Cool, cheap summer fun: How to make a backyard water rocket

A home-made water rocket. (Photo Credit: CC BY/Bryan Tong Minh/Wikipedia)

It’s hot outside, your kids are looking for new outdoor entertainments and you want to stimulate their minds during the long break from school. Why not teach them about Sir Isaac Newton’s third law of motion by learning how to make a water rocket? Instruction in equal and opposite reaction has never been so cool, cheap and fun.

What you’ll need for your backyard water rocket

The first thing you’ll need for your water rocket project is an electric drill and three drill bits, 1/16-, 5/32- and ¼-inch. A No. 4 size rubber stopper is needed to close of the end of the plastic soda bottle, and an 8-inch length of 3/16-inch copper tubing will direct the necessary air from the air pump and into the bottle. The pump itself should be a simple bicycle pump with an inflation needle.

The fins of the water rocket can be constructed from heavy card stock, to be attached with duct tape to the sides of your 2-liter plastic bottle. You’ll also be attaching a drinking straw to the side of the bottle, a straw that should be at least ¼-inch diameter. A ¼-inch threaded steel rod, that’s about 18 inches long is used to hold the rocket in place. It threads through the drinking straw taped to the side of the water rocket. If you want to make the water rocket more aerodynamic, get a paper sno-cone holder and tape it to the bottom of the plastic bottle.

Four 1-inch square wood blocks and a ½-inch plywood board (12 to 16 inches square) create the launch pad. Attach the four feet with four ¼-inch nuts, four 1¼-inch wood screws and two ¼-inch hole, 1-inch diameter washers. You’ll also need some quick-drying glue.

Making the stopper

Before starting any of this work, keep in mind that since power tools and drill bits are involved, the construction work should be performed with adult supervision.

Start by drilling a 1/16-inch hole through the center of your No. 4 rubber stopper. Expand that hole by drilling the 5/32-inch bit around a ½ inch into the wider portion of the stopper. Once this is done, thread the copper tubing through the hole in the stopper. Insert the bicycle pump’s inflation needle into the hole and copper tubing so that it will feed air into the water rocket bottle fuselage. Make sure the stopper is screwed into the bottle opening.

Water rocket to the skies

At this point, cut four water rocket fins from card stock and duct tape them on in an appropriate rocket-like configuration. Tape the drinking straw to one side, length-wise to the bottle.

You now have your rocket, but no launch pad. Get the wood and assemble with the screws, nuts, washers and quick-setting glue. Once the pad is secure and the glue is dry, place the backyard water rocket in the center of the launch pad, stopper side down. Mark the spot just beneath the plastic straw. Drill a ¼-inch hole through the mark. This is where the steel rod goes. Fix it into place with nuts and washers.

Ready for water rocket launch!

Attach the bicycle pump to the inflation needle. Fill the water rocket bottle one-third full of water, below the top of the copper tube. The stopper should fit firmly into the mouth of the bottle. Slide the drinking straw onto the steel support rod. Pump air into the rocket. The amount of pressure needed to fire your water rocket will vary; after several pumps, there will be enough pressure built up to overcome the friction that keeps the stopper in place. As the stopper releases, the water will explode forth, and the water rocket will launch! Getting sprayed by the stream of cool water is a bonus on a hot summer’s day.