A few basic dual-deploy questions

[Joel Shepherd]

I've built an Estes STM-012 with an Apogee ebay to learn a bit about dual deployment. I don't need it but it seemed like a fun challenge. I've done a basic ground test, determined that about 0.3g of 4F each seems sufficient to deploy the drogue and main, and now I'm hoping to actually try it in flight in a couple of weeks (with motor ejection as a backup). Three kinda naive questions:

1. For my tests, I poured the black powder in a small pile onto the sticky side of a piece of masking tape, set the initiator in it and then folded the tape over and pressed it down around the edges to make a tight little envelope. It seems easier than futzing with surgical glove fingertips, etc., as I've seen in videos. Is there any reason not to go with the little masking tape packet?
2. Is there any reason not to prepare those packets, with initiators, etc., well ahead of time? I'd rather not be dealing with BP, etc., in the field, but don't know if there are other concerns.
3. The shock line for the drogue is connected to the motor mount on one end and a small snaplink on the ebay end, so it can be removed and disconnected easily. What about the main chute? I could just attach the shock cord inside the body tube the usual Estes way, but is there any advantage to attaching it to the ebay and if so should I use a snaplink on that end as well?

Small rocket, but hoping to learn enough good practices that I'd be ready to try DD on a larger one someday.

 

[Titan II]

#2....that is the smart thing to do.

 

[Voyager1]

You'll probably get quite a few different opinions about this. However, here is my advice.

1. Don't do it this way because by wrapping the BP and igniter together with tape you are exposing yourself to (a) a potential safety risk if this is done prior to attending the launch site; (b) losing some BP if you change your mind about the launch and wish to unpack the envelope.

2. Don't prepare those packets prior to attending the launch site. It's not safe! What I do is to prepare small centrifuge vials with ematches installed and hot melt glued in place to seal the end of the vial. The BP and dog barf are added just prior to launching before the RSO check is done. The surgical glove fingertip is another valid technique, but I prefer the vials, or avbay bulkhead mounted pots for the larger rockets.



3. I'm not familiar with that rocket model. Others will comment.

 

[waltr]

I also do NOT install the BP charge until at the launch site.

The Vial method is ok and lots off people use them.

What I do for smaller DD rockets that need less than 0.6gram BP:
Roll a pieces of paper (about 1 1/4" square. around the red cover of the Ematch and tape it on to form a tube
Then add the measured BP, I pre-measure at home into vials so don't need to measure at the field.
Fold over the paper 'tube' and apply several wraps of tape.

 

[David Schwantz]

I also like the vials. I do make them up at home and rocket is RTF when I leave. All my rockets have switches to cut all battery to the alts. I have never done the tape method as you describe. But it kind of sounds messy. I like my BP contained better I guess.
You can attach cord via estes but it is way less secure than to the DD bulkhead. If chute deploys early you're going to rip out the Estes style mount. You can use a quick link but on smaller, lighter rockets I just like to use a loop and run it back through itself to secure cord to eyebolt. The chute can go down from the NC, I like to tie a third loop in my cord and again loop the chute through that upon itself. this keeps overall weight down. You also already have a link to disassemble recovery.

 

[Handeman]

As for #1, I started doing something similar using duct tape when I started with DD, now I use charge wells on the ends of the ebay. Using tape works well, doesn't blow holes in the BT like the vials can sometimes, but needs a little more BP than what a contained charge does. I would keep doing it that way.

#2, When I used tape packets I prepped at the field because I wanted to connect the initiators to the altimeter and verifying good continuity and connection before turning the altimeters off and adding the initiator and powder to the tape. I always prep ebays with powder wells ahead of time.
You can continue prepping the charges ahead of time. There is some risk in doing this. Risk is usually charted as % chance of occurring vs. the amount of damage/impact the occurrence has. You can mitigate that risk if you take a few precautions. Keep the initiator wires twisted together, keep them in the trunk, not passenger compartment, keep them in a metal container that will contain the charge and has a hole to relieve pressure if they do go off. You don't want your container to rupture and only want the smoke and cooled gases, not flame, getting out in the event of something happening. Personally I think you have a much higher chance of getting injured in a wreck driving to and from the launch than from those initiators going off.

