How to Make a Water Powered Rocket

If you want to keep your children entertained while teaching them a lessons in physics, work with them to create a rocket ship powered by water. This is a relatively safe project, but younger children will require adult supervision during the launch.

Instructions

Difficulty: Challenging

Preparing the Bottle Rocket

1. Slip the pipe that will be the launch tube inside the 1 liter bottle when you make a water powered rocket. Measure down 27 cm from the top of the pipe and cut it. For a smaller bottle, the measurement will be different.
2. Use a hack saw to make a groove in the pipe where the water powered rocket will rest before it's launched. For a 2 liter bottle, this groove would be about 16 cm from the bottom of the pipe. Wrap PTFE tape around the groove twice or thrice.
3. Check the bottle by sliding it onto the pipe. The theory is that the PTFE tape will form a gasket while the bottle's pressurized. The neck of the bottle should be sealed when you push it down over the tape.
4. Put some cable ties around the pipe just a little below were the bottle mouth sits on the pipe. Do not wrap them around the pipe and tighten them, but have them lying, head downwards, all around the diameter of the pipe. The heads should rest all the way around the neck of the bottle while the tails extend upward toward the top of the pipe. Lash them in place with three more cable ties encircling the pipe. The cable ties will form a clamp mechanism which will hold your water powered rocket in place while you pressurize it for launching.
5. Trim the ends of the cable ties that are running up and down the pipe, and add three more cable ties to secure the cable ties in place. Secure them still further with hot glue.

A Locking Collar

6. Cut two 40 mm waste pipes into 7 cm and 9 cm lengths.
7. Make a slit down the length of the 9 cm pipe. Spread the slit apart so you can slip the shorter pipe inside it.
8. Slip in the locking 22 mm pipe fitting nut in the bottom of the pipe, and secure it with hot glue.
9. Slide the collar down the pip and over the lip of the bottle. If the fit is too tight, file down some of the cable tie heads. Once you have achieved a good fit, proceed to the next step.
10. Drill two holes in the collar at about .5 cm above the 22 mm pipe fitting nut. One hole should be on the front of the pipe, the other on the back.
11. Untwist a coat hanger and straighten it out and bend it so it looks almost like a very large "v" with a curved bottom. You only need to use one of the coat hanger's shoulders, not the entire hanger. Shape the coat hanger some more with a pair of pliers so that the ends turn in toward each other, and there are two bends going outward like shoulders. The top should still retain its narrow "u" turn. Push the hooks you have made with the ends of the coat hanger into the holes on either side of the collar for the water powered rocket.
12. Take a smaller, half liter soda bottle, and cut a two or three inch wide section from the middle. Cut two holes on either side that will be large enough to slip over the pipe. This will hold the locking collar in place until the water powered rocket launches. Slide the locking collar into place on the launch pipe and slide the spring, or the section from the smaller bottle, on after it.

Finishing Touches

13. Slide the 22 mm "compression pipe fitting joint" behind the spring, and make a joint with the PTFE tape.
14. Remove the rubber seal from the end stop, and drill a small hole large enough to slip the pressure valve for the tire through as you make a water powered rocket. If you don't have the right bit to do this, use a Dremmel tool to enlarge the hole to the proper size.
15. Put a lot of hot glue in the end cap, and slip the tire valve into position, creating a tight seal. Wait for the glue to dry.
16. Screw the end cap, valve pointing outwards, onto T joint. Create an even tighter joint by applying more hot glue to the join of the T joint and the end cap as well as PTFE tape.
17. Attach another length of 22 mm pipe that's 25 cm long onto the T joint, and put a 22 mm end cap onto the other end of the additional 22 mm pipe.

Set up the Launcher

18. Get a wooden stake that's about 22 cm in diameter.
19. Fasten two plastic clips onto the stake. These two clips will allow you to attach the launcher of your water powered rocket to the stake to save yourself from getting soaked every time you launch your rocket.
20. Secure the clips to the stake by drilling pilot holes through the clips into the wood and then screwing them in place.

Prepare to Launch

21. Hammer the stake into the ground so that it's pretty firmly in place.
22. Fill the water powered rocket half-way with water and slide the launcher down into the neck of the bottle. Make sure the cable tie heads and the clocking collar go into place.
23. Turn the water powered rocket over and clip the launcher to the stake.
24. Drive a tent peg into the earth beneath the water powered rocket, and secure a length of string from the peg to the wire coat hanger. Keep this length of string pretty long so you can get a distance away from the water powered rocket while it launches.
25. Make a tube that extends from the rocket that allows you to pressurize the water powered rocket without being too close, should it explode. This tube connects beneath the rocket and the other to a bicycle pump.

Blast Off

26. Start pumping with the bicycle pump from a safe distance as you launch a water powered rocket. It can take up to twenty pumps. You can add a valve that gauges the air pressure to the pumping assembly.
27. Pull the string when the gauge reached six bars.
28. Watch with pride as your water powered rocket blasts off.