User`s manual

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since aerodynamic effects may compromise the accuracy of the pressure-derived altitude
reading. Zeroes in these fields means that CHB didn’t fire, either because it wasn’t enabled or
because the conditions to fire CHB weren’t met (i.e. Airstart Delay expired after Nose-Over).
I Burn Timer <1-20>
The Burn Timer is used to indicate to the Eggtimer what the burn time of your motor is. It is
used to arm an airstart ignition on Channel B, and is also used to start the velocity profile testing
in order to prevent premature parachute deployments during high speed flights. The burn timer
begins when the LDA is reached and expires after the selected number of seconds have elapsed
from LDA. Technically, of course, the motor starts burning some time before reaching LDA
while the rocket is on the pad, but for our purposes this is accurate enough since the time from
ignition to LDA is typically one second or less.
In general, the Burn Timer value should be set to the rounded-up burn value of your motor. For
example, if your motor burns for 2.4 seconds, you should set the burn timer to 3 seconds. If your
rocket will be approaching supersonic speeds, we recommend that you never set this value less
than the actual burn time of your motor.
Expiration of the Burn Timer and the altitude at the expiration of the Burn Timer are recorded in
the Flight Summary memory for downloading.
J Airstart Delay <0-9>
The Airstart Delay is used ensure that the second stage igniter doesn’t fire until the first stage
motor has burned out. Used in conjunction with the Burn Timer, it allows you to delay the
ignition of the second stage motor by 1-9 seconds, or have it fire when the first stage motor burns
out (0 seconds). It has no effect if the CHB Enable setting is not 4 (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 fires (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.