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Construction - Launchers

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Dark Shadow Deployment


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How Much Water?

Flying Higher

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Building a Launcher

Using Scuba Tanks


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Servo Timer II




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Flight Log Updates

#221 - Horizon Deploy

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#202 - Horizon Launcher

#201 - Flour Rockets

#197 - Dark Shadow II

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#195 - 3D Printed Rocket

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#188 - Skittles Part #2

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#186 - Level 1 HPR

#185 - Liquids in Zero-G

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#180 - Light Shadow

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#177 - Reefing Chutes

#176 - 10 Years

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#174 - Mullaley Launch

#173 - Oobleck Rocket

#172 - Coming Soon

#171 - Measuring Altitude

#170 - How Much Water?

#169 - Windy

#168 - Casual Flights 2

#167 - Casual Flights

#166 - Dark Shadow II

#165 - Liquid Density 2

#164 - Liquid Density 1

#163 - Channel 7 News

#162 - Axion and Polaron

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#1 to #160 (Updates)


Building a water rocket launcher

Building a Water Rocket Launcher

A water rocket launcher can be as simple or as complex as you like, however, most launchers share common features. This article describes the different components and their function to assist you when designing your own launcher. We provide links to examples of the various features.


Safety should be your number one priority when designing your launcher. As your launcher will be handling compressed air it is important to make sure all fittings are properly rated. It is always better to err on the side of caution and use heavier duty components as weight isn't an issue like it is on a rocket.

The image below shows a typical water rocket launcher setup.

Click on the different components in the image for more information:


Air Supply

Your launcher needs to be connected to an air supply. There are several different kinds of air supplies you can use with the same launcher so it is best to incorporate into your design a way to connect to different supplies as you upgrade.

Bicycle pump / car tyre foot pump - This is the easiest and least expensive way of pressurising rockets. The launcher's air hose connection will need to have a tyre valve adapter in order to connect the bicycle pump directly. Regular pumps can supply in the order of 100-120psi. More expensive models can supply 100's of psi.
Small compressors - These require a power source such as mains or a battery. These make filling much less work, but watch out for cheap models as they can easily overheat and fail. These are less portable due to their power needs. Small compressors will typically go to about 150psi. The larger the rocket and higher pressures will mean the compressor needs to run longer and will  more likely overheat.
Bottled air with regulator - This is a more expensive option for filling your rockets, but it is the only option for using gasses other than atmospheric air. This option can also typically deliver higher pressures compared to normal bicycle pumps and small compressors. You can also fill your rockets quicker as long as air compression heating is taken into account. Depending on the size of the tank and the rocket's capacity you can get from dozens of launches to over a hundred from a single fill. Commonly used tanks include scuba, Nitrogen and CO2 tanks. Depending on the type of tank you use, you may also need certain certifications in order to have them re-filled. DO NOT use combustible gasses in water rockets for obvious safety reasons.

Note that extra care needs to be taken when handling and transporting bottled gasses due to the higher pressures involved.

Here is a full article on how to use scuba tanks for your launcher.

Pressure Gauge

You will need to have a pressure gauge attached to your air supply line. The pressure gauge measures the internal pressure of your rocket. It is important to know what the rocket is pressurised to so you don't exceed the rocket's burst pressure. It is also a useful tool when checking for leaks.

The gauge is best located away from the launcher to allow you to clearly see it without being too close to the pressurised rocket. Be aware that the pressure may be slightly different during pressurisation when the gauge is located away from the rocket. Allowing the pressures to equalize within the launcher, rocket and air supply hose should give the correct reading. The delay in pressure equalization is usually due to small air holes often used in the hoses and its fittings. Water in the hoses can also cause the gauge to give a delayed reading as the water moves through the small holes.

The pressure gauge should cover the range of launch pressures you intend to launch your rocket at. 0-200psi is a typical range for regular rockets. Pressure gauges are often already attached to the air-source so there is usually no need to attach them separately.

