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.

Saturday, December 15, 2007

Fire and Water details available

We have updated the main site with the details of the launch event from last Saturday. The update includes a video of the highlights.


Monday, December 10, 2007

Fire and Water

We had a great launch day event yesterday. We met up with a couple of pyro guys from the Australian Rocketry forum and the weather at the new launch site co-operated as well. We did a total of five flights (all with on-board video) and they too launched a number of theirs. We also did a combined effort and strapped our video camera to the side of one of their rockets. It's interesting to see how similar the view is from both types of rockets, especially when using foam in the water rocket.

I was fascinated to see their pyro rockets close up, and the preparations needed to get them going. The pyro rockets sure are a lot less messy. Ultimately the same parameters apply to both disciplines in terms of drag, stability, thrust etc.

The new George Kendall Reserve launch site was also very good. There were only a few people about and the clearance range is greater compared to our usual launch site. Being only about 35 minute drive from home is not bad. It's definitely a place to test the next stage of development.

Over the next few days I will do a full web update with photos and videos again.


Monday, December 03, 2007

Polaron IV progress

We didn't get to fly this weekend due to the adverse weather conditions, but at least we made progress on the Polaron IV rocket. The 8L rocket main stage pressure vessel is now finished, with reinforcement of the bottle bases based on the technique described during our last update. We had to machine up a new base to base coupling that was longer than normal because it has to go through 4 thick PET walls with washers in between. When we now heat shrink the reinforcing sleeves, we fill the inner bottle completely with water and pressurise it to about 15psi. We also use a blow torch set to a low flame to get better control over the heating location.

We have yet to pressure test the main stage, but I am hoping that 130psi will be a safe launch pressure. After a couple of failures at 120psi of similar Robinson coupled 2-liter bottles, we have been reluctant to push the pressures much higher. Hopefully this reinforcement technique will allow us to do that.

We have also started modeling some of the launcher components and staging mechanisms in 3DStudio Max to get a better idea how it's all going to fit together. It also allows us to check for clearances before cutting any metal.

Dad has also prepared hoses and another pressure regulator that goes up to 25 bar (~360psi) with the associated high and low pressure gauges. This will allow us to launch a rocket with a different pressure to that of the boosters. This way we can optimize the performance depending on the structural integrity of the different elements.

Tuesday, November 27, 2007

Polaron IV boosters

We have been working on Polaron IV and its launcher in the background while doing the foam experiments. We have further refined plans now on how the boosters will be attached and how they will separate. The photo above shows three newly machined 13mm aluminium nozzles for the boosters.

Each booster is 90mm wide, 2.3L capacity weighs ~150grams dry including recovery system, has a 13mm nozzle and uses a 450mm launch tube.

The simulator predicts that individually each booster should reach about 130m (430') @ 120psi, however, each of the boosters is intended to lift an additional 900 gram weight. This additional weight being a third of the total weight of the main stage fully loaded with water. Under these conditions the predicted altitude of each booster is around 35m (120'). Giving the main stage a release velocity of ~ 25 m/s.

The calculation gets a little trickier because the main stage also fires at the same time when boosters are launched. Though the main stage only uses a 7mm nozzle and foam so that the overall thrust from the main stage will be much smaller compared to the boosters. The consequence of this additional thrust from the main stage means that each booster has less to lift and therefore will be released at a higher altitude and higher velocity. We will do these additional
calculations when we finish building the main stage and know its parameters in detail.

At 120psi, each booster will produce around 90N of thrust at release and about 190N at the end of the launch tube. That is a combined booster thrust of around 570N as the rocket clears the launch pad. Compare that to the Main stage that will produce around 55N thrust with water only and likely around 35N with foam. From static experiments we found that the main stage should thrust for about 6-7 seconds. Rough estimates for main stage altitude are around 230m (750') at the 120psi level. Actual flight though may vary from this figure if the rocket does not go vertically.

The launcher under construction will have two separate air supply lines allowing us to use different pressures in the boosters compared to the main stage. This should allow us to experiment with a wider variety of rocket configurations. Full plans will be published once the design is finalised and the rocket is tested.

Wednesday, November 21, 2007

Foam vs. Water-only flight test results

We have updated our main site with the results of the foam vs. water-only test flights.

In the analysis we show that foam flights were about 2-3% lower in altitude than the water only rockets. This was a little dissapointing but also encouraging in other ways and certainly gives us a direction for further research with foam. Since the update We tweaked the simulation's drag coefficient and nozzle loss factor so the simulation matched the highest observed water-only flight altitude. We then added the weight and drag of the attached camera, upped the pressure to 120psi and ran the simulation again. The predicted water-only altitude was 350'. The last camera mission on the day was a foam flight with the camera and the altimeter. The altitude measured was 353'. This would put foam on par with water-only.

The altitudes are too close together to be able to make any definitive conclusions one way or another, and a lot more flights are required.

There are a few reasons we want to pursue foam experiments further:

  1. It's a lot of fun.

  2. The residual foam weight issue, described in the update, could point towards a measurable advantage when solved.

  3. These tests were only carried out at low pressures, enough to get the rocket off the ground. As the pressures increase, the take-off and peak velocities will also increase. Due to the difference in velocities between water and foam powered rockets (water = faster & shorter burn, foam = slower & longer burn) the difference in drag will play a more signigficant role since drag is proportional to the square of the velocity. This should favour foam at higher pressures.

  4. Convergent/Divergent (DeLaval) nozzles are yet to be fully analyzed. Although initial tests showed them to be no better at low pressures, higher pressures and nozzle shape optimization are still yet to be tested.

