Water Rockets - 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
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
|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
- 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
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 . . .
- 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