How to Design a Hydro Rocket

Design and launch your own hydro rocket.

Hydro rockets, or water rockets, are a tool used by physics teachers to help their students understand the principles of inertia, gravity, Newton's laws of motion, and more. In addition to being a great learning tool, building water rockets can also be a fun activity for children. Using empty plastic bottles, kids can design their own hydro rocket and launch it into the air. You might even turn it into a competition to see who can design the most efficient hydro rocket that achieves the greatest height and distance.

Things You'll Need

• Two 2-liter plastic bottles
• Felt tip marker
• Razor blade or utility knife
• Duct tape or clear packing tape
• Cardboard or foam core
• Hot glue or quick-set epoxy
• Spray paint

Instructions

1. Rinse out and peel the labels off two 2-liter plastic bottles. Using a felt tip marker, draw a straight line all the way around the bottle at about one third of its height. Cut around the line with a razor blade or utility knife

2. Insert the bottom of the second 2-liter bottle into the opening cut from the bottom of the first bottle. Push the first bottle as far into the second bottle as you can without making any wrinkles in the plastic. When finished, you should have an elongated bottle with a neck and cap at both ends. Wrap the seam with duct tape or clear packing tape to secure it.

3. Cut the fins for your rocket out of cardboard or foam core. Draw out a template for your fins onto the cardboard or foam core using either a square or a triangular shape. The bottom edge of the fin should be flat and it should slope out and away from the rocket body but the actual shape of the fin is up to you.

4. Trim the inside of each fin where it will connect directly to the rocket body just above the bottom cap. The fins will need to fit the contour of the bottle and it may take a few adjustments for you to get the fit right after cutting out your fins. Create either three or four fins for your rocket and mark the places where they will go on the body of the rocket with a felt tip marker. The fins should be spaced as evenly as possible.

5. Attach the fins to the body of the rocket using hot glue or quick-set epoxy. Make sure each fin is trimmed to the proper size and its position is marked on the bottle before applying any glue. Apply a small amount of glue to the edge of the fin and to its position on the rocket then press the fin into the rocket and hold it firm for at least one minute. Read the directions, if using quick-set epoxy, to determine how long the object should be held in place.

6. Paint your rocket using a color or design of your choice. Spray paint is the easiest option for painting water rockets because it covers a large area in a small period of time and the coverage is more uniform than hand painting.

Tips & Warnings

• You may choose to add extra support to your rocket's fins by gluing small triangles to the rocket on either side of each fin, flush with the fin itself.

• Most water rocket designs do not come with a parachute so after your rocket reaches the height of its climb it will fall back to the ground very quickly. Only launch the rocket in an open space where there are no people or objects around that could be injured or damaged.

References

• NASA; All About Water Rockets
• This Old House; How to Build a Water Rocket; Alexandra Bandon