Instructions to Build a Water Rocket
Water rockets are a heap of fun. Their performance is amazingly
good. Other people have reported getting their rockets to go as high
as 90 metres or even 200 metres for a two-stage rocket. They are
certainly the fastest and most spectacular of any of the toys from the
mechanical toys page. And they drive you to continually improve the
rocket so that it goes higher, or comes back with a parachute, or has
two stages. Some water-rocket competitions have been organised in the
United States. Water Rockets can be made at home with no special
equipment and are cheap as well.
Basically, a water rocket is a plastic fizzy drink bottle (PET
bottle), that you fill half way with water, pressurize with air, and
invert. When you release it, the pressurized air forces the water out
which propels the rocket. Certain water rocket designs are said to fly
as high as 90 metres. Clifford Heath has written up a water rocket design
that can be made very easily. He uses a nozzle that he claims improves
the rocket's peak altitude. Clifford had troubles with the stability
of the rocket until he made a special fin that extended some 200 mm
behind the PET bottle. The design I have written about here is
essentially the one that Clifford created. Unlike Clifford, I haven't
had any problems with stability but that may be because I am using 1.5 litre bottles instead of the two litre bottles that Clifford uses.
See Gary Ensmenger's Water
Rocket Playground for other rocket designs, rocket-building
techniques, water rocket links and a device that allows you to build
multi-stage rockets. Bruce Berggren's Water
Rockets! page includes simulations to estimate how high your
rocket will go and Clifford has a similar
page for simulations. Drag is the biggest factor in water rocket
performance so it is worthwhile reading about drag on model rockets at
Drag Analysis, NAR R&D Report. Another good water rocket resource
page is Dave Johnson's Water Rocket
Annex. Finally, you can join the water rocket mailing list and
details of how to join are given on Clifford's page.
Here is a photo of my friend Rick
launching the rocket. You can see the water falling to the ground. It
is hard to estimate how high the rocket goes when you are standing
beneath it but we think it went to 50 metres, give or take 10. We used
a 1.5 litre bottle in our rocket. Everyone else seems to use 2 litre
bottles which are relatively rare in The Netherlands but as soon as we
get one we'll make a rocket out of it.
Here is a close-up of Rick's face as he launches the rocket. See
Here are some photos of the launch pad after we turned the
hand-held launcher that Rick is using above into a remotely-operated
one. Basically, the hand-held launcher is cut in half and the two
pieces are soldered together with an elbow joint. Then it is mounted
in a wooden frame. The garden connector is operated with a string. The
close-up photo shows the elbow joint and the string passing behind a
nail. 120 mm nails in the wooden frame allow it to be easily staked to
the ground. The last photo shows last-minute adjustments to the launch
pad by the engineering crew (John). Don't worry, the rocket was not
How to Build the Launcher
What You Will Need
For a hand held launcher you will need
The hand held launcher is probably not so good as one that you can
operate remotely for safety reasons and because you get a bit wet
every time you use the hand-held launcher. You also have to close your
eyes as you launch to avoid the initial jet of water from the rocket
and so you miss the best part of the flight which is where the rocket
accelerates to full speed.
If you want to convert the launcher into one that sits on the ground
then you will also need the following.
- 75 mm of garden hose
- 600 mm of 15 mm diameter copper pipe (a plumber gave me this for
free). The outside diameter of the pipe should be slightly larger than
the inside diameter of the garden hose. Do not use a pipe with a
smaller diameter, it will not make an airtight seal when it is
- An automotive hose clamp of the right size for the garden hose.
- a 15 mm end cap (for the pipe)
- a car tyre valve (I got mine from a car tyre seller and the guy
gave it to me for free)
- a garden hose coupling, the female part that fits on the hose
You will need these tools
- elbow fitting for the pipe
- three saddle brackets for holding the pipe
- some string
- a plank of wood
- some nails to knock the wood together
- five 120 mm nails
- plumbers solder and flux
- a propane gas torch
- a wire brush
- a hack saw
- a sharp knife to cut the rubber off the tyre valve
- a hammer
- an electric drill and drill bits
- some vaseline
- a screwdriver
- a tool to remove the inside of the tyre valve
How To Build It
Start with the launcher. The figure below shows how it should look
when it is finished. The instructions below describe how to build the
hand held launcher shown in the photo with Rick. The list of
instructions that follow it describe how to build a wooden support so
that you can launch it remotely with a string.
