Water Rocket Computer Model Details
Something that you have always wanted.

Right click and Zoom In to see better.Version 4.41 has a few improvements such as dart launches, easier editing and it now has optional launch tube (hollow with a specified empty length), T-nozzle, parachute (with deployment at apogee or timed from the launch) and air impulse.

In addition to this, there is context sensitive help (shown on the left with a tip on how to measure the diameter of your rocket) and tips on reasonable values such as coefficient of drag and so on. If you are using the Novice option, there is even a wizard that allows the meaningful input of data - especially useful for young students.

Further, the model is faster as it does not write the data file to disc but stores information taken at regular intervals in memory. This recording time slice can be altered as can the runaway-limit on the model - making a small recording-time-slice and short model-run allows the study of the first few seconds of the flight. You can now print out a full report on the rocket from input parameters, model settings and results

It is shown here, running in a DOS box under Windows 95 - choose a font size that suites you or run it full screen by pressing [Alt][Enter]. (It is shown here with a 4 x 6 font to keep the image small. I would recommend at least 6 x 8 although 8 x 12 is preferable.)

Right click and Zoom In to see better.In addition to the 'expert' version, you can opt to use a simplified 'novice' version to get to know the basics of the model without having too many parameters to change. Once you have familiarised yourself with it, go onto the expert version where you will be able to change more variables.

At the very beginning of the model, you are offered a choice of units for height in feet or metres and pressure in psi or Bar. The files that are saved are all in SI so you will be able to exchange these regardless of units selected.

Right click and Zoom In to see better.Once the calculation has been made, you have the option of quick graphs, including statistics, and graphs of height, velocity and acceleration against time.

The quick graphs all use the standard text display (shown on the left) and should work on any computer therefore users will not find themselves without any graphs should their machine not have the correct display.

The graphs of Height, Velocity and Accelerations against time all use colours to denote periods of launch tube, water thrust, air impulse, coasting, chute opening and full deployment.

Right click and Zoom In to see better.In addition, a table of statistics can be displayed showing most of the numbers that rocketeers should be interested in when testing in this way (it is impossible to please everyone though).
Right click and Zoom In to see better.Further to the quick graphs are the graphs using the VGA display (keeping it down to just VGA should include most people).

On the screen shot on the left, you can see that the X axis does not have to represent time but can, instead, represent any of the variables so, should you be inclined so, you can have a graph of Height against Drag or Velocity against Acceleration.

This is a plot of height against velocity - such a graph giving the optimum time and details for calculating a second stage deployment.

You can select a black or a white coloured background - white resulting in less ink use when printing out from the screen.

If your rocket travels a significant distance downrange, you can choose to see it with the horizontal and vertical scales the same. Also, you can click on Play to get the computer to move the cursor along the line in real time.
Right click and Zoom In to see better.The program includes a 3 dimensional graph plot which calculates an output result (such as maximum height, velocity, acceleration, time to apogee or flight time) against two input variables such as mass of empty rocket and diameter of nozzle. If you are using a launch tube, you can vary the length of this as well and if it is a hollow tube, the length of the empty part of the tube may be specified as remaining the same length (such as if you were using a T-nozzle and had small holes in the launch tube), the same proportion (such as if you filled the rocket using the launch tube and you only managed to blow a certain proportion of the water out when pressurising the rocket) or a fixed filled part (such as if you had a particular launcher that you could put various lengths of launch tube onto).
The number of points along each axis may be specified (between 1 and 31 - 1 if you are interested only in optimising against one input parameter) and if you are only looking at something that happens early on in the flight such as maximum velocity, you can specify a short model run time to make filling the points quicker. Another trick to speeding up the process is to select a longer model calculation interval - selecting 10ms will make the model 10 times faster with granularity showing only in time to apogee. The graph on the left shows Maximum Height (z axis) plotted against Mass of Water (y axis) and T-Nozzle Diameter (x axis). This shows the best fill and T-Nozzle diameter.

The distribution of the colours on the graph may be changed by clicking the mouse on the colour scale on the right - moving this up will make the upper colours represent a narrower range and so on. Doing this allows you to see how well you can optimise your flight.

When using a hollow launch tube, the length of empty tube may be specified on the main model sheet in the main values above. On the 3 dimensional graph values form, you can specify whether you want the model to consider the hollow part of the launch tube in terms of a fixed measurement of space (10cm empty of a variable length tube - specified on the main variables form as a 20cm tube),   Fixed space used for tubes in rockets that are filled slowly - ie, only have a certain volume of air in the water
a proportional measurement of space (50% empty) or,   Proportional spaced tubes used for tubes in rockets that are pressurised quickly so that a fixed proportion of the tube is air with the rest water.
a fixed measurement of filled launch tube (10cm of the tube is not empty ie 20cm - 10cm). Each of these three senarios have a different role to play and the computer model can match these.   Fixed fill tubes used for tubes with a fixed portion filled by, say, a T-nozzle support or an adaptor - something that occupies the same volume regardless of the length of the tube, or tubes that are always dry - ie, compressed air only.
In addition to this, you may elect to view the graph row by row or column by column so as to produce a graph that shows, say, the optimum mass of water for each given T-nozzle diameter as in the graph on the left.

Selecting Fill whilst the graph is split in this way will fill just one row or column.

Version 4.41 includes an automatic Search Cursor to let you know what you are doing.search that will locate the maximum in the current graph for you without having to calculate all of the points - only needing to calculate around 5% of points on a 31 x 31 plot and doing that many times quicker than by hand.

It starts where you click the mouse and then finds a direction of increasing output parameter and follows it until it finds that it starts to decrease and then changes direction again - click here to explain this graph and other curious looking phenomenakeeping on doing this until it has located a maximum. It is able to do this many times quicker than doing it manually because it looks at the numbers rather than the colours.

Plots of Maximum height, velocity, acceleration and so on may be viewed simply by pressing keys to switch between plots without recalculating all of the points.

There are limitations to automatic searches in that where there is more than one maximum, the search may find the wrong one. The graph on the right is of rocket weight and water weight with flight time as the output parameter. For a really lightweight rocket, the thrust pushes the rocket up into the air which then floats to earth (not having much weight to pull it through the viscous air :-).

Version 4.41 allows you to look at chute deployment times showing some interesting results as in the screen shot on the left which is of flight time plotted against deployment time (Y axis) and mass of water (X axis). This is with a 4 metre chute opening delay (the distance that it takes for the chute to open fully from the point of release).

Pressing [A]dopt and then clicking on a point will put the x and y values back into the input parameters form and the 3D form and allow you to optimise two other variables thus speeding up the optimisation process even more.

Pressing [SpaceBar] will change the colour set to one of those on the right.

Version 4.41 introduces a 2 stage optimisation which you can use to make sustainer and booster files interact for maximum height or range. This includes crushing sleeve and expanding tube release mechanisms. Files can be optimised or simply ran as a two stage rocket.


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