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: