Tape the fins to the rocket as shown in the "One-bottle rocket" picture above.
You can also use just playdoh instead of kitty litter. Optionally, you can add playdoh to the outside, as in a one-bottle rocket this adds weight and makes the front more rounded for better aerodynamics, and is softer and hence safer when it comes down. (This is tricky, and may not be necessary - the kitty litter seems to hold well by itself.) Fold a 9 inch piece of duct tape into a U shape with the sticky side out, place it into the bottle with the bottom of the U against the kitty litter, and press the sides of the U against the inside walls of the bottle. If you use too much kitty litter altogether, then the rocket hits hard when it comes down.ĭry the inside walls of the bottle, and add duct tape to help hold the kitty litter in place. If you start with too much kitty litter, the water hitting the top of the litter forms an impermeable barrier before water penetrates all the way through, leaving a layer of dry kitty litter, that could get shaken loose under acceleration. Tip the front chamber upside down, pour in about 1/2 inch of kitty litter, add enough water to wet the whole kitty litter (pour out any extra), add another 1/4 inch and soak again. It is cheap, heavy, and when wetted will stay in place well. I'm a fan of kitty litter, because it is cheap, and it's a great educational lesson for kids to see the use of unglamorous material as kitty litter in a rocket.įor a two-bottle rocket, I use clumping kitty litter in the top end. You need weight up front, to pull the rocket through the air when it is coasting. One group of kids made a three-bottle rocket it was really impressive, although it didn't fly as high. Two-bottle rockets are more stable, and more impressive. I usually have groups of kids make two-bottle rockets it takes longer, so we have more time to talk, they work together more, and it is a longer build-up to the launch. When coasting, the weight up front pulls the rocket through the air, and the rocket corrects itself if it gets a bit crooked.
But the water is pushed out quickly (in about the first 10 feet of flight) and after that the rocket is just coasting. The rocket is not stable when first launched, when it has a lot of water in the bottom. The weight and fins are for stability, like an arrow for a rocket to be stable the center of mass (the balance point) should be ahead of the center of surface area. Optionally, a second soda bottle for greater length and stability, An intact two-liter soda bottle at the bottom to hold water and air under pressure,
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