Water Rocket Computer Model

for a Chinese translation, Click Here

IT IS A BOILING hot, windless day and you are standing in the middle of a circle of curious, excited children. In your hand, you have an inverted, half full, 2 litre plastic pop bottle that you have pressurised to approximately 6 atmospheres pressure with a bicycle pump and a special adaptor that you have made from a Woods/Shrader adaptor and a pop bottle top.

You start to unscrew the top and the water starts to pour out of the screw-thread. Without making any waves inside the bottle, you manage to unscrew the top completely and in just over a sixth of a second, the bottle is travelling at 120 miles per hour - straight up (you remembered to let go - although there is little point trying to hold onto it as it produces around 40kg of thrust). The children have all ran away screaming (It is amazing how fast you learn to step away in the right direction).

You look up and you see a knobbly shaft of water glistening in the sun light as it starts to fall to earth. A few seconds later, the empty plastic pop bottle falls at your feet. You have just made your first water rocket launch and you are now soaked through to the skin (but cool). The children are now volunteering to help you with the next launch (they stand further away the second time).

How did you know how much water to put in it?

Postcardware - 255,756 bytes as a zip. With this Water Rocket Computer Model, you will be able to predict the duration and height of the flight of any water rocket that you make (within reason of course).

The program that appeared in Wilf's Programmer's Workshop and on the cover disc of PC Plus in 1997 was derived from version 1 of this model. That issue had pictures of me launching various models from a wet hillside to the south of Bath in the UK on what turned out to be the only rainy day for weeks (before and after).

Computer models may look daunting to start with - they have many variables on them - but many of them remain unchanged and usually stay at their default values. The model allows you to save these values so that you can look at the rocket again at a later date without having to type all (or any) of the figures in again.

Typically, you would take some measurements of the pop bottles that you are going to use - diameter, weight and so on - and type these figures in. Run the model and see if you can come up with improvements - using the 3D plots, the model can help you out with many of these such as best weight and mass of water for the pressure you are going to use and the optimisation process (equivalent to hundreds of launches) can take only a few minutes. If you are doing this as part of a science olympiad, many specifications will already be there such as pressure and maximum weight.

The model is not the last word with your water rocket, it gives you a good starting point, will save you a lot of time and will give you an idea of what will happen if you change something. There are many variables that either are not practical for most people to measure or cannot be foreseen so, although the model may suggest that you try 436g of water, you will probably end up using 425 or 450 and it will not make much difference as there was a bit of wind turbulence or the parachute deployed late, you could only read the pressure gauge to the nearest 5 psi and you never really trusted the calibration anyway, and so on.

During the initial development of the model (over a number of school summer holidays), I experimented with various sizes of bottle, nozzle, mass of propellant and so on - the model was surprisingly accurate. Since then a great deal of work has been done by Bruce Berggren both with the maths and wet experiments and has involved a great deal of discussion in the group. It is possible to extend the model beyond the bounds of the equations and get interesting results although maybe not that meaningful.

The program runs on MS DOS and so is fairly quick (being completely self contained with none of those nasty Dynamic Linked Libraries (DLLs) to clutter the place up and make a general mess). It will run under Windows 95, 98 and so on. You can also use the palette editor to change the palettes that the computer model uses when plotting the 3D Optimisations. This allows the user to make palettes that can illustrate contours, defining useful regions of optimisation, different colour schemes or even save on printer ink.

Water Rocket Computer Model Help Pages Suitable for WRCM versions 4.30, 4.31, 4,40 and 4,41
Download Help Pages	Click Here for 21,000 words worth of Water Rocket Computer Model Help Pages in HTML format (so that you can view them on your browser). You can download a self contained zip file containing all of the help (in one of five languages) or look at the pages online The help pages allow you to understand better the use of each value that you input and the meaning of the results that you get out of it. Over 4,000 downloads Being in HTML format, you can print them out as large or as small as you wish. There are versions available in: English; Chinese Big5 (using the MTIR translator) - your browser need to support Chinese Big5; Chinese GB 2312 (using the MTIR translator then a Big5 to GB2312 translator) - your browser need to support Chinese GB2312; Spanish (using Babel Fish at AltaVista); and, Portuguese (using Babel Fish at AltaVista). Requirements - HTML browser (like the one you are using at the moment) Note that you also need to download the WR Computer Model (below) as these help pages are for using the computer model and are not about water rocketry generally.
Water Rocket Computer Model v4.41 Updated 16th September 2001
Details	Click Here for Details of the Water Rocket Computer Model, including screen shots.
Details	Look at how the computer model works, seeing the equations . . .
Download Computer Model	the Water Rocket Computer Model. Click Here to read the readme.txt file (29,734 bytes). Note that this is a text file so you will need to use your Back button on your browser to get back here. Click Here to take you to the Water Rocket Computer Model download page. Over 10,000 downloads wrcm.zip 255,756 Bytes MD5 hash = 0aa7c85e9469a321f0958932e19ced18 (Note . . . the hash and the file are on two different servers). Requirements - PC (or Power Mac) with VGA graphics or higher that will run DOS directly or under Microsoft Windows 95/98/2000 Licensing - This program is Postcardware - If you continue to use it, you send me a picture postcard of somewhere close to where you live (not money). Details in the readme.txt file
WRCM 3D Optimisation Palette Editor v1.10 Updated 16th September 2001
Details	Click Here for Details of the Water Rocket Computer Model Palette Editor, including screen shots.
Download Palette Editor	the Water Rocket Computer Model Palette Editor (for version 4.40 or higher of the WRCM). Use this program to individualise the palettes in the 3D Optimisation of the computer model. Click Here to read the readpal.txt file (7,595 bytes) giving details of the Palette editor. Note that this is a text file so you will need to use your Back button on your browser to get back here. Click Here to take you to the Water Rocket Computer Model Palette Editor download page. Over 800 downloads wrcmpal.zip 155,082 Bytes MD5 hash = 5627d6eaca51291cfede3f23804f61bb (Note . . . the hash and the file are on two different servers). Requirements - PC (or Power Mac) with VGA graphics or higher that will run DOS directly or under Microsoft Windows 95/98/2000; Water Rocket Computer Model Version 4.40 or higher
Download More Palette Files	more Palette Files. Another 18 Files - Rainbow Colours - 9 optimised for black background and 9 for White background Click Here to download them. palspack.zip (3,632 Bytes)
Download More Palette Files	and more Palette Files. Another 10 Files - Fruity colours - 5 apple, 5 grape. Click Here to download them. fruitpal.zip (1,866 Bytes)
Download Icon Files	the Icon Files. These allow you to use different icons on your desktop for the computer model, palette editor and help pages. They are standard ICON files and have transparent backgrounds as shown below. Download them all (all three that is) as a zip file wricons.zip (1,259 bytes) or individually (in IE, Right Click and Save Target As) Transparent icon on example ... light med dark backgrounds (ico files can be displayed on any background) Rocket.ico for the computer model, WrHelp.ico for the HTML help files and WrPalEd.ico for the Palette Editor. They are all 32 x 32 pixel, 16 colour icons (766 bytes long) that look okay in the smaller size as used in the Start Menu. When you create a shortcut, you can edit the icon used by the short cut, using the icon file that you have downloaded.
Explain	For fun (or to see if you understand some of the principles of computer modelling), you can look at (and possibly explain) some curious model output. Look at Problem Pages
Download More Palette Files	the Problem Files for you to look at on your own computer thus saving you the trouble of typing in the values. Dowmload all eight as a single zip file wrprobs.zip (2,363 bytes) (in IE, Right Click and Save Target As)

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