#3 Where and how you connect your main shock cord is pretty much your choice and can be based on the rocket design. I've always connect my shock cords to the ebay with quick links on both ends and the payload BT removeable. That makes it easier to get to both ends of the ebay for prep, shock cord connection, etc. It also allows you to swap the ebay between rockets, especially if you can get the holes in the BTs on both rockets to match.

DD isn't hard to learn. The altimeter is usually the easy part. The ground testing, tuning charge sizes based on actual flights, and designing the way you want the ebay and rocket to fit together and work is something you will end up going through and learning with every DD rocket you build.

Good Luck and have fun.

 

[Joel Shepherd]

Hi All - Thanks for the good advice. Sounds like my instincts were a little off on when and/or how to prep the packets, but I can see the issue if I change my mind about the size of the charge or if the initiator is bad: it'd be tough to open it up, etc., in the field.

About those little centrifuge tubes ... I considered using those because they are neat and tidy, but an L2 acquaintance at work said that "shrapnel" might be an issue, and I had questions about how much energy would be expended blowing the cap off the tube. That's when I started playing with the tape packet idea. Don't know if anyone else has opinions one way or the other.

Appreciate all the tips, safety and otherwise. I think I'll just leash the nose cone to the ebay: it's easy enough to change my mind later. Thanks!

 

[David Schwantz]

I have never seen damage from the vials blowing apart.

 

[Tractionengines]

You want the "BP" charge to stay together long enough to burn. If your "containment device" [vials, glove finger tips, tape packet, charge well,, etc] doesn't do that consistently, then the gas generated to produce the pressure will vary.

The main thing is find something you like. Then do it the SAME way each and every time.

I like the centrifuge vials, its easy to be consistent. Just remember to fill unused space with filler [wadding, dog barf, etc] then snap close. I add a wrap of electrical tape, to hold it closed for a few more milliseconds.

 

[PSLimo]

Wildman has an all in one solution for ejection charges that have worked perfect for me.

https://wildmanrocketry.com/collections/wildman-brand-ejection/products/wm01-ejection-lighter-w-cb

 

[Banzai88]

I have never seen damage from the vials blowing apart.

This. And I've used up to 5 grams in large vials with the caps glued on. Several hundred, not one single unit has ever shattered or caused damage to my rockets.

 

[DarthMuffin]

I have never seen damage from the vials blowing apart.

Me either, but I also don't use them on cardboard rockets. I 3d printed a jig to hold them so I can assembly-line them and drill an 1/8" hole in the bottom. Slide the match wire in and add a dab of hot glue right below the head to pull it down and seal it. I'll do a whole batch like this and then I can weigh charges and fill when ready for launch. I usually fill the rest of the vial with a cut down ear plug, at least for the small vials.

 

[Voyager1]

I have never seen damage from the vials blowing apart.

Ditto! Generally the snap lid just pops open. Sometimes it might separate from the vial, but the vials have never disintegrated.

 

[David Schwantz]

My vials do break up, but I use 3 wraps of masking tape. 2 over the top crosswise to keep lid shut, 1 around it to secure the wire to the vial.

 

[Banzai88]

Many of us use nomex and handfuls of barf, no issues.

As to not having a precision scale, you can get these Lee precision powder scoops, already comes with a chart with powder calibrations, and they're good enough that a whole generation of reloaders cut their teeth on reloading with 'em before scales were in common use: https://www.amazon.com/LEE-PRECISION-90100-Powder-Measure/dp/B000N8OIE8/ref=sr_1_2?crid=2ZL9SJ73ZDD6C&keywords=lee+powder+scoops&qid=1674480053&sprefix=lee+powder+scoops,aps,139&sr=8-2

 

[Kframe]

I have nothing to contribute to this but I want to say that as a person looking to get DD/L1/L2 myself, this thread is gold.