  5. Use of foam may be more optimal for upper stages of a rocket than for the main stage. More simulation is needed.

  6. Efficient generation of foam. From foam thrust measurements we found that foam generated using the Jet Foaming technique produced about 14% less total impulse. We have yet to test alternative ways of generating foam that may be more efficient. A couple of new foam generation ideas are already on the drawing board.

  7. Foam optimisation. So far we have only been using the same ratio of bubble bath to water when mixed, but other combinations will need to be tested.

  8. Different foaming agents. So far we have only tested kids bubble bath to generate foam. There are much better foaming agents available and foam density and viscosity are likely to play key roles in the efficiency.

  9. The test results from all these experiments and data from other rocketeers may be used to build a foam simulation model for further research.
If all the above issues can be optimised for a particular application, then it still may turn out that foam can have higher performance in particular situations.

Monday, November 19, 2007

Great Flight Day

We had an excellent flight day on Sunday. The weather was ideal and none of the rockets crashed. We tested the water-only vs foam flights and got altimeter data for all of them. Virtually all the flights were vertical.

I am in the process of doing a full web update but it will take a day or two to collate all the data and get the videos updated.

The update will also cover bottle reinforcing techniques and their results.


Tuesday, November 13, 2007

Flight Computers & Misc

Most of this week has been spent working on a new design for the flight computer. As mentioned in the web update a couple of weeks back, we want to make it more automated to enable remote operation. We are building our own IR remote so that we can have full control over its operation. Most of that hardware is now designed and part of the remote's software has been written.

The new flight computer will not have any buttons except for the power switch, instead it will have the IR sensor module. It will also have a small speaker to acknowledge mode changes as well as serving as a recovery aid should the rocket fall in tall grass. The flight computer will also support two servos for staging and recovery as well as the capability to support the Zlog altimeters. The flight computer will be able to start the altimeter recording once the flight computer is armed.

Most of the design for this new hardware is now complete, with about half of the software still to be written.

We have now repaired J4III's body and fins, and are in the process of remounting components in the payload bay in order to protect them better during impact. J4III will now also sport the new shock absorbing nosecone to help provide even more protection should the parachute fail.

We have also made our first jacketed bottle that includes a Robinson coupling. We have pressure tested it to 100psi to check for leaks around the coupling, but will need to burst test it to see how much it can actually hold. If the burst tests are successful we would be aiming for launch pressures of around 180psi. While we believe the bottle burst pressure will be around 220psi+ the Robinson coupling is the biggest unknown.

If the weather holds up this weekend we will try to go back and do the foam and water comparison flights.

Tuesday, November 06, 2007


This week we continued working on the stager mechanism. We finished enough of it to test it staging just in the back yard. We used only air at 20psi a couple of times and at 50psi once. Although it worked it was a little stiff to release and that is something we need to look at. We will probably try softer o-rings first. We still have a major design issue to resolve, but have some ideas. (More on this later)

The camera that wasn't behaving during the last launch day appears to be OK, and the cause looks like a poor battery contact. The contacts must have become more compressed inside the camera. We tried it with another battery that has taller solder blobs on the contacts and that worked fine, even when shaking the camera.

We also had a go at building the first prototype of the shock absorbing nosecone. It basically consists of the top 3/4 of a PET bottle which is filled with soft foam. The sides of the bottle have 8 longitudinal cuts all the way around that allow the bottle to easily split and slide over the existing nosecone. It is lightly taped over the top to enable the tape to separate easily on impact. During a crash the padded nosecone slides down and the foam compresses against the internal nosecone, but also the whole thing acts as an air piston to dampen the shock even more. The prototype weighs 35 grams so not a very significant weight penalty. For record flights, this can be removed and the existing nosecone underneath can just be used.

We have also been on the lookout for new launch sites around Sydney with great help from the local rocketry community. We looked at one location (George Kendall Reserve) that looks pretty good and is only about half hour from home.


Wednesday, October 31, 2007

J4IIIb crash and foam flights

This weekend we were going to test performance differences between foam and water-only rockets, but after crashing the rocket on the third flight, we went back to just launching another one for fun. The altimeters are working well for us and I am happy with their performance.

The full update is here:

This update includes a highlights video for the day.

Wednesday, October 24, 2007

Polaron IV development & Hybrid Splice

Since the weather has not been favorable this week, we have been doing further development in the workshop. We are currently rebuilding the Polaron rocket and adding three external boosters. With a number of static tests earlier this year we noticed that Polaron was able to produce around 7 seconds of thrust when using foam and a 7mm nozzle. Because of the low peak thrust during take-off we are assiting the rocket with three boosters each with a 13mm nozzle.

We also tested a hybrid splice technique for joining bottles.

The full update including pictures are here:


Friday, October 12, 2007

Glue test results

The glue test results are now available here:

We tested one splice that held at least 170 psi. This glue although not as nice to work with as PL is definitely a viable alternative if you can't get your hands on PL here in Australia. It has good bonding strength to PET.


Monday, October 08, 2007

Glue Tests

This weekend we did some tests with the VISE polyurethane glue that Damo of Damo's Water Rockets found here locally in Australia. PL premium is not sold here and shipping costs can be quite high from the US. The VISE glue seems to have good adhesion properties to PET but its viscosity is much higher compared to PL which makes it more difficult to work with when splicing bottles.

We did tests to change the viscosity of the glue and also glued two splices. One with the regular vise glue and one with the thicker mixture. We will publish the findings in the next update of the main web page.


Tuesday, October 02, 2007

Zero-G experiments

We had a chance to fly an experiment several times this weekend that we have wanted to do for quite a while. The purpose of the experiment was to demonstrate what forces act on internal components of a water rocket in flight. Gravity based parachute deployment systems appear to work on the ground, but are unreliable in flight.

