Making a water bottle rocket
Geoff Searle, Head of Science at Shirley Boys’ High School in Christchurch, demonstrates how he builds a water bottle rocket using 1.5 litre plastic bottles, a golf ball and an ice cream container for fins. These water bottle rockets are very aerodynamic and can travel a horizontal distance of over 200 m with a pressure of just 80 psi.
Cut nice flat sections from an ice cream container. If you lay it out properly, you should be able to get two fins from one side. A good size for a fin is palm width and perhaps a finger width in depth.
A curve in the back with a wee kink on the end seems to help the rocket fly better.
Cut three or four fins, but try not to include the raised edge of the ice cream container.
Fill your bottle with water to the top of the bottle – this way, you can stand it on its base and the heat from the hot glue won’t melt the bottle.
Just by eye, or sometimes different bottles have seams, mark out four equally spaced lines to attach the fins to – you want them in line. Put a guide mark round the top to make sure you leave room for when the bung will go in at the end.
Now, glue your fins on.
Next, take a rounded 1.5 litre bottle to make your rocket nose cone. Budget drink brand bottles often work better than the branded ones. Cut the top part off and then put your golf ball into the nose of the bottle and mark it so you know where you’ll need to cut the lid part off the bottle top you’ve prepared.
Glue the golf ball into your nose cone with a thin layer of glue – you don’t want large blobs of glue here, so be careful to damp down any blobs – and use something other than a dry finger as it will burn!
Now, fit the nose cone onto your main water bottle rocket.
If it helps, you can use a stand for this part of the process or try holding it between your knees.
The ideal position is for the golf ball to touch down in the very centre of the main water bottle/body of your water bottle rocket.
Secure this with some small dabs of hot glue. You may like to use some tape around this top part as well.
Now empty some of the water out – to fly it, you will need to keep it at about one-third full.
Put a small curve on the ends of the fins – these should all go in the same direction.
Finally, you’ll use a bung with a car or bicycle valve in it to replace the bottle cap. The valve needs to work with the pump that you have.
For a simple launch, use a stand to clamp on to the bung. Set it at about 45 degrees and then pump until the bottle launches.