Water Rocket Car MkVII – Launch Day

I think the video sums it up pretty well. We had about 1 hour to do a few tests of the MkVII water rocket car so we went down to our launch track and had 2 runs.

It certainly takes a lot more effort to get the 6.75L bottles up to 120psi. We calculated there is about 39.8 L of (standard pressure) air squeezed inside the 6.75L bottles.

First Test – 1500ml water and 120psi

This wasnt a bad start. The veer to the right was most likely a wheel alignment issue. It was a lot faster than previous launches and even after 70m managed to hit the gutter with enough velocity to cause it to roll and land on its head. We did a few unpowered pushes to get the wheels aligned a bit better.

Second Test – 1500ml water and 120psi + foam

This test was a bit of a disaster. We must have over-compensated on the wheel alignment as it just veered constantly off to the left and hit the gutter at full thrust. The impact sheered off the front wheel and bent the rear metal L bracket holding the rear wheel. It still had enough speed after the crash to make it all the way across the road. The front wheel was a good 25m away from the main car.

Damage

The damage wasnt too bad. The front wheel needs replacing and the rear L bracket holding the rear wheel needs straightening. The bottles themselves are fine. The fins are bent a bit but just needs straightening. We will be able to have it fixed for a few more tests this coming weekend.

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