The experiment shows what happens to a handfull of loose M&Ms inside the rocket during take-off and susequent zero-G (freefall) conditions. The M&Ms were inspired by Mike Melvill's handfull of M&Ms inside of SpaceShipOne.

The update includes lots of photos,videos and an explanation of the experiment.

It can be found here:

The update also includes our first altimeter flights and some interesting results about foam.


Monday, September 24, 2007

Development and repairs

We spent this weekend in the workshop repairing J4 II after its explosion last week. We basically replaced all the bottles with new ones, as some of them had been in use for 6 months or more. All the brass couplings were replaced with new Aluminium ones, reducing the rocket weight further.

We also taped all the inter-bottle rings to the rocket with a wide flexible tape, similar to electrical tape. This made the rocket much more solid.

We also reconfigured Hyperon III into a 3 bottle configuration as it will fly a long payload section when the weather clears up. Hopefully next weekend.

We also finally ordered a couple of altimeters last week, so I am hoping they will arrive this week. If they arrive in time, we should be able to fly them on the next launch opportunity.

We've also been working on a new simple and compact electrical pressure switch which we hope to test in the next few days. The prototype only weighs 10 grams but it should be possible to reduce that down further. The purpose of the switch is to serve the same role as the TDD, but without the exposed external moving parts. We use a TDD to detect when the pressure drops inside the rocket (at burnout) to activate the staging mechanism.


Tuesday, September 18, 2007

Flight computer V1.3.2 test flights

We had a chance to fly a couple of rockets this weekend. It was mostly about testing a new flight computer and doing some foam flights just for fun. We got some good onboard video as well.

... oh and got a good wakeup call on water rocket safety ...

Wednesday, September 12, 2007

Hyperon Flights at Damo's space port

We had an excellent weekend launching rockets with Damien Hart from Damo's Water Rockets. It was good to finally meet him and his family in person. The weather was well behaved and so were the rockets. (Well mostly)

We took turns in launching rockets, and as a grand finale we combined Damo's booster with our sustainer for a two stage flight.

The full details of the flight day are available here:

and Damo's great write up of the day is here.

We'll have to do that again.

Monday, September 03, 2007

Deployment systems

This weekend I spent time making the deployment systems around the two new flight computers. These will be fitted to 90mm rockets. One of them will be fitted to J4II instead of the NOAA deployment system we have been using. The other will be a spare for one of the three rockets (Tachyon II, J4 II and Hyperon). The new flight computers are now using the CR123A lithium batteries.

I also spent time this weekend building and testing a circuit that is going to form the core of a data acquisition system for our rockets. It is again based on the PIC16F628A microcontroller we have been using for the flight computers, but this one will be dedicated for collecting in-flight data. The part of the circuit that I tested was the RS-232 communications between the PIC and my PC through RS232. This way we will able to download the collected data from the unit. Eventually this RS232 interface could also be connected to a telemetry stream back to a base station. Each of these data acquisition units will record one or two channels based on the sample frequency required. It is planned that any number of these small units will be able to be placed on the rocket to gather as many channels of data as required.

I am also hoping to use one of these acquisition modules in our static thrust measuring rig for when we test new rockets.

Hopefully on Sunday we will get to fly more rockets again.

Sunday, August 26, 2007

Quiet week

We've had a quiet week this week, with dad in Europe and I've been busy fixing gutters and do ing paving, there wasn't a lot of time for rockets this week.

I did pressure test the two untested spliced pairs of bottles up to 115psi, and they both held well. We are reluctant to push them too far so that we don't have to rebuild them.

I also pressure tested the Hyperon rocket again to 130psi. And again it held up well to the pressure. I had disassembled a part of it during the week and needed to make sure it still sealed well.

I have finally received the CR123A Lithium batteries I bought on eBay this week. At $1.38 including delivery is pretty inexpensive. I tested them with the new flight computers and they work well. I was surprised that they are relatively light for their size. Since I don't have a battery holder for them, nor could I find one at the local electronics store, I have resorted to simply taping the contacts on with electrical tape. I realise this is less than desirable, but it seems to be holding well, so we will go with it for now.


Monday, August 13, 2007

Hyperon Standard Platform

We have updated the main site with our latest water rocket developments.
The update is available here:

The update includes more details about a standardised rocket platform we are developing for doing a number of experiments.

A video is included that shows how we make our Robinson couplings.

Wednesday, August 08, 2007

Analysis and developments

This week we have been doing a bit of analysis of the Acceleron IIIb flights we captured on video. We noted a few things:

1. It looks as if the stage separation was taking place a little later than we would have liked. The booster was already slowing down when the release happened. This can be seen at the top of the flight path as the booster starts pitching over. Since the release sequence is initiated by the pressure switch, we will need to make the pressure switch activate at slightly higher pressure. We can adjust the tension on the spring of the TDD, or alternatively add slightly less water to that segment with the pressure switch. Less water means that the segment will stop producing thrust slightly sooner compared to the other two segments that are still accelerating the rocket.

2. We now have a better idea of the time it takes to get to apogee and hence can set the parachute deploy delay for the sustainer appropriately. The parachute deployed about 2.5 seconds after passing through apogee.

3. The parachute deploy delay for the booster will be shortened as even the minimum setting allowed by the software on the day wasn't quite enough.

4. After release the booster looks like it falls more like a back-gliding rocket. It actually saved us a whole lot of work after the first launch since the parachute deployed so late. This is actually a favourable feature because if the parachute fails the rocket should land at a lower rate than if it hit nose first.

We have also been continuing with the next iteration of the flight computer. We are trying to reduce its weight and foot print to make the whole deployment system smaller and lighter.