Air Hose

The air hose and its connectors should be rated for the intend launch pressures. The hose should also be long enough for you to stand at a safe distance from the launch pad. You may be able to locate a small compressor close to the launch pad with a short hose, and control it electrically remotely. Seeing the pressure gauge at distance can be an issue.

The smaller the inside diameter of the hose the better as you don't waste energy pressurising a larger volume of air in the hose. A smaller internal diameter usually also means the hose should be able to withstand higher pressures. Air hoses can be purchased at a local retailer that sells compressors. If you are only launching at 100psi or less then a garden hose is a viable inexpensive alternative.


Air Hose Connection

Having a built in air hose connection allows you to disconnect the air-supply from the launcher itself. This makes it convenient for transportation. The type of connection you decide on will depend on your choice of air hose and the air manifold/hose on the launcher. The most convenient connections are quick release ones.



Here are a number of examples:

If you are connecting a bicycle pump to the launcher, you can make a simple adaptor to connect it. It involves using an old tyre valve taken from an inner tube and inserting it into the launcher's hose. Then using a pair of hose clamps to seal it all up.


If you are trying to connect different sized hoses together, or even extend the same size hose you can use hose barb adaptors such as these:


You again would use a hose clamp over the top to secure the hose on the adaptor.

Non-return valves

Non-return or check-valves are used in launchers to prevent water from flowing back down the air hose. These can take many different forms. You should locate your non-return valve as close to the rocket as possible to keep as much water in the rocket as possible.

Here are a couple of cross sections of typical non-return valves. One way flow is from left to right.


Some one way valves come equipped with hose barbs, which makes them very easy to attach to your air hose.

Here are examples of commercially available check-valves:

An alternative to using a non-return valve is to use an S-bend in the air hose whose curved section is above the water level in the rocket.


If your launcher uses a launch tube that emerges above the water level inside the rocket then you don't need a non-return valve.

Launcher Base

The launcher base provides a stable framework to attach all the components to. The launcher base should be designed to be stable and prevent the entire rocket from tipping over when the launch string is pulled or due to wind gust. This can be a flat board, tripod, or any arrangement of pipe work.

Here is a typical launcher base made from PVC piping:

Here is one made from a piece of plywood: 

It is also useful to anchor the launcher to the ground with a couple of tent pegs to prevent it from sliding when pulling on the launch string.

Release Mechanism

The most important part of your launcher is the release mechanism. It is the locking mechanism that prevents your rocket from leaving the launcher while it is being pressurised. Some common release mechanisms include:

Cork/Rubber Stopper

A cork or a rubber stopper is inserted into the neck of the bottle. Friction between the cork and the rocket keeps it on the launch pad as the rocket is pressurised. When the internal pressure exceeds the frictional force the rocket is released. It is difficult to predict when launch will occur. Although these are very simple to make they are only suitable for fairly low pressures. These will also give inconsistent results depending on how hard you push the rocket onto the cork.



Clark cable tie launcher

A very popular launcher named after Ian Clark who developed it. It uses cable ties to hold down the rocket while it is being pressurised. A collar surrounding the cable ties keeps them in place. When the collar is lowered the cable ties open releasing the rocket. This is typically used with fully open nozzles.

There is a huge number of Clark Cable Tie launchers described by various rocketeers available on the net. Here is just a few:

A variation on the Clark cable tie launcher are these copper tube launchers that seal from the outside.

Gardena quick connector

Another popular launcher that uses a garden hose quick connector to hold down the rocket. The rocket is equipped with a matching nozzle made from a garden hose adapter. Typical nozzle sizes include 9mm and 15mm. The Gardena launcher is used frequently for reduced nozzle sizes. You can insert/glue smaller tubes inside the nozzle to reduce the nozzle size even further.

Here are some examples of Gardena launchers:

Twisting bolt

A bolt is mounted vertically in the base with a section of the head removed. When the bolt is rotated into the locked position the head holds the rocket down by the flange of the bottle. Turning the bolt allows the head to release the flange.