 

[firemanup]

1) I use glove tips but whatever works is fine.

2) I’ve always built my eBays to include charges at home before launches.

I’ve even had flights not attempted and the built eBay’s stay built over the winter and work fine in the spring months later.

 

[SolarYellow]

I've read reports of the vial lids popping off with enough velocity to out-dent a cardboard body tube. I'm planning my first DD rockets to be BT-50 and BT-55, so that's a concern. The countermeasure I read was to just use an earplug to fill the rest of the space in the tube and either leave it like that or put some tape over it if it makes you feel better. No real-world experience doing it yet, but of all the stuff I've read, that makes the most sense to me so far and is my plan. Figured it's worth adding to this discussion.

 

[Joel Shepherd]

Just an update ... I've launched the STM-012 in dual-deployment configuration five times now. I ended up going with the little plastic centrifuge tubes, with electric matches hot-glued into the tip, and haven't had any issues related to those. The cap flies off 90% of the time; in one case it stayed attached. My calculations showed that about 0.25g of black powder was needed, but 0.3g seemed marginal so the last three flights I've used 0.4g and that's worked reliably. After the first couple attempts, I also switched to using a streamer for the drogue which improved visibility, and the extra velocity also seemed to help the main chute inflate snappily. This weekend, on the first flight I finally scored the #1 boo-boo of not turning the electronics on, which resulted in a split at the nose cone end of the body: a wrap of scotch tape shored that up for a couple more flights with no additional paint damage. On the next flight, the shock cord (300# kevlar!) broke at a knot, and the two sections of the rocket landed safely, the aft half under a streamer and the forward half under a 24" chute. The last flight, pictured here at launch on an Aerotech F30, worked just about perfectly. The electronics were on, the sustainer deployed, the main deployed at about 300 ft and after a bit of wriggling inflated at about 200 ft, and the whole assembly drifted gracefully into the grass.

It's been a good learning experience, it's really rewarding when it works, and it's given me confidence that with some practice I can make it work reliably. Now I just need to build a rocket big enough to require it.

 

[David Schwantz]

It's a good idea turn get into a habit of doing everything the same every time. The first thing I like to do when rocket is on the rail and vertical is arm all electronics. Before installing igniter.

 

[Voyager1]

Well done!
Many of us have experienced the #1 boo boo of not arming the avionics before launching.
Use a check list in the prep area and at the pad! Don't just rely on memory, because we can get distracted.
Enjoy the experience - even the bumps!

 

[Joel Shepherd]

Thank you both - I know from another nit-picky hobby the importance of doing the same things in the same order to get reliable results. Now that I have a basic working setup, I’ll focus on the routine. Hopefully getting another chance this weekend.

 

[David Schwantz]

I have nothing to contribute to this but I want to say that as a person looking to get DD/L1/L2 myself, this thread is gold.

Kframe, where in MN are you? Have you flown up in North Branch?

 

[Buster]

1) I use glove tips but whatever works is fine.

2) I’ve always built my eBays to include charges at home before launches.

I’ve even had flights not attempted and the built eBay’s stay built over the winter and work fine in the spring months later.

Lost a rocket in a field. Found it 6 months later. Rain, snow, freezing temperatures still fired.

 

[kswing]

I'm glad to hear your DD tests are mostly working.

For #1 on your initial questions, I usually use charge wells on the bulkheads, but, another option that I have used are simple paper straws. I put the e-match in the straw and then fold/kink it along the wire just below the match head. Next I put the BP in the straw over the match head and then fold/kink the straw again just above the BP. I use electrical tape to keep the kinks folded. I've used this a few times as a backup charge on a rocket where I don't have room for another charge well on the bulkhead.