The new flight computer uses a more compact and lighter launch detect switch. It works in two dimensions allowing you to mount the PCB in different orientations. The deploy servo is directly mounted to the PCB and the battery is directly below the PCB giving a more compact design. The full details of the flight computer will be posted once it has been tested.


Wednesday, August 01, 2007

2 Stage successful flights

The full details of the 2 stage rocket are now available here:

There are lots of photos and a video as well showing the day's highlights. The in-flight video turned out quite well.


Sunday, July 29, 2007

Acceleron IIIb flies!

We had a fantastic day of launching the big 2 stage rocket today. We flew it three times in total before we packed up. Both first and second stages behaved well and we got some great inflight video looking back from the sustainer.

The weather was great too with very little wind and mild temperatures.

I will post full details, photos and videos shortly.

(click image to enlarge)

Sunday, July 22, 2007

Acceleron IIIb details available

We have updated the main website with details of the Acceleron IIIb booster, the Tachyon II sustainer as well as the Flight computer used by the booster. The update also includes the burst test results.

The update can be found here:


Thursday, July 19, 2007

Acceleron III rebuilt

Well its two weeks to the day, and we have finished reassembling Acceleron III. There are still little things to be done, but the bulk of the work in doing the rebuild has been done. We need to carry out pressure tests again (this time we will make sure the camera is rolling) and also a full system test during which we had the failure.

Details of the rebuild and the burst tests will be published soon on our website.


Tuesday, July 17, 2007

2L Burst Tests

This week we tested the 2L bottles we use for the Acceleron III rocket. After the failure a couple of weeks back we wanted to see what these particular bottles can hold. We also did a test with a coupling as we suspect it was a bottle that failed near a coupling.

The burst pressures were at 165psi which is about what we found with other 2L bottles tested earlier. We also pressurised one to 130psi and held it there for 3 minutes. After three minutes we started increasing the pressure and it burst at around 150psi. Therefore we will drop the operational pressure of the rocket to 110psi until we start reinforcing the bottles.

We are now in the process of getting more bottles since 5 of them were tested to destruction and can't be used of course. We need about 8 more bottles which we should have this week.

We also completed the large parachute for the rocket yesterday. The parachute needs to be fairly big as the booster weighs around 2Kg dry.

Monday, July 09, 2007

Rebuild commences

This weekend we spent a few hours on the rebuild of the Acceleron III booster. The booster is now completely disassembled. We can reuse three of the lowest bottles from the booster so that's good. They were new anyway and don't show signs of excessive stress. We made a new base-base coupling to replace the lost one. We replaced all the regular bottle caps used in some of the couplings with longer thread ones and put reinforcing rings on those. This was done for additional reliability, as we have had the smaller lids let go on previous occasions with other rockets. The pod is now also repaired.

One of the things that was quite apparent before the explosion was that the sustainer had quite a wobble to it when it was sitting in the staging mechanism. A number of fellow wrocketeers mentioned that the sustainer could snap off during take off, so we took their advice and started adding better support for the sustainer. This is now mostly complete, but we had to remove the fin assembly on Tachyon and will have to attach fins a different way.

We will also do a couple of burst tests on these particular 2L bottles we are using to see if the upper limit of these bottles is similar to other 2L bottles we have tested. One of the tests will include a coupling.

Friday, July 06, 2007

Catastrophic Failure

Yesterday, we had a catastrophic failure of the Acceleron III booster while pressure testing the entire system. There was a pretty loud boom that echoed through the neighbourhood. Full details of the test and what happened will be posted along with pictures in the next couple of days.

Most of the components can be recovered and we have already started making repairs. Hopefully in two weeks we should be able to have it fully rebuilt again.



Saturday, June 30, 2007

Acceleron III Pod and Flight Computer

This week we finished building V1.4 of the flight computer. It is specifically designed for the Acceleron III booster. The majority of the new flight software has also been written. A few minor changes will still be made to the code, but they are mostly cosmetic. The flight computer now detects the burn-out in the booster to trigger the staging mechanism a short time later. Then after a settable delay the parachute is deployed.

Acceleron III payload pod. (staging mechanism - upper left, long thin tube is the sustainer air supply, the pressure switch is the device with the spring, and the flight computer, actuators are attached to the yellow bulkheads. The parachute is located on the other side of the pod.)

We temporarily mounted the FC into the pod and tested to see how it fits and operates with the staging mechanism. We are quite happy with the overall design and operation. Although it is probably heavier than it needs to be, it is only the first prototype, so a little more weight is acceptable.

The pressure switch (Trevor's TDD) now has a microswitch and is connected by short cable to a connector. This way the unit can be removed from the booster segment for filling with water and then fitted again.

We also manufactured a second 5mm nozzle that has a better fit for the staging mechanism to reduce the amount of wobble the old one had.

We are now pretty much ready to commence full system tests.

Friday, June 29, 2007

MySpace Upgrades

It appears that MySpace is doing some upgrades at the moment, so a number of the videos on our site are not available during this upgrade. Check again later, if there was something you wanted to see.

Sunday, June 24, 2007

Tachyon test flights

We had a sucessful weekend flying the Tachyon sustainer. We wanted to test it as a single stage first to make sure it will perform as expected when it is boosted by Acceleron III.

The full details of the flights can be found here:

A video is included in the update that shows the highlights of the day.

We are now just finishing the Acceleron flight computer (V1.4) and should be ready to do some end to end testing of Acceleron III systems fairly soon. Once all the tests have been successfully completed, the two stage rocket should be ready to fly.

