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| Bob... |
 Posted: Tue Oct 13, 2009 5:04 am |
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On Oct 13, 7:29 am, AdmiralDonSnider <a0403... at (no spam) unet.univie.ac.at>
wrote:
Quote: Concerning the flash bag, I imagine it very hard to realize in such a
small casing. Now should these bags resemble their larger relatives in
can shells, or does kind of a newspaper "canulle" work well too (I
remember a video by Tony Petro who used such nitrate flash filled
canulles to break his cylindrical rocket headings...)?
I tried doing it in 5/8" OD (1/2" ID) Ti salutes when I was trying to
get ignition of spheric Ti according to instructions given here with a
different flash compo inside from outside, and tried rolling the
coupette directly on the visco I was using as time fuse, and loading
was just beyond my finger dexterity. I don't remember whether I even
succeeded in constructing it once. I gave up and got sponge Ti, which
needed no such treatment to ignite.
Until recently I always used a burst bag (or burst cylinder) in 1.75"
OD cylindric shells. I've never tried it in film canister shells,
which are close to your 30 mm. If the time fuse comes in a roll, its
curve makes it difficult to center a burst cylinder in a small shell;
a bag can be more precisely placed in that regard, because the curved
fuse doesn't have to come directly out of its bottom.
Robert |
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| Lloyd E. Sponenburgh... |
| Posted: Tue Oct 13, 2009 5:43 am |
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Bob <robgood at (no spam) bestweb.net> fired this volley in news:3cd0e345-f8a0-4d65-
a400-b88f564b344b at (no spam) v36g2000yqv.googlegroups.com:
Quote: For film canister shells, approximately the same as 30 mm, I usually
use loose whistle mix.
One Thanksgiving weekend back somewhere between 1997-1999, Stephen
Haussmann and I built what I think was the first symmetrically-breaking
film cannister peony.
After that success (and our wild celebration dance in the field that
followed), he literally "took off" with the film-can shells. Our first
success was with a tiny hyper-flash coupette and grain powder.
Subsequently, he was able to tune the design using a mixture of 7:3 flash
and grain powder. He perfected almost every conceivable effect, including
tiny 6mm crossettes in rings! He went on to give a seminar and demo at
PGI, and initiated the miniature shell category of competition.
Many Class-C shells are burst with that combination of mixed flash and
grain powder (or coated rice hulls). A coupette helps with symmetry when
the shell casing is not heavy, but when you can put as much paper on the
shell as you wish, the problem of wall strength becomes a non-issue, and
the coupette becomes unnecessary.
Here's the deal on star ignition. First you must assume that if a star
lights, it will not blow out during the high-speed part of its flight.
If the star isn't capable of that, the rest is wasted work.
Envision a mass of stars with an explosion beginning at the center of
mass. The stars are forced outward against the shell walls. Partly,
they remain in position because of the strength of the shell, partly they
remain in place due to their own inertia. The inertial effect is
maximized if the force of the explosion rises very rapidly. If it's a
slow "heaving" explosion, the stars are simply pushed outward toward the
wall of the shell, and inertia plays little part.
If the pressure rise-time is slow and the shell walls are weak, the shell
may open before the flame ever reaches the outermost stars. Those stars
that have not had contact with the flame will be projected away without
lighting.
On the other hand, if the flame fully engulfs the contents of the shell
before the casing fails, every star has been enveloped in flame for a
time and stands a good chance of lighting.
You can strengthen the walls and lower the speed of the burst powder, or
weaken the walls and increase the speed of the burst, and accomplish the
same thing. In the former case, the inertial effect is essentially
disregarded, and casing strength does the task. In the latter, the
inertia of the stars plays a large role in keeping the mass together
until the fire does its work. In either case, a gas-producing burst
charge results in a larger break.
The second method is less labor-intensive to build.
LLoyd |
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| Lloyd E. Sponenburgh... |
| Posted: Tue Oct 13, 2009 5:49 am |
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AdmiralDonSnider <a0403986 at (no spam) unet.univie.ac.at> fired this volley in
news:e6723e37-c52d-4b69-a5fb-55b9a144e2d4 at (no spam) a7g2000yqo.googlegroups.com:
Quote: Concerning the flash bag, I imagine it very hard to realize in such a
small casing. Now should these bags resemble their larger relatives in
can shells, or does kind of a newspaper "canulle" work well too (I
remember a video by Tony Petro who used such nitrate flash filled
canulles to break his cylindrical rocket headings...)?
It is difficult, and that's why most bombettes are broken with a mixture
of flash and grain powder or coated rice hulls.
Quote:
In my autopsies of commercial bombettes I realized that all of them
use a 2mm thick waste paper casing. I currently make use of the same
material, but only roll them 1mm thick. Would switching to 2mm give
any improvement, or why is this 2mm casing so "standard" at all? I
assume itïs used because you donït necessarily need a mold to press
the clay in...
