Gas Gun Design Tool

Hall Consulting's Gas Gun Design Tool is a simulation program to aid the design of pneumatic cannons. It is available here.

Physics model

As of version 4.2, in modeled the following features:

1. Valve configuration and opening times. In fact, GGDT models five different types of valve: chamber sealing pilot (see piston valves), barrel sealing pilot (ie, barrel sealing diaphragm valves and piston valves, burst disk, hammer valve, and "generic." Each of these valves have different behaviors and GGDT accounts for these behaviors (more on that below).
2. Pressure drop across the valve orifice.
3. Temperature (and thus pressure) increase in the valve pilot due to work performed by gun gases on the valve piston/diaphragm.
4. Gas leakage from the main valve body into the upper valve chamber (pilot).
5. Performance differences due to different gases.
6. Temperature effects on gas properties (and thus, performance).
7. Performance limitations due to flow choking in the valve or the barrel.
8. Valve effective orifice increases due to lowered valve throat Mach number.
9. Temperature (and thus pressure) drop in the barrel due to work performed by the gas accelerating the projectile.
10. Gas leakage around the projectile in the barrel.
11. Compressibility (Mach) effects on air pressure both in front of and behind the projectile to include the creation of shocks. (see shock heating)

However, it does not consider:

1. Energy losses associated with turbulence or frictional forces between the gas and the gun's reservoir/barrel walls. In other words, pressure drops due to bends or rough edges in the gun's plumbing.
2. Reservoir fineness ratio's effect on performance.
3. Freezing or liquification of gun gases.

However, these are not a major concern in most launchers, as they require very long barrels or very high pressures to notice. Typically, the GGDT outputs numbers within 5-10% of the measured value, although this is somewhat clouded by not knowing the proper input numbers.

Use

See Hall's page on use

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