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  1. #1
    Join Date
    16th January 2015
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    Perry, UT
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    Black Powder charge

    I have been searching the forum and reading up on how to calculate a proper BP charge. There is a lot of discussion on the 'proper' formula. So how do I figure out the proper amount of BP to use? Also the discussions on size, I have FFFFg which is very small.

    Thanks !

    Am I a Good Man?
    --Doctor Who

    NAR: 211218 TRA: 15593
    L1: Madcow Twitch DD - CTI I297SK 4328'

  2. #2
    Join Date
    13th June 2014
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    4F is what you want so you are good there. There are a lot of online calculators which will get you in the ball park but ground testing will really determine your actual needs.

    Tim
    L3 NAR 98225

  3. #3
    Join Date
    15th September 2009
    Location
    Silverton, Oregon
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    937

    Black Powder charge

    As stated, there are online calculators that will give you a starting point, but ground testing is always your best bet.

    We found that online calculators gave us a much larger charge than necessary. Our rocket is quite large - 12.75" in diameter - which is part of he reason.

    In the end it boils down to a few variables:
    Pressure produced by a given amount of BP in a known volume
    Surface area that said pressure acts upon (that of NC bulkhead)
    Amount of force needed to separate NC (calculated from shear pin size/number)


    Sent from my iPhone using Rocketry Forum

    Dan Feller
    Silver Crest Rocket Club

  4. #4
    Join Date
    26th November 2009
    Posts
    4,939
    Invest in a remote altimeter like a Quantum or a wireless switch. It makes ground testing so much easier. An alternative is use an empty motor casing and thread the wires through the empty motor from the charge well and put a charge holder there to test the sustainer charge with your launch system.
    For the main charge, as long as you have a static port that's big enough to put shooter's wire (or any 22 or 24 ga. wire through) you can twist the leads to
    your main charge terminal and run the wire out the static port for the ground test.

    Being able to put your flight electronics directly in the rocket really makes it easy to ground test if it has a wireless remote activation. The Quantum, TRS and others have this option and some remote switches can be temporarily mounted for a test. Kurt

  5. #5
    Join Date
    20th June 2015
    Location
    Vermont
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    398
    I have been wondering about this as well since I'm building my first dual deploy rocket. One other thing I was curious about is how does one accurately measure out the BP? I have a scale that I use for weighing parts and completed rockets but it isn't quite accurate enough to weigh out a single gram of BP.
    Jim V

    Champlain Region Model Rocket Club
    CRMRC
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  6. #6
    Join Date
    18th January 2016
    Location
    St. Louis
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    894
    1. Use FFFFg powder. The smallest grain stuff gives the best results.
    2. Look up any powder scales from Amazon. Try to get one with a weigh boat. That makes it handy. Here's a good, affordable example: https://smile.amazon.com/Frankford-A...s=powder+scale
    3. A popular charge calculator is: http://www.rimworld.com/nassarocketr...alc/index.html
    4. GROUND TEST! It will give you the confidence that whatever you measure out will be the right amount of BP.
    5. If possible, have a backup charge, and give it +20% BP more than what you determined works best in ground testing. It's your, "Oh !@#$" charge.
    Mark
    NAR#: 100890 / TRA#: 16580
    L1 - Binder Design Excel Plus 38 - CTI I242 2,540'
    L2 - Binder Design Excel Plus 38 - CTI J330 3,672'
    L3 - Scratch built 8" PAC-3 MSE Patriot - Loki M1969 6,338'

  7. #7
    Join Date
    13th October 2014
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    SouthEastern, WA
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    I use a set of Lee Powder Dippers https://www.midwayusa.com/product/10...er-measure-kit
    Which measure volumetrically, however when used with a scale the .3cc measure is pretty close to .3 grams of BP and the others are pretty close as well, at least close enough that I no longer use the scale ( dipping technique does play a factor in charge weight, and I always card the mound of powder off the top to be level with the top of the dipper).

