Fins

Fins

Water rocket fins can be made from a variety of materials. I personally tend to use either cardboard (the thin type e.g. cereal boxes) or a thin plastic sheet, similar to corrugated cardboard. I believe it's called correx, however I've heard it called by other names. It can be somewhat difficult to locate unfortunately, which is why I sometimes use cardboard. Correx comes in several thicknesses - I first managed to get my hands on some 4mm thickness sheet, which worked very well; it's extremely stiff and so isn't susceptible to vibrations or bending during flight. 4mm is fairly thick however, resulting in increased drag. Recently I found some 2mm sheet which is much better aerodynamically but obviously also much weaker. As long as you make sure you cut out the fins so that the 'corrugated' parts will be perpendicular to the body of the rocket the material is still strong enough. This also applies to fins made out of balsa wood - make sure that the grain of the wood runs outwards! Another thing that is useful when making fins out of cardboard is to glue two layers of cardboard together. For example, I cut out 8 identical fins and then glue them together using rubber cement (a fairly flexible glue) so that I have 4 double thickness fins (greatly improving the strength).