Water Rocket Car MkVIII – Launch Day

The goals of this launch day were to try to control the thrust of the water rocket car and bring the car home in one piece. We tried to achieve this by

– Adding a rear wing to provide down force to the back of the car
– Reducing the size of the nozzle to 6mm to even out the thrust

Here is the video


First Test – 1500ml water and 80psi

This was just to see if the car was running straight. We found that with the 6mm nozzle insert in and 80psi most of the water actually didn’t come out of the bottle and it just trundled along. That was ok, we made some wheel alignments. Distance was probably 30m and stopped by foot

Second Test – 1500ml water and 80psi
Another low pressure test run. It was tracking pretty straight – distance about 40m stopped by foot. 2 broken screws .. remember to bring more next time

Third Test – 1500ml water and 120psi
This was the first high pressure launch with the 6mm nozzle insert and wing. The thrust was pretty good and most of the water was expelled from the bottle. The thrust was definitely lower than previous 12-psi launches and it lasted longer which is what we expected. We are not sure how much difference the wing made as the car wasn’t traveling that fast. There was a bit of left movement and the car hugged the gutter a little but didn’t hit it. It ended up hitting the gutter at the end of the road pretty hard damaging the front bumper. It could have easily gone another 30-40m if there was road available. Distance ended up being 84m, a new record for us… just :)

Fourth Test – 1500ml water and 90psi
We were really keen to try to get the 100m distance record, so we moved the launcher back 20m. Unfortunately we had an issue with the valve in the launcher quick connect and it basically was only letting 90psi into the bottle, the rest wouldn’t get through and just the air line was pressurizing up to 120psi. This is something we know how to fix, but couldn’t do it on site, so we launched at 90psi anyway. It doesn’t go very fast as a lot of the water is still in the bottles. It did go left but we are pretty sure this was just a steering alignment issue. We were breaking the heads off screws (4 of them) trying to realign the front wheels, so this was as good as we could do. The car glanced the gutter but it did keep rolling and rolling. It eventually stopped at 96m .. so close …not very dramatic .. but a good distance run.

Conclusion
We had basically accomplished what we set out to do and that was control the thrust and rear end of the car. We were probably too conservative on the nozzle and will test higher diameter nozzle inserts to get the speed up again. Good news is that the car came home with all wheels in place and a new distance record for us under the belt. Now to get that 100m record :)

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