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Ejection Charge Fizzle

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mccordmw

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Ground testing my ejection charges last night once more before this Saturday's launch. By calculations, I need 1.5g for drogue and 0.6g for nosecone main. Drogue worked well. Broke the two shear pins and tossed out the laundry about 6' away. When testing the main, I heard the e-match pop and then just a sizzle. On inspection, I see the 0.6g FFFFg BP did get consumed, but no detonation; just deflagration.

Does this mean I didn't contain the BP tightly enough? Until now, I've typically wrapped an e-match with the BP in a foil pack and then wrapped that with duct tape to make a ball. With only 0.6g of BP, it might not have enough oomf to detonate vigorously or such a small amount was not tightly enough wrapped?

I have access to buckets of free 1.5ml eppendorf tubes. I might remake the charges as cannisters in those tubes and ram cotton in to tightly contain the whole thing before taping it shut. I might get more consistent results that way.
 

djs

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I can't speak to why yours failed, but you might not have had it packed tightly enough, or was not next to the e-match when it went off.

I use centrifuge tubes for my ejection charges. Here's how I do it:
1. drill small hole in the bottom of the centrifuge tube.
2. feed ematch into hole, using poster tack to plug up the hole. Ematch should be sitting as low as possible- just above the sticky tack plug
3. Measure out and fill BP into tube.
4. Fill the top of the centrifuge tube with dog barf- packed in as tightly as I can do it.
5. Snap lid of centrifuge tube closed
6. trim the bottom of the ematch wire to desired length, and strip the wire ends as needed.
7. Pack in my range box ready to be used.

I think this is how many people do it?
 

mccordmw

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I can't speak to why yours failed, but you might not have had it packed tightly enough, or was not next to the e-match when it went off.

I use centrifuge tubes for my ejection charges. Here's how I do it:
1. drill small hole in the bottom of the centrifuge tube.
2. feed ematch into hole, using poster tack to plug up the hole. Ematch should be sitting as low as possible- just above the sticky tack plug
3. Measure out and fill BP into tube.
4. Fill the top of the centrifuge tube with dog barf- packed in as tightly as I can do it.
5. Snap lid of centrifuge tube closed
6. trim the bottom of the ematch wire to desired length, and strip the wire ends as needed.
7. Pack in my range box ready to be used.

I think this is how many people do it?
Yes. Luckily, being a scientist, I'm swimming in free 1.5 - 2.0 mL centrifuge tubes. I was planning on setting up cannisters just how you elaborated there. Thanks for the details. It'll make sure I don't miss anything. I'll also write down the BP amount on the sides of the tubes to make sure I don't accidentally mix them up. Probably pack extras in case others need some.
 

ttabbal

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To be pedantic, BP never detonates. The idea is to produce increased pressure in the rocket body for ejection. If it burned, you should have as much gas as it's going to produce. Containment helps ensure that the powder all burns, but it's not usually necessary with BP. If you're using smokeless like Pyrodex, you will need better containment. I often use paper tubes with no problems. I suspect you didn't get full combustion, there is a leak preventing pressurization, or you just need more BP. 0.6g isn't much at all, I think the smallest charge I usually use is about 2g. I'm a "blow it out or blow it up" kinda guy though, so overkill is just how I do things. :)
 

Zeus-cat

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I can't speak to why yours failed, but you might not have had it packed tightly enough, or was not next to the e-match when it went off.

I use centrifuge tubes for my ejection charges. Here's how I do it:
1. drill small hole in the bottom of the centrifuge tube.
2. feed ematch into hole, using poster tack to plug up the hole. Ematch should be sitting as low as possible- just above the sticky tack plug
3. Measure out and fill BP into tube.
4. Fill the top of the centrifuge tube with dog barf- packed in as tightly as I can do it.
5. Snap lid of centrifuge tube closed
6. trim the bottom of the ematch wire to desired length, and strip the wire ends as needed.
7. Pack in my range box ready to be used.

