The VSSEC Water Rocket Launcher
[Draft: photos of pull cord release still to be added.]
The most effective, quickest to build, most versatile but cheapest water rocket launcher you have
Every educator who has ever played or worked with water rockets will appreciate that they are a
great way to introduce concepts such as conservation of momentum, force, pressure, potential and
kinetic energy, and basic aerodynamics. For many educators who wish to use these great tools with
their classes there is often one significant stumbling block: the lack of readily available launchers.
The net abounds with instructions for building launchers some of these are fairly crude and some are
very sophisticated. The VSSEC Launcher is one of the more sophisticated types, but is very easy and
quick to build and is also very cheap.
There are two common classes of water rocket launcher; the cable-tie style (invented by Ian Clark)
and the garden hose connector style. The Clark launcher has the advantages of being light, guiding
the rocket for the initial boost and not restricting the flow of water from the mouth of the bottle. It
has the disadvantage of being harder to construct. The garden hose types are mostly easier to
construct but the smaller nozzle diameter slows the “exhaust” velocity of the water. As well as this,
standard garden hose “tails” (tap fittings) do not fit soft drink bottles and modification of the tails
and bottle caps is not necessarily easy.
Here we introduce a garden hose style with the advantage of very easy construction and a large
nozzle diameter. This launcher will comfortably handle pressures of 11 Bar, 154psi, about the
maximum safe pressure for soft drink bottles. This water rocket launcher is assembled from
common gardening equipment which is readily purchased from most large hardware stores in
Australia. In 2010 the cost of all the materials was less than $23. It can be put together by any
person who knows which end of the hammer to hold. It requires a minimum of tools and no
specialist skills such as welding or brazing.
We use a hose connector with a bottle cap glued inside to lock into a quick-release hose fitting which
is attached to a plastic water pipe. A bicycle valve inserted into the pipe allows the bottle to be
pressurised. The quick release is triggered by a simple pull cord. The entire assembly is mounted on
a wooden base with a fixed launch angle.
The fittings used are larger than standard garden hose fittings. This gives the nozzle an
internal diameter of 16mm instead of 8mm, (four times the cross-sectional area).
The pipe fittings are all threaded plastic producing airtight seals with little effort and a light
The quick release connector, which is designed to go on the end of a flexible hose, is fitted to
a threaded pipe joiner allowing it to be connected to the rigid pipe fittings. No hose clamps
used at all.
Minimum Parts Required (See Fig1. ):
35mm snap fitting “tail” (1.)
Quick release hose connector. (2.)
¾ inch pipe connectors (3. & 4.)
¾ inch elbow (5.)
¾ inch end cap (6.)
Bicycle tube with Schraeder valve.
Miscellaneous timber and wood screws.
Spanner to suit pipe fittings
2 mm & 8.5 mm drill bits
25 mm drill/spade bit Figure 1
Hot glue gun.
Cup of boiling water
Small sharp knife which you can afford to throw away.
Parts/tools for nylon cord trigger. (Not needed if you use some other trigger mechanism.)
5m or more of light nylon cord
45cm piece of the same cord
2 threaded eyelets
2 bicycle spokes
Pliers (needle-nosed type)
Thin file (2mm ) or small saw
Two large pull ties.
You will also need a bike pump with a pressure gauge. ( Not
included in cost.)
Building the nozzle
1. Discard the light grey adapter and the washer from
inside the “tail”.
2. Screw the bottle cap onto a bottle. Hold the bottle
while you carefully cut a 16 mm hole in the centre of the bottle cap. Heat
the point of the sharp knife in a gas flame and then use it to cut the hole.
Cut the hole undersize and then use the sandpaper wrapped around a
pencil or similar to enlarge the hole. Try a few times to find out what
works best for you.
3. Remove the bottle cap from the bottle.
4. While your hot glue gun is heating up boil a cup of water.
5. Put a thick bead of glue around the corner edge of
the bottle cap, another bead around the inside of the
“tail” and quickly then press the bottle cap into the tail.
Don’t be surprised if the glue hardens before you get the
cap pressed all the way in and straight. The next step will
6. Drop the tail and cap assembly into the cup of hot
water. Fish it out after ten seconds. The glue will be very
soft. Screw the tail onto a bottle and use the bottle to press
the cap firmly straight in as far as it will go. Run the tail under cold water to
set the glue.
