Water Rockets

Water rockets are a great system for flying model rockets where the authorities do not permit the use of flammable propellants. You'll need to buy water rocket kits, and a launcher, and you'll need to provide your own bicycle pump with a pressure gauge and reused plastic bottles for each of the rockets you want to fly. The right bottles are the sturdy soda bottles in 1 liter, 24 ounce, or 2 liter sizes, not the cheap water bottles with the thin walls and short caps.