See how creative you can become. If you don't have time go to the site, I've added the short form of the instructions below.
Most of all have fun!
Items to Bring: Your Completed Water Rocket and spare supplies
Step 1- Get your Supplies
List of materials:
2 Soda Bottles (empty)
1 sharp knife (kids get your parents help here!) I prefer X-acto brand for cutting foam core.
1 Large sheet of Foam Core (I prefer Black, but any color will do). Foam Core can be found at almost any arts and crafts supply store. To learn more about foam core try wikipedia: http://en.wikipedia.org/wiki/Foamcore
5 Min Epoxy (This stuff is nasty! Do not inhale, and use in a well ventilated area. Do NOT get it on your skin or eyes, or hair, etc... read all safety warnings before using.) Feel free to experiment with other glues. This can usually be found at any hardware store - kids, ask your parents for help with this glue.
2 (or more) Markers - I used Sharpies, one black and one Silver Clear Shipping Tape - It's thicker than regular scotch tape and about 2" wide.
2 (or more) cans of spray paint - Pick your own favorite colors!
Step 2- Cut bottle
Peel all labels off of the bottles.
Measure up from the bottle about a Third and cut the bottle. Try to keep your cut line as straight as possible. It may help to mark a straight line around the bottle first. Be sure to recycle or reuse any scrap pieces.
Step 3- Merge the Bottle
Take the cut bottle from the previous step and insert it directly over the bottom of the other bottle -this becomes the nose cone of the rocket. Try your best to keep everything straight. If you put the nose on crooked, your rocket will fly crooked. Place the nose cone on loosely at first, then gently press down until firm. Turn bottle upside down and let it drop on a hard surface several times. If you press the nose cone on too hard, you'll start to get "crinkles" in the plastic. Crinkles are bad.
Step 4- Tape the Bottle Together
Once the nose cone is on tight (but not too tight) use the clear shipping tape to tape the seams. Try to keep tape smooth.
Step 5- Cut the Fins
Next you gotta cut some fins to keep your rocket flying straight. I will attempt to upload a PDF file here, so that you can use it as a template. I used a Pepsi bottle, so again, you may need to adjust the curves to fit your bottle. Kids - this is the step that you will need your parents help. Parents... cutting foam core can be tricky. The key is to cut one time all the way through in a smooth motion. You'll need to press hard to make sure the knife is all the way through the foam core. If you feel more comfortable using a utility knife by all means. Be Careful!
Please! Experiment with your own fin designs. You'll need a minimum of 3, no more than 4 (unless you really really want to!). If you do 3, you need to split your bottle into 3rds, which equals 120 degrees.
Step 6- Fin Supports
This step may not be needed, but I figured better safe than sorry...
Using some of the scrap pieces of foam core, I cut 6 small triangles. (approx 1" x 1.5"). These will be added to your fins later for extra support.
Step 7- Attach the Fins
Ok, this is the tricky part. Open your adhesive (or glue of your choice). Squeeze out a small amount (enough to do one fin). Mix the epoxy with a scrap piece of foam core (this will be your "brush" too). PRE-Mark your bottle (with the marker) where you want your fins to line up. Make sure the fins fit your bottle BEFORE putting any glue on them. Trim, or adjust if needed. Apply the Epoxy to your fin, and attach it to the bottle. WARNING: This step requires patience! 5 minutes is a LONG time. If you can figure out a way of setting up some clamps, more power to ya. While holding the fin, don't let it shift... you will be able to move and adjust the fin while the epoxy is drying, but once it starts to set, it gets difficult to adjust. You'll feel it start to set. Once it gets to the point where you can't really adjust it anymore, you can place the bottles and fin, on the table to set without holding it.
Prepare your next "glob" of glue for the next fin. REPEAT for all of your fins.
Step 8- Attach the Fin Support
This is the added step for extra support. Glob out another dab of Epoxy and glue your triangle to the bottle and the fin. Glue the Supports on each side of each fin. Wait approx 10-15 minutes to be sure Epoxy has set.
Guess what... Your done all of the assembly at this point!!