Calculating amount of black powder for ejection charge
Connery
necessary for an ejection charge. For instance, if I had a
compartment that was 5.5" in diameter, and 20 inches long, how
much BP would be necessary to cause seperation to occur.
Connery Carroll
NAR #77226 L1
http://www.vzinet.com/rocketry
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William Beggs
Here ya go. The amount required is (.0076) X [(Dia of the tube)squared] X
(length of the tube). For your 5.5" dia by 20 inch long compartment you would
need a charge approx equal to 4.5 grams of 4F BP. Generally I've found that for
a compartment of this size an adequate amount is approx 2/3 of the calculated
amount. This just comes from 100's of flights. My equation looks like (.0051) X
[(Dia of the tube)squared] X (length of the tube). When using pistons or other
types of baffling ejection devices, the total BP may also be reduced. If you
want to make sure, just test it out. Make sure that when the charge goes off
that the shock cords get completely stretch out. I've found this to be an
exciting thing to do on my off weekends of launching. As always, use extreme
caution and safety when testing the charges out.
William Beggs, Jr.
TRA 5258 L3
NAR 70094
wbe...@uswest.net
Lewis Garrow
charges I used in my Syonic, which about matches the volume you are working with).
Keep in mind (unless you meant the volume was already reduced by the volume of
parachute, shock cord etc. ) that you really are only pressurizing about 2/3 of
the calculated volume.
Dave
William Beggs <wbe...@uswest.net> wrote:
> I've found this to be an exciting thing to do on my off weekends of
> launching. As always, use extreme caution and safety when testing the
> charges out.
There's nothing quite like the report of a ground-tested ejection
charge to attract unwanted attention in the neighborhood. Sounds too
much like a gunshot.
Dave
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Before you buy.
Dean Roth
>
> Can some one tell me how to calculate how much black powder is
> necessary for an ejection charge.
You will find information in Rocketry Online's Infocentral.
> For instance, if I had a
> compartment that was 5.5" in diameter, and 20 inches long, how
> much BP would be necessary to cause seperation to occur.
I cannot tell you the minimum amount of BP without performing tests
with your particular rocket. However, a starting point is
0.004 * D * D * L = grams of BP
D = diameter of airframe, inches
L = length of recovery section, inches
0.004 * 5.5 * 5.5 * 20 = about 2.5 grams
This will produce pressure of about 10 pounds per square inch.
I suggest using this as a starting point and work down, performing
tests on the ground. Or use that value and a long (20-30' or more)
tether to the nose cone/parachute.
--
dean _ roth at yahoo dot com
William Beggs
Those are some pretty neat tables but how do you know what your psi range is
suppose to be?
William Beggs, Jr.
TRA 5258 L3
NAR 70094
Bob Chmara wrote:
> Connery:
>
> I have a couple of tools on my web site that might be of help. The first is
> a BP calculator, http://www.chmara.com/bt/rocketry/bpcalc.html .
>
> The second is a BP usage chart that relates the quantity of FFFFg, airframe
> diameter, airframe length and PSI ratings. It was designed specifically for
> the Lee precision powder measuring spoons.
> http://www.chmara.com/cgi-bin/bptable.pl
William Beggs
You're assuming that I live in a city or a neighborhood of a large
population. I don't. I'm just giving an example of what I do. It doesn't
mean that you should test BP charges out in back of your residence. Out
here in the West we have a lot of open space. It actually sounds like a
cannon.
William Beggs, Jr.
TRA 5258 L3
NAR 70094
Albuquerque Rocket Society
Tai Fu
Dave wrote:
>
> In article <39183A81...@uswest.net>,
> William Beggs <wbe...@uswest.net> wrote:
> > I've found this to be an exciting thing to do on my off weekends of
> > launching. As always, use extreme caution and safety when testing the
> > charges out.
>
> There's nothing quite like the report of a ground-tested ejection
> charge to attract unwanted attention in the neighborhood. Sounds too
> much like a gunshot.
