Water Rockets - Fins

Fins made from the side of a pop bottle


Ideally the fins should be as far back as possible (without getting in the way of the launcher) and present as little drag to the rocket as possible when flying straight. they can be virtually any shape as long as the do the job of providing a sideway area at the rear of the rocket (see the next section on stability).

I have found the best material for fins to be the same plastic that the bottles are made from. There is enough of this material in two 2 litre bottles to make the 3 or 4 fins that you require.

Cut out the part of the bottle with the straight sides (1) and cut along one side (the bit with the glue on it is the best place to cut as this is unsightly)(2).

Rough shape and position of fins
The real thing. Note that there is tape all around the edge.

Flatten this bit out and fold back on itself so as to cancel out the tendency to curl (3).

Make a template of the fin shape that you want (sized so that you will get two out of each bottle with a minimum of waste) and cut them out (4). You can either glue the two sides of each fin together, or you can tape them around the edge - the latter making it easier to see the fins when in the air.

Fixing the fins

Two methods:

  1. Glue. Glueing them has some problems. Holding them in the right place long enough for the glue to set and choosing a glue that will not break when the bottle expands during pressurisation (PL Premium is suitable for this). It can take days for glue to dry properly.
    Outline the position of the fins with a marker pen (you only need mark the corners) and apply the glue according to the instructions.
    Tape the fins in place until the glue dries and then remove the tape;
    OR . . .
  2. Tape. The alternative to glueing them is using sticky tape of some sort (Gaffer Tape, Elephant Tape, Duct Tape et cetera) - this has the advantages of being instant and flexible although the tape can start to peal off. Taping can take only a few minutes.
    Cut out three or four thin pieces of tape and position them on the rocket where you want the fins to go, repositioning as appropriate.
    Put lengths of tape on each of the fins and position them on the rocket.
    Finally, put down some extra straps of tape around the fins to stablalise them.
    Once this is done, a further step to make the fins stable is to use a soldering iron to melt a hole through the fins near to where they join the rocket such that a cable tie can pass through all of them, linking them and holding them close to the rocket. This will stop the glue of the tape from creeping and keep the fins in place.

Back to the Fins Index
Back to the Water Rocket Index

Site Map
Back to the Index Copyright 1994 - 2003 P.A.Grosse.
All Rights Reserved
Fins made from the top of a bottle Fins made from CD ROMS