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Where do I get started with making ejection charges?

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ActingLikeAKid

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This feels like something that there should be a good primer on (pun intended, I guess) ...

So it seems like the next build I do, I'm going to try to use electronically-triggered ejection. Fun!

I don't know a ton about firearms, but I know I need black powder for the charges....but beyond that (and some neat online calculators that will show how much you ought to use)...Help!

From the bit of research I've seen it sounds like Pyrodex can or will work if it's packed tightly. That's fine, I'm OK with packing tightly. Do I need to get a LEUP for storing pyrodex?
Do I need a LEUP for black powder? What's the difference between FFFF, FFFG, etc. Which is "better"?
What about e-matches? From the wording on Apogee's site, it sounds like you need a LEUP to buy or sell them, but if you buy the kit and make them, you're OK.

Is there a good place to start researching this besides "advice on the internet"?
 

Nytrunner

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FFFFG (4F) is finer in structure than FFFG (3F). Finer grain structure -> more surface area per mass-> faster combustion -> Don't need to back it as much (unless you're going super high altitude, which I doubt you are at this stage).

If you want real blackpowder, I'd suggest looking at Bass Pro. Cabela's and other similar places have purodex, hogden, and other smokeless powder or gunpowder substitutes that require different containment or amounts to achieve the same effect (if they work at all). Those online calculators are usually geared towards legitimate 4F blackpowder.

My old IREC team never found a good routine for pyrodex, so we switched to 4F.
 

markkoelsch

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Thanks, that's helpful! Sounds like Pyrodex P will give me a good pop AND I don't have to do any paperwork!

What do you do about e-matches?
I have used a ton of the Pratt Hobbies ejection canisters as mentioned on that site. Work really well. Ground testing is mandatory.




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Zeus-cat

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The number of F's tells you how finely ground the particles are. More F's, smaller particles. Fewer F's, coarser particles. Smaller is better for rapid combustion.

Pyrodex will work, but black powder is better in my opinion as it does not require containment. However, black powder is hard to find. Pretty much everything at Walmart or any place that sells powder is selling a black powder substitute similar to Pyrodex.

My understanding is that if you use black powder for use in guns you do not need a permit or any special equipment for storage. If you use it for anything else you need to store it in a special container. I do not think this applies to Pyrodex. I could be wrong.

I use ematches similar to the ones on ebay. Made in China, orange wires. I cut the bottom off centrifuge vials and hot glue the ematch in place.
 

DGBrown

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I use the MJG Firewire matches and have never had any issues with them. MJG claims that they are the only e-match on the market that isn't regulated by the ATF.
 

Andrew_ASC

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I have used FFFg powder P substitute inside a cut to length 9/32" autozone VaC tube that matched the FireWire end for SEDS flight L-1 impulse multistage rocket. Run a charge calculation, it will likely be low. You need to compress the charge so it pressurizes rapidly rather than burns. We wrapped the charges in HVac tape as its stronger than duct tape. Test charges in a spare airframe tube with wadding and a chute in .1 gram charge increments. We worked our way up on charge size.
 

Andrew_ASC

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You can legally buy smokeless powders such as IMR4064 for reloading modern ammunition. It in theory has less mass of charge size for more pressure. I would NOT recommend smokeless powder for an HPR deployment charge as it could easily rupture the fiberglass tube if using more than several tenths of a "grain" not a gram of powder.

Consider a standard hunting rifle in .30-06 may use 40 grains of smokeless and you have a 150 grain bullet go 2800 feet per second. A .50 cal black powder musket using 50 grains or a pyrodex pellet moves a sabot at 900-1200 feet per second. The pressure difference per time is staggering to say the least. A CTI H motor has about 1.2 grams of black powder as a deployment charge. Even when reloading ammo for rifled steel barrels it was constantly stressed work your way up on charge sizes very very slowly in small increments for safety.

Lastly high moisture content can make ejection charges unreliable. You've heard of Taketa airbags and they didn't test their products in a high moisture environment so those units failed in actual use in high moisture climates.
 

kswing

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I've used 4F powder in multiple rockets with great success. I've never tried Pyrodex, but, I've heard that if you contain it it will work. If you have a friend who shoots muzzle loaders, he/she may be able to get you some 4F powder or you may be able to find it at a local gun store. You can also get small amounts of 4F, pre-measured, by buying ejection charge kits from places like buyrocketmotors.com.

I use orange e-matches that I found on Amazon or e-bay and so far they have all worked. I've used them for about 15 dual-deploy flights. I also used them in 10 or 15 ground tests without a problem. They were fairly cheap and they came in batches of 100. They have orange wires with red plastic covers over the match head. If you search for e-match on eBay you'll probably find them. I think they're from China. I check the resistance on them before use and if I see one that varies greatly from the bunch I plan to discard it. So far, they have all been within tolerances.

I use 1/2" or 3/4" PVC end caps for my charge containers. They are glued to the bulkheads with epoxy. I put the e-match in, followed by the powder, then dog barf or other wadding to fill the empty space. I tape over the whole thing with black electrical tape so that it stays put. I've also successfully tested charges made by putting an e-match into a straw or 1/4" launch lug with the powder. I folded the straw above the match head and past the powder and then taped over it to keep it folded. Lots of different things will work as long as you keep the powder contained. Whatever you try, it is important to ground test your configuration before flying it.
 

RocketFeller

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I, too was brand-new to electronic ejection not long ago. After reading a lot online and talking with experienced fliers I decided to go with FFFF for reliability's sake.

We use double-walled PVC cups (plugs inside of couplings) that are attached to the bulk plate with SS bolts. The cups are filled half full of BP. We then pack in as much dog barf as we can cram in to compress the charge. The dog barf is then covered in several layers of 3M blue tape.

We have done several ground tests and four flights (with two charges per flight) with this setup so far and it has yet to fail us. It is pretty much identical to the way our mentor does it, he is L3 with dozens of complex flights under his belt.


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jdbwizzard

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I also use pvc end caps. Get the cpvc ones that are flat on the bottom. Bolt them to the bulkhead then for good measure I drop some epoxy on the bolt to insulate it. As mentions before not matter what you use always pack what every you use with dog barf. This keeps the powder in contact with the ematch.

If you are limited on space I use the method mention above from pratts hobbies but modified. I didn't have a lot of the canisters laying around so instead I use 1/4" launch lug. They work great and I don't have to worry about pieces of plastic stuck through my rocket which I saw happen over the weekend.
 

afadeev

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[...]I use orange e-matches that I found on Amazon or e-bay and so far they have all worked. I've used them for about 15 dual-deploy flights. I also used them in 10 or 15 ground tests without a problem. They were fairly cheap and they came in batches of 100. They have orange wires with red plastic covers over the match head. If you search for e-match on eBay you'll probably find them. I think they're from China. I check the resistance on them before use and if I see one that varies greatly from the bunch I plan to discard it. So far, they have all been within tolerances.
Are these similar to yours?
http://www.ebay.com/itm/100-pcs-1M-...740093&hash=item41ac93f1ca:g:1ZQAAOSwBahVKTQY

Does anyone have feedback on Magnalite / pyrogen ignitors?
Rocketflight/PML claim no LEUP is required, and they also they work reliably with clustered motors:
https://publicmissiles.com/product/igniters

a
 
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