Water Rocket Car Mk IV

We managed to design and fit two rear fins to the back of the water rocket car. These are to try to improve rear stability under high thrust. There are two fins due to the fact that it was difficult to mount a single fin big enough on top of the bottle.

The fins are made out of 7mm plywood and are 250mm x 200mm in size (approx). Each weigh approx 130g. They are attached to the body of the wrocket car front and rear with small “L” brackets and screws. They are very solid and there is no flex in the fins.

This pic is the cardboard template and the first fin

Cardboard Fin Template + Plywood Fin

Cardboard Fin Template + Plywood Fin

The fins are notched out around the metal bracket that attaches to wheels. You can see the rear L bracket. There is 50mm overhang of the fin past the rear of the wrocket car

Left Rear Attachment (wheel removed)

Left Rear Attachment (wheel removed)

Here is the attachment at the other end of the fin

Fin front attachment

Fin front attachment

Here is a pic of the fins in place without the bottle

Fins attached minus bottle

Fins attached minus bottle

Rear shot of Fins minus Bottle

Rear shot of Fins minus Bottle

And finally with bottle attached

Bottle attached + fins

Bottle attached + fins

Rear shot of Fins + Bottle

Rear shot of Fins + Bottle

For the launch we found a 15kg (approx .. its small but heavy) rock nearby and sat it on the launcher to stop the recoil. We only had time for 3 launches due to fading light. Here is the video

First Test – 1485ml water and 120psi (not on video)

The first launch is not on the video. The wrocket car arced off to the right. We didn’t do a wheel alignment after a test at home to check the bike computer. That test ended up crashing into a rock and flipping. So we did an unpowered test and it was obvious that a wheel alignment was required. After a quick wheel alignment we fueled up and tested again

Second Test – 1485ml water and 120psi ( on Video)

The second test was again at 120psi and 1485ml (2/3 full). This one went straight out of the launcher and continued straight. There was a bit of deviation right at the end of the thrust phase but not very much. This launch was measured at 20.2km/hr. Not super fast, but a good test of the bike computer. The rock worked well as the launcher didn’t recoil at all. The slow motion shows the pretty straight launch

Third Test – 1485ml water and 130psi (not on video)

After the second launch and refill to 2/3 full, we put the car on the launcher only to see the rear wheel nut was very loose. I tightened it by hand it was holding but wobbly. we decide to launch it anyway and see what happened. At launch the rear wobbled a bit and as soon as the car started heading left it was uncorrectable and it ended up doing a 180 degree turn and in the bushes.

We will do some more work before next weekends tests

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This entry was posted on Sunday, July 19th, 2009 at 11:11 pm and is filed under Development, Launch Days. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

 
 

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