Alain JUGE : Contribution on water rocket
The main characteristics that we will look for are lightness, resistance, good resistance to humidity and low cost. Depending on the parts of the rocket, the requirements may vary.
Voici une description des principaux matériaux utilisés pour les différentes parties de la fusée, le détail de leur mise en oeuvre sera repris dans les pages relatives à la construction des différentes parties de la fusée
Although one can imagine the use of various and more or less sophisticated materials, PET soda bottles are the preferred material. These bottles are designed to hold 10 bars of pressure. With children, you should stick to half if possible, especially if the bottles in question are a little damaged. If they have suffered bends or violent impacts or if they have too marked scratches, they must be eliminated for this use.
The simplest nose cone is made from the top of a bottle. But it is true that the aerodynamics of this cone are not the best so we can improve it by using balsa, cardboard, PET recovered from a bottle. We can also use the technique of "papier maché", which consists of coating with wallpaper glue, strips of newspaper and which is then assembled on a plaster or polystyrene mold. In the same spirit, it is possible to use fiberglass and epoxy or polyester resin, but more expensive and less justified solutions are then attacked.
The biggest choice is on this part of the rocket.
Cardboard is easy to "machine" and obtain, but it is not very water repellent. So if we want to ensure a certain durability to this tail, it will be necessary to protect it with paint or plasticization for example.
Balsa is just as easy to machine, but it is more expensive and quite fragile
PET, from a sheet cut from a bottle, which is folded into a wallet and then cut to the desired size. It is an almost ideal material because it is light, inexpensive, strong.
Cellular plastic is a kind of corrugated plastic cardboard (polypropylene), also quite easy to "machine", resistant, water-repellent and inexpensive. But it is a little thick. The most famous brand is Akylux.
Recycling CD ROMs, you may have unused CD ROMs in stock. It is then possible to recycle them into fins, but the machining is not very obvious (tendency to chip) and they are also quite brittle.
There are still quite a few possible materials, without going as far as metals (too heavy), there are plastic sheets (Nylon, PVC) or thin polystyrene plates (very light, but very fragile).
As for the cones, you can also use papier maché, and why not fiberglass coated with epoxy or polyester resin. But here too we enter into more expensive solutions which are hardly justified, except to practice the technique.
For water rockets, there is no question of using "hi-tech" materials, the most commonly used is the plastic of the lightest possible garbage bags. Another interesting plastic is the garment cover for dry cleaners, which is lighter than garbage bags.
We can also use scraps of light fabrics (like fabrics for lining or umbrella canvas)..
For the lines, butcher's twine will work perfectly.
To assemble a rocket, glues are essential. Unfortunately the PET widely used in this field is difficult to glue.
Among the existing adhesives, we can mention:
The guns, but beware of the temperature which deforms the PET. NEVER PUT HOT GLUE DIRECTLY ON THE TANK, which would weaken it and therefore create a risk of explosion.
Cyanoacrylates (super glue type) require good preparation of the surfaces to be glued: degrease well and sand lightly with medium sandpaper. Quite dangerous to use (you can stick your fingers together very easily).
Polyurethane adhesives (Sykaflex 11 FC type), quite expensive and also dangerous for health (must be handled with gloves and in the open air), they also require long drying times. But these are the best for gluing PET, and especially putting two bottles together to make a bigger tank.
The neoprene glues that are spread over the two parts to be glued, are left to dry for 5 to 10 minutes then the two parts are strongly pressed. Bonding is instantaneous.
Adhesive tapes. There is a whole variety of them, but you will have to choose them sturdy and very adhesive. Prefer the width of 25 mm if possible, which will avoid overloading the rocket. I use a fiberglass reinforced variety with a very strong adhesive a lot, but that is not easy to find.
the table below lists the most common materials.
| Designation | advantages | disadvantages | Uses |
| PET bottles (soft drinks) | easy to find, light, inexpensive, strong, fairly easy to work with | Difficult to paste | Tanks, nose cone, skirt, fins and a lot of other things. It is the basic material. |
| Strong cardboard (wall calendars, packaging) | easy to find, inexpensive, fairly easy to work with | a little heavy, fears humidity | Fins, nose cone |
| Elastic | their elasticity | aged badly | recovery system |
| Butcher's twine | cheap, easy to find | |
recovery system, parachute lines |
| Cellular plastic sheet (Akylux brand for example) | light, strong, easy to work | thick | fins |
| Extruded polystyrene sheet (Depron brand) | Very light, fairly inexpensive, easy to work with | Very fragile | fins |
| Thin bin bag 100L | inexpensive, light, strong, easy to work | parachute | |
| Paper clips | cheap, eazy to work | recovery system | |
| Adhesive tapes | assemblies | ||
| Glue | assemblies | ||
| Balsa | light, eazy to work | expensive, very fragile | Fins, nose cone |