1 safety for my kids (the bottle can be painful on face),
2 build a launching pad with materials found in woodshed and garage of a country house.
The materials used are:
(2) wooden pieces 10x10 cm (sz)
(1) 15x1,8 cm (sz)
The measures are approximate they depend on materials that you will find in your garage. The important thing is the final result: launching pad must force the rocket to follow a trajectory how to the video's shows: