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.

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.