied later than normal because the rocket went quite high. The parachute deployed as the rocket was still ascending at a fairly rapid rate, and the dummy load had separated from the rest of the rocket. It obviously still had enough water in it with sufficient momentum. The dummy payload is secured with two wire loops (for redundancy)  that should prevent this from happening, and I remember checking that these were hooked on, but during takeoff it looks like they unhooked, because there was no damage to the loops nor to their attachment points.

    In hindsight it was probably a good thing, because if it remained attached it may have damaged the parachute. Everything ended up landing well so we were happy.
  • During the flights and especially later during analysis of video and photos we noticed that most of the water coming out of the nozzle was in quite a bit of a wide turbulent spray rather than the normal laminar column of water. This was happening for both rockets I was going to blame it on a faulty nozzle again, but I am beginning to suspect another cause.

    Both rockets had the lowest bottle almost entirely full. This means that as the rocket is released the air pushing on the surface of the water is unevenly distributed since most of it is coming in through the 8mm hole in the Robinson coupling. If this jet of air is basically blowing into the water it is likely to produce a lot of bubbles. Perhaps the water is super frothed by the time it comes out so that the bubbles in it are expanding as they come out. This may be a good experiment to do on a static test stand to see what actually happens. If the water is full of bubbles, then that may be directly applicable to an expanding nozzle design for better nozzle efficiency.

water rockets day 25 highlights

 (If the video does not play, try downloading the latest Flash player from Macromedia)

Flight Day Events - Part 2

  • We flew the Cena rocket again three times from under water. We wanted to see the effect of the increased depth on the flight above water. The first launch was at 90 psi the same as the last launch from 1m. The water depth had a significant effect on the flight as it only flew a couple of meters above the surface.
  • We increased the pressure to 130psi and this time the rocket left the water at a good speed with the tether keeping it from going next door.
  • On slow motion underwater video we noticed that while the rocket was still moving underwater you couldn't see anything really coming out of the rocket, because what was coming out was water of course. I had half expected to see a bubble trail. Dad wouldn't let me use food colouring in the rocket in his pool. I wonder why?

Underwater Launches of water rocket


(If the video does not play, try the latest Flash player from Macromedia)

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

Flight Record

Launchh Rocket Pressure (PSI) Notes
1 Polaron III 120 Great flight, with parachute deploy right at apogee. FC deploy setting was set to 7. Both parachutes deployed well, and the rocket also landed well. The rocket carried a video camera.
2 Polaron III 130 No camera this time, with FC setting at 7 again. The flight was excellent, but ended up arcing over a bit.
3 Polaron III 130 Again without camera and same FC setting. Another great flight, good landing and good deploy.
4 J4 II 130 A perfect flight. Very straight and very high. The rocket seemed to hang at apogee, parachute deployed as the rocket flipped over.
5 J4 II 130 A repeat of the above performance. An excellent flight.
6 Acceleron 120 A great flight, with a relatively vertical flight profile. Parachute opened later than on other flights. The parachute opening caused the dummy payload to separate from the rest of the rocket.
7 J4 II 130 A good flight, but the parachute opened a little early on the way up, and the rocket didn't reach its potential altitude. Peter caught the rocket before it hit the ground.
8 Cena 90 Underwater launch from around 2m. Rocket didn't fly very high above the water.
9 Cena 130 Underwater launch from around 2m. Rocket had higher velocity when it emerged from the surface, but the tether stopped it from flying very high.
10 Cena 130 Underwater launch from around 2m.Similar flight to #9.

Design and Development

To date, probably other than Acceleron, Polaron III with its 4 bottles, 3 couplings, flight computer, camera and twin parachutes, is our most sophisticated water rocket. We have used a few new construction techniques on Polaron III for better performance and survivability. These include:

  • Attaching fins with only rubber bands made from bicycle inner-tubes. This has the advantage of you being able to remove the fins for rocket storage and transportation. It also prevents them from snapping off when the rocket hits the ground. The rubber band stretches with the bottle where tape didn't. Tape often stretched, the glued surface would slip and always leave some kind of sticky residue.
  • A second parachute loosely held in a horizontal tube in the payload section. The main chute line passes around the second chute in the tube so that when the main chute opens, there is enough force to pull the second chute out.
  • The inter-bottle aerodynamic adapters are no longer taped in place. These are allowed to move slightly. A rubber collar is made from an ordinary kitchen rubber glove. This is placed over the join and allows the bottles at either end to stretch but without the aerodynamic drag of buckled tape. Tape was avoided for the above mentioned reasons. The thin rubber collar weighs about the same as the tape.

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