The launcher is essentially complete. You can operate it by hand but I
recommend that you follow the next set of instructions and make it so
that you can launch it remotely. A diagram of the wooden support is
shown in the figure below. The cyan parts are the 120 mm nails.
- Remove the inside of the tyre valve with the
- Cut all of the rubber off the car tyre valve. Make sure every bit
of rubber is removed or you will not be able to solder it to the end
cap (which is what you are going to do soon). Use a sharp knife and
wire brush to clean the rubber off. You may be able to burn small,
hard-to-remove pieces of rubber away with a propane gas torch and the
- Drill a hole through the centre of the end cap the same diameter
as the tyre valve. The valve must be a close fit in the hole so that
you can solder it.
- With a wire brush clean one end of the copper pipe till it is
bright with the colour of fresh metal.
- Smear some plumbers flux on the
cleaned metal and on the end cap and valve. Put the end cap over the
pipe and insert the valve into the hole that you drilled. Solder the
pieces together with a propane gas torch and plumbers solder as shown
in the photo. Try not
to get solder on the threads of the valve. Make sure the solder fills
all of the gaps.
- File all burrs off the copper pipe at the other end to the
valve. Smear some vaseline onto the pipe. Warm up the piece of garden
hose with hot water so that it is soft and slip about 25 mm of it over
the end of the pipe. Using the screwdriver, clamp the hose firmly in
place with the hose clamp.
- Fix the female garden connector to the free end of the garden
hose. Cut the hose short with the knife, if you need to, so that the
hose connector sits close to where the end of the copper pipe is.
The launcher is complete! A 6mm rod may optionally be placed inside
the copper pipe so that it extends 200 mm or so into the rocket when
the rocket is attached to the launcher. This launch tube
helps guide the rocket as it takes off although, so far, I haven't
really needed one.
- Remove the core of the tyre valve
and the hose so that they don't melt when you solder the pipes in
the next step.
- Cut the copper pipe in the middle. Clean the
pipe ends with the wire brush. With the flux and propane gas
torch solder the two pieces of pipe into the elbow fitting.
- Put the tyre-valve core and the hose back on the copper pipes.
- Wrap the string around the hose connector so that the ends come
out on either side. The string has to be fixed tightly enough that you
can use it to pull back the hose connector without it slipping
- You need to build a wooden support for the launcher. With
whatever pieces of wood you have handy, build the support with nails
and butt joints as shown in the figure.
- Use the three clamps to fix the copper pipe to the wooden
support: two at the bottom and one on the vertical part. Put a long
nail through the side pieces, in front of the pipe. The string on the
garden hose will pass behind the nail so that it may be pulled to
launch the rocket. The 120 mm nails will probably split the wood when
you hammer them in so drill holes for them first. The holes
should be about 0.5 mm diameter less than the nails.
- Put the four remaining nails through the wooden support so that
they point downwards. They make an easy way of staking the
launcher to the ground so that it will not topple over when you
pull the launch string.
How to Build the Rocket
It is now time to build the rocket. You need to prepare a nozzle from
the male garden hose fitting. The nozzle can be screwed onto any
rocket you build so one nozzle can be used with all of your rockets.
What You Will Need
- two 1.5 or 2 litre PET bottles including their tops
- the male part of a garden hose coupling, the part that screws
onto a tap
- some ordinary packing tape.
product like silcon sealer, seems to be the best glue to use.
- a piece of plastic to use as a gasket for the mouth of the
bottle. Some PET bottle tops have
their plastic gaskets placed inside without glue. These would be
ideal. I used a piece
of teflon sheet about 0.5 mm thick but that might be hard to get
- some material to use as struts for the fin of the rocket. They
need to be at least 250 mm long each. I used
anti-static tubes that are made to protect integrated circuits in
transit. Any tube will do but ones made for PLCC-packaged
integrated circuits have the lowest profile. You should be able
to get one or two tubes for free from any place that buys lots of
integrated circuits. If you can't get integrated-circuit tubes
try using some light-weight pieces of dowel or anything similar.
How To Build It
Here is how to build the nozzle and one way of building a rocket.
Of course, half the fun of water rockets is trying to improve your
rockets so that they go higher. The rocket construction that I give here was
designed by Clifford
Heath. I haven't changed it in any way. I have had good flights
with it and it has been robust enough to survive many hard
landings. Because it is also to easy to make (no glueing) this is a
good one to do first.
