Backup deployment charge disable switch

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Chris_H

Well-Known Member
Joined
Sep 13, 2017
Messages
543
Reaction score
106
Does anyone use disable switches for backup deployment charges? If the initial deployment charge works as it should, there is no need for the backup deployment charge to fire.

It seems like it would be pretty easy to install 2 switches in the AV bay which protrude through the AV bay wall, and are held in the 'closed' position by the fact that successful deployment has not yet happened. Thinking of 2 NO SPST switches that, when the AV bay is installed into the booster, give a closed circuit, and are installed in the backup deployment charge circuits. When successful deployment occurs with the main deployment device, the separation occurs, and the switch opens the crcuit, causing the backup charge not to fire by interrupting the backup device deployment current.

While not entirely in line with the KISS principle, it does prevent unnecessary events from happening.

Any thoughts on this?
 
Why? Now you got a live charge to deal with. Sure you can toss it in an ammo box but you'll forget what it was for unless you keep really good records. I've found unused charges (my bad) after I took loaded but not flown rockets apart for winter storage
and I'll be danged, I always forget what charge was what so I go out back, dig a hole, bury them and blow them with a battery. (That way they don't make a real loud BANG and upset the neighbors). Like I said, me bad for tossing the charges on a bench and "forgetting" about them. I'd rather all the charges blow in the rocket when I get to it, then I don't have to contend with them. Just my point of view and I'm a crotchety old man. :wink: Kurt:smile:
 
Seems to me that it introduces additional risks:

1) It's an additional part, that can decrease the reliability of the backup.
2) Altimeters might react in unexpected ways. For example, an Altacc will fire the main immediately, if continuity on the drogue gets lost
3) Rockets will land with live charges. It is possible to unintentionally create an armed rocket by putting the rocket together again, for example for easier transport. If someone else finds your rocket, he will not be aware of this.
4) The switch is likely to be triggered in case of a failure that results in incomplete separation.

Reinhard
 
Last edited:
Agree. I think #4 above is the biggest risk. I’ve seen a lot of successful separations, but the laundry is stuck or too tight. The backup is not just for separation. If everything is out and clear the second charge is a very little incremental wear and tear, since it is wide open and isn’t under much pressure.
 
Over the years I have experienced what "alldigital" discusses.
My nosecone popped off but chute was still hanging in tube. The second charge pushed it out. Had a 'disabling' switch for second charge been employed my rocket would have been toast.

This has happened 3 times over the 15 years...always with 6in. or larger tubes, where the chute did not "plug" the tube & gases were able to go around it and push off the cone. Yes the charge was energetic enough, probably 40ft of the 50ft cord was extended, which normally is perfect. When I experienced this phenomena payload was always horizontal.
The price of a E-match and couple grams BP is just not worth the risk of a more complex than needed recovery design....to me anyhow.
 
Agree. I think #4 above is the biggest risk. I’ve seen a lot of successful separations, but the laundry is stuck or too tight. The backup is not just for separation. If everything is out and clear the second charge is a very little incremental wear and tear, since it is wide open and isn’t under much pressure.

Agree with this, too.
 
The preference from a safety POV is to set off all charges in the air, so when the rocket lands it is entirely safe. Try to aim for this sort of configuration to minimise the possibility of unexploded charges.
 
I wouldn’t disable the backup charge. As others point out sometimes the backup charge helps shake the parachute out. The other thing is that having a second charge go off is a good confirmation that all systems worked as designed and sometimes helps to locate your rocket while it’s still in the air.
I agree that it’s also a safety concern. Better to expend them all in the air than have an unspent charge in your rocket.
Besides that, this would be an unneeded level of complexity which could reduce reliability.


Steve Shannon
 
All answers appreciated. Thank you, all.

No disable for the backup charges!
 
The back up can also be a very useful audible indicator if you happen to loose site of your rocket. Of course that sort of thing NEVER happens to us..... :)
 
The back up can also be a very useful audible indicator if you happen to loose site of your rocket. Of course that sort of thing NEVER happens to us..... :)

The only problem there Gary is the size of the charge. I find a long open tube has a tendency to muffle the charge unless of course the secondary is on the
apogee bulkhead out in the breeze. But then if the rocket is at 20k, might not hear the backup "blow'in in the wind".:wink::smile: Kurt
 
Back
Top