2 liter soda bottle, water, cardboard, duct tape, ballast, air at 80 psi, and 100 yards of range to fly. We create rockets out of soda bottles and launch them as part of the school science fair competition. Last year we launched 120 student rockets. Several teachers use the rockets as part of their science curriculum, dividing students in groups to test one variable each (fins, mass, water)
Along with the science fair the school has competitions that included soda bottle rockets. The launcher used previously by the school was not available. A fellow parent volunteer (an Engineer from a Northwest aerospace company) and I were recruited to each build a launcher. Two launchers would give us more capacity during the increasingly popular competition.