CALM

Compressed Air Launcher Modelling Program

by AKBiocca

 comcast.net

The CALM modelling software works by computing the amount of air that passes through the valve every 100 microseconds, subtracting the from the pressure chamber and adding it to the bore. The force on the (tennis ball) Projectile is computed, the net acceleration, velocity, and new position. New pressures are computed for the bore and chamber. This is repeated until the ball leaves the bore. This allows us to see what is happening in some detail.

The CALM program is written in the Python language, and is in source code format, so you can see how it works and even make changes.

CALM is available at http://www.qsl.net/wb6zqz/calm.html

CALM Example

example launcher webpage at: http://www.qsl.net/wb6zqz/csv19/index.html

Computer Modelled Launcher Performance*

CSV-19 Compact Sprinkler Valve 19 inch Launcher

system Cv 5.0 Ballwt 4.0 ounces

chp oal chl bbl  fps   sec  xbp  xcp  ht tofl

 30  19   8  14   79 0.020  0.2 20.5  76  4.4
 40  19   8  14  105 0.017  1.3 29.7 117  5.4
 50  19   8  14  123 0.015  2.5 38.8 146  6.0
 60  19   8  14  138 0.014  3.7 48.0 168  6.5
 70  19   8  14  151 0.013  4.8 57.1 188  6.9
 80  19   8  14  162 0.013  5.9 66.3 205  7.2

Cv = system flow coefficient, gpm per psi
chp = chamber pressure in psi
oal = overall length inches
chl = chamber length
bbl = barrel length
fps = velocity feet per second
sec = barrel time in seconds
xbp = exit bore pressure
xcp = exit chamber pressure
ht = peak trajectory height in feet
tofl = time of flight in seconds

* note that these performance numbers are uncalibrated and subject to change 
based on measurements with your own launcher. The Cv value can be adjusted to 
fit your specific results. They seem to be quite close to the Dacron line 
measurement, however measurements with new synthetic line were somewhat higher.