Examples: The first of these is a twisting bolt variation:

Pull wire

The pull wire launcher is based on a similar principle to the twisting bolt mechanism, but the bottle is held down by the flanges on either side of the bottle with a strong wire. To launch the rocket, the wire is quickly pulled free to release the rocket.

Examples of pull wire launchers:

Internal grip

This is not a very common design mostly due to more advanced construction techniques required. This launcher holds the rocket down by the internal walls of the rocket. In the above example a set of ball bearings are used to retain the bottle. These are held in the locked position when the internal piston is in the up position. Lowering the piston allows the ball bearings to retract into the launch tube releasing the rocket. There are a number of variants based on this launcher design.

Another variant incorporates a compressible rubber stopper that uses friction against the inside of the bottle neck to both seal and retain the rocket.


Inflatable bulb

This launch system was developed by Antigravity Research.  It is a very simple mechanism that has a flexible bulb fitted on the end of the air hose which is then inserted into the nozzle. The bulb has a tiny hole in it. As air pressure is applied the bulb swells preventing it from being ejected and the rocket is filled through the tiny hole. When pumping is stopped the pressure starts to equalise and the bulb shrinks until it is small enough to fit through the nozzle and then is ejected launching the rocket. It is difficult to predict when the bulb will release though. This system is only suitable for small rockets due to the size of the nozzle. Once you start filling, there is no launch abort option.

Seals and O-rings

To prevent the pressurised air and water from leaking out of your rocket you need to use a washer or an o-ring between your rocket and the launcher. The type that you use will depend on the type of launcher you are using. The higher the pressure you want to use, the tighter the tolerances have to be for the o-ring grooves. Always make sure that the o-ring grooves are clean and free of scratches or burrs. Always use correctly sized o-rings.


Rubber washers are also commonly used when sealing rockets against the launcher. These can be typically purchased from the hardware store. In an emergency if you really need to make a specific sized one they can be cut from sections bicycle inner tubes.

Pressure release valves

It is a good idea to add a safety release valve to your launcher. Sometimes it is important to abort a launch and safe the rocket after it has been pressurised. How this is achieved will depend on how you configure your supply connection and where you locate your non-return valve. The pressure release valve needs to be on the rocket side of the non-return valve otherwise you won't be able to release the pressure from the rocket.


Here are some examples:

Trigger Mechanisms

Trigger mechanisms are actuators that actually start the launch. This is typically a string attached to the release mechanism to release the locking lever.

Pull String

This is by far the most common and easiest way to launch your rocket. The string simply connects to the release mechanism and when it is pulled the release mechanism activates. If the release mechanism takes a bit of force to release you may consider using a lever arm to help with the activation without putting undue force on the launcher. Too much pulling force on the launcher could make it topple. Make sure the string is long enough to launch the rocket from a safe distance.

The best kind of string to use is a braided nylon string. Thin or cheap strings can easily break. 


Air or water pressure can be used to activate a pneumatic/hydraulic piston to activate the release mechanism. These systems are not very common mostly due to the added expense and complexity. 


Like the pneumatic or hydraulic pistons an electrical solenoid can provide the required force to activate the release mechanism. These also are not very common due to the need for a separate power source. Use only low voltage ones. You don't want to mix mains voltage and water.



Larger servo motors can also be used to activate the release mechanism. They have the advantage that they do not need a lot of power like the solenoid, and when connected to a receiver can be controlled through a remote control.



A launcher needs to have a stable base. If the launcher is not stable it could topple when the launch string is pulled or due to a wind gust. The last thing you want is a fully pressurised rocket pointing horizontally. Make sure you either have a wide base on your launcher or that it is pegged into the ground, preferably both. If it is not pegged to the ground you may find that the launcher may slide as you pull the string. A couple of tent pegs is usually enough to secure the launcher.


When designing your launcher keep portability in mind. Is it light enough to carry a fair way to the launch site from your car? Make sure you can easily fold it down so that it fits in your car.

