My favourite, and highest altitude achieving (350+ feet) rocket is made using a 660ml Pepsi bottle. If the bottle becomes damaged it can readily be replaced as the fins and nose cone are removable. I have only ever retired these 660ml bottles as a precaution, they are very tough, surviving impacts that crumple a 2 litre bottle nose like it has been jumped on. I have never experienced an exploding bottle. Part of a similar bottle is used only as a nose cone, the other entire bottle is the rocket body which contains the water and compressed air. The nose cone is simply pushed into place, no glue or tape is required, a gum-nut (Eucalyptus seed capsule) is pushed into the neck to act as a nose weight and to improve the aerodynamics. Depending how hard the ground is this gumnut may hammer itself inside the neck after several impacts, this rocket comes down FAST and hits whatever is in the way HARD. The fins are made from unexpanded polystyrene that an art teacher gave me, it is rigid (it can crack, one of six fins cracked after 15 flights, though it was still functional), it is around 0.8mm thick and is easy to cut into a fin shape. The fins are attached to a cylindrical section from a 35mm film canister, held in place using small pieces of packing tape. The film canister has the base cut out, leaving a small lip. A PET bottle cap has a hole cut through it at least as wide as the internal diameter of the neck of a PET bottle. This threaded section from the bottle cap is inserted into the film canister from the open end, so that it can screw on to a bottle through the previously closed end of the canister. Leave the small plastic ring that proves a new bottle has not been opened on the bottle, this prevents the canister moving forward on impact. The illustration is not quite right, the canister does not conceal the lip around the bottle neck. All up, I'd say this rocket cost me less than a cent in materials (the tape).
P.S. More recently I made the nose more streamlined in various ways, the simplest being to fill in the spaces with Blu-Tac (adhesive stuff for sticking posters on walls). This also helps by adding weight, which in some circumstances will increase the altitude reached by water rockets.
P.P.S. The pictured fins do not suit the twisting-bolt release, they often hit the bolt on the way up, I have more recently used four larger fins. Back to homepage