The thicker wall helps... see the other post about how a burst does or
does not ignite stars.
Also, a pressed-in clay bulkhead in that weak paper won't hold much
pressure. Other sorts of closures, such as multiple internal disks
covered with a drawn cap or poured-in-place hot-melt adhesive are
stronger solutions.
LLoyd |
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| mikes2653... |
| Posted: Tue Oct 13, 2009 8:10 am |
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Flash powder must be used very sparingly as a burst for pupadelles.
Those that have success with the technique generally use "pencil
bags," i.e., rolled on a former the diameter of a blacklead pencil,
just large enough to slip over and tie onto the end of a piece of 1/4"
time fuse. For uniform effect, flash powder burst must be measured
very carefully, and preferably weighed. One gramme is probably too
much for a 1-1/4" pupadelle. You will have to experiment.
Lloyd's advice about using grain powder in the interstices between the
stars is good. There's a definite advantage to its use. Cost is not
that great, even though it's a high-cost component; you don't use that
much of it.
Pressed clay ends, etc., are outside my experience for pupadelles.The
method works for fusillading shots, but you will not get good star
breaks using rigid tubes and weak end plugs. I'd advise dry-rolling
the cases using 2 turns tagboard and 3 turns lightweight kraft paper,
chipboard end discs, then spiking and pasting them with 2 or 3 turns
of kraft..
On Oct 13, 6:29 am, AdmiralDonSnider <a0403... at (no spam) unet.univie.ac.at>
wrote:
Quote: A nice solution for really rapid pressure rise is to center a "coupette"
(flash bag) in the shell, and fill the interstices among the stars with
grain powder. The coupette contains the flash until it explodes
forcibly, and the powder creates the gas necessary for large, symmetrical
breaks.
Very good explanation. I´m currently using Shimizu Flash Thunder #2,
which is a perc based flash with greasy Al and sulphur. A sulphur
containing flash also seems to produce more gaseous products.
Concerning the flash bag, I imagine it very hard to realize in such a
small casing. Now should these bags resemble their larger relatives in
can shells, or does kind of a newspaper "canulle" work well too (I
remember a video by Tony Petro who used such nitrate flash filled
canulles to break his cylindrical rocket headings...)?
In my autopsies of commercial bombettes I realized that all of them
use a 2mm thick waste paper casing. I currently make use of the same
material, but only roll them 1mm thick. Would switching to 2mm give
any improvement, or why is this 2mm casing so "standard" at all? I
assume it´s used because you don´t necessarily need a mold to press
the clay in...
Admiral |
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| Bob... |
| Posted: Tue Oct 13, 2009 11:41 am |
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On Oct 13, 2:10 pm, mikes2653 <ekim2... at (no spam) gmail.com> wrote:
Quote: Pressed clay ends, etc., are outside my experience for pupadelles.The
method works for fusillading shots, but you will not get good star
breaks using rigid tubes and weak end plugs. I'd advise dry-rolling
the cases using 2 turns tagboard and 3 turns lightweight kraft paper,
chipboard end discs, then spiking and pasting them with 2 or 3 turns
of kraft..
Wow, spiking a 30 mm cylinder. I did use to spike 1.75# shells with
regular string, but for 30 mm do you need bakery string? Or are you
just that good with regular thickness twine that you can get it to
"bite" that curved an edge? I have "pasted"-in approx. 1" inserts
with white glue.
BTW, I thought it would be a simple geometry problem to figure how
large a diameter of 3 circles I could inscribe in a larger circle --
fitting rows of cylinder inserts into a cylindric shell -- but I
abandoned it a while ago! I've got to take it up next time I try a 3"
shell of shells; it's got to be better than working the crosswords
puzzles in a book of them I was given for my birthday.
Robert |
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| mikes2653... |
| Posted: Tue Oct 13, 2009 12:04 pm |
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I use 2 strands of thin (2-ply) Italian flax running together, heavily
pasted. 6 or 8 vertical passes with circumferential spiking to make an
approximately square pattern on the sides ought to do the trick. It is
very quick to spike these little shells, and also to paste them, since
you can break two or three dozen pieces of paper in paste at a time,
rolling them up right from the stack of paper.
The formulae for calculating the number of inserts of a given diameter
that will fit in a shell case of gven diameter, etc., may be found on
p. 26 of Pyrotechnica XII. There are also four pages of tables
summarizing these calculations for all the common shell case sizes and
insert sizes.