    As others have said GROUND TEST, GROUND TEST, GROUND TEST!
    Rich

    NAR# 99154

    L3-4x upscale Estes Cherokee-D- AT M1297W 5/28/2016 http://www.rocketryforum.com/showthr...r-rharshberger

    TriCities Rocketeers NAR section# 736 http://www.tricitiesrocketeers.org/

  8. #8
    Join Date
    22nd May 2015
    Location
    Middletown, Ohio
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    63
    I just use the tubes that come in the aerotech reloads. Can measure up to 2 grams at a time and if you always use the same powder it will keep the results fairly accurate. If you have an android phone I just release an update to my app that has a calculator for black powder changes. But as memtioned before an calculation is just a starting point and you should always ground test before putting a bird in the air. You can get the app at https://play.google.com/store/apps/d...cketcalculator
    Justin Bray (Videos) NAR# 102401 | TRA# 16961 | L2
    Member of Wright Stuff Rocketeers #703
    Android App: Rocket Calculator

  9. #9
    Join Date
    5th December 2013
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    MD
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    Second on Lee Powder Spoons. I never weight anything. 1cc = 1g to within a very small tolerance.

    As others have said, no calculator can know everything there is to know about your rocket. Run a calc., ground test multiple times until you hone it in. For a drogue, you just need separation and to get the laundry out. For the main, you will want slightly more separation to leave room for the chute to expand; but you don't want to stress the harness and cause the NC to snap back into the airframe. There's also shear pin breakage to consider.

    John S. ---- NAR #96911 ---- TRA #15253 ---- MDRA #067 ---- BARC #028
    L1, 3/15/14: Aerotech Sumo, CTI H133BS
    L2, 6/21/14: Giant Leap Vertical Assault, CTI J240RL
    L3, 3/12/16: MAC Performance Radial Flyer, CTI M1101WH
    Altitude: 13,028', L3 flight; Speed: Mach ???, L3 flight

  10. #10
    Join Date
    18th January 2016
    Location
    St. Louis
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    894
    For containment, I generally use my 1.5 ml Eppendorf tubes. They hold about 2 g of BP. Access to labs = limitless free tubes.

    People have all sorts of different setups, but here's what I do:

    Click image for larger version. 

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    1. drill a hole into the bottom of the Eppendorf tube
    2. pull your igniter through it until the head is at the bottom
    3. apply a drop of hot glue to the outside bottom to seal up the hole and hold the igniter wire in place
    4. add BP
    5. add enough cellulose insulation to pack down the BP tight and prevent it from moving away from the igniter head
    6. some like to tape the lid shut, but I find the tubes slap closed plenty tight for me
    Mark
    NAR#: 100890 / TRA#: 16580
    L1 - Binder Design Excel Plus 38 - CTI I242 2,540'
    L2 - Binder Design Excel Plus 38 - CTI J330 3,672'
    L3 - Scratch built 8" PAC-3 MSE Patriot - Loki M1969 6,338'

  11. #11
    Join Date
    18th March 2012
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    One thing to remember, the method you use to pack your charges will affect the performance of your charge. If you put the powder loosely into a glove fingertip, it will not be anywhere near as powerful as packing it tightly into a charge well and taping it tightly shut.

    Pick a method and stick with it as long as it works.
    Matt, Tripoli #14257
    L1 11/13/16
    L2 2/25/17
    L3 Spring 2018....
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  12. #12
    Join Date
    16th January 2015
    Location
    Perry, UT
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    Thanks! Couple more questions now. As I use the BP calculator on NASSA, it asks for length, I have NC with some space in it to the bulkhead, measured that, and in the BT do I measure to the centering ring or top of the MMT? as there is a few inches, but I figure that area around the engine will be packed with shock cord. There is about 4" in length between top of MMT and centering ring. Do I just figure it as is, empty, or with all the shock cord, and parachute and Nomex?

    Thanks again for the help!
    Am I a Good Man?
    --Doctor Who

    NAR: 211218 TRA: 15593
    L1: Madcow Twitch DD - CTI I297SK 4328'

  13. #13
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    13th October 2014
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    Ignore the shock cord and chute, basically you are looking at theempty space. I would use top of CR to next solid bulkhead as length, ignoring any motor tube sticking through the CR.
    Rich

    NAR# 99154

    L3-4x upscale Estes Cherokee-D- AT M1297W 5/28/2016 http://www.rocketryforum.com/showthr...r-rharshberger

