Hall Consulting's
Gas Gun Design Tool


Configuration Window

Because different users have different preferences and different projects have different requirements, GGDT allows the user to customize the unit system(s) used for simulation input/output as well as vary the amount of input required in the first place. The configuration screen is accessed through the File pulldown menu. A description of the effects of each option is found below.

Unit System -> Temperature
When selected (checked), GGDT uses Centigrade as the temperature scale for input and output. When not selected, the Fahrenheit scale is used.

Unit System -> Pressure
When selected, GGDT uses bars as the unit of measure for pressure input and output. When not selected, pounds per square inch (guage) are used.

Unit System -> Linear Dimensions
When selected, GGDT users centimeters for all linear dimensions and derrivatives thereof (ie, square centimeters for area, cubic centimeters for volume). When not selected, inches are used instead. Output does, however, vary a small amount. When the input dimensions are centimeters, meters may show up in the output screen. Similarly, feet will show up when inches are the input unit of choice.

Unit System -> Valve Flow Parameter
Nominal valve flow input format is determined by the selection of one of three radio buttons. The three choices are Kv, Cv, and efficiency.

Unit System -> Valve Piston Mass
When selected, GGDT uses grams to define the mass of the piston (for pilot valves, obviously). Otherwise, ounces are used.

Unit System -> Projectile Mass
Another option with three choices (pick one of the radio boxes). The mass of the projectile can be expressed in grams, ounces, or - for those with very light projectiles - grains.


Automation -> Volume by Length
When selected, the user must input the reservoir's length and a volume is calculated. When not selected, the user must input the reservoir's volume and a length is calculated

Automation -> Valve Flow
When selected, the user must input the valve flow coefficient (Cv/Kv/eff). When not selected GGDT simply assumes an efficiency of 35%.

Automation -> Piston Diameter
When selected, the user must input the valve piston diameter. When not selected, GGDT assumes a diameter 1.414 times that of the seal.

Automation -> Piston Mass
When selected, the user must input the valve piston mass. When not selected, GGDT makes a somewhat optimistic, but still reasonable guesstimate based on the piston diameter and the density of PVC.

Automation -> Pilot Volume
When selected, the user must input the valve pilot volume. When not selected, GGDT assumes that the volume is equal to that of a right cylinder of the same diameter as the valve piston and a length 0.275 times the valve seat diameter.

Automation -> Dead Volume
When selected, the user must input the valve dead volume. When not selected, GGDT assumes a reasonable value based on the valve nominal size.

Environmental -> Altitude
Atmospheric conditions (read: pressure and density) have a small but noticable effect on gun performance. At the same time, they have a huge effect on ballistic trajectories. With this in mind, GGDT accepts launch point elevation (above sea level, of course) as an input. The atmospheric model goes up to 90km, so feel free to see what your gun would do if that pesky atmosphere would only get out of the way!


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