Hall Consulting's
Hybrid Gun Design Tool

Main Window Input

The main window of HGDT is horizontally divided in two regions. The upper portion contains all user gun-specific imulation input. The lower portion contains all simulation output. Obviously, this page is concerned with the upper portion.

This is nothing more than a place for the user to put any special comments about the gun design. The name of the gun? The revision number? The telephone number to that cute girl across the street? It simply doesn't matter.

Chamber -> Insulation
This input has to do with the heat transfer from the gases in the chamber to the chamber walls. I'll skip the BS and just put it to you this way: For a metalic chamber, use "none." For a plastic chamber, use "insulated." To see what is possible in theory (but never in reality), use "adiabatic."

Chamber -> Diameter
HGDT assumes that the combustion chamber is cylindrical. The diamater is... the diameter of the cylinder. Maybe?

Chamber -> Length
The length of the right cylinder that defines the chamber volume.

Chamber -> Volume
The volume of the right cylinder that defines the chamber.

Chamber -> C:B Ratio
The ratio of the volume of the chamber to the voluem of the barrel.

Chamber Fan -> Diameter
Many in the spud gun community use fans in the combustion chamber to introduce turbulance and thereby increase flame propogation rates. This input corresponds to the diameter of such a fan (if it's used). Note that as of this typing, this input is not actually used in any calculations; it is merely a place holder for more advanced algorithms in the future.

Chamber Fan -> Flow
The flow rate of the chamber fan. If no chamber fan is installed in the gun, then use 0. Note that 20-25 cfm is a decent ballpark for the surplus cooling fans that most spudders use.

Transition -> Profile
If the transition from your chamber to your barrel is smoothly contoured, selected "countoured." If not, select "blunt." For most guns it doesn't really matter, but for some it will.

Transition -> Disc Failure
The puressure at which your burst disc fails. Note that those wishing to model simple combustion guns should use 0.

Transition -> Diameter
The diameter of the oriface opened when the burst disc fails.

Load/Mix -> Propellant
Nothing more than the choice of fuel for this gun. Current options are butane, MAPP gas, and propane.

Load/Mix -> Mix
HGDT assumes a stoichiometric mix of fuel and air (equiv. ratio of 1.0). The "mix" is the number of standard atmospheres (pressure) that the fuel/air mix is under in the chamber. In other words, a 1x mix is at 14.7 psia, a 2x mix is at 29.4 psia, etc.

Igniter -> Number
The number of spark gaps employed in the design. Note: HGDT uses a very simple combustion model. It does not account for many nuances in igniter type and placement. Suffice to say that two closely spaced gaps should be input as one. The user should only list multiple gaps if those gaps are separated by a significant distance in the design.

Barrel -> Bore
The inner diameter of the gun's barrel. Duh. Actually, I shouldn't say that. If you are attempting to model something akin to an Airburst Rocket you'll want to use the outer diameter, but now I'm getting into some pretty advanced stuff that's probably gonna confuse a lot of you so perhaps I should have just stopped at the first sentence?

Barrel -> Length
The length of the gun's barrel. Duh. Actually, I shouldn't say that. If you are attempting to model something akin to an Airburst Rocket you'll want to use twice the length, but now I'm getting into some advanced stuff and.... Well, you know.

Projectile -> Friction
Most projectiles will experience some friction in the barrel. As the reader may imagine, this variable defines frictional forces in the simulation. However, it should be noted that this value is NOT the coefficient of friction that many with physics training may expect to see. Such data can be difficult or impossible to obtain. Instead, HGDT uses a more practical approach to friction; that of equivelent pressure. Place your projectile in your barrel and begin to pressurize the breech. At what pressure does the projectile first begin to move at? Whatever that pressure is, put it in the blank! (Note: Human lungs can produce about 2 psi. If you can use the barrel like a blowgun and get the projectile to move....)

Projectile -> Mass
I've nothing cute to say here. 'Tis nothing more exotic than the projectile mass.

Projectile -> Diameter
Again, nothing fancy. This defines the projectile's outer diameter.

Projectile -> Init Position
Not all guns operate with the projectile flush with the barrel breech. Some guns require that the projectile be at a non-zero position in the barrel. Use your imagination and do what you think is right.

Compute Performance
When you've got all your input data to your satisfaction, push this button and HGDT will do it's thing! Be patient though. HGDT takes a fair amount of CPU cycles. It may take a few seconds for it to return with it's answer.

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