>
> Dave
I tried to ground test and it sounded like gunshots. i did it in my
garage. I get scared when I hear gunshots because I dont like people
complaining. You could probably test small samples (less than one gram)
in your house, just make sure wife/parent is going to be away for a LONG
time. for more than one gram, I dont recommend testing anywhere near
houses because people will think a pipe bomb went off. This is probably
very dangerous so dont try it, but anyone know what it would be like if
someone used flash powder as ejection charge? they are powerful stuff.
small amounts of it makes flash, and a gram of it goes KABOOOOOOMMMM!!
--
Tai Fu
NAR# 76089
Website: http://web.wt.net/~taifu
Joe Pfeiffer
> Dave,
>
> You're assuming that I live in a city or a neighborhood of a large
> population. I don't. I'm just giving an example of what I do. It doesn't
> mean that you should test BP charges out in back of your residence. Out
> here in the West we have a lot of open space. It actually sounds like a
> cannon.
Having recently lost a rocket to an insufficent ejection charge (near
as I can tell), how do you ground-test the charge? Put the charge in
the motor's cap, put it in the model, and use an Estes igniter to set
it off?
--
Joseph J. Pfeiffer, Jr., Ph.D. Phone -- (505) 646-1605
Department of Computer Science FAX -- (505) 646-1002
New Mexico State University http://www.cs.nmsu.edu/~pfeiffer
VL 2000 Homepage: http://www.cs.orst.edu/~burnett/vl2000/
Bob Chmara
I have a couple of tools on my web site that might be of help. The first is
a BP calculator, http://www.chmara.com/bt/rocketry/bpcalc.html .
The second is a BP usage chart that relates the quantity of FFFFg, airframe
diameter, airframe length and PSI ratings. It was designed specifically for
the Lee precision powder measuring spoons.
http://www.chmara.com/cgi-bin/bptable.pl
--
Bob Chmara
remove -noloaf for personal replies
Connery wrote:
| Can some one tell me how to calculate how much black powder is
| necessary for an ejection charge. For instance, if I had a
Bob Chmara
That's a good question but as you seem to be aware, there's no simple
answer. In general, the larger the airframe diameter, the less pressure is
needed. In his original post, Connery mentioned a 5.5" airframe. For that
I'd use the 10 psi table as a guideline. That would indicate about 2.5g or
slightly less than the amount you recommended.
I also usually calculate the pressure applied to the base of the nose cone.
For a 5.5" airframe at 10 psi, that works out to about 235 pounds, clearly
more than enough move most 5.5" nose cones assuming an "average" fit.
Most importantly, I've started ground testing the ejection charges in all my
rockets (even though I live in the burbs).
--
Bob Chmara
remove -noloaf for personal replies
Les Kurz
gets a Machbuster back. It's not the altitude / small size combination, the
600+ psi must blow it to pieces!
Mr. Les
NAR# 74240 L1 SR Insured / CATO# 47
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Visit our club at-------> http://www.catorockets.org
Les Kurz
supposed to be very clean burning. Smallest grind is FFFg. Costs just under
2x BP. Local gun shop guy says the muzzle loader crowd (maybe bunch is more
accurate) likes it for cleanliness. Obviously they don't rely on fast burning
like we do. I'm wondering if I should be the first in my neighborhood to try
it out. Don't feel like risking my new Sudden Rush without some background.
Connery
I'm also interested in the answer to your question. Plus, does
anyone know how much an Aerotech/Dr Rockets 38mm ejection charge
well holds?
Kevin Trojanowski
>
> I tried to ground test and it sounded like gunshots. i did it in my
> garage. I get scared when I hear gunshots because I dont like people
> complaining. You could probably test small samples (less than one gram)
> in your house, just make sure wife/parent is going to be away for a LONG
> time. for more than one gram, I dont recommend testing anywhere near
> houses because people will think a pipe bomb went off. This is probably
> very dangerous so dont try it, but anyone know what it would be like if
> someone used flash powder as ejection charge? they are powerful stuff.
> small amounts of it makes flash, and a gram of it goes KABOOOOOOMMMM!!
Tai...
