This blog covers the day to day progress of water rocket development by the Air Command Water Rockets team. It is also a facility for people to provide feedback and ask questions.

Monday, July 28, 2008

Testing, testing and more testing

With the NSWRA launch day being postponed this weekend due to unfavorable weather conditions, we spent more time in the workshop testing all sorts of things and building a new two stage rocket that will use the Mk2 Stager.

First we pressure tested the new 3.35L sustainer to 120psi. It is using a new bottle we have not used before so we were curious to see how well it would hold up. Then we pressure tested the reinforced FTC to 180 psi. 180 psi will be the first launch pressure of this rocket. This is the actual FTC pressure vessel we will be using for our first FTC flights. The nozzle and end-cap are already attached and the entire length of the FTC has a single wrap of glass strapping tape.

After some recent great discussions on the Yahoo water rocket forum, about thermal properties of bottles, we spent some time doing thermal tests on how warm the air gets inside a rocket during pressurisation. This is important as high temperatures can weaken a bottle. The glass transition temperature for PET depends on a number of factors but can be as low as 69 degrees C.
Wikipedia lists this temperature as 75C.

"The glass transition temperature, Tg, is the temperature at which an amorphous solid, such as glass or a polymer, becomes brittle on cooling, or soft on heating. "

We are in the process of collating the information and we will try to publish it sometime this week.


Tuesday, July 22, 2008

Repairs and painting

After the CATO of the reinforced rocket (Tachyon IV) at Doonside, I have rebuilt a new reinforced bottle and pressure tested the entire rocket last night to 170psi. There were no visible stress marks on it so should be good to go for this Saturday.

I am also replacing the fin section on this rocket with 3mm plywood fins directly glued to the bottle. I coated the fins with 5 minute epoxy to add a little strength and water proofing. They will be sanded and painted tonight.

At the last Doonside launch event a couple of the members suggested trying vinyl paint for the rockets. I bought some white vinyl and plastic spray paint at SuperCheap Autos, but at $15 a can that is not all that cheap. I tried the paint on a PET bottle a couple of days ago. I lightly sanded half of the bottle with very fine sand paper and left the other part untouched. After a few goes I realised that you have to spray in multiple thin coats to get good coverage without runs. The paint dried within minutes.

The paint is a little flexible so bending and squeezing the bottle had no effect on it flaking off, like we have had with other paints. The paint on the unsanded side, however, did come off very easily when scratched with a finger nail. It was a different matter on the sanded side though. The paint held very well even when scratched. I'm keen to see how well it holds up in the sun with heat and UV.


Wednesday, July 16, 2008

Mk2. Staging Mechanism Details

We have posted the launch report on our website from the latest Mk2 Stager test flights. We have also included the full details of how the staging mechanism works.

The launch report is available here:

The stager details are available here:


Monday, July 14, 2008

Mk2. Stager Test flights

On Sunday afternoon we finally made it to the local park to test fly the Mk2 Stager, with a small booster and sustainer.

It was a good day of test flights. The first launch was good with good staging. We had a failure on the second launch with no release, but no damage was done to the staging mechanism. We made a couple of minor adjustments and then the final two flights of the day went well again. We had to leave the oval after flight #4 as it was getting too dark to shoot good video.

From simulations and the observed flight times which were relatively close to the simulated predictions the sustainer reached over the 100m (330') mark. Not bad for a little 600ml bottle with 200ml of water at 110psi.

This is a couple of frames taken from ground video of the staging taking place. The sustainer arced over a little probably because its stability is marginal mostly due to its short length. Seen here staging is happening around the 10-15m mark.

We will post the full results of the test launches in the next few days with photos and video. Soon after that we will also do the full write up of the mechanism itself.

The next test flights of stager will likely be on a medium sized booster and a bigger sustainer. We haven't settled on the configuration yet as we were waiting to see how these tests would go. The bigger booster and sustainer will have to be flown at Doonside.


Friday, July 11, 2008

Drop Away Boosters Explained

This week we've updated the main site with the theory and an explanation of how the drop away boosters work on the Polaron rocket.

Other than that only small amount of work has been done on actual hardware due to other commitments. The weather looks a little windy for this weekend, but hopefully it will settle down on launch day.

Monday, July 07, 2008

Booster and sustainer work for stager test

The booster is now complete for the flight test of the Mk2 stager. The sustainer needs a little more tape, and a coat of paint on the fins and it too is ready to go.

The booster is only a 2.1L spliced pair, and the sustainer is only 600mL. We built both of them small so we could test the stager at the local park. For this test we weren't all too concerned with aerodynamic efficiency. The booster uses the same parachute deployment technique that the drop away boosters use on the Polaron rocket. The parachute is behind a flap held by a wire. The other end of the wire is attached to the sustainer and as soon as the sustainer is released, it pulls the wire and deploys the parachute on the booster.

The sustainer does not have a recovery system. It just has a soft nosecone to protect it (somewhat) on landing.

We don't expect this combination to go very high, and we still need to run simulations to see what to expect. If the weather is good this weekend we will launch it.


Wednesday, July 02, 2008

15mm Nozzles

We had a good weekend launching rockets despite a couple of CATOs. We launched the Axion rocket with a 15mm nozzle and a long launch tube which gives the rocket a nice kick on take-off.

The full update is available here:

The update also includes a video of some static fire tests of the Mk2 stager we have been working on. We are keen to fly it as soon as we finish the little booster and sustainer. We will be able to test it locally without having to wait until the next launch day at Doonside.