Monday, June 18, 2007

Bad weather

We didn't get a chance to test the sustainer this weekend as it literally rained non-stop the whole weekend, as well as strong winds on Saturday with gusts up to 80km/h. This is the second weekend we haven't been able to launch. :(

We stayed indoors and continued the development. We made good progress with the Acceleron III pod, mounting the servos in it and connecting the staging mechanism to the servo. We did a dry test to see if the servo had enough strength to release the Gardena staging mechanism and it looked good. We also fitted a micro-switch to the TDD so now the flight computer will be able to know when burnout has happened.

We now only really need to finish building the flight computer and making the parachute and the rocket will be ready to go. We will still need to do a few full system tests with staging and parachute deployment before the actual launch.

We also tested the spliced bottle we glued a few weeks back. We pressurised it up to 100psi and it held well. We didn't want to burst test it as there is no guarantee that the next splice will be as strong. We will test these splices to perhaps 20% above operating pressure without destructive testing.

We will make up a number of these spliced pairs (as opposed to sliced pears) and then make our first rocket out of them.


Wednesday, June 13, 2007

Tachyon sustainer and staging mechanism testing

We have updated our website with the latest progress update. There is a video showing the details of the Tachyon parachute deployment mechanism as well as a test of the staging mechanism under pressure.

Update is available here:


We have also added a site index to the website to make it a little easier to find things.

Sunday, June 10, 2007

Tachyon completed

We have finished building the Tachyon sustainer this week, and pressure tested it up to 130 psi.

We wanted to fly it during this long weekend, but due to the heavy storms here in Sydney we were unable to. We had wind gusts of up to 100km/h, huge seas with up to 15m (40 foot) waves and drenching rain. Our local park had quite a bit of standing water on it, so it was unsuitable for launching as well. We will fly it at the next opportunity.

Meanwhile we have been continuing with the staging mechanism on Acceleron III, and plan to continue with it tomorrow.

Monday, June 04, 2007

Tachyon Sustainer Development

This week we concentrated on the Tachyon sustainer. We need to have it built so we can see how it mates to the booster and add the necessary supports. We had our first attempt at gluing the fins directly to the bottle, but found out that PL Premium does not stick to the plastic the fins were made out of. (The glue held great to the PET bottle.) So we connected the fins in a more conventional mechanical manner. The new fin arrangement is removable and does not require to be glued or taped to the bottle.

We also completed the deploy mechanism utilising V1.3.1 of the flight computer. (V1.3.1 includes a software upgrade to drive RC servo motors directly and bypasses the DC motor driver part of the circuit). We are trying a hinged door mechanism for the parachute bay to see how well it works. We wanted to get a more streamlined recovery system compared to the Polaron III rocket. The computer/servo and parachute bay are removable from the rocket skin for easier servicing.

We really need to only manufacture one more aluminium coupling for the inter bottle connection, and then the sustainer should be complete.

We hope to test fly it this weekend to test the deployment system and dynamic stability.

Sunday, May 27, 2007

Multi-stage Details, Acceleron III assembled

We have updated our main site with some development photos showing the Acceleron III booster with the sustainer on top. The details may be found here:

There is still lots more work and testing to be done, but finally we have an idea of the overall dimensions.

Saturday, May 26, 2007

Our First Splicing tests

We had our first go at splicing yesterday. We used the symetrical splicing method first to see how well it will work. We used PL Premium glue kindly donated by Team Parental Advisory.

The symmetrical splicing method is described here:

We need to leave it for a few days to dry and then we will pressure test it. The collar was made by heat shrinking a section of a larger bottle over another cold water filled bottle. It was a little warped, but should be okay. Doing it this way gives you a really tight fit over the bottles to be spliced.

We will probably make up sections like this and then join them neck to neck so that the number of splices is minimised. The 22mm throat is big enough that any choking effects are negligible within the rocket. The sections being screwed together also means you can replace a section should it burst or get damaged.

Tuesday, May 22, 2007

development progress

This last week has been a bit quiet on the development side of things due to other commitments, parties and the like. With those things out of the way, development will again continue this week.

I also received the 10 new micro-servos I've been waiting for for a couple of weeks. I built a small test circuit from a 555 timer to check them out and they seem pretty good and look like they will do the job. I have yet to measure the current consumption so that we can choose our batteries in case we need more power. Having the servos on hand now means we can complete the deployment systems for a number of rockets. We will also need to update the flight computer software to generate the appropriate pulse train to drive them.

This week we also plan on having a go at doing some splicing of bottles, so we can do some more burst tests.


Tuesday, May 15, 2007

Flight Computer V1.3

We have finished the V1.3 Flight computer code and also took some photos. The full details of the design is available here:

While retaining the same functionality of V1.2, the new flight computer is lighter ( 37 g with battery), uses a single battery design and has a greater selectable range of delays ( 3 - 11 seconds in .25 second intervals.)


Monday, May 14, 2007

Staging Mechanism Update

This weekend we spent a few hours in the workshop building the necessary components for the staging mechanism and upgrading the booster.

Some photos of the progress of the staging mechanism are available here:


Friday, May 11, 2007

Starting Multistage Work

Having flown the Acceleron I & II booster a total of 16 times now, we are happy with how it has been performing.

So last night we spent a couple of hours designing the staging mechanism for the booster. And I think we finally have a good plan. The release will be based on a Gardena release mechanism rather than a crushing sleve. The main reason is that with the gardena mechanism, you can release the rocket exactly when needed, rather than when the pressure drops inside the main booster as with a crushing sleve. Also all our existing nozzles will fit the sustainer. The other main reason is that we know that the Gardena mechanism can hold higher pressures up to at least 220+ psi. We want to be able to retain the design once we start reinforcing the bottles. Lastly the crushing sleeve method doesn't lend itself very well to the construction of CD nozzles, which we plan to revisit especially with the sustainer.