    TriCities Rocketeers NAR section# 736 http://www.tricitiesrocketeers.org/

  14. #14
    Join Date
    16th January 2015
    Location
    Perry, UT
    Posts
    33
    Okay. So I have 5.5" diameter by 17" length and say 7psi for approximately 200 pounds of force = 1.46 grams of BP and use 4x 2-56 nylon screws. So a beginning spot for me to work with. Well time to load it and see if I can get it to work.
    Am I a Good Man?
    --Doctor Who

    NAR: 211218 TRA: 15593
    L1: Madcow Twitch DD - CTI I297SK 4328'

  15. #15
    Join Date
    18th March 2009
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    Wisconsin
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    Quote Originally Posted by rharshberger View Post
    I use a set of Lee Powder Dippers https://www.midwayusa.com/product/10...er-measure-kit
    Which measure volumetrically, however when used with a scale the .3cc measure is pretty close to .3 grams of BP and the others are pretty close as well, at least close enough that I no longer use the scale ( dipping technique does play a factor in charge weight, and I always card the mound of powder off the top to be level with the top of the dipper).

    As others have said GROUND TEST, GROUND TEST, GROUND TEST!
    I use these as well.


    Sent from my iPhone using Rocketry Forum
    Mark Koelsch
    Tripoli 6155 L3
    Owner of http://www.rocketryfiles.com/
    Editor of http://www.thrustcurve.org/
    Member of the Tripoli Motor Test Committee, and keeper of the motor file

  16. #16
    Join Date
    10th July 2007
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    Melbourne, Australia
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    Ignore the shock cord and chute, basically you are looking at theempty space. I would use top of CR to next solid bulkhead as length, ignoring any motor tube sticking through the CR.
    +1

    Also to consider is the location of the eMatch. If it is under the BP it can cause the unburnt BP to disperse before igniting to some extent. I usually put the eMatch above the BP in the well.
    TRA 13430, Level 3

    "Everybody's simulation model is guilty until proven innocent" (Thomas H. Lawrence 1994)

  17. #17
    Join Date
    6th September 2009
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    Quote Originally Posted by mccordmw View Post
    Click image for larger version. 

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    Perfect picture! My setup is exactly the same. So convenient to whip up a batch of these at home ahead of time, and no fumbling with filling charge wells at the field.

  18. #18
    Join Date
    6th September 2009
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    1,648
    Keep in mind that an Aerotech 29mm or 38mm reload comes with about 1.4g. 24mm reload includes about 0.75g. If you have past experience with motor ejections, then those numbers are good reference points for your ground testing.

    I have a little red cap (looks like an Aerotech hobby reload red cap) with a coffee stirrer handle that came with a set of flashbulb igniters from back in the day. This holds one gram of powder and is all I ever used. I just eyeball 0.25 gram increments in the cap. No need to be super precise. Also, reloads now come with powder in a graduated centrifuge vial. 1cc = 1g is a good enough assumption.

  19. #19
    Join Date
    11th April 2017
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    Quote Originally Posted by OverTheTop View Post
    +1

    Also to consider is the location of the eMatch. If it is under the BP it can cause the unburnt BP to disperse before igniting to some extent. I usually put the eMatch above the BP in the well.
    Interesting... so would that mean you would recommend that if one was using the Eppendorf tube method as mccordmw was suggesting, that the e-match would be at the top of the BP if you used such a method? Or were you referring to a more cylindrical charge well?

    I'm paying attention as I can foresee a time in the next few months where my thinking and planning will be progressing from the MPR and entry level HPR builds I'm currently doing towards the beginnings of DD entry level HPR.. (long way to go, but I'm hoovering up learnings as I progress...)
    Reasonably new to rocketry and hailing from the land down under.. I speak metric... I know not of these feet and inches you speak of...

    QRS: #193
    AMRS: #148

  20. #20
    Join Date
    20th January 2009
    Location
    British Columbia, Canada
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    798
    I use a blackpowder measure. Remember, the measure is in grains and not grams if you use one of these. You need to do a conversion. I was shown a really simple way to make a charge holder. Simply roll paper up into a tube of the appropriate size. Feed in an igniter. Fold the bottom over the wire and tape it up with masking tape. Pour the BP into the tube. Fold it over and use masking tape over it all. Very fast and effective. It worked consistently for me at a launch this summer.
    Click image for larger version. 

