How to build a rocket
To build a rocket you need to start with a plastic bottle.
You need to choose one which contains a fizzy drink as these are designed to handle pressure.
Choose your bottle carefully
You can choose a bottle of any size you can find – the smallest might be 500ml, and the largest are up to 3litres. The bottle MUST have a screw cap neck with an internal diameter of 22mm. Most fizzy bottles do – it is the standard size. But you must check the size is correct or the rocket will not fit on the launcher. Bottles with straight sides work better than ones with curved sides.
You need to choose one which contains a fizzy drink as these are designed to handle pressure.
Choose your bottle carefully
You can choose a bottle of any size you can find – the smallest might be 500ml, and the largest are up to 3litres. The bottle MUST have a screw cap neck with an internal diameter of 22mm. Most fizzy bottles do – it is the standard size. But you must check the size is correct or the rocket will not fit on the launcher. Bottles with straight sides work better than ones with curved sides.
Add some fins
You can launch a plain bottle – but it will tumble in flight and not go very far. To stabilise the rocket, you will need to add some fins. These need to be stiff and waterproof, so you could use plastic, Correx sheet or Funky Foam. You’ll need to experiment with the shape and the positioning to find out what works best.
Which glue?
You’ll also need to experiment to find a way to fix the fins to the bottle. This can be tricky as the plastic that these bottles are made from is difficult to glue onto. Contact glue can give good results (Try Evo-Stick Impact), and duct tape works quite well, if you can’t find anything else. Do not use hot glue, as this will melt or weaken the bottle and create a bursting risk. Again, you will need to experiment to find what works best.
You’ll also need to experiment to find a way to fix the fins to the bottle. This can be tricky as the plastic that these bottles are made from is difficult to glue onto. Contact glue can give good results (Try Evo-Stick Impact), and duct tape works quite well, if you can’t find anything else. Do not use hot glue, as this will melt or weaken the bottle and create a bursting risk. Again, you will need to experiment to find what works best.
The example on the right is similar. This time the foam rugby ball is yellow, fixed to the neck of a clear plastic bottle with the bottom cut off and slipped over the end of the lower green bottle.
The rocket pictured on the right is mounted on a different launcher to the one which will be used for this challenge. |
Nose cone
The bottom of a bottle is not really very aerodynamic, so you will need to find a way to round off the nose cone. In the example on the left the neck of a second bottle is stuck on the bottom of the first bottle. There is also a soft foam rugby ball to cushion the landing and increase nose weight and aid flight. |
Launcher
The launcher we will be using will be similar to the one pictured left— a Cable Tie launcher. In the middle of the cluster of surrounding black cable ties you can just see a large cork which has been drilled through to allow an air hose through. The cork has been shaped to fit inside a 22mm bottle neck. The friction between the neck of the bottle and the cork will normally be enough to hold a rocket in place until you pump it up to around 20psi. Above this and the pressure inside the bottle tends to make the cork pop out. |
How it works
The fuel for these rockets is plain tap water. You need to decide how much to pour into your rocket before launch—about a third of the volume is usually best.
Pumping air into the rocket stores up energy.
Pumping air into the rocket stores up energy.
Once you slide the ring down, the cable ties are released and spring back.
This releases the neck of the bottle, and now the pressure inside can force out the cork, launching the rocket. This design has the added safety feature of not containing pressures above 40psi. Even if you try to add more pressure the cork will not keep the water inside and it will all leak away safely. |
A launcher similar to the one pictured will be provided on the day of the challenge, but you are welcome to make your own if you like.
If you do make your own launcher it must be able to launch with the operator standing about five metres away - so a long string would do. It must also have a pressure gauge so everyone can see that the launch pressure is 30psi, and there must be some way of letting the air out in case of emergency. It should be capable of being angled to 30 degrees of vertical - which is the angle we will be launching at to reduce the risk of rockets coming straight down and landing on someone's head. |
Safety
Safety is very important for this challenge and you enter at your own risk. We must also take steps to make sure no bystanders get hit by flying parts. Whatever you stick on to the rocket must be glued on firmly to prevent bits flying off at launch. Rockets must be safe to fly and the Range Officer will check all rockets before they fly to make sure they won't tumble in flight and bit's don't fall off. The way to check this is to tie a piece of string around the middle of the rocket and dangle it so it balances. Then you swing the rocket around and around in a circle. If it tumbles around then you will need to change the design to stop this happening. |
The Challenge
Rockets entered in the challenge will have three attempts at launch. Rockets will be judged on the height and distance they travel, as well as on appearance and technical merit, and there will be prizes for the best entries in each category and for an overall winner.
Need help?
If you need help with your rocket design then get in touch with Andy Lakin-Hall at the RSM Centre on 01892 853021, or by email at [email protected]
Rockets entered in the challenge will have three attempts at launch. Rockets will be judged on the height and distance they travel, as well as on appearance and technical merit, and there will be prizes for the best entries in each category and for an overall winner.
Need help?
If you need help with your rocket design then get in touch with Andy Lakin-Hall at the RSM Centre on 01892 853021, or by email at [email protected]