On Oct 13, 4:41 pm, Bob <robg... at (no spam) bestweb.net> wrote:
Quote: On Oct 13, 2:10 pm, mikes2653 <ekim2... at (no spam) gmail.com> wrote:
Pressed clay ends, etc., are outside my experience for pupadelles.The
method works for fusillading shots, but you will not get good star
breaks using rigid tubes and weak end plugs. I'd advise dry-rolling
the cases using 2 turns tagboard and 3 turns lightweight kraft paper,
chipboard end discs, then spiking and pasting them with 2 or 3 turns
of kraft..
Wow, spiking a 30 mm cylinder. I did use to spike 1.75# shells with
regular string, but for 30 mm do you need bakery string? Or are you
just that good with regular thickness twine that you can get it to
"bite" that curved an edge? I have "pasted"-in approx. 1" inserts
with white glue.
BTW, I thought it would be a simple geometry problem to figure how
large a diameter of 3 circles I could inscribe in a larger circle --
fitting rows of cylinder inserts into a cylindric shell -- but I
abandoned it a while ago! I've got to take it up next time I try a 3"
shell of shells; it's got to be better than working the crosswords
puzzles in a book of them I was given for my birthday.
Robert |
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| Bob... |
| Posted: Tue Oct 13, 2009 5:29 pm |
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I just find that when the radius of curvature is low, I have a lot of
trouble keeping the longitudinal loops from slipping off. But then, I
was slow learning to tie my shoes too. |
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| Lloyd E. Sponenburgh... |
| Posted: Tue Oct 13, 2009 5:33 pm |
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Bob <robgood at (no spam) bestweb.net> fired this volley in news:dad8cc0b-ccef-4417-
a166-e494df20b7ef at (no spam) p9g2000vbl.googlegroups.com:
Quote: Wow, spiking a 30 mm cylinder. I did use to spike 1.75# shells with
regular string, but for 30 mm do you need bakery string? Or are you
just that good with regular thickness twine that you can get it to
"bite" that curved an edge? I have "pasted"-in approx. 1" inserts
with white glue.
We do it all the time on certain effects, with Italian flax twine -- the
same stuff we spike large shells with.
Quote:
BTW, I thought it would be a simple geometry problem to figure how
large a diameter of 3 circles I could inscribe in a larger circle --
fitting rows of cylinder inserts into a cylindric shell -- but I
abandoned it a while ago! I've got to take it up next time I try a 3"
shell of shells; it's got to be better than working the crosswords
puzzles in a book of them I was given for my birthday.
There's a neat insert calculator on passfire.com. It'll work out any
geometry you like with no pain or sweat.
LLoyd |
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| Lloyd E. Sponenburgh... |
| Posted: Wed Oct 14, 2009 6:26 am |
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Bob <robgood at (no spam) bestweb.net> fired this volley in news:d2e6d10b-003c-49eb-
99a8-c87f24c5887c at (no spam) m1g2000vbi.googlegroups.com:
Quote: I just find that when the radius of curvature is low, I have a lot of
trouble keeping the longitudinal loops from slipping off.
They cannot slip if the paper is damp with paste from the paste-soaked
twine, and the twine is drawn tight enough to "bite" into the paper at the
end-caps. Thus, each line of longitude is securely retained.
LLoyd |
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| AdmiralDonSnider... |
| Posted: Wed Oct 14, 2009 7:06 am |
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Lloyd, your posts from October 13 are a great read and will certainly
provide a good starting point for improvements of my own units. Thanks
a lot!
However, there is one more issue that I´ll have to put forward for
discussion: rising tails as an added effect in bombettes.
Leaving aside the fact that the comps have to be selected with care
(to get them burning long enough but not too long, to prevent them
from fragmenting due to premature burn-out), I still wonder how these
tracer comps are best attached to the bombettes. I tried using dextrin
based comps dampened with water, applied with hand pressure and a
dowel; sometimes they work, sometimes they flake off prematurely.
Plain perc color seems to work better than tailed comps, charcoal
works particularly bad, but this is no surprise.
Some pyro buddies suggested the use of stronger binders such as gum
arabic or NC, I don´t know.
How are these tracer comps attached commercially to work well? Note
that I intend to use comps such as tiger tail, as plain ascending
color doesn´t give the same impressive effect.
Admiral
Admiral |
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| Bob... |
| Posted: Wed Oct 14, 2009 4:36 pm |
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On Oct 14, 8:26 am, "Lloyd E. Sponenburgh"
<lloydspinsidemindspring.com> wrote:
Quote: Bob <robg... at (no spam) bestweb.net> fired this volley in news:d2e6d10b-003c-49eb-
99a8-c87f24c58... at (no spam) m1g2000vbi.googlegroups.com:
I just find that when the radius of curvature is low, I have a lot of
trouble keeping the longitudinal loops from slipping off.
They cannot slip if the paper is damp with paste from the paste-soaked
twine, and the twine is drawn tight enough to "bite" into the paper at the
end-caps.
