EVBEC v1.5
 Energy & Volume Based Estimator for Combustions
 Instructions & Documentation

1: Introduction (background information)
2: Use instructions
3: inner workings
4: limmitations
5: Version history
6: Credits

1: Introduction:
EVBEC is based on Burnt latke's chamber:barrel test data.
 Accuracy of predictions has not been recorded, and data to verify it's predictions would be nice.
 The arthor can be contacted at dylan.foltz@gmail.com
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2: Use intructions:
To use EVBEC for a COMBUSTION SPUDGUN, you simply enter your projectile mass, 
  the dimentions of your chamber and barrel, and the atmopheric pressure (if you don't know it, use 14.7).
  It is important that you enter your chamber and barrel dimentions in ONLY ONE of these places:

  *In the boxes near the top. These are used if you know the volume of your chamber or barrel.
    Data should be entered directly below the bold font, to the left of the "inch^3".
    I'v included a volume calculator. Simply enter the data in the top 2 cells, to the left of the "in",
    and copy-paste the result into the input box.
    If using "volume ratio" or "length ratio", set cells C4 and F5 to zero.

  *In the "Volume ratio (ci)" row. I'm not sure what use this is, but it's there anyway.
    Total value is the volume of your chamber and barrel in cubic inches.
    If using the top boxes or "length ratio", set cell C14 to zero.

  *In the "Length ratio (in)" row. This is usefull if optimizing your gun for the most power/length.
    Total value is the length of the launcher in inches, chamber  is the diameter of the chamber, 
    barrel  is the diameter of the barrel. 
    (With ratios adjusting the values will shorten one and lengthen the other;
    a 2:1 ratio is a chamber twice the length of the barrel.)
    If using the top boxes or "volume ratio", set cell C15 to zero.

Once the data has been entered, look in the output section. There will be a vertical line - 
  this shows the current ratio. Note that the graph is configured as barrel length
  (B:C ratio) rather than the typical C:B ratio. If you are interested in your C:B ratio,
  look above the graph on the left; there will be a cell labeled "current ratio", which is the C:B ratio.

To use EVBEC for a HYBRID SPUDGUN, enter the above data plus the pre-ignition chamber pressure ("interior pressure").
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3: inner workings:

EVBEC V1.5 is mostly volume based; it does not consider the shape (length, width) of the barrel or chamber,
 except when considering the effective mass of the gas flows.

It does it's calculations in two distinct steps: (you can veiw the acctual calculations on sheet 2)

1) Adjusting the latke test velocities to account for the pressures you specified.
This is done by calculating the energy of the projectile, adding the energy required to
  purge the barrel of air at 14.7 psia, multiplying this sum by the interior pressure in atmospheres,
  subtracting the energy required to purge the barrel of air at the pressure you specified,
  then turning this energy back into a velocity.
  sqrt( (("latkeMass"*"LatkeVelocity"^2)+("barrel volume"*"constant")) * ("interior pressure") - ("barrel volume"*"exterior pressure"))

2) Secondly, it adjusts the velocity of the projectile at a certain ratio so that it's energy is
 porportional to the ratio in chamber sizes; 
 sqrt(("LatkeChamberVol"/"specifiedChamberVol")*("LatkeProjectileMass"/"SpecifiedMass"))

The masses (both of them) include the masses of the gasses involved - chamber flow, barrel propellent flow,
 and barrel atmospheric gas flow. These are calculated through rather complex formulas (contact me if you want more info).

It then tells you the ratio of your launcher so that you can look up the relevent datapoint on the graph on page 1.
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3: limmitations:

EVBEC does not take into account:
 *The burn time of the propellent
 *Flow issues in the pipe
 *Cooling of the propellent gasses
 *Blowby in the barrel

As such, it's accuracy will degrade if you try to model:
 *very light, high velocity projectiles
 *Very heavy, long dwell time projectiles
 *Lose fitting projectiles
 *very short barrels
 *VERY long barrels

...in short, your system should be as close as possible to Latke's test system:
  *for 1.5 and 2.5" data, a 4" chamber with a volume of ~3 liters, 3 spark gaps, metered propane and a chamber fan.
  *for 3/4" data, a 2" chamber with a volume of 360 ml, 2 spark gaps, metered propane and a chamber fan.
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5: Version history:
v1.0 - First release.
v1.1 - Jimmy's mod; added vertical line on graph, changed graph to xy plot, merged graphs.
v1.2 - Revised density data (1.1g/ml) for potatoes changed the 1.5" results.
v1.3 - Flopped graph around to focus on relevent domain, added "projectile data" calculations.
V1.4 - Added support for hybrid spudguns. (tennative and untested in the extreame)
V1.5 - Added modling of the gasses involved. (uncertain accuracy, but almost certainly better than V1.4)
V1.6 - Chris's mod, revised user interface.

inquire at dylan.foltz@gmail.com if you want an old version.
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6:Credits:
BoilingLeadBath of the spudtech, spudfiles forums - arthor
Latke at www.BurntLatke.com - information donor
Jimmy of the spudtech forums - graphs (see v1.1 under version history)
Chris Keiser - user interface (see V1.6 under version history)
Benstern & Gort of the spudtech forums, for bringing to light my flawed asumption of potatoe density
The International Starch Institute, for having a usefull density graph for potatoes. 
microsoft - creators of excel