HHWRSA

We were very fortunate this month to be invited along to Killara High School here in NSW to give a demonstration of our Water Rocket Car.

Murray Arnison contacted us through the HHWRSA website explaining he would  be  teaching his engineering class about water rocket cars this term and if we would be interested in coming along to do a demo. We were more than happy to oblige We organised for Mark to get the morning off school for this special science excursion.

We spent about an hour with the class showing the Green Hornet Water Rocket Car as well as the launcher and pump and how it all worked.

We used 100psi and 1L of water to ensure the car wasn’t travelling too fast across the quadrangle and several volunteers from the class waited on the other side of the quadrangle to stop the car plowing into surrounding  brick walls. Here is the short video of the launches.

A big thanks to Murray and the students, we had a great morning.  Good luck with your water rocket car designs and testing this term !!

Mark did a powerpoint presentation to his class the following week explaining about  water rocket cars and how we had developed it from a 1 bottle car to what it is now. He  even took the Green Hornet  in to show the class. Everyone including his science teacher was very impressed.

Even though it was a cold and slightly rainy winters day here, we were very keen to try out the Green Hornet with its new configuration, so we had a lunch day on Sunday afternoon.

The new rear end fins and low traction wheels were designed to make the water rocket car act more like a rocket for stability rather than a car, ie: The rear fins straighten the back of the rocket car. This means the rear fins need to overcome the friction of the rear wheels to effectively straighten the rear of the car.

Sounds good in theory .. time to try it out.

New Rear End of Water Rocket Car

Here is the video of the launch day. We managed only 2 launches due to the rain. We also had a father and his son on motorbikes stop to watch our second launch, that’s the noise you can hear in the background.

Results
Well we had partial success in that the launches were pretty straight, especially the first one, until there was any r/c steering input, as soon as the front steered, the rear of the car had no grip to follow and just fishtailed or did a 180 degree turn.  Obvious really after thinking about it, just like doing a handbrake turn in a normal car, …. On both runs we hit the gutter, we haven’t done this for a long time, even the r/c steering couldn’t control the cars direction when fishtailing.

Positives from the tests were the rear fins look to be working but we will need to put rubber back on the rear wheels, so we will see if there is enough force generated by the fins to straighten the car under thrust with the old wheels on.

The launcher updates worked great. The lightened chassis did work well as the car definitely accelerated quicker than the last revision.

We will keep working on it

The Easter break allowed a chance to actually do some work on the water rocket car and to upgrade the car to test some stability ideas we have been working on. These include

- outrigger rear wheels
- rear wheels rear of the nozzle
- larger rear wing
- bottle alignment guides

All of these design changes added a bit of weight to the car but we wanted to test for stability rather than just increase distance. What we were after was a straighter launch

We also had a small update to the launcher with the addition of a 20L container to hold 20L of water to hold the launcher down and reduce recoil. It also doubles as a good water supply for rocket fuel

Here is the video of the launch day

The longest distance recorded was 87m but that was uphill so over 100m on the flat isnt too much trouble even with the extra weight. We were happy with the results of the stability upgrades with the last 120psi run going straight up the middle of the road.

We will do some more work on this model before we build the next one, there are a few more things to test yet. Hopefully the next update wont take soo long