For motor eject as a backup, you want the adjusted delay to be about two
seconds past what you expect your apogee to be, so if it's a bit short it
shouldn't be a problem. Motor delays almost never run long. If your
projected time to apogee is 14 seconds and your maximum delay is 15 seconds,
that's a bit close... don't be surprised if the motor eject happens before the
altimeter fires.
Eggtimer Cris
________________________________
From: roc-chat-bounce@xxxxxxxxxxxxx <roc-chat-bounce@xxxxxxxxxxxxx> on behalf
of Terry McKiernan <terry@xxxxxxxxxxxxx>
Sent: Tuesday, July 16, 2019 7:57 AM
To: roc-chat@xxxxxxxxxxxxx <roc-chat@xxxxxxxxxxxxx>
Subject: [roc-chat] using motor ejection charge as backup?
Polling the ROC crowd for opinions here ... I'm wondering if it's
recommended to use a motor ejection charge as a backup to the altimeter
on high-power flights.
Specifically this Saturday I'll be flying my Firestorm 54 "stretch" on a
CIT J360 Skidmark. It has a Raven3 altimeter to fire the drogue and
main ejection charges. I'm wondering if I should leave the J360's
charge in place as a backup to fire the drogue just in case.
The OpenRocket sim says time to apogee after motor burnout is 14.8. The
J360 conveniently comes with a 15-second delay grain. So that seems
about perfect as a backup.
My concern is that OpenRocket sims are just sims after all, and may not
be very accurate. Plus delay grains are not very high-precision
either. I'm mostly worried about the flight being longer to apogee than
the sims says, and the delay grain burning through faster than expected,
and thus releasing the drogue a few seconds before apogee while the
rocket is still moving pretty fast.
What do you think? Leave the motor charge in as a backup, or avoid it
due to the possibility of early ejection, and just count on the Raven to
do its thing?
Thanks!
Terry
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