Graphs are plotted with the x and y axes selected from the Variables part of the form. The variables are either on the Input Parameters form or relate to it. If you have elected not to use a particular part of the model - such as a launch tube - the variables relating to it will not be available for selection. In addition, if you do not select a hollow launch tube, the fill mode (explained below) will not be available.

The variables that are available are:

Mass of Rocket Empty - You will see the optimum mass for whatever output variable you select - weights for horizontal distance are usually heavier than for maximum height;

Nozzle Diameter - With wider rockets, such as those made from pop bottles, the optimum diameter is usually smaller than fully open as the drag force on the rocket comes into play and a longer, slower accent is better;

Launch Tube Diameter - Generally the wider the better although limited to the diameter of the nozzle. This is not available if a launch tube is not selected;

Launch Tube Length - The longer the better up to a point. With smaller diameter bottles and long, effectively solid launch tubes, the launch tube takes up a significant proportion of the capacity of the rocket and the pressure can drop too much so there is a maximum for narrower rockets. This is not available if a launch tube is not selected;

Hollow Launch Tube Fill Mode - With a hollow launch tube, the optimum length will vary with the fill. The model can take this into account by giving you the option of selecting a type of fill for varying the length of the launch tube. This is not available if a hollow launch tube is not selected:

		Fixed Space - Fixed space used for tubes in rockets that are filled slowly - ie, only have a certain volume of air in the water;
		Fixed Proportion - 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; or,
		Fixed Fill - Fixed fill tubes used for tubes with a fixed portion filled by, say, a T-nozzle support or an adapter - something that occupies the same volume regardless of the length of the tube, or tubes that are always dry - ie, compressed air only.
	T-nozzle Diameter - This is the diameter of the hole in the t-nozzle. Needless to say that it cannot exceed the diameter of the bottle's nozzle. This is not available if a launch tube and a t-nozzle are both not selected;
	Mass of Water - There are optimum values for different types of flight - maximum height, downrange distance and so on, depending upon the pressure and the weight of the empty rocket;
	Pressure in Vessel - Higher pressure means better performance but this variable is included so that the graphical output of the model can be used to select optimum values for other parameters such as weight of rocket, mass of water and so on, for use in the field;
	Angle of Elevation - find an optimum launch angle for the downrange distance. This can give surprising results for t-nozzles when the weight becomes close to critical; and,
	Timer Deployment Time - find the optimum time for deployment of the recovery method. This should be a little before apogee dependent upon the distance the rocket needs to travel to deploy the chute fully.

Copyright ©2000 Paul Grosse. All Rights Reserved