[roc-chat] using motor ejection charge as backup?

  • From: Terry McKiernan <terry@xxxxxxxxxxxxx>
  • To: "roc-chat@xxxxxxxxxxxxx" <roc-chat@xxxxxxxxxxxxx>
  • Date: Tue, 16 Jul 2019 07:57:52 -0700

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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