Full details of the design will be published once we build it and we know that it works.

Acceleron II has now been disassembled and will get a couple of upgrades:
1. Each booster segment will be extended by a further 2L capacity to help with the greater payload. This means that the total capacity of the booster will be close to 25L.
2. The dummy payload will be replaced by a new payload pod that will house the flight computer, camera, parachute and staging mechanism actuator. The staging mechanism will be mounted just above the pod. The pod will also be used to support the sustainer and protect the payload contents from the spray during separation.

The first sustainer will most likely be based on two 1.25L bottles joined together and will look similar to "OO", with the exception that it will also have a flight computer, camera and side deployment. Eventually when we buy an altimeter we will put that in there as well.

We are more likely to spend this weekend in the workshop rather than launching rockets as we are keen to see how it will go.

Monday, May 07, 2007

Vertical racing

We had a go at simultaneous launches again this weekend. It was fun as usual, and we even tried foam in all three rockets at the same time.

Of the 12 launches all the rockets survived the day well so we were happy. The update contains photos and a highlights video as usual.

We are going to rebuild a couple of the rockets now so there should be something new to see in the next update.


Tuesday, May 01, 2007

Progress continues

Because it was too windy to fly this weekend we decided to do more work in the workshop. We manufactured three more aluminium Robinson couplings for extending Acceleron II's capacity by another 6 liters.

We want to fly Acceleron II again before the upgrade, so it will be couple of weeks before it is done. We first need to drink lots of lemonade before that happens!

Otherwise progress is going well on the V1.3 flight computers, with two of them now being finished and tested. We are now creating two 90mm diameter payload/nosecone sections with the deployment system inside them. These are more aerodynamic then our previous ones.

One nosecone will go onto J4 II and the other one will be used for Acceleron II's yet to be named sustainer.

Friday, April 27, 2007

Foam and CD Nozzle Thrust Data

We have finished processing the thrust data from a couple of weeks ago that compares Convergent-Divergent (CD) nozzles to straight trough nozzles. We did 12 tests in all comparing 7mm and 9mm CD nozzles to 7mm and 9mm straight through nozzles.

The update is here:

The tests were done in exactly the same fashion as the last set of static tests when comparing foam and water thrust.

The results were interesting, although not unexpected. The update also includes the data in a spreadsheet format if others want to use it for further analysis.

Sunday, April 22, 2007

Simultaneous Launches and foam flights

In order to get back into flying we decided to have a go at launching multiple rockets simultaneously. Other than being lots of fun, one of the biggest problems was knowing which rocket you should be watching and the other things like nosecones falling off.

We then also flew a number of flights using the Jet foaming technique and 7 mm nozzles. The slow take-offs are quite a contrast to fully open nozzles using only water.

The update is here:
The update also includes pictures and a video of the day's highlights.


Sunday, April 15, 2007

CD Nozzle Tests

We tested two CD nozzles this weekend. There were 12 tests in all:
  • 3 tests with 7 mm straight through nozzle
  • 3 tests with 7 mm CD nozzle
  • 3 tests with 9 mm straight through
  • 3 tests with 9 mm CD nozzle
Since it takes a bit of work to translate the video frames (around 6000 in total) into a spreadsheet it will take some time to do that. Once we have the data in a usable format we will publish it again.

We went through almost a liter of bubble bath solution, but collected the water during the tests so it just didn't go onto the lawn.

We think this will be it with the static tests for a while, as we are keen to get back to real flying.

Friday, April 13, 2007

Convergent Divergent Nozzles

In order to see if a water rocket can benefit from CD nozzles (de Laval nozzle) while using foam we have built a couple to hopefully test this weekend.

One is a 9mm nozzle (aluminium above) and the other a 7mm (black plastic). The divergent part is conical in shape and has a slope of 4 degrees from the centerline. This value was obtained by reviewing the video and seeing at what angle the spray emerges. The actual angle of the spray varies over time from quite wide to quite narrow near the end as the pressure drops.

The average angle was about 4.7 degrees during the middle of the burn. We chose a value of 4 degrees because our thinking was that if it was more than 4.7, there would be nothing touching the sides during the middle of the burn and hence ineffective. That is just a guess and not based on any scientific or mathematical calculations.

We just want to test to see if there is a noticeable effect when a CD nozzle is used with foam compared to a straight through nozzle. If there is a difference, further tests will be performed to see how the shape can be optimised.


Tuesday, April 10, 2007

Thrust Data for Water-only and Foam rockets

Well it has taken a while but we finally managed to get some good thrust data for a water-only water rocket and compare it to a water rocket using foam generated by our Jet Foaming technique.

The update includes the thrust data curves for 6 firings in total (3 water and 3 foam), as well as an analysis of the results. There is a video that shows how we measure the thrust.

The write up is a bit lengthy but we wanted to make sure that as much data was available for others if they wanted to process the data further or use it in their designs.

Feedback is always welcome.

Monday, April 09, 2007

Thrust Measurements for Water and Foam

We finally managed to get some good thrust data for water and for foam today. We ran three identical tests for water and three for foam so that we could see how reproducible the results are and how much the two differ. The only thing that differed was the addition of bubble bath to the mix, and use of our Jet Foaming technique to generate the foam. All rocket, pressure, water volume, and other parameters were as close to identical as possible in all the tests.

We were quite happy with the data and were quite surprised by the results. The data will be published on our website as soon as we are done processing the raw data, and had a chance to properly analyse it.


