Step 1: Get Materials
A Garbage bag or plastic bag (for the parachute)
Cardboard or foam core
A Tennis ball
Dental floss or string
Step 2: Cut the Bottles
One bottle you're not going to anything to, which will be your bottom bottle that will connect to the launcher.
The other bottle you're going to cut the top so you have the bottom of the bottle.
Put the bottles together (DO NOT TAPE THEM) to make sure they're cut right before you move on.
(The picture is what the bottles should look like after you attach the wings and make the parachute.)
Step 3: Make the Wings
Get the cardboard or foam core and cut out a wing that will a good size for the bottle.
Cut out 3-4 wings that are the same in size. If the size is off it will effect how high the rocket launches. You can make them whatever size you want and whatever shape you want.
Once the wings are cut out, tape them onto the sides of the bottom bottle of your rocket so it looks somewhat to the picture. Make sure they're taped around the same height because the wings effect the direction and the height of the rocket.
Step 4: Making the Parachute
You can use a garbage bag or a plastic bag. If you use a plastic bag you don't need to cut it but if you use a garbage bag you'll need to cut it so it's smaller, thinner, and it can fit inside your rocket.
Cut your garbage bag so it's in the shape of a circle. You do this by folding it slightly and then cutting it out.
No matter what you use you have to cut about 4-6 small holes so you can tie the string to the bag. Then once the string is tied to the bag you cut a hole in the tennis ball so the string can fit through and get to the other side of the tennis ball. Then make a hole in the piece of cardboard or foam so the string can also get through. This will hold the tennis ball and string in place. Then tie the string so the tennis ball stays attached to the bag.
Step 5: Putting the Rocket Together
Once your rocket is together you are now ready to fill it up, half way, with water and launch it.