ihbarddx
Well-Known Member
So you have a single axis accelerometer/barometric altimeter recording flight computer and, though the launch was vertical, the flight wasn’t perfectly vertical. Barometric and inertial altitude curves are close but don’t match exactly. Here are some good approximate corrections you can do on the vendor numbers from the accelerometer.
DISCLAIMER: In a vertical launch, there is no valid reason that the barometric altitude should noticeably exceed the inertial altitude. If this occurs, maybe it was very cold and the barometric data are not temperature-adjusted. Always temperature-adjust data. Otherwise, the instrument is no good. Really. In my experience, it’s an accelerometer that has a nonlinear response – data for entertainment only. (Not mentioning brand names…)
Barometric data normally have anomalies near launch and in high-speed regions.
The approximating assumption used is that the work done by thrust and drag in the true trajectory is about the same as that done in the trajectory rendered by the vendor software. There are “exact” formulas, but they propagate noise more than these formulas do.
DISCLAIMER: In a vertical launch, there is no valid reason that the barometric altitude should noticeably exceed the inertial altitude. If this occurs, maybe it was very cold and the barometric data are not temperature-adjusted. Always temperature-adjust data. Otherwise, the instrument is no good. Really. In my experience, it’s an accelerometer that has a nonlinear response – data for entertainment only. (Not mentioning brand names…)
Barometric data normally have anomalies near launch and in high-speed regions.
The approximating assumption used is that the work done by thrust and drag in the true trajectory is about the same as that done in the trajectory rendered by the vendor software. There are “exact” formulas, but they propagate noise more than these formulas do.
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