- Remove the rubber washer from inside the male garden hose
- Note: If you have a metal-working lathe with a collet chuck then
you are going to find this step easy. Otherwise it is going
to take a lot of work with a hacksaw, vice and files.
Cut off the threaded part of the garden hose coupling. Be
careful not to scratch the inside face of the coupling as
you do it (that is, don't scratch the inside surface that
the rubber washer normally lies against. Cut the diameter of
the coupling down to the point where it will fit snuggly
inside a PET bottle top.
- Smooth off the face of the coupling with very fine
abrasive paper. This face will mate with the mouth of the
rocket and to make the contact air tight it must be
perfectly smooth. Put the abrasive paper on a flat surface
and rub the garden hose coupling over it with a circular motion.
- Cut a hole through the centre of a PET bottle top. The hole
must accept the shoulder of the hose coupling. For me the
hole needed a diameter of 19 mm. If you use a twist drill
the hole may not be properly round so use an 18 mm drill bit
and carefully shave off extra plastic with a sharp
knife. Remove what remains of the plastic seal from inside
the bottle top.
- Make up a gasket from the thin plastic. Cut a circle of the
material to the same diameter as the hose coupling and then
cut a hole in the middle of it. The gasket helps to make a
good seal between the coupling and the mouth of the PET
bottle as well as protects the coupling from being scratched
as you screw it on and off the bottle.
- Put the hose coupling, the bottle top and the gasket
together as shown in the photo. No glue or sealant is
necessary. This becomes the nozzle for the rocket and can be
screwed onto any rocket that you care to make.
- With a hacksaw, cut one of the PET bottles into three parts
as shown in the figure. The top part will become the nose
cone, the middle will become the fin and the bottom can be
- Push the nose cone over the base of the second PET
bottle. Tape it in place with some duct tape.
- Using the duct tape, tape the struts to opposite sides of
the second PET bottle. The struts should point down and
extend at least, say, 100 mm below the mouth of the second
- Tape the cylindrical fin section from the first PET bottle
to the struts with the duct tape. The rocket is
complete and should now look something like the one shown in
the figure. Note that the longer and further back that you
make the fin the more stable the rocket will be.
Testing and Launching the Rocket
WARNING: There is enough energy stored inside a pressurized
PET bottle to seriously injure yourself if it explodes. And the rocket
flies with enough speed to break bones if it should become unstable in
flight and head back to earth. Please adhere to the safety precautions
You need a car foot pump to pressurize the rocket. It needs to be
sturdy to withstand the amount of use it will get. And it needs to
have an in-built pressure gauge so you know how far it has been
The pressure test will allow you to check that there are no leaks in
your system and that the bottle will withstand the pressures required.
- Fill the rocket completely with water. It must be full of water
so that it cannot explode if the PET bottle ruptures.
- Attach the rocket to the launcher. Keep yourself and other
people clear of the launcher.
- Pressurize the bottle to 3 bar (45 psi) and check all joints
and connections carefully for leaking water. Make sure that the
pressure reading on the pump's pressure gauge does not fall; it
should stay constant if there are no leaks.
- Increase the pressure to 7 bar (110 psi) and check again
for leaks. You will not pressurize the rocket beyond 6.5 bar
(100 psi) when you launch it.
Launching the Rocket
Launch your rockets only in large open areas where there are no people
around. The best rocket flights go straight up and then come straight
back down. If the rocket is unstable it can fly in any direction. It
will often fly horizontally. Rockets have been reported to fly as high
as 90 metres so if it is windy they may land a large distance from the
launch pad. Your launch string should be at least 10 metres long.
If the rocket does not go straight up it may be unstable. To improve
the stability of the rocket you must either increase the length of the
cylindrical fin or move the fin further back (by increasing the length
of the struts).
- Push the launch pad into the ground so that the nails hold it
stable. Make sure the rocket sits level.
- Fill the rocket 40% with water.
- Attach the rocket to the launcher and make sure that it is
securely held and pointing directly up.
- Pressurize the rocket. Use 3 or 4 bar (50 psi) for your first
launch in case the rocket is not stable. Do not go higher than
6 bar as the bottle may be at risk of exploding. Keep yourself
(and everyone else) as far from the bottle as you can while you
are pumping it.
- Warn everyone that you are about to launch and check that
everyone is paying attention to the launch.
- Count down to 1 and pull the launch string (from 10 metres
Last modified: Thu May 14 08:55:52 1998
© Malcolm Goris