I think this is how many people do it?
Pretty much what I do except I use a hot glue gun for step 2.
 

mccordmw

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Pretty much what I do except I use a hot glue gun for step 2.
I recall reading somewhere that hot glue will melt on ejection and stick on stuff like the cord and chute; generally making a mess. Is that not the case? I was planning on a small wrap of electrical tape instead.
 

MCriscione

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I haven't followed your build thread, but from the general size of your rocket, if you're using shear pins on the nose, you may need to up your charge size. I did a test on my L1 bird, which looks to be a somewhat similar size with .75g BP charge and got a similar 'pop' with no separation. The calculator had suggested .66 would be adequate. I had to up it to 1.2g (double the calculated value!) before I was getting a confident ejection. How tightly your laundry packed into the payload bay can impact this too.
 

mccordmw

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I haven't followed your build thread, but from the general size of your rocket, if you're using shear pins on the nose, you may need to up your charge size. I did a test on my L1 bird, which looks to be a somewhat similar size with .75g BP charge and got a similar 'pop' with no separation. The calculator had suggested .66 would be adequate. I had to up it to 1.2g (double the calculated value!) before I was getting a confident ejection. How tightly your laundry packed into the payload bay can impact this too.
Yeah. I'm testing tonight with 1.0g to see. I've got until tomorrow night to hammer it all out before heading to Walnut Grove Sat. morning. No pressure. :eyepop:
 

soopirV

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I build up several charge canisters using centrifuge tube (yay fellow scientists!), and like ZeusCat says, use hot glue, but don't preload with powder. Never gave a thought about it melting and sticking- seems plausible. I have never used less than .8g in a tube, though, and am using smokeless, so give the tubes several wraps of electrical tape.
 

crossfire

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I use hot glue all the time.
 

AlfaBrewer

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BP doesn't have to be all that tightly contained. At least compared to Pyrodex and similar substitutes. The main thing is to make sure and have enough (.6g seems pretty low), and in contact with the match. For reference, my 4" rockets with similar sized bays as the Excel use 1g for drogue (no shear pins) and 1.5g for main (3 shear pins). The 1.5 is a little overkill, but it's not so much as to put any strain on the recovery train.

I use masking tape similar to your foil and duct tape ball.
 

Banzai88

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I recall reading somewhere that hot glue will melt on ejection and stick on stuff like the cord and chute; generally making a mess. Is that not the case? I was planning on a small wrap of electrical tape instead.
I use hot glue, just a dab is enough. Never had the glue melt on ejection burn.
 

rms

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Glove tips from thick nitrile gloves have served me well as ejection charge holders for over 10 years. Pour in powder, put in ematches, roll tip tight and apply masking tape, can't use too much tape. Perhaps this old school approach as gone the way of bag cell phones and it is just this old fart that still uses this technique?:bang:
 

mccordmw

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Tested last night. I made 10 cannisters and all 10 popped with no problem. My cannisters are made with the following steps:

1. drill 1/8" hole in the bottom of the centrifuge tube.
2. remove cover from ematch and thread the wire through until head of the ematch is at the bottom of the tube. Note: keep the wires twisted to short it and be safer.
3. secure wire and seal the hole with 1/2" of electrical tape wrapped tightly on the outside bottom
4. weigh appropriate amount of BP. Write that amount on the outside of the tube for reference (and for sharing :-D )
5. fill tube with BP. I find the tube can hold about 1.8g max. Most were filled with no more than 1.5g.
6. pack the BP tightly by pushing dog-barf cellulose insulation into the tub until full.
7. snap lid closed and tape tightly shut with 1" of electrical tape tightly wound.
8. store in portable field magazine for safety.

I tested the ejection on my nose cone. Curiously, the calculators say to use about 0.6g. That sheared the pin but only pushed the nose cone a couple inches clear of the frame. The chute was still firmly in the tube. I eventually went with 1.5g. That pops the cone cleanly out and pushes the main about 4' clear of the tube. Still plenty of shock cord to pull out and ease the shock of deployment.
 
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