Friday, April 06, 2007

Thrust Measurement Rig - First Trials

We finished building the water rocket thrust measuring rig today, and did four firings to test it out. The first two tests did not use any dampening on the lever arm and as a result it was virtually impossible to see the scale needle as it flew around so much.

No Dampner in this photo

We then put a disk in a bucket of water on a long lightweight dowel mounted near the scale to act as dampner. This was suggested by Clifford Heath a while back and a similar technique was used by Antigravity Reaseach when they did their thrust measurement. The needle motion was much more steady. Thanks also to Jim Fackert for suggesting the camera pointed at the scale to take readings. We should also thank Gordon M, Richard W, David L, Trevor, Brian and others for useful suggestions on how to set up the thrust measurement rig.

Dampner Added to lever arm

We have plotted the initial thrust curves of an 8L rocket with a 7mm nozzle using only water and then again using foam and the difference in curve shape was quite substantial. We will not publish these initial results just yet, as we would like to confirm the data by repeating the experiment a number of times and then averaging the results. Full data will be published once we obtain it. Hopefully in the next few days.


Monday, April 02, 2007

Acceleron II Flights

We test flew the Acceleron II booster (18.75 L capacity) three times this weekend with very good results. The encouraging results in the booster's almost always vertical launches means that we are ready to progress to the next stage of development - staging mechanism and the sustainer.

Full details can be found here:

We also took some measurements of the speed of the booster just after the start of the air pulse and had a close look at the sound the rocket generates in order to extract accurate timing of events during launch.

The twin parachutes also worked well to bring the booster to a safe landing each time.


Tuesday, March 27, 2007

Tips for producing water rocket videos

We have updated our site with some useful tips in helping to produce videos relating to water rockets. The update can be found here:


Sunday, March 25, 2007

Acceleron II Details

We have updated our main site with detail photos and diagrams of the Acceleron II cluster booster.

The booster is now finished awaiting launch when the weather improves.


Friday, March 23, 2007

Acceleron II Development

We continue to further develop our Acceleron II booster. We have now added another 6 L of capacity, which makes it almost 19L in total. The nozzles are now 10 mm which is almost 30% more nozzle area.

The top bottle is still the same dummy payload that carries about 600mL of water for ballast that represents the weight of the second stage. That means as it stands the booster lofts about a 750gm sustainer (including water).

The dry weight is now ~1.3 Kg (including the empty dummy payload) which is a bit on the heavy side, but simulations predict an altitude beyond 100m. The booster will, however, only need to travel around 12m before it releases the sustainer at roughly 50m/s = 180 km/h = 112 mph. The simulation is based on 120psi which is what we currently use on this booster. 15-20 more psi is easily achieved, and gain us a few more m/s.

Simulations also show that this Booster / Sustainer combination should be able to achieve altitudes beyond 200 meters (650 feet) with the 120psi - 130psi range.

In this photo the booster still does not have the parachutes fitted. We hope to have it finished this weekend and take it on a test flight weather allowing. Full details of the rocket will be posted on the website once we had a chance to fly it.

Wednesday, March 21, 2007

Continuing Development

This week we have continued development and design work for the thrust measurement rig, and have manufactured a number of parts for it. We have also bought an analog kitchen scale that will be used to measure the thrust.

More research has been done into nozzle design, and we now have a plan for what designs we will test.

More work has also been done on Acceleron II including bottle reinforcement. More details will be posted in the next web update. There were no launches this week due to other commitments.

Tuesday, March 13, 2007

Jet Foaming Test Flights

This weekend we had a chance to fly a couple of rockets using the Jet Foaming technique.

The results of those flights including video and photos are here:

We definitely need to do more testing on the foam, as it seems to be giving the rocket a bit more performance, but we won't know for sure until we can build a thrust measuring device and performs some static fire tests again.

Feedback and suggestions are always welcome.

Monday, March 12, 2007

Foam generation tests and Baffle tests

We have updated our website with the latest static fire tests showing in detail how the water behaves inside a water rocket when a baffle is fitted to the lowest Robinson coupling.

The update also shows the Jet Foaming technique we developed to generate foam inside the rocket to provide a different thrust profile to the normal water/air mix.

We intend to develop CD nozzles to help improve the rocket efficiency.

The update is here:

We have now test flown the rocket with very good results. The video and update will be posted on the website soon.

Wednesday, March 07, 2007

Updated Day 25 Flight Log

Today we updated flight log 25 with a couple of pictures from our under water tests from 2 meters. There is also underwater video showing what happens to the rocket under water.

Otherwise construction of the two new flight computers is continuing, and Polaron III is ready to be tested with the new coupling baffle. Just need to get some nice weather now.

Sunday, March 04, 2007

Coupling baffle and Burst Test

Yesterday a new aluminium coupling nut was made that incorporates a baffle to direct the air sideways onto the walls of the bottle. This should help eliminate the blow-through seen in the static fire tests. This will be tested this week to see what effect it has on performance. The holes are 6mm in diameter, with a total of 4.

We also performed some pressure tests on a reinforced bottle based on the reinforcing technique described by Richard Wayman here:

We didn't quite get up to the burst pressure of the 1.25L bottle, because we had an issue with the hose failing to hold onto the rocket. We went up to 220psi, before it flew off the test stand. We are making a new attachment that will prevent the bottle from flying off. But all the signs were encouraging for a significant improvement in strength.

We ended up using hot water instead of the heat gun to shrink the outer bottle which worked quite well and pretty evenly.

We also finally have a new proper domain name:


Friday, March 02, 2007

Progress update

Last night, I continued soldering up the new flight computers (FC) for Acceleron and J4 II. It's still will be a couple of days before they are both finished and tested. A preliminary weigh-in of the entire FC including battery and motor & gearbox was 37 grams. This may increase slightly.

