Airstarts + dual-deploy with single altimeter?

[Spurkey]

I have a Cosmodrome Aerobee Hi kit that I'm using to learn about HPR staging. The booster is small with very little room for electronics so I thought for simplicity I would stick with a single flight computer in the sustainer, say a Blue Raven. There's the potential for the sustainer to hit a few thousand feet so dual-deploy seems like a wise addition, giving 4 charges/igniters:

* booster separation
* sustainer ignition
* apogee/drogue
* main

The problem I'm stuck on is this: with the booster sep and sustainer ignition, two igniters will run down to the aft end of the rocket, no surprise. When it comes time for the drogue to make an appearance, "standard" dual-deploy has the av-bay go with the nose cone, but in this case those two now-burnt igniter wires will hang things up, no? Do people just greatly oversize the drogue charge and hope the igniter wires get cut? Or do people instead use the single-separation-dual-deploy with a Tender Descender or Jolly Logic Chute Release?

Another Or: is it perhaps misguided to stick with a single altimeter, my original thought was that with two altimeters it was double the chance to program something wrong.

 

[Titan II]

Question 1. You do not cut wires. They separate freely.

https://www.rocketryforum.com/threads/how-to-break-wires.177885/#post-2389940
Question 2. Misguided

 

[Rocketclar]

For my sustainer I use an Eggtimer Proton. I set it up for 4 (of the 6) channels. One for a separation charge....I tried several times to get drag separation, but didn't so the sep charge works great. Only takes a little BP. Another channel is for the airstart. I use 2 channels for recovery. One is at apogee and the other is a backup at apogee +1.3 sec. I really like DD, but it's more involved as you found out with the wires. So I use a JLCR. I use 2 altimeters in the booster (Missileworks RRC2+ and an Eggtimer Apogee). Both essentially go off at "apogee" of the booster with one on delay. Again, I use a JLCR for the booster as well.

 

[waltr]

I do like Rocketclar but the 4th channel fires a Cable Cutter that releases the Main chute (like a JLCH would).

Booster is simple motor eject.

 

[cosmodrome]

* booster separation
* sustainer ignition

These are one in the same thing. When the sustainer lights it will push the booster off.

 

[Rocketclar]

Yes, when the sustainer lights with the booster still attached it will push off the booster. However, the ISC/booster can get crispy. Even though I tried several times for drag separation which I didn't get, I had painted the inside of the ISC with high temperature paint and stuffed it full of dog barf and wadding. I got some video of that getting blasted out when the sustainer lit. I've found it much better to use a separation charge before sustainer ignition. I've gotten some video of that....since you can see the exhaust trail below the booster, it looks like it's being held up by that trail.

 

[cosmodrome]

Yes, when the sustainer lights with the booster still attached it will push off the booster. However, the ISC/booster can get crispy.

True. Coating the inside of the booster coupler with fiberglass/epoxy helps. I designed the kit before there where any COTS timers/stagers on the market. My first prototype that I still fly has a capacitor/Mercury switch in the booster covered with fiberglass. (Please don't use this method). Drag separation should not work with this kit as the booster is a smaller diameter than the sustainer.

 

[Jmhepworth]

In my high power two stage rockets, I have used an altimeter in the booster to fire the separation charge, but there is no reason you could not do that from a Blu Raven in the sustainer. I have always lit the sustainer from an altimeter in the sustainer av bay. The wire for the sustainer motor e-match goes through a conduit up to the av bay. I usually put a wrap of that wire around the eye bolt in the av bay so that separation doesn’t stress the altimeter connection. In every instance, the drouge ejection charge broke the wire.

 

[Jmhepworth]

I’ve always used a separation charge. Even though my two stages are all fiberglass, I don’t like the idea of the motor causing the separation.

 

[cerving]

If you use motor eject for the booster stage, you can do that with a single Eggtimer Quasar in the sustainer, AND you get GPS tracking and telemetry too. The booster should be free to slide off the sustainer, so it will either drag-separate (common if the booster is a larger diameter than the sustainer) or the ignition of the sustainer will separate them (like an Estes two-stager).

 

[waltr]

I have done the Motor ignite to separate stages. This did work and surprisingly, no ISC damage. That was with an Eggtimer Quantum (only two outputs) firing ignition & main chute.

This is the minimum required for a 2-stage. An important piece is the main chute deployment controlled by the altimeter. Chute is still deployed even if the sustainer motor never burns. Has happened but all recovered safely.

 

[boatgeek]

Wire separation is noted above. I would suggest using one altimeter for all of your staging stuff, and a second altimeter that's just backup dual deploy if you're not using motor eject for a backup. An Eggtimer Proton + Quark or Quasar + Quark would do the job. If you're more in the mood for commercial altimeters, a Missileworks RRC2+ is a great backup altimeter.

 

[Spurkey]

Question 1. You do not cut wires. They separate freely.

https://www.rocketryforum.com/threads/how-to-break-wires.177885/#post-2389940

Gaaah. "Break wire" is a set of search terms I did not try, thank you very much for that link. I figured there had to be a way to get the wires to pull apart somehow.

 

[Spurkey]

I usually put a wrap of that wire around the eye bolt in the av bay so that separation doesn’t stress the altimeter connection. In every instance, the drouge ejection charge broke the wire.

Interesting idea. Damaging the altimeter as you say was exactly my concern as well, with the sustainer-ignition wire running down the rocket to the motor then back up inside it it would be a competition between the edge of the motor and the terminal block to see what would let go first... Even using a break wire method that many have mentioned, wrapping the altimeter-side portion of the break wire around a solid point like an eyebolt is a good idea.