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, September 29, 2008

Calibrated Testing

This weekend we performed a number of calibrated tests on the test stand. We first measured the load cell's linear response by suspending successively heavier weights on the load cell, and then flipping the test stand over and applying the same weights again so that force was applied in the other direction. The load cell responded very well.

The first test was an attempt to measure the power loss due to the blow through effect in a rocket with Robinson couplings. The test results from the three identical firings were very good as the thrust curves were in very close agreement with each other. That gives us confidence on the repeatability of the experiments.

When we were testing the rocket without the couplings we had a small problem where the thrust curve just exceeded the gain setting and as a result the top of the curve was clipped. We will re-run this again but with a lower gain setting. We try to keep the gain as high as possible in order to get maximum resolution.

Full details of the tests and data analysis will be put on the main site in due time. We will rerun the non-coupling tests before publishing the results.

There were a couple of minor issues we had to resolve with the test stand initially such as the little locking tabs in the gardena release mechanism flying out during release. But once fixed the tests were quite quick.

Because we had the test stand and equipment setup on Saturday we didn't go launching any water rocket with NSWRA, although I went over with the kids to watch other people's pyro rockets. It was nice for a change not to have to go and spend a couple of hours setting and packing up, and I got to enjoy other people's rockets and actually had time to talk to them. I've put together a highlights video from the day up to about lunch time here:


Sunday, September 21, 2008

Test Stand Details

We've put the details of the test stand on our main website here:

It includes a couple of thrust curves.


Friday, September 19, 2008

Test Stand First Firing

We ran our first couple of thrust tests on the new test stand. The tests were uncalibrated as we wanted to see what the overall performance was and if the gain on the amplifier is set correctly for the range of thrusts we will start testing with. Overall everything went really well and I am looking forward to doing the actual tests.

There are still a number of small modifications we need to do like automating the release of the nozzle and adding a non-return valve to it. We also still need to try PK's suggestion with a couple of resistors to eliminate noise a bit more.

I'm hoping we will get to do some calibrated firings this weekend with exactly measured pressure and water volume. We will suspend known weights from the setup so we can get reference values to measure the actual thrust.

Overall setup. The stand is normally firmly attached to one of the house pilons, and the table is well away from the splashing water.

The large spike at the start of the thrust curve is mainly due to me pulling the release head off the nozzle by hand. This should be smaller when automated where it falls away freely.

Full details of the test stand and first tests should be published on our website early next week.

Monday, September 15, 2008

Test stand work

It's been a fairly quiet week as we have had a number of non-rocket related engagements. This weekend I continued work on the test stand. The test stand now has the basic frame and the load cell and load cell amplifier attached. The load cell to rocket coupling is also almost finished. We still need to support the rocket under test to stop it moving from side to side, but that will be done over the next day or so. We are quite keen to try the test stand and we will likely do a few test runs this week.

My mum has also started helping out in preparing the bottles and sleeves for splicing. This has drastically reduced the amount of time it takes to splice bottles together. I was able to do 4 splices in less than an hour.

I'm also in the process of writing up the full details of the test stand, but those will only be published after we have fired the rockets a few times so we can also report on the repeatability and accuracy of the setup.

If people have suggestions for tests they would like to see results for please let us know in the comments section below.

Some of the thrust tests we have planned are:
(each test is likely to be run 3-5 times to eliminate variance in water and pressure levels)
  • 9mm nozzle with water only
  • 7 mm nozzle with water only
  • 5 mm nozzle with water only
  • 9mm nozzle with Jet foaming
  • 7mm nozzle with Jet foaming
  • 5mm nozzle with Jet foaming
  • 9mm CD nozzle
  • 7mm CD nozzle
  • 15mm nozzle with water only
  • A look at the chocking effect of Robinson coupled bottles vs full bore tornado couplings.
  • Variable nozzle performance with water
  • Variable nozzle performance with foam
  • Different foam generating techniques
  • Comparison of different foaming agents
  • Comparison of foaming agent concentration
  • Test differences in the convergent section of the nozzle

Tuesday, September 02, 2008

Multi-stage rocket

We flew our new two stage rocket with drop away boosters last Saturday. While things didn't go exactly according to plan, we still learned a lot from the two flights.

The full update is available here along with photos and video: