Electronic ejection with no electronics bay - location of BP

[2-0turbo]

Hey guys, getting back into rocketry after a couple decade absence. Electronic ejection didn't exist when I last flew rockets. I have several of my old kits and had a couple questions on electronic ejection for "single tube" rockets like an old Loc Graduator or Minnie Magg. If I wanted to do electronic ejection at apogee (single chute full open, or reefed with a JLCR), where do I have to put the charge? Can I modify my nosecone and have a BP charge there to blow the nose cone off? Of do I need to run the leads down near the top of the motor so the BP charge pushes everything out? Sounds like the latter, but I can't seem to find much guidance on this. If I look at where the expanding gas is "working," it makes sense to put it down low underneath all the laundry I want to get out of the tube.

For folks that do single or dual deploy, is is customary to put the charge up at the top (near the nosecone or ebay if you've got one) and just have it fire from there? Downward? I realize that the BP just creates over-pressure and will for sure blow the nosecone off, but it might push the chute the opposite direction I want it to go. Thanks.

 

[tsmith1315]

Can I modify my nosecone and have a BP charge there to blow the nose cone off?

Yep.

Of do I need to run the leads down near the top of the motor so the BP charge pushes everything out?

The charge pressurizes the airframe to separate it, not really a situation of pushing anything out unless you use a piston.

The shock cord pulls everything out as the two ends of the rocket move apart.

 

[cvanc]

Yeah it's not so much where as how much. You need enough pressure to pop the nose, then the wind finishes the job for you.

But to pass along a technique, some folks make "remote charges" on a long wire out of a fingertip snipped from a latex glove. Add BP & a match, seal it up tight so it has to fight its way out, and you can then place the electronics and the charge any distance from each other you wish.

Have fun!

 

[kjhambrick]

While I can't disagree with @tsmith1315 or @cvanc, I've always been a 'pusher man' ...

Probably because I started with Estes rockets where the ejection charge pushes the shock cord and the chute which together push the nose off.

It always seemed 'wrong' to place the charge between the nose and the chute where it would seem that the charge might tend to pack the laundry in the bottom of the tube.

I suppose if the nose is heavy and draggy enough, once it is ejected, it will pull the chute out.

That may be true with a 2.6 inch LOC Graduator.

But I've always placed the charge behind the chute and shock cord so that the chute comes out first after pushing off the nose cone followed by the shock cord.

This means that my apogee drogue charge has a long ematch wire so that it sits below the chute and the shock cord.

And my main charge has a very short wire so it can sit just forward of the AV-Bay Bulkhead, behind the shock cord which is behind the main and the nose.

BUT !

More times than not, the long ematch wire tangles with the drogue shock cord, and sometimes it screws up the drogue but it doesn't matter too much as long as the separate main deploys when it should ( it has a short wire ).

So, I don't know if my way is the best way for a single BP charge with a chute release.

My $0.02: Avoid long ematch wires when it's packed with your main ...

HTH ...

-- kjh

p.s. As I said, my long ematch wires tend to tangle with the drogue shock cord which might cause issues with a single chute or a JLCR or a cable cutter.

If I was doing was a single charge, I would be inclined find a way to use a short wire.

It's hard to see but the long ematch and the 19-inch Walston Transmitter Antenna wire tangled the yellow drogue chute and shock cord pretty badly last Saturday ( edit: drogue -> yellow drogue )

 

[bad_idea]

The charge pressurizes the airframe to separate it, not really a situation of pushing anything out unless you use a piston.

The shock cord pulls everything out as the two ends of the rocket move apart.

A light nose cone and imperfect packing can derail this. Even without a piston, I believe it's best when possible to put the recovery gear in between the charge and the tube mouth. (Not always possible of course.)

 

[rcktnut]

A light nose cone and imperfect packing can derail this. Even without a piston, I believe it's best when possible to put the recovery gear in between the charge and the tube mouth. (Not always possible of course.)

Agree 100% Even with "conventional" ejection without enough of a charge with the nosecone separating have seen the chute, shock cord remaining inside the rocket.

 

[cerving]

Either way should work, however I HAVE seen the "pusher" method just cram the chute/Nomex into the nose cone and not pop it if the charge is too small and/or the shear pins are too big. #1 thing is to get the nose cone off... even if the chute jams in the tube, if the nose cone is off then chances are good that you're not going to completely destroy your rocket with the subsequent hard landing.

 

[cvanc]

I'm trying to recall how many flights I've seen make it to the ground with the nose loose but the laundry still in the tube? Might just be me but I think not all that many.

I think sooner or later the wind adds enough energy to finish the job if you can just pop the nose. Now that don't mean it's schedule matches your needs at the moment if you follow me lol.

 

[pbahorich]

Get an Eggtimer Apogee

 

[DirkTheDaring]

I'm trying to recall how many flights I've seen make it to the ground with the nose loose but the laundry still in the tube? Might just be me but I think not all that many.

I think sooner or later the wind adds enough energy to finish the job if you can just pop the nose. Now that don't mean it's schedule matches your needs at the moment if you follow me lol.

You obviously haven’t been hanging out with me….

 

[Handeman]

I'm trying to recall how many flights I've seen make it to the ground with the nose loose but the laundry still in the tube? Might just be me but I think not all that many.

I think sooner or later the wind adds enough energy to finish the job if you can just pop the nose. Now that don't mean it's schedule matches your needs at the moment if you follow me lol.

I have seen a half dozen or so. Most of them were G-Force models or similar types flying on G motors with motor ejection. The charges were too small and the nose cone popped off, but didn't pull the chute out. Since the nose cone and rocket both fall at the same rate, wind had no effect and didn't pull anything out. In most cases, when the rocket was picked up and tilted downward, the chute fell out of the BT.

I also used a long wire on my first DD rocket for the apogee charge. I got some tangling in the apogee shock cord, but not enough to affect the drogue chute. The spinning fin can as it falls is what really twists up the shock cord, and if it spins fast enough for long enough, it can twist the drogue up inside the twisted shock cord.

For the OPs setup, I would consider a large charge at the nose cone, to get the nose cone moving well so it does pull everything out. I would avoid the long wire to the bottom of the BT that can snag on the shock cord, chute, or other items and can prevent the nose cone from pulling everything out.. Another option would be a small drogue/pilot chute attached near the nose cone to add drag and pull the shock cord and main out of the rocket if the nose cone doesn't pull it out.

 

[rcktnut]

If I were OP I would just use motor ejection for the older, bigger, single deploy rockets and a JLCR. That is what I do, and with a 100% success rate so far. I even prefer it over making up charges, prepping etc. for DD.

 

[neil_w]

Probably because I started with Estes rockets where the ejection charge pushes the shock cord and the chute which together push the nose off.

I don't believe it does, generally. I suppose it is possible if packed a certain way. I also wonder if it behaves differently with balsa vs. heavier plastic nose cones. Hmm.

I'm trying to recall how many flights I've seen make it to the ground with the nose loose but the laundry still in the tube? Might just be me but I think not all that many.

I've certainly had it happen (although not often).

Someone should do a ground test with a high-speed camera to show how this works.

 

[mbeels]

Can I modify my nosecone and have a BP charge there to blow the nose cone off?

Yes, but ground test. I have a rocket configured like that. The flight computer is in the nose cone, and the ejection charge is on the nosecone bulkhead. With this configuration, you're relying on the momentum of the nose cone to pull the parachute out of the tube.

Here is a video of a flight where the nose cone came off, but the parachute didn't come out until the motor ejection (as backup) pushed it out.

Skip to about 00:45

 

[mbeels]

Oh, I found a ground test video. 0.7 g wasn't quite enough. I can't remember what I flew it with, I assumed I increased it slightly from there.

 

[rcktnut]

Oh, I found a ground test video. 0.7 g wasn't quite enough. I can't remember what I flew it with, I assumed I increased it slightly from there.

"It smells delicious", you have a born rocketeer there!!!

 

[2-0turbo]

This has been an interesting conversation. As I’ve continued to look into this, I ran across this product that takes the place black powder but accomplishes the same goal.

https://www.tinderrocketry.com/rocketry-co2-ejection-system
Interestingly enough, it “acts” up at the top of the rocket, near the nose cove or eBay. It seems to work fine. I think some experimentation is in order.

“Honey, I need to spend a couple hundred dollars on rocket motors and associated do-dads to prove a hypothesis I have!”

 

[Handeman]

10 to 15 years and this discussion is still going on.
Back then, I was in the school of "the nose cone pulls the laundry out". Others were sure the ejection charge pushed the laundry out and the nose cone with it.
The conclusion then was that it was a bit of both.
The ejection charge pressurizes the BT and pushes the nose cone off. At that point, the pressurized air moves quickly to the open end of the BT and takes the laundry with it. If your shock cord and chute is loosely packed and can easily move, it goes out with the gases. If the shock cord and chute are heavy and tightly packed, the air will move around it and impart little movement to it. The inertia of the nose cone can have a big effect on when and how the laundry comes out. A light nose cone with little inertia will have little effect on heavy tightly packed laundry while a heavy nose cone with a lot of inertia will easily pull light, loosely packed laundry out. The placement of the chute vs. the shock cord can also effect how everything works.
The whole recovery system is just that, a system. It all has to work together. Everything effect everything else. When you get into DD, then add in the whole fall from apogee to main deploy as another complicated part of the system.

Don't just worry about the motor thrust, and the up part. The recovery system and down part is just as complicated and takes just as much time and effort to design it correctly.

 

[2-0turbo]

If I were OP I would just use motor ejection for the older, bigger, single deploy rockets and a JLCR. That is what I do, and with a 100% success rate so far. I even prefer it over making up charges, prepping etc. for DD.

And I'm currently doing motor ejection now as I'm just getting back into rocketry and NONE of my rockets are setup for dual-deploy. The JLCR is on my list of "needs" that I hope to get sometime soon.

Where this also come into play is clusters. I really like clusters and having a "backup" ejection event if you don't get all the motors lit is nice. Or maybe you ejected a motor out the back and all your ejection charge went backwards instead of blowing the nose off. The most recent launch I was at Oct 29 at Battlepark, it was pretty cool to have the rockets all nicely eject at Apogee. No zippers, no highspeed deploys because you didn't adjust the delay just right, no pucker factor because it didn't go straight up and that parabolic arc leaves you with less altitude than you desire...the list goes on.

I recently pranged my LOC Graduator on a flight on an Estes E12-4 motor with a slightly too long delay (4.5 secs) , not a straight-up boost and a chute deploy at 20' AGL. An apogee deploy with a secondary device would have likely saved that rocket.

So, I'm probably sticking with motor eject for the foreseeable future. But having a backup event in case any of the scenarios above present themself is attractive. But I am looking to experiment with a JL chute release too--they seem quite cool!

 

[Titan II]

For folks that do single or dual deploy, is is customary to put the charge up at the top (near the nosecone or ebay if you've got one) and just have it fire from there?

Top or bottom? It does not matter, and they both work if the charge is sufficient.