Warning: Water Rockets and similar devices are dangerous. Anything you do with them is entirely at your own risk. Not Ours.

Intro

Nairn and myself started of trying to make a smoke ring generator, inspired by something called an Airzooka. After about 1/2 an hour, we found we'd done it, using the box my gameboy came in and an old speaker. Using joss sticks as a smoke source, we could fire little smoke rings about a metre before they disappeared. This left us with nothing to do, so we tried something I'd once made as a 12 year old.

Water rockets

The idea behind a water rocket is that a container is filled half with water, half with pressurised air. If you open up a hole in the container, the air forces the water out, pushing the container. This time we used drink bottles and the lids from washing up bottles.

Parts list

We got all the parts from the high street round the corner from my parents house (where all of these days seems to take place). You'll need:

• A washing up liquid bottle lid (Fairy seemed to work well for us)
• A 500ml (or smaller) Fizzy drink bottle (I went for Sprite, Nairn went for Dr Pepper)
• A Car valve (available from car tyre shops like QuickFit, or some bike shops)
• A drill (you could probably get away without one, but they make it easier)
• A bike or car tyre pump

Making the rocket

The first thing to do is to fit the valve to the top of the bottle. You need to drill a hole in the centre at the top. We started with the smallest drill we could find and worked up. The largest drill still wasn't big enough, so we used a dremel drill with a sanding bit on to enlarge the hole.

When the hole gets to 14mm it's about big enough to fit the valve. If you have any silicone sealant, smear a little around the base of the valve. You don't need the sealant, but it also helps the valve slide into the hole. Push the valve into the bottle so the end of the valve pokes out of the hole you made. Pull the valve through until it's popped into place. We needed to use pliers to so this. Once done you'll have something like this.

Now screw the washing up liquid bottle lid on and the rocket is complete.

Testing the rocket

It's VERY important to test that the rocket can withstand high pressures, since you have to hold them to launch them and you really don't want one exploding in your hands. To test the rocket, fill it 3/4 full, attach it to a pump with a reliable pressure guage, and cover the rocket in some way that'll stop it hitting you if it explodes. We put the rocket into the leg of an old pair of jeans. Pump the rocket up as high as you're comfortable with. We used about 80 PSI. Assuming the rocket hasn't exploded, showering everything in water and plastic, let the pressure down again by flipping the cap.

Flying the rocket

To fly the rocket add water, pump up the bottle and throw it whilst flipping the cap. It's as simple as that. There's 2 variables to play with with these rockets: ammount of water and air pressure. We found somewhere between 1/4 and 1/2 water was best. For air pressure, we started at 30 psi and worked up from there. In the somewhat blury action shot below you can see the rocket heading upwards leaving a trail of water behind it.
One of the comedy side-effects of this kind of rocket is that it's inherently pretty unstable. This often results in it flying a few metres up and then falling over at such an angle that it comletely empties itself all over you. If you look at the picture below you can see a line of water running all the way from Nairn's shoe to his shoulder.