Intentionally setting off explosives in the house, or advocating that
others do it isn't a smart thing to do. It's a good way for someone to
get HURT!
Why not just pack the rocket up, take it out to where you launch, and
ground test the ejection charge THERE? Then, if someone hears the noise
and asks what you're doing, the answer is quite easy -- "I'm ground
testing the recovery system deployment so that I can make sure the
rocket recovers safely."
-Kevin
Dean Roth
> Any of you BP users try GOEX 'Clear Shot'?
I discovered Clear Shot a year ago via Goex's web site.
I have not yet acquired any for ejection system testing.
> I'm wondering if I should be the first in my neighborhood to try
> it out. Don't feel like risking my new Sudden Rush without some background.
Ground test it first. BP replacements have worked in some rockets with
pistons. I've seen Pyrodex work in a Sudden Rush. BP replacements
generally
do not work with non-piston deployment systems due to the lower
efficiency
of non-piston deployment systems. In other words, if Clear Shot works in
your Sudden Rush don't automatically expect it to work in a rocket
without a piston without more testing.
William Beggs
Tai Fu wrote:
> Dave wrote:
> >
> > In article <39183A81...@uswest.net>,
> > William Beggs <wbe...@uswest.net> wrote:
> > > I've found this to be an exciting thing to do on my off weekends of
> > > launching. As always, use extreme caution and safety when testing the
> > > charges out.
> >
> > There's nothing quite like the report of a ground-tested ejection
> > charge to attract unwanted attention in the neighborhood. Sounds too
> > much like a gunshot.
> >
> > Dave
> I tried to ground test and it sounded like gunshots. i did it in my
> garage. I get scared when I hear gunshots because I dont like people
> complaining. You could probably test small samples (less than one gram)
> in your house, just make sure wife/parent is going to be away for a LONG
> time. for more than one gram, I dont recommend testing anywhere near
> houses because people will think a pipe bomb went off. This is probably
> very dangerous so dont try it, but anyone know what it would be like if
> someone used flash powder as ejection charge? they are powerful stuff.
> small amounts of it makes flash, and a gram of it goes KABOOOOOOMMMM!!
> --
> Tai Fu
> NAR# 76089
> Website: http://web.wt.net/~taifu
I don't recommend or condone any minor playing or experimenting with BP! I
would hope that any individual that will be ground testing their ejection
charges would use a LITTLE common sense! Please Tai, don't become a
statistic.
Connery
mothers carpet.
Dave
Joe Pfeiffer <pfei...@cs.nmsu.edu> wrote:
> William Beggs <wbe...@uswest.net> writes:
>
> > Dave,
> >
> > You're assuming that I live in a city or a neighborhood of a large
> > population. I don't. I'm just giving an example of what I do. It
doesn't
> > mean that you should test BP charges out in back of your residence.
Out
> > here in the West we have a lot of open space. It actually sounds
like a
> > cannon.
>
> Having recently lost a rocket to an insufficent ejection charge (near
> as I can tell), how do you ground-test the charge? Put the charge in
> the motor's cap, put it in the model, and use an Estes igniter to set
> it off?
Uhh, I think we're talking about two different things, here. We meant
ground-testing altimeter-activated ejection charges, not motor-
activated charges. I don't know how to test a motor-activated charge.
All I can suggest is, on your next flight use more black powder ;-)
Joe Pfeiffer
>
> Uhh, I think we're talking about two different things, here. We meant
> ground-testing altimeter-activated ejection charges, not motor-
> activated charges. I don't know how to test a motor-activated charge.
> All I can suggest is, on your next flight use more black powder ;-)
Sorry, I must have missed some posts in the middle -- I was thinking
we were still on sizing the charge...
Mike Pearson <see .sig>
> I'm still wondering how Tai got the black powder out of his
> mothers carpet.
I'm wondering who gave the BP to an underage kid.
--
Mike
NAR #70953 - Sr/Insured/Level-1 ~ SeaNAR - The Seattle NAR Section #568
NO Junk Email, please! Real email to: amphoto [at] blarg [dot] net.
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