Well duh, that's my very problem. It seems only thinner string would
be "sharp" enough to dig into that curved a surface when I do it
without a horse. |
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| Bob... |
| Posted: Wed Oct 14, 2009 4:46 pm |
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On Oct 14, 7:25 pm, "Lloyd E. Sponenburgh"
<lloydspinsidemindspring.com> wrote:
Quote: AdmiralDonSnider <a0403... at (no spam) unet.univie.ac.at> fired this volley innews:0d7ce286-7fe4-47c2-866c-529f97dcafc9 at (no spam) o10g2000yqa.googlegroups.com:
How are these tracer comps attached commercially to work well? Note
that I intend to use comps such as tiger tail, as plain ascending
color doesnït give the same impressive effect.
Tracers are difficult on small shells, if they're attached externally.
In my 1.75" 2 break shells, the end plug (glued circles of cardboard)
of the 2nd break (inside the outer case) winds up somewhat recessed,
and often cockeyed a bit. The effect produces a rim like that of a
tin can. I've been filling it in with sawdust & glue before pasting
over, but it seems one could deliberately produce a rim and trowel
onto it some dampened tailed compo, which could be built up into a
tall enough layer to have enough burn time.
Robert |
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| Lloyd E. Sponenburgh... |
| Posted: Wed Oct 14, 2009 5:25 pm |
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Guest
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AdmiralDonSnider <a0403986 at (no spam) unet.univie.ac.at> fired this volley in
news:0d7ce286-7fe4-47c2-866c-529f97dcafc9 at (no spam) o10g2000yqa.googlegroups.com:
Quote: How are these tracer comps attached commercially to work well? Note
that I intend to use comps such as tiger tail, as plain ascending
color doesnït give the same impressive effect.
Tracers are difficult on small shells, if they're attached externally.
The only good way to do it is with lots of cement (hot-melt doesn't work
very well, but old sodium silicate/carbonate "pyro glue" works pretty
well). After they're glued on (or before if you want to fiddle a bit)
they themselves should be pasted-round with a couple of wraps of 30lb
paper with "petals" cut around the bottom to flare out the attachment to
the shell. The petals should be glued down well with white glue, then
another layer of pasted paper put around and over them to hold the
assembly down. The comet burns from the exposed end, candle fashion.
The way the Chinese do it is odd, but simpler to make work well. They
press a "spolette" of the tracer composition, as large in diameter as
they wish it to be up to the diameter of the shell. They then use that
comet as the time fuse, eshewing any fusing at all, except that they bore
a small hole in the shell, and push in a bit of slurry to pass fire
between the comet and the shell contents. Sometimes, they'll insert a
few strands of "helper match" through the hole before stuffing full of
slurry, just to ensure it passes fire -- usually not, though.
Some of the Spanish plastic RAP bombette casings are purpose-made to
accept a pressed-in comet of rising effect as the time fuse.
LLoyd |
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| Lloyd E. Sponenburgh... |
| Posted: Thu Oct 15, 2009 5:36 am |
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Bob <robgood at (no spam) bestweb.net> fired this volley in news:ed0ab5b3-243e-43b6-
86a0-15f8d4d2006b at (no spam) g31g2000vbr.googlegroups.com:
Quote: It seems only thinner string would
be "sharp" enough to dig into that curved a surface when I do it
without a horse.
We use a horse, even for 30mm effects. In this case, the "horse" is just
a short lenght of 2x4 attached vertically to one end of a workbench. The
Italian twine is simultaneously slathered with paste while being wound
around the upper bitter end of the 2x4. It's allowed to steep in the
paste for five or ten minutes before spiking begins.
Then the operator simply unwinds sufficient twine to get good working
room, and begins spiking while holding tension on the wet twine. Because
it has soaked for a time and is quite wet, the twine shrinks
significantly as it dries, further tightening the lines.
We use only the one twine for all spiking, using more strands as more
strength is required.
LLoyd |
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| Lloyd E. Sponenburgh... |
| Posted: Thu Oct 15, 2009 5:39 am |
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Bob <robgood at (no spam) bestweb.net> fired this volley in news:90346ee8-62fc-41d4-
a08a-1a93fc88c0b8 at (no spam) z34g2000vbl.googlegroups.com:
Quote: The effect produces a rim like that of a
tin can. I've been filling it in with sawdust & glue before pasting
over, but it seems one could deliberately produce a rim and trowel
onto it some dampened tailed compo, which could be built up into a
tall enough layer to have enough burn time.
You've described an arrangement similar to the plastic RAP bombette
construction. The cavity so made is about 10-12mm deep on those casings.
It's not an artifact of assembly - as it is in your case - but purpose-
made to hold the rising effect/timing element.
LLoyd |
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