How to Build a Rocket Launcher

The water rocket is a fun and relatively safe way to study rocketry, as well as understanding the difference between water and air pressure. This is a great rocket to make with children for a science project. It is best to have the launcher already made, however, as it can be a little time consuming and uses materials that are not safe for children. Here is how to built a rocket launcher.

Things You'll Need

• 75 mm of garden hose
• 600 mm of 15 mm diameter copper pipe (the pipe’s outer diameter should be slightly larger than the inside diameter of the garden hose)
• Automotive clamp
• End cap that is approximately 15 mm
• Car tire valve
• Garden hose coupling
• Elbow fitting for the pipe
• 3 saddle brackets
• String
• Small wood pieces
• Nails
• 5 120 mm nails
• Plumber's solder and flux
• Propane gas torch
• Wire brush
• Hack saw
• Sharp knife
• Hammer
• Electric drill and drill bits
• Vaseline
• Screwdriver
• 2 1.5- or 2-liter soda bottles and tops
• Male part of a garden hose coupling
• Packing tape
• Piece of plastic to use as a gasket for the mouth of the bottle

Instructions

1. Remove the core of the tire valve. This is done so that the soldering does not melt them. Cut the rubber off the valve, leaving the metal. Use a small knife and wire brush to do this. Cut a hole in the end cap the same size as the tire valve. Clean one end of the copper pipe until it shines. Use plumbers flux to place the pipe inside of the cap. Put the valve inside the drilled hole. Solder everything together. File the burrs off the other end of the pipe. Using Vaseline, place the hose over the other end of the pipe. Clamp the hose to the pipe with the hose clamp.

2. File the burrs off the other end of the pipe. Using Vaseline, place the hose over the other end of pipe. Clamp the hose to the pipe with the hose clamp. Cut the hose so that it only hangs off the end of the pipe a little. Put the female garden connector over the end of the hose.

3. Remove the tire valve core and the hose. Cut the copper pipe in the middle. Stick it inside the elbow pipe, and solder it together. Stick the end pieces back on. Wrap the string tightly around the hose connector. Build a stand by nailing two pieces of wood together into a cross shape, then adding a piece to stick in the air, and two little pieces to hold the launcher in place along one of the cross pieces. Use the clamps to hold the launcher in place; two for the bottom and one for the top. Put a nail through the two side pieces, leaving the string to pass behind them. Use large nails to stabilize the launcher when it is in the ground. They will take the place of stakes.

4. Remove the washer from inside the garden hose coupling. Cut off the threaded part of the coupling. Cut the coupling down until it fits snugly into the soda bottle. Smooth the coupling face with very smooth abrasive materials. Cut a hole through the center of the soda bottle cap. It needs to be about 19 mm. Make a gasket from the thin plastic the same size as the hose coupling, and cut a hole in the middle. Screw the whole assembly into the top of the soda bottle. This part can be reusable. Cut one of the bottles into three parts, with the top and bottom being smaller than the middle piece. Discard the bottom. Put the top piece with the cap attached over the bottom of the second bottle. Secure with duct tape. Use the struts and tape them to opposite sides of the bottle. Place the middle piece of the first bottle over the struts. Tape all pieces together.

5. Fill the rocket completely with water. Attach it to the launcher. Stand back and increase the pressure to 110 psi, and check for leaks. If the pressure remains, then your rocket is ready to go.

6. Fill the rocket 40 percent with water. Stabilize the launcher into the ground. Place the rocket on top of the launcher. Pressurize the rocket to 50 psi for the first launch. Stand well back (about 10 m), and pull the string to launch the rocket.

Tips & Warnings

• Some soda bottles use a piece of plastic inside the lid of the bottle that would make the ideal gasket for the mouth of the bottle.

• Be sure to keep people well away from the launch site when launching the rocket.