Hi Dave,

Ok, it sounds like you are talking about problems
associated with using these systems for parachute
ejection. I thought you meant there were significant
problems with using accelerometer-based altimeters for
simple rocket altitude logging. If the rocket launch
fails in that way, I would hardly expect accurate
altitude data :-)

I just thought of another thing that you (or someone
else on the list) might be knowledgeable about: my
altimeter contains one crystal and one ceramic
resonator. Considering the mass and thrust of my
rocket, it should experience a peak acceleration of
about 14 G. Would this damage either the xtal or
resonator?

Thanks,

Sean


You wrote:

You can read acceleration pretty easily.
SRB's are noisy, but integration solves that.
Accelerometers will show the engine burn and coast
characteristics pretty
well, but they have no idea which way is up.
Unfortunately, it's not
uncommon, especially during a problem launch, for the
airframe to be
horizontal at burnout, doing mach at 6' altitude.  You
can have this happen
due to booster failure, fin failure, weathercocking, or
a shear layer.


If we factor out the at-rest acceleration of gravity,
what you expect is a
large acceleration, transiting to a surprisingly large
negative
acceleration at burnout, which decays during coast to
near zero. If the
flight is mostly horizontal, that zero doesn't occur!


One sensor that does not get fooled about "up"
and "down" is a three axis
magnetometer.
At launch, you back up in the data till just before
launch, and call that
vector "up" (or rotate it till it's conveniently 0,0,0)


Aluminum launch rod highly recommended!


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