How to Make a Water Rocket With Your Child
If you and your child did not build and launch water rockets, you are missing out on an amazing project. With $ 10 or so spare parts, an air pump, and one or two empty soda bottles, you can have a good day and learn basic rocketry. Even the most exhausted child will be overwhelmed by the power and height of a properly designed water rocket. Promise.
How water rockets work
Water rockets work just like their older brothers at NASA. The reaction mass is displaced from the compressed gas vessel, sending the payload into the air. In this case, the pressure vessel is a soda bottle, the reaction mass is ordinary water, and the compressed gas is supplied by air using a bicycle pump. With these simple concepts, you can send a Coke bottle hundreds of feet into the air and impress all the kids in the playground. It may not be as remarkable as the launch of the Apollo rocket, but I bet Elon Musk’s first launch was a water rocket.
We build our rocket
The rocket you see above, the Zeus III , is as simple as possible, built in about 20 minutes with some of the stuff we had in the house. This is an empty soda bottle, some plastic fins, a styrofoam soccer ball tip, and a glitter ribbon for decoration.
Some water rockets make double-balloon rockets, build self-expanding parachutes, or design complex multistage water rockets, but we keep it simple: just a plastic bottle, nose cone, and some fins.
Any brand of pop will fit your rocket bottle and you can use any size, but we have had better results with the standard 2 liter bottle. Just make sure it’s a bottle of soda . Bottles designed for non-carbonated drinks may not withstand the internal pressure you are about to put them and may fail or explode. You don’t want that.
We used the tip of a styrofoam soccer ball instead of the nose of our rocket. While the general rule of thumb for any kind of rocketry is to keep things as light as possible, a little extra weight at the top helps ensure a smooth and stable lift, so you’ll need to place something in there.
A longer, thinner nose cone will probably do better aerodynamically, and a little extra weight can provide a smoother lift-off, but for your first try, the tip of a Nerf soccer ball should be more than enough. Your rocket is about to hit the ground, and you’ll be glad you had a soft nose cone if it accidentally hits the windshield of a car or the skull of a child.
Making a nose cone is easy: measure the circumference of the top of the bottle, find the same point on the soccer ball, mark the area to cut out, and drive into town. You can use a utility knife or an old kitchen knife, but I used an electric saw because I will use any excuse to start the electric saw.
If you want to create a more sophisticated vessel, there are plans on the net to add a self-expanding parachute to water rockets and even multistage guide rockets . Personally, I don’t think parachutes are worth the effort. Earlier this summer, we built a parachute rocket that took off majestically 150 feet … but the wind caught it as it descended and crashed into the top of a huge North Hollywood oak tree. RIP, Zeus II .
All missiles need fins or they will flip over shortly after launch, killing everyone on board. We used store-bought reusable fins to avoid problems and just get started, but making your own is easy too: cut out three or four Styrofoam fin shapes and glue them to the side of your rocket. For the rocket to fly straight, all of your fins must be the same size and evenly spaced along the sides of your rockets.Here is a detailed video that explains exactly how to make and attach the fins of a water rocket.
When your rocket is built, decorate it! Add a glitter or scary face, or make it NASA-appropriate with glitter white paint. The only marking required is the filling line for your water. You should mark the spot where the bottle is one-third full so you can easily find the sweet spot of water for air.
To keep your flight as comfortable as possible, keep your weight as low as possible. Try to steer your child away from decorating with too many ribbons or anything heavy. We kept our pair of strips of tape, one to hold the nose cone and the other to mark the water level. It’s brighter this way, and it shows that we’re not fooling around here: we’re going into space, not a beauty pageant.
Now that you’ve built your rocket, you need to build a launch pad. This is the hardest part of your water rocket journey. There are many launcher options available, from very simple designs that basically insert a cork into your bottle and insert an air valve, to tri-rocket launchers or launchers with a built-in pressure relief valve and gauge.
Our launcher is pretty simple. It’s made from about ten dollars worth of parts from Home Depot, and we’ve used tons of it with no problem. We used a small chopping board for the base, air valve, PVC elbow and release mechanism from cable ties, PVC sleeve and piece of rope. It is close to the Make water rocket launcher , but with a different base and no vinyl tubing.
It works like this: When you pump air into the tank and the pressure builds up, the cable ties and sleeve keep the rocket in place. When you’ve added enough air, you lower the PVC sleeve and the cable ties release your rocket into the air. This is called the Clarke Cable Tie Release Mechanism. It’s a simple, elegant design and an incredibly boring fact that I should be aware of.
(If you’re not very comfortable and just want to avoid the trial, error, and headaches of making your own launcher, you can buy it on Amazon . I won’t tell anyone.)
Now that you’ve built and decorated your rocket and launcher, it’s time to see if the bird flies!
In addition to the rocket and launcher, you will need water for fuel and a bicycle pump. Make sure it is a pump with a pressure gauge. You cannot appreciate without it, and it is important to avoid over-inflating the rocket.
Don’t launch from your backyard unless it’s huge. Even perfectly made water rockets can fly far off course due to the wind, and any flaw in design will manifest itself in flight that knocks your rocket off course. So make sure you have plenty of room and are away from trees, houses, power lines and other obstructions … and don’t be discouraged if you end up on the roof anyway.
I’ve never heard of anyone getting hit by a water missile, but I think it’s possible: you put a ton of air pressure into a small space and they fire pretty fast, so use some common sense.
- Don’t aim them at anyone.
- Don’t stand over them when adding air.
- Do not shoot them near electrical wires.
- Make sure everyone stands at a safe distance from the machine during startup.
- Do not inflate the rocket too much.
Conventional wisdom says that the bottle should be 1/3 full with water to achieve the optimal height, but feel free to experiment with other ratios; it won’t hurt anyone.
When pumping a rocket, keep an eye on the PSI indicator. Standard soda bottles usually fail at around 150 psi, but you don’t want to come close to that level; Your carefully constructed rocket, detonated with plastic shrapnel, will ruin your day, I promise. A rocket launched at 50 psi is still impressive and you should never push it above 90 psi.
Oh, and don’t forget the countdown before yanking the string and taking off. The stress of waiting is the best part of any rocket flight. And don’t forget to film it! I mean, check this: