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| Velocity and Action Time Matching |
PT Expansion includes a matching algorithm. Given measured Chamber Pressure data, the matching algorithm adjusts four parameters, within limits specified by the user, to fine tune the results to match the measured muzzle velocity and/or action time. The four parameters are:
The first two parameters allow adjustment of the assumptions used in the IB analysis. Resistance pressure is calculated based on empirical relationships and can vary by a significant margin. The Base Pressure Factor is a constant used in the Otto Heiny model for projectile base pressure. It is related to caliber and velocity but like resistance pressure is not known with precision for a specific design. More information on this constant can be found in the PRODAS Technical Manual. These two factors are ideal candidates to help match muzzle velocity and action time as determined by the PT Expansion analysis with the observed test data.
The Chamber Pressure Factor and Offset can also be used as adjustments. The Factor is simply that - each value in the chamber pressure vs. time data is multiplied by this constant. The offset allows the entire curve to be shifted up or down by a constant value. These two variables can be viewed as correcting for inaccuracy in the chamber pressure instrumentation.
| © 2002 Arrow Tech Associates |