Water Rockets Launcher Index

When launching a It's that bloke again!rocket like the one on the right, it goes without saying that a launcher of some sort is needed.

This index will, hopefully, give you a starting point for building a launcher of your own.

The methods I have used here are suited to the situation regarding materials availability that I have found myself in, in the UK - things are different elsewhere in the world and I suggest that you use the information and ideas that are on this site along with the content of other sites to come to a design of your own that suits your needs.

Discussion

Discussion about fundementals of different types of laucher.

Right-Click and press Zoom In to see betterCopper Tube Launcher

This is the launcher that I built using materials available in the UK. It is an outside groove sealing launcher built from copper and it allows you to launch using restricted nozzles if you wish.

Modification for use with only an air line

Following a question on the group, I came up with this design - there is another way of doing it using a double acting piston and a one-way valve

 
Right-Click and press Zoom In to see betterHose Connector Launcher

This launcher is extremely easy to build. It uses basic parts that are available in any reasonable hardware shop. It is made from quick connect lawn hose parts and allows you to launch a rocket with a reduced nozzle. The use of the launcher is extremely strightforward.

 

Launcher Bases

Stakes have the advantage that you just need to knock them into the ground and once there, they will not slide all over the place then your ground crew pulls the launcher release too enthusiastically. However, a hot, dry summer will render them useless when the ground dries up. A H-Base will just sit on the surface and is easy to set up although the can fall over if care is not take with them or precautions such as staking the ends of the feet with 6" nails :-)

Stake

This is shown on the Copper Tube launcher with a swingball base along with a piece of wood as a support and some cable ties to hold everything in place. Basic but quick to asRight-Click and press Zoom In to see bettersemble and sturdy.

H-Base

This is a more civilised and better looking base for the launcher. The H-Base is lighter and more portable, quick to assemble and can be used on hard ground.

Right-Click and press Zoom In to see betterGantry

The Gantry is for those larger rokets (10 litres or bigger, 2 stage using 3 litre bottles on the booster) that are too heavy and have a centre of gravity too high for the launcher on its own.

Performance Improvements

The basic launcher will get your rocket into the air without getting you wet but there are still some things that you can do that will improve the performance of your flights.

Restricted Nozzles

The copper tube launcher allows you to use a restricted nozzle on the rocket. One of the main considerations regarding performance is that of drag and this force increases proportionally to the square of the velocity. Keeping the speed down will reduce this force and by reducing the diameter of the nozzle, the 'burn' will last longer resulting in a greater height (a gain of around 3 metres - see table below). Nozzle restrictions are shown in the variations section of the Copper Tube launcher page.

The hose connector launcher uses a restricted nozzle to work.

Launch Tubes

A Launch Tube is a tube that acts like a plunger inside the nozzle allowing an extra, initial push with very little loss of water in the process. This can give the rocket an initial burst allowing it to get to a greater height without having to carry as much water. A hollow tube will give better results as the air inside the launch tube will contribute to the total air of the rocket while it is on the tube (Use the Water Rocket Computer Model to play around with this - the effect is significant but becomes more so as the volume of the launch tube becomes a greater proportion of the capacity of the rocket's pressure vessel). A height gain over the launch tubeless, fully open nozzle of around 7 metres.

T-nozzles

Combining the benefits of a small nozzle diameter with a launch tube, a T-nozzle is a device that sits on top of the launch tube while the rocket is on the launcher. When the rocket is released, the launch tube provides as much acceleration as possible with as little loss of liquid as possible until the nozzle reaches the end of the launch tube. Then, the T-nozzle engages, sealing off the full bore nozzle with a smaller nozzle which allows the slower release of water during the rest of the burn. This allows even greater height gains as even less water is needed. Again, with a standard 130g rocket at 5.1 Barg, a T-Nozzle gives a gain of nearly 19 metres, beating the launch tube only by over 10 metres.

Look at Scott Chesnut's site and Brad Calvert's site for T-Nozzles.

Description Parameters Flight
Height
Weight
Water
Nozzle
Diameter
Launch
Tube
Diameter
Launch
Tube
Length
T-Nozzle
Diameter
Units g mm mm cm mm m
Basic 2 litre 550 21.75 - - - 52.2
Restricted Nozzle 550 8.0 - - - 55.3
Launch Tube 440 21.75 21.5 25 - 59.7
T-Nozzle 415 21.75 21.5 25 3.7 71.1
Comparison of different launch types on basic 2 litre bottle weighing 130g pressurised to 5.1 BarG


General Improvements

Even a 6 year old can pump hard enough to make a 2 litre rocket shoot 40 feet into the airAll of the above relate to the fundemental functioning of the launcher and the rocket. However, there are some other improvements that can be made to improve on safety and convenience.

Air Line

Using an air line will put valuable distance between yourself and the rocket whilst you are pressurising it. Should the rocket fail catastrophically, the further you are away from it when it does this, the better. I use a 5 metre " diameter flexible PVC tube with a one-way valve at the pump end as filling this air-line at 5 BarG will take one pump stroke so keeping it up to pressure means that all of my efforts fill the rocket rather than repressurise the air-line with each stroke of the pump.

5 metres relates to the amount of cash I had in my pocket when I bought the tubing but is reasonable for pumping ductile plastic pressure vessels to 5 BarG. For higher pressures I would recommend at least 10 metres, maybe 20. Remember to pressure test anything that you are using - I cannot be held responsible if you fail to carry out simple testing procedures.

Air Pump

A hand-held bicycle pump is all right for a start but if you are going to pressurise many rockets, a stirrup pump is far better. I have one with a metal casing and pressure gauge that will pump to a pressure of 10 BarG (I have tried this) and is a lot easier to use than a hand held pump. Being able to put your weight onto a handle that you can hold with both hands is a lot easier than using a hand held unless you really want to develop your chest muscles.

An alternative is to use an electric pump that runs from a car battery but thought should be given to:

  • Its cost;
  • How much effort will be required to get it to any launch site (carrying the pump and associated batteries);
  • The effects on its longevity caused by pumping hundereds of litres of air through it at 5 BarG instead of topping up the pressure of a few car tyres to 2 or so BarG every few months; and,
  • The fact that if you are going to have to pressurise 30 rockets for a school science class in as many minutes, you will still be able to stand without the aid of pure oxygen at the end of it by using an electric pump.

Water Delivery

Filling a rocket and then putting it on the launcher - whether you do this on the ground and spill some of the water or you put the launcher on the rocket and then turn the rocket with the launcher the right way up - is not as convenient as being able to mount the empty rocket on the launcher (being able to position the T-Nozzle) and then fill it to exactly the right level.

Using a pressurised water reservoir has the advantage of reducing handling problems and making launches more reproducable. The disadvantage is that you will be using the same pressure vessel each time and thought should be given to the expected life of this vessel bearng in mind the fact that it will get more sunlight and be pressurised for longer than the rockets and therefore need to be replaced more often. Once way around this is if you are launching near to a water supply (if you launch at home) in that the water is already pressurised and in a useful pipe.

Emergency Pressure Dumping

Should you suspect that the rocket is about to fail or, for some reason it does not launch, or maybe an animal (such as dog or a boy scout) strays into the launch area, you may wish to dump the air as quickly as possible.

The best way of doing this is to use a launch tube. If you are not using a launch tube to gain extra height, a small diameter (6mm) tube will be sufficient to dump the air in a rocket in a reasonably short time - a launch tube used to gain extra height will have a larger diameter but you will still have to go through whatever size of fitting you are using unless you operate an emergency valve mounted on the side of the launcher that, with the pull of a string, rotates a ball valve through 90 and allows the air to discharge quickly.



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