We are trying to beat the version 1.2 weight. On Polaron III the entire parachute deployment system including nosecone, but not parachute weighs 133 grams. With V 1.3 we are hoping for under 100 grams.


Tuesday, February 27, 2007

Static Fire Tests and Development

This week we carried out some static fire tests on the 8L rocket to see what was happening with the nozzle spray. The full details of the tests are here:

We were quite surprised at what goes on inside the bottle when there is some water in the upper bottle. We're working on a solution to the problem.

We're also continuing the development of the Acceleron rocket. With newly manufactured couplings the rocket can be fitted with another three 2L bottles. (Each booster segment capacity will be increased by 2L). We have also created new nozzles that have a 10mm hole rather than the 8mm hole as before. The O-rings are now on each nozzle and not in the launcher. This was done because after every launch the o-rings were flushed out of their groove and had to be reseated. Because of the new nozzles, we have also needed to make the corresponding launcher seats.

Yesterday we received a shipment of the PIC microcontrollers we use for the flight computers. At AUD$2.48 each they are as cheap as chips! We now have all the parts build two new V1.3 flight computers. They will be smaller and lighter than the V1.2 prototype that currently flies on Polaron III. The two new FC's will be fitted to Acceleron and J4II. Polaron III will continue using V1.2 for the time being.


Tuesday, February 20, 2007

Flight Day 25 - Polaron III, Underwater.

We had a successful launch day this weekend. We flew Polaron III, J4 II and Acceleron. All three rockets performed very well and we obtained some nice in-flight video. We also performed more underwater launches from a greater depth.

The full details of the flight day are now available very on our website.

Thursday, February 15, 2007

Polaron III payload attached

Last night I attached the payload section to the rest of the rocket. I also added a horizontal cardboard tube into the payload section. This tube will hold a second parachute that is pulled free when the deployed parachute opens.

A second parachute was added as this a fairly big rocket and one small chute would not have been enough.

The entire rocket including camera, flight computer and parachutes weighs 689 grams empty. It stands at 1520 mm long, with 110mm diameter.

The water fill capacity will be just over 1900 ml, so basically almost the entire lower bottle.

At the first launch pressure of 120 psi, the simulator predicts around the 125 meter mark, with slightly higher pressure and no camera predictions are around the 150 meter mark.

Hopefully the weather will be good this weekend for a launch.

Tuesday, February 13, 2007

Polaron III

Today I finished assembling the Polaron III stack. This rocket has all new bottles joined by aluminium Robinson couplings. Each aluminium coupling including washers weighs 9 gms compared to a brass one that weighs 21 gms. This means about 35 grams was saved in coupling weight.

Each bottle's base has been reinforced with fiber glass strapping tape to minimise the distortion around each coupling. I have also tried using minimum tape overall this time to reduce weight further.

The pink bands are thin flexible rubber aerodynamic seals for some joints. Made out of common kitchen rubber gloves.

A new set of fins was also made that are attached with rubber bands to the rocket, for shock absorption on landing, and together they are also lighter by about 20 grams compared to Polaron II's. The fins are made from plastic VHS covers.

The entire stack was pressure tested to 100 psi without leaks. The first flight will be around 120psi, with max pressure targetted for around 135 psi.

The payload section is still to be attached.

Monday, February 12, 2007

Flight Computer V1.3 Prototype

Last night, I finished preliminary testing of the V1.3 flight computer. The new design is intended to reduce the overall weight of the flight computer. The hardware was changed to now only run from a single battery rather than the dual power supply like V1.2.

Extra capacitor filtering was added across the PIC and the motor, and a snubber diode placed across the motor (should have been in V 1.2) The source of the PIC resets when the motor activated was also discovered - The PIC's reset on brown-out functionality was still activated. Turning this feature off solved the problem.

The whole computer and deploy mechanism will also be smaller to fit in smaller diameter bottles. Full details of the computer and deploy mechanism will be published once flight tested.

Friday, February 09, 2007

Polaron payload rebuild

Today I finished rebuilding the destroyed payload section from the last Polaron crash. The computer PCB was re-soldered back together, and several new ejection mechnism components had to be rebuilt, but overall it was a fairly quick job.

The payload bay is ready to be mated to the rest of the rocket. I will replace the green bottle in the stack as we suspect that the green bottles do not handle pressure well. We have had a number destort during pressurisation.

Tuesday, February 06, 2007

Attaching Fins

Today we have been experimenting with a different way of attaching fins. One problem with tape is that it tends to leave sticky residue when its removed, it peels off when subjected to heat or water. If wrapped all around it tends to stretch or break as the bottle expands.

We are trying a couple of elastic rings around the bottle, and the fins are simply tucked under these essentially rubber bands. We have made them out of bicycle inner tubes and glued them with contact adhesive. This holds very well on the bottle, but is a bit heavier than tape. We also tried cutting a ring out of kitchen rubber glove which also worked quite well. It is nice and thin so lightweight, and there is no glue required. It is perhaps not as strong but should be adequate.

We may also use the glove ring to join the bottle separators between bottles, as these give a nicely aerodynamic shape.

Monday, February 05, 2007

Underwater Launches and New Launcher

Today we finished updating the website with our latest experiment with launching water rocket from under water.

We are also pleased with our new launcher that can support our long rockets. Details can also be found in the link above.

If you have any questions or comments you can simply ask here on the blog.

Friday, February 02, 2007


Welcome to the Air Command Water Rockets blog. This blog intends to keep you up to date with the day to day developments, with major events being updated on the our main website:

Feel free to leave comments or ask questions about what you see.

- Air Command Team.