Building the launcher
7. Remove the hose collar from the back of the
quick connector. Knock the inner hose protector
from the threaded collar and discard it.
8. Carefully prise up the twelve little fingers which
would normally grip a hose.
9. Push the longer pipe connector up into the
fingers. Line up the fingers so that they will
eventually go between the four small ridges
on the middle section of the pipe connector.
It will only go on a short distance before it
becomes difficult to move.
10. Stand the quick release connector on a flat hard
surface, place a block of wood against the end of
the pipe connector and hammer it all the way
into the connector. It will be quite hard to get
on. This is good, it makes sure the seal is airtight.
When the pipe connector is driven all the way in
the fingers will reach just past the end of the
thread. If yours don’t you haven’t driven it on far
11. Slip the threaded collar over the fingers and
screw it onto the quick release connector. Screw
it up as far as it will go without interfering with
the quick release mechanism. It does not need to be very tight.
You now have a quick release connector which can be screwed on to any combination of
plastic pipes to suit your particular needs.
Building the launching base.
12. Take a flat piece of wood about 16mm thick. Any piece at least 15cm
square will work. Drill a 25mm or 1 inch hole through the middle.
13. Drill a pair of 2 mm – 2.5 mm holes each 10mm from the edge of the
large hole and at opposite sides.
14. Push the threaded end of the quick release through the hole in the
wood. It should be a firm fit.
15. Put some Teflon tape on the thread and screw on the elbow as tight
as you can.
16. Put some tape on the other pipe connector and screw it into the
elbow as tight as you can.
17. Cut the bicycle tube around the valve leaving a flange of rubber
about the same size as the inside of the cap.
18. Drill an 8.5 mm hole through the cap.
19. Push the valve through the cap from the inside. A little hot glue
around the hole on the inside before you push the valve
through won’t hurt but isn’t necessary if you do a good job of
fitting the flange of rubber to the inside of the cap.
20. Screw the cap over the end of the pipe connector. Do it very
tight so that the rubber flange seals around the valve.
21. Nail or screw your piece of timber to whatever you have
available to give it a stable set up. Allow for the weight of the
water filled rocket. Use wedge shaped pieces if you want your
rockets to cover some distance. Use straight bits if you are
aiming for altitude. (But remember: what goes up ...)
Building the trigger (nylon cord pull type)
[Photos still to come.]
23. Screw the two small threaded eyelets into the two holes in the piece of wood.
24. Pull down the quick release and carefully prise off the snap ring underneath.
25. Remove the quick release collar completely, taking note of the arrangement of the three
white plastic “teeth” and the large spring inside.
26. Choose two places opposite each other on the top edge of the collar which do not conflict
with the three “teeth”.
27. Slot the top edge of the collar with the file or saw so that the two spokes can be hooked into
the slots and run along the side of the collar. The slots need to be deep enough for the
heads of the spokes to clear the top edge of the collar.
28. Cut the spokes 5 cm from the end.
29. Use the pliers to bend a loop into the cut end of the spoke. Bend the spoke in the opposite
direction to the head of the spoke.
30. Replace the “teeth”, collar, spring and the snap ring.
31. Hook the two spoke pieces into place on the sides of the quick release and secure them with
the two large pull ties.
32. Twist the quick release in the piece of wood so that the spoke loops line up with the eyelets.
33. Tie one end of the 45cm cord to one of the spoke loops.
34. Thread the cord down through the eyelet below, back through the other eyelet and then tie
the end to the other spoke loop.
35. Attach the 5m piece of cord to the centre of the “yoke” you have made with the shorter
36. Trickle a few drops of lubricant on to each of the three teeth inside the quick release
connector and down into the mechanism just to be sure it releases smoothly.
37. Test the launcher by pulling on the long cord which should pull down on the collar.
38. Add tent peg/spike holes to anchor your launch pad.
You now have a functioning rocket launcher.
Add a water hose connection so that you can fill the bottle after it has been clicked
Add a compressor connection so that you don’t have to pump air by hand.
Add a pressure release so that you can safely vent the air and water without
launching the rocket if something fails.
Use a longer cable or cord arrangement to allow triggering from a greater distance.
Essential if you are using a compressor and higher pressures.
Add a hinge to make the trajectory adjustable.