User`s manual

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really high value (over 15°). If the pressure ports in your payload bay aren’t sized properly, this
can introduce an error, particularly if they’re too big and you have two of them opposite each other
(you’ll get a crossflow through the payload bay which makes the pressure readings very noisy).
Finally, differences in the processor’s timing may introduce errors, although the readings are taking
at relatively precise intervals so it’s going to be very small.
The good news is that the magnitude of these errors tend to be proportionate to velocity as the rocket
ascends, so they respond well to being filtered with mathematical noise filters. We use a variation of
a Kalman filter to smooth out this “noise”, so burnout and transition to supersonic speeds and back
can be detected with relatively good accuracy.
As the samples are taken, maximum values for altitude and velocity are logged, at the rate
determined by the Burn/Coast samples/sec setting.
Mach Transition…
As your motor continues to burn and the velocity increases, if the velocity exceeds 800 ft/sec
aerodynamic shock wave buildup can fool the pressure sensor into thinking that the rocket is
descending when in fact it is actually ascending at a rather rapid speed. If this were not taken into
account, the flight computer might deploy parachutes at near-mach speed, which would undoubtedly
break something and ruin your day, not to mention what an object falling from the sky at these
speeds could do.
To prevent this from happening, the Eggtimer uses a predictive mechanism to hold off deployments
until it’s safely out of the mach “danger zone”. Real-time altitude readings are run through a
Kalman filter, which “smooths” the noise from the pressure readings. The smoothed readings
produce a much gentler velocity profile, which allows it to be used to obtain reasonably accurate
velocity samples. If the velocity reaches 500 ft/sec, it is assumed that the rocket may reach Mach
speeds, and deployments are inhibited so that the sudden pressure spike (and perceived loss of
altitude) does not result in a premature deployment. When the velocity drops below 100 ft/sec
(presumably near apogee) for at least 1 second, deployments are enabled.
Note that if Channel B is configured in Airstart mode, it WILL fire the igniter during mach
transition. Once your rocket hits LDA, airstarts are under the control of the timers and are not
dependent on altitude readings. It is assumed that you have modeled the flight and appropriately set
the timers, so if you do NOT want the second stage to fire during mach transition you must set the
Airstart Delay to a higher value so that the rocket will coast for a longer period of time.
Apogee and Nose-Over
Assuming that your rocket is moving more or less straight up, it will continue to slow down during
the coast phase until it gets as high as it’s going to go. If the rocket was going absolutely straight up,
the velocity at this point would be zero; it would simply start falling to the ground. In reality, this
almost never happens, because you usually angle the rod/rail at a slight angle so that the rocket takes
off away from the flight line. This results in the velocity disparity that we’ve previously mentioned.
The rocket usually has some forward velocity at apogee; hopefully it’s relatively small so your
parachute deployment happens at a low velocity and won’t cause any mechanical problems like a