With the success of the (probably annual) NortHACKton rocketry day just behind us and the ever likely possiblility that there will be another day shortly to launch the chemical rockets; I thought I would take the opportunity to write up my two little rocket launcher designs so that other people can copy and expand upon should they wish. Alternately it’s only 363 days till the next rocketry day so get going now and consider that to be tinkering time.
Cork and Valve Launcher
I wanted to start with something so simple that anyone could make their own and then go play with it. You will need:
- A cork (I bought Youngs wine corks from Wilkinson)
- A schraeder valve (Just ask at your local tyre garage)
- Some selotape
- Cut one of the corks in half
- Drill a hole through the cork a little smaller than the neck of the schraeder valve
- Insert the valve into the cork
- Wrap the cork in one or two layers of selotapec
- Fill the rocket with water and then insert the cork into the neck of the bottle
- To Launch turn the rocket upside down and fill with water, wedge the launcher into the neck of the bottle and then prop the bottle into a vertical position, I did this using some metal camping pegs. Start pumping, when the pressure inside the bottle is sufficient it will force the cork out of the bottle and the rocket will take off.
The reason I think this simple launcher was so effective is that it takes time for the cork to slide out of the neck. If you pump quickly then you can get a suprising amount of pressure into the bottle before it launches. Mine were often getting to 80 PSI. If the cork becomes too loose in the bottle then just wrap another layer of tape around the cork.
Cable Tie Release Launcher
The cable tie release mechanism is a rather elegant solution to the problem of holding the bottle onto the launcher. This design is a very much minimalist version of the system but was employed with great effect on the rocket day. All the fizzy drink bottles have a little lip of solid plastic just below the cap. This launcher makes use of that lip by gripping it with the cable ties, holding the bottle down until it is ready for release.
You will need:
- 21.5mm outer diameter pipe (this is tricky to get hold of and I resorted to the internet)
- 40mm diameter waste pipe (available from B&Q etc and the 40mm I believe is the inner diameter)
- 20-30 cable ties (these need to fit around the edge of the bottle but inside the waste pipe)
- A schraeder valve (might as well get several from the tyre place, they’re handy)
- Hot Glue
- Place the 21.5mm pipe into the neck of a bottle, I used a 250ml coke bottle as it’s easier to wave around at this construction stage.
- Loosely pull the black cable ties together and place them around the pipe, these will be used to hold the white cable ties in place. (It’s only black and white so your know what I’m talking about)
- Add white cable ties around the pipe making sure they all line up with the lip around the bottle neck. My design used 15 cable ties and I found it much easier to space them by using an extra cable tie between every third tie.
- Pull the black ties tight, this will hold all the other cable ties down. There should be roughly 50mm between the first outer tie and the top of the horrizontal ties. Then carefully remove the spacer cable ties, try not to move the other ties at this point.
- Trim the cable ties to the desired length and apply a liberal coating of hot glue to the pipe and the ties. Make sure to get the glue right down into the gaps where the spacers were and also into the end of the outer ties to prevent any possibly loosening.
- Cut a length of waste pipe to go over the cable ties, locking the bottle into place. I pulled mine manually so I kept mine long to grip it, but it could be as little at 20-30mm for other methods as long as it covers all the cable ties.
- Finally hot glue the schraeder into the bottom of the pipe. A better design would be to pack the valve with a cork to make it fit the gap better/tighter but hot glue will do the job adequately.
- Add a few layers of tape to the make the pipe fit the neck of the bottle snuggly, this will allow you to build up the pressure inside the bottle before release.
- To launch the rocket, fill the bottle with water and connect the launcher to it while it’s upside down. Slide the waste pipe down over the neck of the bottle and the cable ties securing it in place. Turn the rocket the right way up and prop it in a vertical position (again with the tent pegs). Pressurise the bottle and then when you are ready to launch simply pull the waste pipe down from around the neck.