Eggtimer Rocketry Eggtimer User Manual page 24

allows you to delay the ignition of the second stage motor by 0.1-9.9 seconds (100-9900 ms), or
have it fire when the first stage motor burns out (0 seconds). It has no effect if the CHB Mode
setting is not 4 or 5 (Airstart mode).
There is a debate in the hobby rocketry community over whether it is "better" to have the second
stage fire as soon as the first stage motor burns out (to achieve maximum velocity) or to hold it
off for a few seconds and have the rocket coast awhile first (to achieve more altitude since there
will be less aerodynamic drag when the motor fires). That's the fun part of rocketry... you're
free to try things for yourself and see how it works!
Some igniters take a significant amount of time to start composite-propellant motors, so this time
must be considered. If your igniter takes about 2 seconds to start the second-stage motor, you
will need to take 2 seconds off the Airstart/Delay value, if you make it zero then the airstart will
be delayed by the time that the igniter takes to fire your motor. Black powder motors (like the
Estes motors) igniter almost instantaneously, so you don't need to worry about it with them.
Note that if the Burn Timer expires during the mach transition phase, the Channel B igniter
WILL fire if Channel B is in airstart mode. Unlike the Main deployment channel, or Channel B
in drogue mode, airstart ignition is not "held off" during mach transition. This is intentional,
because if you have a very fast rocket and you set the Burn Timer and Airstart Delay so that it
fires during supersonic flight the assumption is that you wanted to do this.
Also note that if you set the Airstart/Delay too long (way too long...) and it expires AFTER Low-
Speed detect or Nose-Over is detected, the CHB channel will not fire. This is a safety feature, so
you don't ignite the second stage while it's moving slowly or pointing downward. If you are
using the second stage's motor for drogue or main chute deployment, obviously those
deployments aren't going to happen; if you are using the Eggtimer's Main channel for
deployment, it WILL fire, hopefully saving your rocket so you can try it again later with more
accurate settings.
Airstart firing altitude and time is recorded in Flight Summary memory as CHB, since CHB is
used for airstarts. Zeroes in these fields means that CHB didn't fire, probably because either the
breakwire didn't open up or your delay was too long and Low-Speed/Nose-Over occurred first.
J Airstart/Delay <0-200> [CHB Mode=6]
When CHB Mode is set to 6, this value controls the Delay from the expiration of the Burn Timer
to CHB firing, regardless of any other flight event. This basically emulates the delay grain in a
typical solid fuel model rocket motor, which burns for a given number of seconds after burnout
then triggers the ejection charge. In the case of the Eggtimer, the delay starts at the end of the
Burn Timer, which starts from the last pre-LDA reading <= 5 ft rather than the actual ignition of
the motor. Since most rockets will hit 5 ft within a few hundred milliseconds of ignition, this
error is minimal in most cases..
This value can be up to 200 seconds, so it can also be used to trigger any other timed event; for
example, separating drop-off boosters one second after their burnout (if you set the Burn Timer
to be the value of the boosters rather than the sustainer), or a timed backup for a drogue for those
really high-flying and long-coasting flights.
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