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    Last edited by Len B; 14th October 2017 at 11:05 PM.
    Len Bryan
    CAR-ACF S620 L3, NAR 98782 L2, Tripoli 10220 L2

  21. #21
    Join Date
    19th January 2009
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    Quote Originally Posted by Len B View Post
    I use a blackpowder measure. Remember, the measure is in grains and not grams if you use one of these. You need to do a conversion. I was shown a really simple way to make a charge holder. Simply roll paper up into a tube of the appropriate size. Feed in an igniter. Fold the bottom over the wire and tape it up with masking tape. Pour the BP into the tube. Fold it over and use masking tape over it all. Very fast and effective. It worked consistently for me at a launch this summer.
    I used a similar method years back when I was using xmas tree bulbs for lighting the BP. I twisted two bulbs together for redundancy and hot glued them into a paper tube. Added powder, folded over and taped. It does work very well.

    Since I went exclusively to e-matches, I just use copper pipe caps as charge wells and that's been very good and consistent too. You don't need to over think this. You just need a single method that gives consistent results. It really doesn't matter which method you use, as long as it opens the rocket and gets your drogue or main into the air stream so they can open and pull everything into alignment on the way down.
    Handeman

    TRA #09903 L3 3/29/2015

    "If you don't use your head, you have to use your feet!" my Dad

    Tripoli Central Virginia #25 - BattlePark.org

  22. #22
    Join Date
    16th January 2015
    Location
    Perry, UT
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    33
    Ground test went well. 1.46g of BP deployed the NC about 6-8 feet across the lawn. Did use the little lab tube design that Mccordmw picture showed, worked great. Thank you all for the help and input. Now to work on the next part.
    Am I a Good Man?
    --Doctor Who

    NAR: 211218 TRA: 15593
    L1: Madcow Twitch DD - CTI I297SK 4328'

  23. #23
    Join Date
    18th January 2016
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    St. Louis
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    Great to hear. A handy tip is also to write the amount of BP on the side of the tube. That way, if you make any up ahead of time, you won't get them mixed up with others. I usually have a primary charge and a backup at +20% more BP.
    Mark
    NAR#: 100890 / TRA#: 16580
    L1 - Binder Design Excel Plus 38 - CTI I242 2,540'
    L2 - Binder Design Excel Plus 38 - CTI J330 3,672'
    L3 - Scratch built 8" PAC-3 MSE Patriot - Loki M1969 6,338'

  24. #24
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    Quote Originally Posted by mccordmw View Post
    Great to hear. A handy tip is also to write the amount of BP on the side of the tube. That way, if you make any up ahead of time, you won't get them mixed up with others. I usually have a primary charge and a backup at +20% more BP.
    Yeah, once you have 4 or 5 DD rockets, the numbers start to run together. You can write them on the bulkhead, but be careful that they don't get stained over with burnt BP.

    John S. ---- NAR #96911 ---- TRA #15253 ---- MDRA #067 ---- BARC #028
    L1, 3/15/14: Aerotech Sumo, CTI H133BS
    L2, 6/21/14: Giant Leap Vertical Assault, CTI J240RL
    L3, 3/12/16: MAC Performance Radial Flyer, CTI M1101WH
    Altitude: 13,028', L3 flight; Speed: Mach ???, L3 flight

  25. #25
    Join Date
    15th February 2009
    Location
    North Texas
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    568
    I always measure the length of open tube to the top, not the area between the bulk plate and the nosecone or second bulk plate. You want to pressurize the entire empty area to make sure you have enough power to completely separate the pieces.

    I also use the Rocket Calc app on the iPhone. It has a BP calculator that will tell you how many shear pins your charge will break, in either 2-56, 4-40, or 6-32 sizes. It makes it really easy to figure some margin of safety. I think most folks tend to use too much BP, myself included, because we are all used to the fact that many reloads come with 1 gram. Seeing how many screws the charge will break makes it a lot easier to dial in the amount. Of course things like nosecone weight also come into play.

    For best results and especially for repeatability BP should be contained in a tube (think of a barrel). When the powder is ejected from the tube it will be directed into the flame front so the grains are much more likely to ignite. If it's in something like a glove tip or latex tubing it's likely some of the grains will not ignite as they are blown in random directions. Jim Jarvis did some excellent testing that shows that using a tube greatly improves the effectiveness of BP as an ejection charge.

    Just something to think about.


    Tony

    why do people put so much stuff in their sigs?

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