Launch tube

Adding a launch tube to your launcher can improve the performance of your rockets. The launch tube ideally should be as long as possible. The diameter should be slightly smaller than the nozzle you are using. This will minimize water loss as the rocket accelerates up the launch tube. If the launch tube is permanently attached to your launcher, you will be limited with the types of rockets you can fly and what nozzles you can use. Consider making a removable launch tube if you want to experiment with various rockets.


Guide rails

Guide rails are very important in helping your rocket fly vertically especially during the first part of the flight. The guide rail keeps your rocket moving straight before the rocket has enough air speed for the fins become effective. There are different types of guide rails you can choose from:

Guide Rail and buttons

These are suitable for larger rockets and consists of a single slotted rail. The rocket is fitted with rail buttons that slide into the rail groove.


Guide Rod and lugs

The guide typically consists of a round steel rod securely attached to the launcher. The rocket is fitted with small lugs or short tubes that slide over the rod. These are very common in model rockets. These are generally suitable for smaller rockets.



This launcher arrangement includes 3 or 4 guide rails surrounding the rocket without the need for the rocket to use rail buttons. The lack of rail buttons saves weight and drag on the rocket.

If you are building a tower launcher incorporate into your design a way to adjust the spacing so that you can put in different diameter rockets.


Launch tube

For certain rockets you can use the launch tube itself as a guide rail. The rocket does not need additional guide rails.

Examples of rockets using a launch tube as a guide rail:

When deciding on your guide rail arrangement think about the types of rockets you will want to fly from your launcher and in particular their fin arrangements. If you are using ring fins, make sure the release mechanism will fit through the ring fin. If you are using regular fins then make sure they will not get caught on any part of the launcher. If you are going to use a tower launcher then you need to consider the fin count and whether they will all fit between the rails.


When making the launcher keep in mind that it will get soaked from repeated launches. Stay away from materials like MDF and chipboard which love to soak up water. Use materials that can withstand typical outdoor conditions. Plastic and metal are the best.


Test your launcher the same way you test your rockets. When testing it to new pressures for the first time use a hydro test and stand well clear and listen & look for leaks.

Make sure you fix any leaks on your launcher. A rocket can depressurise quite quickly while waiting to launch even if there is a small leak.

Water Supply

A launcher can have an integrated water supply for the rocket. This means you put the rocket dry onto the launch pad and then fill the rocket while it is on the pad. Pressurised air is usually used to force the water from a reservoir into the rocket. This is typically done prior to filling the rocket to full operating pressure. A small bicycle pump is usually all that is necessary to force the water into the empty rocket. A valve is needed to isolate the water reservoir before pressurisation can begin.


Usage Tips

  • When you launch a rocket, dirt and mud can be kicked up under the launcher and contaminate various components. Always make sure the release mechanism and launch tube are clean before each launch. Sand on the launch tube can be enough to wedge a rocket so it won't fly off.
  • Use silicone grease on all moving components of your launcher. This prevents things from sticking and ensures smoother operation. Also grease your o-rings to prevent them pinching when fitting your rockets onto the launcher.
  • Some materials degrade when exposed to UV radiation from the sun. If you are using these materials in your construction make sure you store your launcher out of the sun when not in use. The little bit of exposure the launcher gets during your launch days shouldn't be an issue.
  • As you use your launcher, repeated pressurising cycles can work-harden some components and eventually cause them to fail. Inspect your launcher after each launch day for signs of hairline cracks.
  • When designing the entire launcher consider how you will place the rockets on the launcher. If you fill the rocket with water first, then how easy will it be to place it on the guide rails? Will you be able to reach the release mechanism easily to lock your rocket in?
  • If you are using a string to launch the rocket, make sure you use a strong string that is not going to break. The best kind of string to use is a braided nylon.
  • Don't use MDF or chipboard to make the base out of, as these will absorb a lot of water and warp and perhaps fall apart. Use only water proof materials.
  • The type of release head your launcher uses will depend on your rocket design and chosen nozzle types. If you plan on flying lots of different rockets with different nozzle types, you may want to consider making swappable release heads for your launcher.

References and other launcher examples:

There are about as many launchers as there are water rocketeers. Here are just a few examples of their work:


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