Backup altimeter delay

New to dual altimeter setups and it was suggested to add a 1 second delay to my backup altimeter apogee event. I thought I would post this thread and see what others are doing as well.

If it matters there are two rockets I will be launching with this config.

One I have already launched twice with a 1 sec delay but the main worked fine so the delay was never tested. It is a 54mm min diameter rocket that I will be launching to 17K @ Mach 1.1

The other is new and a 3” build that will hit 14K @ Mach 1.3

If there is anything else that I should take into consideration please let me know. It would be good to know if the delay should change based on the flight profile?

I think the delay is fine, and I have done it. The reality though is that it is unlikely that your altimeters would fire simultaneously.

If you use two altimeters with the same electronics and algorithms (such as a TeleMetrum and TeleMega), then it's not at all impossible for them to detect apogee at nearly the same time, within the data sampling interval. I always use a short delay between the primary and backup as a result, and I use a significantly larger backup charge as well; if the airframe has separated, the larger charge will be harmless, and if it hasn't, then the larger charge may do the trick.

Most altimeters have an "apogee +1" setting, and same for mains. You want both charges to fire at apogee, and both at your mains altitude--but not at exactly the same time (or else you are doubling your charge amount).

Though some/many don't suggest using the same altimeters in 2 altimeter setups, I use PerfectFlite's Stratologger CFs in a twin configuration for redundancy and have no problems with them. In fact, Stratologgers have worked well for me in the year or so I've been using them with some 30-35 flights with them.

Like Keithp, I boost the backup charges (by about 50%) to be sure I'm going to get the desired separation at the desired time. My main charges (AV Bay is in about the center of the rockets I fly) are about twice the size of the drogue charges, again with the backup charge being about 50% larger than the primary charge.

In the 4" rocket pictured in my posts, which flies to about 8000' on a mid-K motor, I use .5g/1g in the drogue charge wells and .8g/1.5g in the main charge wells. All flights 100% successful to date...

For what it's worth, I also use dual igniters in each charge well (be sure your altimeter is capable of firing more than one at a time) in case one is bad. It's cheap insurance.